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Patent 2460374 Summary

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(12) Patent Application: (11) CA 2460374
(54) English Title: UNIPOLARITY POWDER COATING SYSTEMS INCLUDING TRIBOCHARGING AND CORONA GUN COMBINATION
(54) French Title: SYSTEMES DE POUDRAGE UNIPOLAIRES COMPRENANT UNE COMBINAISON DE PISTOLET-PULVERISATEUR A CHARGE TRIBO-ELECTRIQUE ET CORONA
Status: Dead
Bibliographic Data
(51) International Patent Classification (IPC):
  • B05B 5/047 (2006.01)
  • B05B 3/02 (2006.01)
  • B05B 5/03 (2006.01)
  • B05B 5/04 (2006.01)
  • B05B 5/053 (2006.01)
(72) Inventors :
  • MESSERLY, JAMES W. (United States of America)
  • REHMAN, WILLIAM R. (United States of America)
  • LADER, HARRY J. (United States of America)
  • SANNER, MICHAEL R. (United States of America)
(73) Owners :
  • NORDSON CORPORATION (United States of America)
(71) Applicants :
  • NORDSON CORPORATION (United States of America)
(74) Agent: MACRAE & CO.
(74) Associate agent:
(45) Issued:
(86) PCT Filing Date: 2002-10-04
(87) Open to Public Inspection: 2003-04-17
Availability of licence: N/A
(25) Language of filing: English

Patent Cooperation Treaty (PCT): Yes
(86) PCT Filing Number: PCT/US2002/031820
(87) International Publication Number: WO2003/031076
(85) National Entry: 2004-03-18

(30) Application Priority Data:
Application No. Country/Territory Date
60/327,222 United States of America 2001-10-05
10/139,939 United States of America 2002-05-07

Abstracts

English Abstract




A plurality of unconventional negative tribo-charging materials are described
for use as the powder contact surfaces in tribocharging and corona powder
spray guns, gun components, and powder delivery system components. The
invention also provides a short s barrel tribo-charging powder spray gun (200)
having an interchangeable powder contact insert (220) and nozzle (230), with
turbulence inducing air jets. The invention further provides novel
tribocharging and corona gun designs. Improved powder coating systems are made
possible wherein, for example, negative tribo guns can be utilized with
negative corona guns to coat different parts of the same workpiece in a powder
coating system. Also provided is an inside-out configuration in which
pressurized air directs powder coating material outward towards a charging
surface. Additional configurations provide air jet (981) induced tribocharging
and conventional tribocharging portions combined in a single gun. Also
provided is a spraying apparatus that combines tribocharging and/or directed
air tribocharging with corona charging. A switch arrangement (1000) is
provided to select or change charging modes of the spraying apparatus.


French Abstract

L'invention concerne une pluralité de matériaux non classiques produisant une charge tribo-électrique négative lorsque la poudre entre en contact avec des surfaces de pistolets-pulvérisateurs de poudrage à charge tribo-électrique et corona, de constituants de pistolet-pulvérisateur et de constituants de système de distribution de poudre. L'invention concerne également un pistolet-pulvérisateur de poudrage à charge tribo-électrique à canon court (200) comprenant une pièce rapportée en contact avec la poudre et une buse interchangeables, des jets d'air induisant des turbulences. De plus, l'invention concerne de nouvelles conceptions de pistolet-pulvérisateur à charge tribo-électrique et corona. Les matériaux selon l'invention permettent d'obtenir des systèmes améliorés de poudrage, par exemple, grâce à l'utilisation conjointe de pistolets-pulvérisateurs à charge tribo-électrique négative et de pistolets-pulvériseturs à charge corona négative, en vue de revêtir différentes parties d'une même pièce à travailler dans un système de poudrage. L'invention concerne en outre une configuration intérieur-extérieur dans laquelle de l'air sous pression projette un matériau de poudrage vers l'extérieur, en direction d'une surface de charge. D'autres configurations permettent de combiner, en un seul pistolet-pulvérisateur, des parties de charge tribo-électrique induite par jets d'air (981) et de charge triboélectrique classique. L'invention concerne enfin un appareil de pulvérisation combinant une charge tribo-électrique et/ou une charge tribo-électrique à air dirigé avec une charge corona. Un agencement de commutateurs (1000) permet de changer des modes de l'appareil de pulvérisation.

Claims

Note: Claims are shown in the official language in which they were submitted.



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CLAIMS

Having thus described the invention, we claim:

1. A powder spray gun, comprising:
a rotatable nozzle driven by a spindle and motor;
said nozzle having a powder flow path through which powder flows out of
the spray gun;
said spindle having a passageway there through in fluid communication with
said
nozzle powder flow path; and
a non-rotating powder feed member that provides powder into said spindle
passageway;
a corona electrode for corona charging powder sprayed from said nozzle; and
at least one of said nozzle, spindle and powder feed member comprising
triboelectric
charging material to tribocharge powder flowing therethrough.

2. The spray gun of claim 1 wherein each of said nozzle, spindle and powder
feed member comprise triboelectric charging material.

3. The spray gun of claim 1 wherein said triboelectric charging material
produces negative polarity tribocharging of the powder and said corona
charging is negative
polarity.

4. The spray gun of claim 1 comprising a ground electrode that discharges
triboelectric surface charges of said tribocharging material.

5. The spray gun of claim 1 wherein said triboelectric material produces
positive polarity tribocharging of the powder and said charging is positive
polarity.

6. The spray gun of claim 1 wherein said tribocharging material comprises an
acetal resin blend.

7. A powder spray gun, comprising:
a rotatable nozzle, a powder feed path in fluid communication with said
rotatable nozzle, and an electrode for corona charging powder sprayed from
said rotatable
nozzle;
wherein said powder feed path comprises triboelectric charging material.



-47-
8. The spray gun of claim 7 wherein said nozzle comprises triboelectric
charging material.
9. The spray gun of claim 7 wherein said triboelectric charging material
charges
powder with a positive or negative polarity.
10. A powder spraying apparatus, comprising:
a spray gun having a triboelectric charging section and a trigger for
controlling flow of powder through said spray gun;
an electrode for corona charging powder sprayed by said spray gun; and
a switch actuated by said trigger for selecting and changing charging modes
of the spraying apparatus, wherein said charging modes comprise tribocharging
with corona
charging and tribocharging without corona charging.
11. The spraying apparatus of claim 10 wherein said electrode is external said
spray gun.
12. The spraying apparatus of claim 10 wherein said electrode is internal said
spray gun.
13. The spraying apparatus of claim 10 wherein said spray gun comprises a
nozzle and said electrode is disposed in powder flow path of said nozzle.
14. The spraying apparatus wherein said spray gun comprises a rotatable nozzle
and said electrode is external said rotatable nozzle.
15. A powder spraying apparatus, comprising:
a manual powder spray gun having a triboelectric charging section;
an electrode for corona charging powder sprayed by said spray gun; and
a switch on said spray gun for selecting and changing modes of the spraying
apparatus, wherein said charging modes comprise tribocharging with corona
charging and
tribocharging without corona charging.
16. The spraying apparatus of claim 15 wherein said tribocharging section
comprises at least one air jet in fluid communication with a source of
pressurized air to



-48-
increase tribocharging contact of the powder;
said switch being operable to control said pressurized air to select directed
air
tribocharging as a third charging mode.
17. The spraying apparatus of claim 15 wherein said tribocharging section
comprises a nozzle.
18. The spraying apparatus of claim 15 wherein said tribocharging section
comprises negative tribocharging material.
19. The spraying apparatus of claim 18 wherein said electrode negatively
charged
powder.
20. The spraying apparatus of claim 15 wherein said tribocharging section and
said electrode positively charge powder.
21. The spraying apparatus of claim 15 wherein said electrode is either
internal or
external said spray gun.


22. The powder spraying apparatus of claim 10, wherein said spray gun further
comprises:
a rotatable nozzle driven by a spindle and motor;
said nozzle having a powder flow path, through which powder flows out of the
spray gun;
said spindle having a passageway there through in fluid communication with
said nozzle powder flow path; and
a non-rotating powder feed member that provides powder into said spindle
passageway;
wherein at least one of said nozzle, spindle and powder feed member comprises
a triboelectric charging material to tribocharge powder flowing therethrough.
23. The spray gun of claim 22 wherein each of said nozzle, spindle and powder
feed
member comprise a triboelectric charging material.
24. The spray gun of claim 10 wherein said triboelectric charging section
produces
negative polarity tribocharging of the powder and said corona charging is
negative
polarity.
25. The spray gun, of claim 10 comprising a ground electrode that discharges
triboelectrio
surface charges of said tribocharging section.
26. The spray gun of claim 10 wherein said tribocharging section produces
positive
polarity tribocharging of the powder and said corona charging is positive
polarity.
27. The spray gun of claim 10 wherein said tribocharging section comprises an
acetal
resin blend.
28. The spray gun of claim 10 wherein said tribocharging section comprises at
least one
air jet in fluid communication with a source of pressurized air to increase
tribocharging
contact of the powder.

Description

Note: Descriptions are shown in the official language in which they were submitted.



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Title of the Invention
UNIPOLARITY POWDER COATING SYSTEMS INCLUDING
TRIBOCHARGING AND CORONA GUN COMBINATION
RELATED APPLICATIONS
This application is a continuation-in-part of pending United States patent
application
serial no. 10/139,939 filed on May 7, 2002 for UNIfOLARITY POWDER COATING
SYSTEMS INCLUDING IMPROVED TRIBOCHARGING AND CORONA GUNS, which
1 o is a continuation-in-part of pending United States patent application
serial no. 09/901,162
filed on July 9, 2001 for UNIPOLARITY POWDER COATING SYSTEMS INCLUDING
llVIPROVED TRIBOCHARGING AND CORONA GUNS, which is a continuation-in-part of
pending United States patent application serial no. 09/724,363 filed on
November 28, 2000
for UNIPOLARITY POWDER COATING SYSTEMS INCLUDING IMPROVED
15 TR1BOCHARGING AND CORONA GUNS, the entire disclosures all of which are
fully
incorporated herein by reference. All of the above patent applications and the
present
application also claim the benefit of United States Provisional patent
application serial no.
60/217,261 filed on July 11, 2000 for A UNIfOLARITY POWDER COATING SYSTEM
INCLUDING AN IMPROVED TRIBOCHARGING GUN, UNIPOLARITY GUN AND
2 o METHOD FOR MAKING SAME, the entire disclosure of which is fully
incorporated herein
by reference. The present application also claims the benefit of United States
Provisional
patent application serial no. 60/327,222 filed on October 5, 2001 for
COMBINATION
POWDER SPRAY GUN, the entire disclosure of which is fully incorporated herein
by
reference.
2 5 Field of the Invention
This invention relates to powder coating systems which use corona and
tribocharging
powder spray guns to apply an electrostatic charge to powder for deposition on
a substrate.
Background of the Invention
There are two basic types of powder spray guns which are commonly used in the
3 o electrostatic powder spray coating of articles. The most common type of
spray gun is the
corona type, which has a high voltage charging electrode which produces a
corona to charge
the powder. Typically, corona guns are designed to charge the powder
negatively. One
maj or disadvantage of corona guns is that they do not coat the interior
corners of parts well
due to the strong electrostatic field or Faraday caging effect produced by the
corona electrode.
3 5 A second disadvantage to corona guns is that back ionization may occur due
to the formation
of free ions which results in pinholing or an orange peel surface of the part
to be coated.
Another disadvantage to these type of guns is that the system components such
as the nozzle,
and diffuser as well as the powder deliver system components such as the pump,
hopper and


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other parts in contact with the powder delivery system are typically made of
materials such as
polyethylene or polytetrafluoroethylene (PTFE). While these materials have the
advantage of
low impact fusion, they have the disadvantage of positively charging the
powder, which can
impair the negative corona charging process because the final or maximum
charge on the
powder is diminished. Further, more voltage is often required in order to
counteract the
positive polarity charging of the system. In addition, this positive polarity
tribocharging may
cause breakdown of the powder conveying components such as the hose, which
connects the
pump to the spray gun.
A second type of gun which is also commonly used is a tribocharging gun in
which
1 o the powder is charged by frictional contact with the interior surfaces of
the gun. One
advantage to triboelectric guns is that the powder can easily penetrate
corners of parts to be
coated because the gun does not produce a strong electric field like a corona
gun does.
Summary of the Present Invention
The invention provides novel electrostatic powder coating guns and system
1 s components in which powder is pre-charged to the same polarity as a charge
applied by the
powder spray gun in order to increase and enhance the applied charge and the
transfer
efficiency. Also novel powder coating methods are described.
In accordance with one aspect of the invention, an apparatus for spraying
powder
coating material is described. The apparatus has a powder flow path, wherein
the powder
2 o flow path has a charging surface for triboelectrically charging powder
coating material which
comes in contact with the charging surface, and the charging surface comprises
a negative
tribocharging material selected from polyamide resin blends, fiber reinforced
polyamides,
aminoplastic resins and acetal polymers.
In accordance with another aspect of the invention, an apparatus for spraying
powder
2 s coating material has a powder flow path, wherein the powder flow path has
a charging surface
for triboelectrically charging powder coating material which comes in contact
with the
charging surface, and wherein one or more air passages are formed through the
charging
surface, the air passages being in a fluid communication with a source of
compressed air.
In accordance with another aspect of the invention, an apparatus for spraying
powder
s o coating material is described. The apparatus has a powder flow path
through which the
powder coating material flows, wherein the powder flow path has a first
charging surface for
triboelectrically charging powder coating material which comes in contact with
the first
charging surface, the first charging surface comprising a tribocharging
material having a first
charging polarity, the apparatus further comprising a component through which
powder
3 s coating material also flows, the component having a second charging
surface which also
comprises a tribocharging material having the first charging polarity.


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In accordance with another aspect of the invention, a system for applying
powder
coating materials to articles is described. The system includes a powder feed
apparatus for
supplying powder coating material and an apparatus for spraying powder coating
material
received from the feed apparatus. The spraying apparatus has an electrode for
charging the
powder coating material a first charging polarity. The feed apparatus includes
a component
having a charging surface for triboelectrically charging powder coating
material which comes
in contact with the charging surface, the charging surface comprising a
tribocharging material
having the first charging polarity.
In accordance with another aspect of the invention, a system for applying
powder
s o coating materials to articles is described. The system includes at least
one corona charging
spraying apparatus and at least one tribocharging spraying apparatus. The
corona charging
spraying apparatus has an electrode for charging the powder coating material a
first charging
polarity. The tribocharging spraying apparatus has a powder flow path, wherein
the powder
flow path has a charging surface for triboelectrically charging powder coating
material which
comes in contact with the charging surface, the powder coating material being
charged to the
first polarity by the charging surface of the tribocharging spraying
apparatus.
In accordance with another aspect of the invention, a tribocharging powder
spraying
apparatus is described. The apparatus includes a body having an internal bore,
a wear tube
located within the internal bore, and an open passageway provided between the
internal bore
2 o and the wear tube, with at least one air jet passageway being provided
through the wear tube.
The air jet passageway provides fluid communication between the open
passageway and the
interior of the wear tube. The wear tube has a charging surface for
triboelectrically charging
powder coating material which comes in contact with the charging surface. The
open
passageway is in fluid communication with a source of compressed air, whereby
compressed
air flows from the open passageway through the air jet passageway into the
interior of the
wear tube to affect the flow of powder coating material through the wear tube.
In accordance with another aspect of the invention, a system for applying
powder
coating materials to articles is described. The system includes a powder feed
apparatus for
supplying powder coating material and an apparatus for spraying powder coating
material
3 o received from the feed apparatus. The feed apparatus includes a component
having a
charging surface for triboelectrically charging powder coating material that
comes in contact
with the charging surface. The component charging surface is comprised of a
negative
tribocharging material selected from polyamide resin blends, fiber reinforced
polyamides,
aminoplastic resins and acetal polymers.


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In accordance with another aspect of the invention, a triboelectric powder
coating gun
has a component which includes a triboelectric charging surface, wherein the
component is
capable of assembly into the gun in at least two different positional
orientations. Still a
further aspect of the invention provides a triboelectric powder coating gun
having a
s triboelectric charging surface and an air jet which impinges on the charging
surface, further
including a ground element which is positioned upstream of the charging
surface.
In accordance with another aspect of the invention, spray patterns from
electrostic
spray guns are shaped so as to slow down and to more uniformly distribute
powder
throughout the powder cloud or spray that is ejected from the spray gun
nozzle. In one
1 o embodiment, a nozzle is provided with two or more primary openings or
slots formed therein
that are angled so as to direct respective portions of the powder at each
other. The impinging
powder spray portions slow down the powder spray and cause a ballooning or
spreading
effect to widen the primary spray pattern. The nozzle slots are arranged so as
to reduce or
minimize the likelihood that powder particles could pass through the nozzle
and out a slot
15 without contacting a surface of the nozzle. The nozzle slots also produce a
backpressure
effect that increases random powder particle collisions with each other and
nozzle surfaces to
enhance tribocharging of the powder.
In accordance with another aspect of the invention, spray patterns are shaped
by
adjusting flow characteristics about the outer periphery or envelope of the
primary spray
2 o pattern. In one embodiment, a spray nozzle includes one or more secondary
openings that
function as vents to reduce pressure build up within the nozzle and to provide
an air flow and
powder flow about the outer periphery of the powder cloud or spray pattern
produced by the
primary nozzle slots. This additional flow about the periphery of the primary
spray pattern
adds more powder particles to the peripheral region of the spray pattern
thereby increasing the
2 5 uniformity of powder distribution in the resultant spray pattern. The
vents may be used in
combination with the angled nozzle slots or with a conventional nozzle orifice
design.
Further powder spray pattern shaping and uniformity, as well as velocity
reduction
and forward direction, may be augmented by the use of one or more deflectors.
The deflector
may be made of tribocharging material.
3 o In accordance with another aspect of the invention, a circular spray
pattern is effected
with a spray nozzle that is preferably but not necessarily a unitary
structure. In one
embodiment, a spray nozzle includes a conical slot provided by a cone shaped
deflector that is
integrally supported at one end of the nozzle by a number of ribs. The size of
the spray
pattern may be determined in part by the size, shape and angle of the conical
slot.


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In accordance with another aspect of the invention, a spray nozzle is provided
that
includes material or a surface that produces a tribocharging effect to powder
particles ejected
through the nozzle. Various openings and slots may be used to enhance the
tribocharging
effect. In accordance with another aspect of the invention, a spray gun
operator is grounded
in common with the ground feedback of a tribocharge spray gun. In one
embodiment this is
effected by a grounded gun handle coupled to the feedback or discharge ground
path for the
spray gun. A further aspect of the invention contemplates a modular
tribocharging gun design
that accommodates gun length modifications as needed including "on the fly"
gun length
changes.
1 o In accordance with another aspect of the invention, corona charging and
tribocharging
technologies are combined into a single powder spraying apparatus to derive
synergistic
benefits from each technology. In one embodiment, a rotary atomizing spray gun
includes a
tribocharging section and an internal or external electrode for corona
charging. Tribocharging
may either be positive.or negative polarity, with the corona charging being
the same polarity
as the tribocharging polarity.
In accordance with another aspect of the invention, a powder spraying
apparatus is
contemplated to have a tribocharging section and a corona charging section,
and a gun
mounted switch arrangement by which a charging mode can be selected or
changed. In one
embodiment, the charging modes include but are not limited to tribocharging
with corona
2 o charging and tribocharging without corona charging. A third charging mode
may be, for
example, directed air tribocharging. In a specific exemplary embodiment, the
switch
arrangement is actuated with a spray gun trigger control device.
The various aspects of the present invention may be used individually or in a
number
of different combinations and subcombinations for a spray gun.
2 5 These and other aspects of the invention are herein described in detail
with reference
to the accompanying Figures.
Description of the Figures
Figure 1 is a cross-sectional view of a tribocharging gun which incorporates
the novel
unconventional materials of the invention;
3 o Figure 2 is a cross-sectional view of a novel short barrel tribocharging
gun of the
presentinvention;
Figures 3A through 3D illustrate a portion of the insert of the gun of Figure
2 in
which the airjets are arranged in various opposed configurations;
Figure 4A illustrates a cross-sectional view of the insert of the short barrel
3 5 tribocharging gun of Figure 2, aft looking forward, in which the airj ets
are not vertically
offset from each other;


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Figures 4B through 4E illustrate cross-sectional views of the insert of the
short barrel
tribocharging gun of Figure 2, aft looking forward, in which the airjets are
vertically offset
from each other a perpendicular distance H;
Figures SA and SB each illustrate a cross-sectional view of the insert of the
short
barrel tribocharging gun of Figure 2, aft looking forward, in which a first
set of airjets as
shown in Figure SA are not rotationally offset from a second set of downstream
airjets as
shown in Figure SB;
Figures SE through SF each illustrate a cross-sectional view of the insert of
the short
barrel tribocharging gun of Figure 2, aft looking forward, in which a first
set of airjets as
to shown in Figures SC and SE are rotationally offset from a second set of
downstream airjets as
shown in Figures SD, and SF, respectively;
Figures SG and SH each illustrate a cross-sectional view of the insert of the
short
barrel tribocharging gun of Figure 2, aft looking forward, in which a first
set of airjets as
shown in Figures SG are not rotationally offset from a single downstream
airjet as shown in
Figure SH;
Figure 6 illustrates a cross-sectional view of a corona gun which incorporates
the
novel unconventional materials of the invention;
Figure 7 illustrates a cross-sectional view of a flat spray nozzle which
incorporates
the novel unconventional materials and one or more airjets of the invention;
2 o Figure 8 is a cross-sectional view of a powder pump of a powder coating
system
which incorporates the novel unconventional materials of the invention;
Figure 9 illustrates a perspective schematic view of powder coating system
which
includes a corona and tribocharging gun which charge the powder to the same
polarity;
Figure 10 is a cross-sectional view of an alternate embodiment of a
tribocharging gun
of the present invention which incorporates airjets;
Figure 10A is a cutaway view of the gun shown in Figure 10 in the direction
10A-
10A;
Figure 11 is a cross-sectional view of yet another alternate embodiment of a
tribocharging gun of the present invention which incorporates airjets arranged
in a helical
3 o pattern;
Figure 1 1A is a cutaway view of the gun shown in Figure 11 in the direction
11A-
1 1A;
Figure 12 is a cross-sectional illustration of another embodiment of a
tribocharging
gun using air j ets;
3 5 Figure 13 is a cross-sectional illustration of a modified version of the
gun in Figure
12 having a portion with air jets and a tribocharging post-charge portion;


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Figure 14 is another cross-sectional illustration of a modified version of the
gun in
Figure 12 in which there is a pre-charge portion with air j ets followed by a
tribocharging
portion;
Figures 15 and 16 are cross-sectional views of two embodiments of an inside-
out gun
in accordance with the invention;
Figure 17 illustrates an embodiment of an air jet induced charging gun in a
conventional manual spray gun configuration;
Figures 18A-D illustrate additional embodiments of the gun style of Fig. 17
using
different extension lengths;
1 o Figure 19 illustrates an inside-out gun in a manual gun configuration;
Figure 20 illustrates a spray gun that incorporates an inside-out
configuration with an
outside-in configuration;
Figures 21-24 illustrate another embodiment of the invention;
Figures 25-27 are longitudinal cross-section, elevation and front end views
respectively of a spray nozzle with angled slots;
Figure 28 is a perspective view of the spray nozzle of Figures 25-27;
Figures 29-31 are longitudinal cross-section, elevation and front end views
respectively of a conical spray nozzle;
Figure 32 is a perspective view of the spray nozzle of Figures 29-31;
2 o Figure 33 is a perspective view of a first embodiment of a deflector;
Figure 34 is the deflector of Figure 33 in longitudinal cross-section;
Figure 35 is a longitudinal cross-section of a spray gun using the nozzle of
Figure 32
and deflector of Figure 34;
Figure 36 is a perspective view of an alternative deflector design;
Figure 37 is the deflector of Figure 36 in longitudinal cross-section;
Figure 3 8 is a longitudinal cross-section of a spray gun using a nozzle of
Figure 32
and a deflector of Figure 36;
Figure 39 is a gun extension assembly in longitudinal cross-section;
Figure 40 is a longitudinal cross-section of a splice used in the assembly of
Figure 39;
3 o Figure 41 is a spray gun in longitudinal cross-section using a gun
extension assembly
of Fig. 39;
Figure 42 is a partially exploded illustration in longitudinal cross-section
of the gun
of Figure 41 to show assembly of the gun extension for modifying gun length;
Figure 43 illustrates in longitudinal section a combination tribocharging and
corona
3 5 charging rotary atomizing powder spray gun in accordance with the
invention; and
Figure 44 illustrates a switch arrangement with a combination tribocharging
and


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corona charging spray gun in accordance with the invention.
Detailed Description of Preferred and Alternate Embodiments
The following Detailed Description of Preferred and Alternate Embodiments is
s divided into the following sections. Section I provides a detailed
description of a novel
tribocharging gun which charges a powder to a negative polarity by frictional
contact with
novel use of unconventional materials as described in more detail below.
Section II provides
a detailed description of a novel short barrel tribocharging gun which can
charge powder to a
positive or negative polarity depending upon the materials selected for
frictional contact with
s o the tribocharging surfaces of the gun. Sections III and IV concern a
corona gun and powder
supply system, respectively, with the corona gun and system including
components which
charge the powder to the same polarity as the corona gun by frictionally
contacting the
powder with tribocharging surfaces comprised of the desired positive or
negative
tribocharging material. Section V provides a detailed description of a powder
coating system
15 which includes corona and tribocharging guns which charge the powder to the
same polarity
so that the tribocharging gun can be used in conjunction with the corona gun
to coat the same
workpiece. Section VI provides a detailed description of an alternate
tribocharging gun
embodiment which utilizes air jets. Section VII provides a detailed
description of a
combination powder spraying apparatus having a tribocharging section and a
corona charging
2 o section, and various aspects and control features thereof.
I. NEGATIVE TRIBOCHARGING GUN CONSTRUCTED FROM
UNCONVENTIONAL MATERIALS.
2s A. UNCONVENTIONAL NEGATIVE CIiARGING
TRIBOMATERIALS
A part of this invention is the discovery of what will be referred to herein
as
"unconventional negative charging tribomaterials". These materials are useful
as powder
3 o contact surfaces for negatively charging powder coating material by
frictional contact with the
powder contact surfaces of a powder spray gun. The term "negative charging
tribomaterials"
means materials which impart a negative charge to powders, such as powdered
paints, upon
frictional impact with the surface of the negative charging tribomaterials.
As described in more detail in this application, the unconventional negative
charging
3 5 tribomaterials could be used as the interior surfaces of tribocharging or
corona powder spray
guns, as well as spray gun components and powder delivery system components
such as the
diffuser, powder tube, feed hopper, and pump as described in more detail in
Section IV.
Although the unconventional negative charging tribomaterials are lrnown
generally, they have


CA 02460374 2004-03-18
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not been previously known to be useful in spray guns in order to tribocharge
powder coating
materials.
The non-conventional negative charging tribomaterials are selected from
polyamide
blends, fiber reinforced polyamide resins, the aminoplastic resins, acetal
polymers or mixture
thereof, and are described in more detail, below. These materials not only
charge well
negatively but they also do not experience impact fusion problems as
significant as negative
tribo charging materials which have been used in the past such as nylon.
The Polyamide Blend
The polyamide blend comprises a blend of a polyamide polymer and a second
1 o polymer selected from the group consisting of: polyethylene,
polypropylene, halogenated
hydrocarbon resin, and mixtures thereof. The polyamide polymer is preferably
present in the
polyamide blend from 50% to 96%, more preferably from 70% to 90%, by weight.
The
second polymer is preferably present in the polyamide blend from about 4% to
about 50%,
more preferably from about 10% to about 30%, most preferably from about 15% to
about
s5 25% by weight.
The halogenated hydrocarbon resin is preferably a fluorinated hydrocarbon
resin,
such as for example, polytetrafluoroethylene, (also known as PTFE); a
copolymer of
tetrafluoroethylene and hexafluoropropylene (also known as FEP); and a
copolymer of
tetrafluoroethylene and perfluorinated vinyl ether (also known as PFA).
Suitable fluorinated
2 o resins are commercially available under the tradename TEFLON~ from DuPont.
The polyamide polymer in the polyamide blend is preferably a nylon. Preferred
grades of nylon are nylon 6/6, nylon 6/12, nylon 4/6 and nylon 11. A suitable
polyamide
blend is a 20% polytetrafluoethylene and 80% nylon 6/6 commercially available
under the
trade name Lubricon RL 4040 from LNP Engineeripg Plastics, Division of ICI
Advanced
25 Materials, Exton, Pennsylvania. A suitable blend is about a 5%
polytetrafluoethylene and
about a 95% nylon 6/6 commercially available under the trade name Lubricon RL
4010 from
LNP Engineering Plastics, Division of ICI Advanced Materials, Exton,
Pennsylvania.
Example 1
Individual discs of a 20% polytetrafluoethylene and 80% nylon 6/6,
3 o polyamide/halogenated hydrocarbon resin blend were prepared. For
comparison, coupons of
conventional material, that is, nylon and Teflon were also prepared.
The relative transfer efficiency was determined by spraying powder paint from
a flat
spray nozzle with a 0.450 inch by 0.065 inch slot at an air flow rate of 4
cubic feet per minute
onto a disc at a 45° angle. The powder impacted the surface of the disc
of the tribocharging
3 5 material and was deflected from the disc onto a grounded metal target. The
powder exiting
the nozzle had a measured initial charge of zero. Thus, all of the powder
charging was due to


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impacting the tribomaterial. The amount of powder adhered to the target as
compared to the
total powder sprayed is defined as the relative transfer efficiency.
Typically, 50 grams of
polyester epoxy powder from Ferro Corporation was the powder used for the
tests. Since this
relative transfer efficiency test is done by a single impact from a coupon,
the values tend to be
lower than for numerous contacts using a tribocharging gun.
The powder used in the evaluation was a polyester epoxy powder, designated
153W-
121, from Ferro Corporation. The results are shown below in Table I.
Example 2
Individual discs of a 5% PTFE and 95% nylon 6/6, polyamide blend were prepared
to and the transfer efficiency was evaluated as in Example 1. The results are
shown below in
Table I.
The advantage of using the polyamide blends in powder spray guns is that they
increase the powder charging due to increased discharging of the tribocharged
gun surfaces.
The increased surface discharging is due to the incompatible polymers which
provide for a
leakage path that is not present in the homogeneous polymer. Another advantage
of using
these polyamide blends is that reduced moisture absorption of nylons occur
when they are
filled with PTFE or polyethylene.
2. The Fiber Reinforced Polyamide Resin
The fiber reinforced polyamide resin comprise a polyamide polymer filled with
2 o polyaramide fibers. Preferably there is from about 50% to about 99%, more
preferably from
about 85% to about 95% of the polyamide polymer. Preferably there is from
about 1% to
about 50%, and more preferably from about 5% to about 15% of the polyaramide
fiber in the
polyamide polymer.
The polyamide polymer in the fiber reinforced polyamide resin is preferably
z 5 commercially available polyamide polymers. Suitable polyamides are for
example, nylons.
The polyaramide fibers are long chain synthetic aromatic polyamides in which
at least
85% of the amide linkages are attached directly to two aromatic rings. A
suitable
polyaramide fiber is a polyp-phenylene terephthalamide) commercially available
under the
trade name KEVLAR~, from DuPont. The polyaramide fiber, poly(m-phenylene
3 o terephthalamide), commercially available under the trade name Nomex, from
DuPont, is less
preferred. Examples of other polyaramide fibers are the polymer comprising
polymerized
units of p-aminobenzhydrazide and terephthaloyl chloride; a suitable such
polymer is
commercially available under the trade name PABH-T X-500 from Monsanto.
A suitable fiber reinforced polyamide resin is 10% KEVLAR~ in 90% nylon 6,6
3 5 available under the trade name Lubricon RA from LNP Engineering Plastics,
Division of ICI
Advanced Materials, Exton, Pennsylvania.


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Example 3
Individual discs of the fiber reinforced polyamide resin were prepared. For
comparison, coupons of conventional, non fiber containing nylon and Teflon
were also
prepared. The relative transfer efficiency was determined as in Example 1. The
results are
s shown below in Table I.
TABLE I
EXAMPLE MATERIAL DISK POLARITY RELATIVE


THICKNESS TRANSFER


(IN~ EFFICIENCY



ComparativeNylon 6,6 0.155 - 16.5


1 5% PTFE in Nylon0.250 - 21.3
6,6


2 20% PTFE in Nylon0.250 - 24.7
6,6


3 10% I~EVLAR~ 0.123 - 39.2
in


Nylon 6,6


Comparative100% I~EVLAR~ --- + 54.3
tow


fibers


4 Nylon R MoS2 0.118 - 22.4
filled


Surprisingly, despite the fact that the KEVLAR~ tow fiber charges powder
positively
in the comparative example, the addition of such fiber to the nylon which
charges negatively,
1 o increased the relative transfer efficiency.
The Aminoplastic Resins
The aminoplastic resins are comprised of polymerized units of an amine monomer
and an aldehyde monomer. Preferred aminio plastic resins are aniline
formaldehyde resins,
urea formaldehyde resins and melamine formaldehyde resins. ~ptionally, the
aminoplastic
15 resins further comprise cellulose such as alpha-cellulose and pigments.
Suitable molding grade melamine formaldehyde resins filled with alpha
cellulose, are
commercially available under the trade name Perstorp 752026 white melamine or
Perstorp
775270 red melamine available from Perstorp Compounds, Inc. in Florence,
Massachusetts.
Another suitable melamine resin is a melamine phenol-formaldehyde copolymer,
z o commercially available under the trade name Plenco 00732, from Plenco
Plastics Engineering
Company in Sheboygan, Wisconsin.
Another suitable melamine resin is a melamine formaldehyde polymer, Perstop
752-
046, available from Perstorp Compounds, Inc. in Florence, Massachusetts.
Example 4
2 s Individual discs of the white melamine formaldehyde resin, Perstorp
752026, filled
with alpha cellulose were obtained. For comparison, discs of conventional
nylon 6/6 were
also prepared. Relative transfer efficiency was determined as in Example 1.
The results are
shown below in Table II.


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Examule 5
Individual discs of the red peppercorn melamine formaldehyde resin, Perstorp
775270, filled with alpha cellulose were obtained. For comparison, discs of
conventional
nylon were also prepared. The relative transfer efficiency was determined as
in Example 1.
The results are shown below in Table II.
Example 6
Individual discs of the melamine phenol-formaldehyde resin, Plenco 00732 were
obtained. For comparison, discs of conventional nylon were also prepared. The
relative
transfer efficiency was determined as in Example 1. The results are shown
below in Table II.
s o Example 7
Individual discs of the white melamine formaldehyde resin Perstorp 752-046,
were
obtained. For comparison, discs of conventional nylon were also prepared. The
relative
transfer efficiency was determined as in Example 1. The results are shown
below in Table II.
TABLE II. RELATIVE TRANSFER EFFICIENCY OF FERRO 153W-121
ON CONTACT WITH AMINO RESIN COUPONS
EXAMPLE MATERIAL POLARITY RELATIVE


TE


Com arative Nylon 6/6 Negative 16.5


4 Perstorp 752026 white Negative 37.7


Melamine


5 Perstorp 775270 red Negative 37.0


Pep ercorn melamine


6 Plenco 00732 melamine/ Negative 28.7


henol formaldehyde


7 Perstorp 752-046 Negative 44.9


Melamine-formaldehyde


Powder flow rate = 1.5 g/s
2 o Examples 8-10
A short barrel tribo gun as described herein in Section II and shown in Figure
2, was
fabricated, in which the interior surfaces of the gun, specifically the
interior surface of the
powder conduit insert and flat spray nozzle, were made of red peppercorn,
melamine
formaldehyde, designated Perstorp 775270 from Perstorp Compounds Inc.,
Florence,
2 s Massachusetts. The gun used in the test had two pairs of air jets and two
electrodes. The air
jets were offset from the centerline which is perpendicular to the
longitudinal axis by one jet
diameter and the second set of air jets was rotated about the longitudinal
axis by 5 degrees
relative from the first set of air jets. The angle of the air jets was 90
degrees.
The relative transfer efficiency was determined by spraying a set amount of
powder at
3 o a target, moving perpendicular to the spray gun at the rate of 10 feet per
minute. The powder


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in the spray gun was an epoxy polyester powder, designated 153W-121 from Ferro
Corporation. The results are presented below.
TABLE III.
EXAMPLE NO. MELAMINE FORMALD. POLARITYRELATIVE TRANSFER


GRADE EFFICIENCY



Com arative Nylon 6/6 Negative79.3


Ex. 8 Melamine G-9 from Negative80.6
Atlas


Fibre Co. of


Skokie, Illinois


Ex. 9 Red peppercorn melamineNegative74.3


Persto 775270


Ex. 10 White melamine 700 Negative74.7
Series


Molding Compound
from


Perstorp


4. Acetal Resins
The acetal resin is a polyoxymethylene engineering thermoplastic polymer. The
acetal resin is a homopolymer or a copolymer. The acetal resin is optionally
combined with
polytetrafluorethylene, polytetrafluoroethylene fibers, and polyethylene, or
other polymers or
1 o additives. Suitable acetal homopolymers are conunercially available under
the trademark
Delrin~ from E.I. DuPont de Nemours & Co., in Wilmington, Delaware. A suitable
example
is an acetal homopolymer resin comprising 20% Teflon PTFE fibers, and is
commercially
available under the trade name Delrin AF. One advantage of this material is
that electrical
shocks from stored capacitance to operators handling this gun are less with
this material than
other materials tested.
A suitable modified copolymer resin is an acetal copolymer modified with an
ultra
high molecular weight polyethylene (UHLMWPE) which is commercially available
under the
trade name UltraformOO N2380X available from BASF Corp., Parsippany, New
Jersey.
Another suitable acetal copolymer is commercially available under the trade
name CelconOO
2 o from the Hoechst Celanese Corp. in Chatam, New Jersey.
Example 11
A short barrel tribocharging gun as described below in Section II and shown in
Figure 2, was fabricated, in which the interior surfaces of the gun,
specifically the interior
surface of the insert were made from the acetal polymer Delrin 150 from
DuPont.
2 5 The powder in the spray gun was an epoxy polyester powder, designated 153W-
121
from Ferro Corporation or a polyester/urethane powder, designated 153W-281
from Ferro
Corporation. The transfer efficiency was determined as in the Examples 8-10.
The results are
presented below.


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Transfer efficiency results are about 62% for both powders as shown in Table
IV.
below at a flow rate of 2.5 g/s.
TABLE IV.
AVERAGE TRANSFER EFFICIENCY
OF DELRIN SHORT TRIBO
GUN



SAMPLE AVERAGE TE


153W-121 61.9


155W-281 62.3


One advantage to these acetal resins is that they are capable of being
injection
molded, thus making it possible to fabricate a low cost powder spray gun. The
Delrin acetal
resin relative transfer ef~~iciency results were surprising and unexpected
because the Delrin
resin does not contain nitrogen atoms, which are typically found in negatively
charging
materials such as nylon and melamines. It was also discovered that the
presence of PTFE
1 o fibers in the Delrin acetal resin, such as with the Delrin AF acetal
resin, resulted in an
increase in transfer efficiency over the Delrin acetal resin.
B. NEGATIVE TRIBOCHARGING GUN WITH UNCONVENTIONAL
MATERIALS
Referring now to Figure l, there is shown a tribocharging powder spray gun 10
for
use with the method and apparatus of the present inventions. The gun 10
includes a gun body
12 having a central opening extending therethrough. The gun 10 may be
supported by a
suitable gun mount assembly which is known by those skilled in the art. The
gun 10
2 o comprises a powder feed portion 20, a tribocharging portion 30 and a
sprayhead portion 40 at
the outlet end of the gun.
The tribocharging portion 30 of the gun comprises an inner core 34 positioned
within
an outer cylinder 32 in which the surfaces 34a, 32a cooperate to provide an
annular charging
path for the powder flowing through the charging path of the gun. As shown in
Figure 1, the
surfaces 34a, 32a may optionally comprise a wavy or undulating surface so that
the annular
gap provides a tortuous path for the powder, thereby enhancing powder contact
with the
surfaces 34a,32a so that charge is imparted to the powder.
In the preferred embodiment of the invention, some or all of the powder
contact
surfaces of the gun are comprised of a material selected from the group
consisting of: a
3 o polyamide blend, a fiber reinforced polyamide resin, an acetal polymer, an
acetal polymer
homopolymer, a copolymer, preferably filled with PTFE fibers (hereinafter
collectively
referred to as acetyl polymer), an aminoplastic resin or mixtures thereof.
These are the
unconventional negative charging tribo materials of this invention which have
been found to
charge well. Thus the powder contact surface may be coated with the above
mentioned


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material or the respective component having the powder contact surface may be
constructed
in whole or in part from the above mentioned materials. Thus as shown in
Figure 1, the
powder contact surfaces of the outer cylinder 32, the inner core 34 and the
nozzle 40 may be
comprised of a material selected from the group consisting of a polyamide
blend, fiber
reinforced polyamide resin, acetal polymer, aminoplastic resin or mixtures
thereof.
Additionally, the powder contact surfaces of the inner wear sleeve 38, the
outer wear sleeve
40, the inlet wear sleeve 41, the inlet distributor 36, the outlet distributor
37, and the outlet
wear sleeve 42 may be coated with or made entirely of a material selected from
the group
consisting of a polyamide blend, fiber reinforced polyamide resin, acetal
polymer,
z o aminoplastic resin or mixtures thereof. Other powder contact surfaces not
specifically
referenced herein may also comprise the above referenced materials.
A grounded electrode 43, discharge ring or other means know to those skilled
in the
art (not shown) may be utilized to discharge the powder contact surfaces of
the inner core and
outer cylinder from the build up of charge. The grounded electrode or
discharge ring may be
placed in any position known to those skilled in the art.
As shown in Figure 1, powder and the conveying air is fed to the powder feed
portion
20. Powder enters the charging portion of the gun from the feed portion 20 and
is channeled
into the annular charging path located between the inner core 34 and the outer
cylinder 32.
As the air entrained powder repeatedly contacts the powder contact surfaces
32a, 34a of the
2 0 outer cylinder 32 and inner core 34, the powder is tribocharged to a
negative polarity.
Finally, the tribocharged powder is discharged into the sprayhead portion 40
of the gun. In
that unconventional negative charging tribo materials are used, the powder
will be negatively
charged, but the gun will not experience unacceptable impact fusion of the
powder on the
charging surface.
II. SHORT BARREL TRIBOCHARGING POWDER SPRAY GUN
CONSTRUCTED FROM EITHER POSITIVE OR NOVEL NEGATIVE
TRIBOCHARGING MATERIALS.
3 o As shown in Figure 2, a first embodiment of the short barrel tribocharging
gun 200 of
this invention provides a novel powder spray gun of relatively simple
construction and small
size which charges powder by the tribocharging process. The invention has the
advantage of a
removable insert 220 which can be easily changed for fast color change of the
powder. One
important advantage to the short barrel tribogun is that it does not have the
disadvantages of
3 5 strong electric fields or back ionization issues which are present with
corona guns. The gun
as described in more detail below can positively or negatively charge a
powder. The
triboelectric powder charging gun, indicated generally at 200, has an overall
length in a range
of approximately one to ten inches from the powder inlet to the nozzle tip,
and more


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preferably in the range of one to six inches, which is substantially less than
the overall length
of tribocharging guns of the prior art, which typically run from 14-36 inches
in length.
The main components of the gun are a body 210, a powder conduit insert 220
which
fits within the body 210, and a nozzle 230 which also fits within or is
otherwise attached to
s the body 210. The insert 220 and nozzle 230 together form the barrel of the
gun. The body
210 can be fabricated out of any structurally suitable material. The body 210
has an intake
end 212 having an opening adapted to receive an insert 220, and an output end
214 adapted to
receive or connect to the nozzle 230. For manual use, a handle or pistol grip
(not shown)
may be attached to or formed as an integral part of the body 210.
z o The powder conduit insert 220 is preferably a cylindrical tube having an
interior
powder passageway 222. The inner diameter of the powder passageway 222 may
preferably
be in the range of about 0.25 inches to about 1.5 inches, and most preferably
is 0.5".
It is preferred that the insert 220 be removably or releasably connected to
the body by
conventional methods. For a negative polarity gun, it is preferred that the
insert 220 be
15 entirely made of, or have an interior surface 222 coated with, the
materials selected from the
polyamides, preferably nylon 6/6, a polyamide blend, Eber reinforced polyamide
resin, acetal
polymer, aminoplastic resin or mixtures thereof. For a positive charging gun,
the insert 220
may be entirely made of, or have an interior surface 222 coated with a tribo-
charging material
such as, but not limited to, fluoropolymers particularly
polytetrafluoroethylene, or mixtures
2 o thereof. Thus depending upon the type of tribocharging material selected,
a negative or
positive charge is imparted to the powder particles upon contact with the
interior powder
contact surfaces of the insert 220.
The spray gun 200 may further comprise one or more air jets 240 which are
provided
within the interior passageway 222, 234 of the gun. The air jets 240 may be
located within
2 5 the insert 220 or the nozzle 230, and function to create turbulence
resulting in the increase of
frictional contact of the powder with the walls 222 of the insert 220 or the
nozzle 230. Air or
other fluid (hereinafter air) is supplied to the air jets 240 via air passage
250 formed in the
body 210, which leads to a chamber 252 about the insert 220 or nozzle (not
shown). One or
more air jets 240 lead from chamber 252 to the powder passageway 222, 234 in
insert 220 or
3 o nozzle 230 (not shown).
The air jets 240 may comprise any orifice shape such as round, rectangular,
square or
oval. Each air jet cross-sectional area may range from about 0.001 to about
0.03 square
inches (which corresponds to a round hole size of about 0.03 to about .2
inches in diameter).
More preferably, each air jet cross-sectional area may be in the range of
about .003 to about
3 5 .005 square inches (which corresponds to a round hole size diameter of
about 0.06 to about
0.08 inches). Most preferably, the air jet cross-sectional area may be about
0.0038 square


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inches, which corresponds to a round hole size diameter of about 0.07 inches.
As shown in Figure 2, the air jets 240 define an angle 8 with respect to the
longitudinal axis or insert or nozzle side wall of the internal passageway 222
in the range of
about 0 to about 90 degrees, and more preferably in the range of about 45 to
about 90 degrees,
and most preferably about 60 degrees.
The air jets may be arranged in one or more groups of air jets with the same
or
differing diameters. A group may be two or more air jets which may be arranged
in either an
opposed or unopposed configuration. Figures 3A-3D illustrate alternate
configurations of the
arrangements of upper and lower air jets 240 of the insert 220. Figure 3A
illustrates an upper
to and lower air jet 240 in which the air flow from the jets intersect on the
longitudinal axis (or
centerline CL). Both the upper and lower air j ets form an angle of 45 degrees
with the insert
sidewall 222. Figure 3B is almost the same configuration as Figure 3A except
that the center
of the upper air jet is longitudinally offset from center of the lower air
jet, resulting in the air
flow from the air jets intersecting at a point offset from the longitudinal
axis. Figure 3C
z5 illustrates that the air jets may have different air jet angles which
results in the flow of the air
jets intersecting at a point offset from the longitudinal axis. Figure 3D
illustrates that the
upper and lower air jets may be longitudinally offset and have different
angles yet result in
the flow of the jets intersecting at the longitudinal axis.
If two or more air jets are utilized, one air jet may be offset relative to
another air jet a
2 o distance H perpendicular to the longitudinal axis as shown in Figures 4B-
4E. Thus, in
Figures 4B-4E the air jets are vertically offset from one another by varying
the perpendicular
(or vertical) distances H relative to the longitudinal axis. The distance H
may vary from 0 (no
offset) as shown in Figure 4A, to one diameter of the insert as shown in
Figure 4E.
As shown in Figures SA through SH, if two or more groups of air jets are
utilized, one
25 group of air jets may be angularly rotated about the longitudinal axis
relative to the first
group of air jets in the clockwise or counterclockwise direction. It is
preferred that the
downstream group of air jets be angularly rotated in the range of about 0 to
about 90 degrees
relative to the first group in either the clockwise or counterclockwise
direction. Figures SA,
SC, SE and SG each illustrate a first or upstream group of air jets located
within the insert 220
3 0 of Figure 2. Figures SB, SD, SF and SH, represent a second or downstream
group of air j ets
which are rotated 0, 45, 90 and 0 degrees in the counter-clockwise direction
with respect to
the corresponding first set of air jets of Figures SA, SC, SE and SG,
respectively. Figure SH
also illustrates that the second group of air jets need only comprise one air
jet.
The total air flow to the four air jet orifices 240 in Figure 2 may range from
about 0.3
35 cubic feet per minute (CFM) to about 6.5 cubic feet/minute. If two pairs of
air jets are
utilized, the total air flow rate to the air jets is preferably 4.2 CFM. The
air jet orifices 240


CA 02460374 2004-03-18
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typically have an air velocity in the range of about 100 to about 1,000
feet/second, and more
preferably in the range of about 400 to about 800 feet/second, and most
preferably about 655
feet/second. These variables can be scaled appropriately for different
diameter tubes.
The internal charging gun 200 is further provided with one or more electrodes
260 or
other means known to those skilled in the art which function to discharge the
tribocharging
surfaces 222, 234 due to the build up of charge as a result of frictional
contact with the
powder. For example, the electrode may be a conductive pin, a pressed solid
metal ring, an
air washed porous ring, or a metal strip located along the longitudinal axis
inside the charging
tube. The one or more electrodes are preferably electrically grounded.
However, the
1 o electrode 260 may also be charged to either a positive or negative
electrical potential as
shown in Fig. 2, preferably in the range of about 0 to about 10 kilovolts
(kv). The electrode
260 may be positioned within the interior of the insert 220 or the nozzle 230,
however it is
preferred that the electrode be positioned upstream from the air jets. The one
or more
electrodes 260 may be airwashed, i.e., an air flow is provided from chamber
250 through
z5 passages 262 and 264 to blow powder off of the electrode 260.
A flat spray nozzle 230 is shown in Figure 2 in conjunction with the
invention,
although other prior art nozzles would also work for the invention. The nozzle
230 has a slot
232 which creates a generally flat spray pattern, and an interior passageway
234 which is in
fluid communication with the interior passageway 222 of the insert 220. It is
preferred that
2 o the nozzle 230 be removably or releasably connected to the gun body 210 by
any
conventional methods. Because the nozzle is a high powder contact area, for a
negative tribo
charging gun, it is also preferred that the nozzle 230 be entirely made of, or
have an interior
surface 234 coated with a tribo-charging material such as a polyamide,
particularly nylon 6/6,
a polyamide blend, fiber reinforced polyamide resin, acetal polymer,
aminoplastic resin or
2 s mixtures thereof. For a positive tribo charging gun, it is also preferred
that the nozzle 230 be
entirely made of, or have an interior surface 234 coated with a tribo-charging
material such as
fluoropolymers particularly PTFE. Thus depending upon the type of
tribocharging material
selected, a negative or positive charge is transferred to the powder particles
upon contact with
the interior surface 234 of the nozzle 230. Thus the nozzle 230 works in
conjunction with the
3 o insert 220 to tribocharge the powder particles to the desired polarity as
they contact the inner
surface of the gun 200.
Although not shown, the insert 220 and nozzle 230 may be formed as an integral
one
piece unit which is releasably connected to the body 210 (not shown).
Alternatively, the
insert 220 and nozzle 230 may be releasably connected together and then
releasably
s 5 connected to the body. Thus, a particular advantage of the short internal
charging gun 200 of
the invention is the simple configuration of the insert 220 and nozzle 230,
which allows these


CA 02460374 2004-03-18
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components to be fabricated out of, or coated with any of the described
tribocharging
materials and easily interchanged with the gun body 210. An array of inserts
220 and nozzles
230, made of or coated with different tribocharging materials, can be provided
for use with a
single gun body. An appropriate insert and nozzle can then be selected
according to the type
of powder to be sprayed, and according to the type of polarity to be applied
to the powder.
Since powders charge differently from one another depending on their
chemistry, a material-
specific insert can be used for a particular powder chemistry. For example,
epoxies tend to
charge positively, so a PTFE insert would be ideal for this powder.
Polyesters, on the other
hand, tend to charge negatively, and would therefore be charged better using a
nylon insert.
s o The following examples illustrate several gun configurations having
varying
placement of air jets, type and position of electrodes and use of
tribocharging materials.
However, the invention is not limited to these examples, as many other
combinations and
configurations are possible.
Example 12
In one example of the invention, a tribocharging gun 200 having an insert 220
was
fabricated out of nylon 6/6 material. The insert had two pairs of aligned,
opposed air jets, with
each air jet angled in the insert sidewall at an angle 8 of 60 degrees, and
having a velocity of
about 655 feet/second and a total air flow rate of 4.2 cubic foot/minute. The
centerline of the
first pair of air jets is longitudinally spaced 0.625" apart from the
centerline of the second pair
z o of air jets. A grounded electrode was mounted flush with the internal
surface of the
powderflow passageway and was angularly offset from the air j ets by 60
degrees. The gun
was 5.75 inches long as measured from the powder inlet to the tip of a flat
spray nozzle. The
powder flow rate was 20 lbs/hr using Ferro 153W-108 polyester urethane powder.
The
transfer efficiency for this configuration was 78.0%.
z 5 Example 13
In another example of the invention using the same gun configuration as
described in
Example 12, the electrode was charged to -8 KV. The transfer efficiency was
measured at
84%.
Example 14
s o In another example of the invention, a short barrel tribocharging gun was
fabricated
out of Delrin 100 AF material. The total combined length of the insert and
nozzle was 3.375
inches. A 4 mm Delrin 100AF flat spray nozzle was used. As shown in Figure 2,
the insert
inlet diameter was 0.375 inches for a length of 1.25 inches, and was followed
by a 45 degree
step opening the insert diameter to .5 inches for the remainder of the tube
length of 2.125
3 5 inches. Two pairs of opposing air jets were used, with each air jet having
a diameter of 0.07
inches, and having an angle 8 of 60 degrees. The downstream set of air jets
was rotated


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about the longitudinal axis by 5 degrees relative to the first pair of air
jets. All of the air jets
were offset a perpendicular distance from the longitudinal axis by .035
inches. Each air jet
had an airflow rate of about 1 standard cubic feet per minute and a velocity
of 655 ft/sec. A
single grounded sharp tipped electrode was located upstream from the air jets
as shown in
Figure 2. The electrode was angularly rotated about the longitudinal axis by
60 degrees
relative to the first set of air jets. The transfer efficiency for this
configuration was 70% using
Ferro 153W-121 at 20 lbs/hour.
In summary, the above described short barrel tribocharging gun provides a
novel
lightweight spray gun which is easily maneuverable into tight spaces due to
the guns shorter
length and smaller diameter. Conventional tribcharging guns are typically 14-
36 inches in
length, while the short tribocharging gun provides a gun of about 6 inches
long. The gun
lends itself as a manual gun or use as a low cost automatic gun. The straight
flow powder
path allows for easy cleaning, as well as a removable insert which can be
easily replaced by
an inexpensive insert for quick color changes. The novel materials which are
used to make
~5 the gun are injection moldable, thus reducing the machining costs
significantly. Thus the
invention provides a short barrel tribocharging gun which can accommodate a
powder flow
rate of up to about 30 lbs/hour and a reasonable transfer efficiency.
The invention further provides a short barrel negative tribocharging gun which
can be
used alone or in conjunction with a negative corona gun as described in more
detail below.
2 o While providing all of the above described advantages, the short barrel
negative tribocharging
gun further provides the advantage of excellently applying and charging
polyester powders
such as TGIC polyesters, epoxylpolyester hybrid powders, and polyester
urethanes, as well as
thermoplastic powders such as PVC and PTFE powders.
2 5 III. UNIPOLARITY CORONA GUN WITH TRIBO-CHARGING
COMPONENTS.
Referring now to Figure 6, a unipolarity corona spray gun 300 is provided for
spraying fluidized powder that has been charged to either a positive or
negative polarity. The
3 o term "unipolarity" refers to a powder spray gun or powder supply system
wherein the
components are selected to charge the powder coating material to a single
polarity. An
example would be a corona gun with a negative polarity power supply which
includes
tribocharging components such as the spray nozzle which also charges the
powder negatively.
The gun 300 comprises a rearward barrel 328 which may be secured to a mounting
block.
3 5 The rearward barrel 328 has an internal bore 332 and an angled bore 333
for connection to a
powder supply tube 334. The powder supply tube 334 functions to introduce
fluidized
powder through the angled bore 333 into the throughbore 332 of the rearward
barrel member


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328. The forward end of the rearward barrel member 328 is connected to a
forward barrel
member 338, which further comprises a throughbore 346 which is axially aligned
with bore
332 to form a powder flow passageway 350 for transferring powder from the
powder supply
tube 334 towards the forward end of the gun 300. A flat spray nozzle 394 is
located on the
s forward end of the forward barrel member 3 80.
A barrel liner 352 extends axially within the powder passageway 350 which is
mounted within the end of the rearward barrel member 328. The barrel liner 352
receives and
supports a high voltage electrostatic cable assembly 358. An electrode 362 is
mounted at the
forward end of the cable assembly 352 and extends through a bore 396 of the of
the nozzle tip
Zo 390 and extends forward of the spray nozzle 394 between the rectangular
slot 398. The
electrode 362 extending forward of the spray nozzle 380, produces a strong
electrostatic field
between it and the object to be coated. The electrode may be charged
positively or negatively
depending upon the desired gun polarity. It is preferred that the electrode be
charged to the
desired polarity in the range of about 60 to about 100 kv.
15 The powder contact surfaces of the corona gun 300 are the barrel liner 352,
the
powder passageway 350, the powder supply tube 334, and the passageway 372
through
nozzle 380. For a positive polarity corona gun which charges the powder to a
positive
polarity, one or more powder contact surfaces 334, 350, 352, or 372, for
example, are
comprised of materials which tribocharge the powder positively. These
materials are
2 o selected from the group consisting of polyethylene, a fluoropolymer or
mixtures thereof. It is
preferred that the fluoropolymer comprise polytetrafluoroethylene. For a
negative polarity
corona gun which charges the powder to a negative polarity, one or more of the
powder
contact surfaces 334, 350, 352, or 372, for example, of the corona gun 300 are
selected to be
of a material which tribocharges the powder negatively. These surfaces are
comprised of a
2 s material selected form the group consisting o~ a polyamide, a polyamide
blend, a fiber
reinforced polyamide resin, an acetal polymer, an aminoplastic resin or
mixtures thereof, as
described in detail in Section I.
Thus the unipolarity corona gun of the present invention utilizes
tribocharging to
charge the powder as well as the corona charging. The tribocharging which
occurs is of the
3 o same polarity as and therefore increases the charge on the powder which
results from the
corona charging electrode. Because the powder contact surfaces add to the
charge on the
powder produced by the corona electrode, less electrode voltage is needed to
produce the
same amount of charge as in prior art guns. Thus for a negative polarity gun,
reduced back
ionization occurs because the voltage is lower. This results in an improved
surface finish.
3 5 This reduction in electrode voltage also reduces the Faraday Cage effect.
In addition, a
smaller power supply can be used to produce the same voltage.


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In an alternate embodiment of the invention, the corona gun 300 may
additionally
include an enhanced tribocharging nozzle 400 as shown in Figure 7.
Tribocharging nozzle
400 may be used with other prior art corona or tribocharging guns and is not
limited to the
corona gun 300 as described above. Tribocharging nozzle 400 provides a large
interior
surface area which may be utilized in order to tribocharge the powder. The
powder may be
charged positively or negatively as desired depending upon the triboelectric
material selected,
as described in more detail, below.
The nozzle shown generally at 400 has a powder inlet end 410 and an interior
flow
passageway 412 which is in fluid communication with the interior passageway of
a prior art
1 o corona gun or triboelectric gun (not shown). The inlet end 410 may be
threaded or otherwise
configured to be releasably connected to the body of a prior art spray gun.
The interior
passageway 412 is preferably cylindrically shaped with a transition surface
414 leading to the
nozzle slot 420. The nozzle 400 has a slot 420 shaped to create a generally
flat spray pattern.
The depth and width of the nozzle slot 420 may be sized as needed for the
particular
application.
Because the nozzle surfaces 412, 414 are in contact with the powder, it is
preferred
that the nozzle 400 be entirely made of, or have an interior surface coated
with a tribo-
charging material. For a positive polarity corona gun, it is preferred that
the nozzle be made
or have interior powder contact surfaces coated with a material selected from
the group
2 o consisting of: fluoropolymers particularly PTFE. For use with a negative
polarity gun, it is
more preferable that the nozzle 400 be entirely made of, or have interior
surfaces 412, 414
coated with the materials selected from the group consisting of: a polyamide,
particularly
nylon 6/6, a polyamide blend, a fiber reinforced polyamide resin, an acetal
polymer, an
aminoplastic resin, or mixtures thereof. Thus depending upon the type of
tribocharging
2 s material selected, a negative or positive charge is transferred to the
powder particles upon
contact with the interior surfaces 412, 414 of the nozzle 400. Thus the nozzle
400 can work
in conjunction with the corona charging electrode of the prior art spray guns
in order to
charge the powder with the same polarity as the corona electrode.
The nozzle 400 may preferably include one or more air jet orifices 430 which
are
3 o positioned for fluid communication with the internal passageway 412 of the
nozzle. Air or
other fluid is provided to the air jet orifices 430 for example by chamber 440
which is
connected to an external fluid source (not shown) via port 450. It is
preferred that the air jet
orifices 430 be sized and configured to provide an air velocity in the range
of about 100 to
about 1,000 feet/second, and more preferably in the range of about 400 to
about 800
35 feet/second. It is additionally preferred that the air jet orifices) 430
comprise an angle a with
respect to the longitudinal axis of the insert internal passageway in the
range of about 0 to


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about 90 degrees, and more preferably in the range of about 45 to about 90
degrees. It is
preferred that the angle of the air jet orifices 430 be such that the air jets
intersect to provide
turbulence resulting in increased frictional contact with the charging
surface. It is preferred
that the impact angle R of the air jets upon the transition surface 414 should
be in the range of
about 45 to about 90 degrees, and more preferably about 60 degrees.
The nozzle 400 may additionally comprise one or more electrodes 460 to
discharge
the interior surface 412 from charge build-up and/or to include corona
charging enhancement
for charging the powder. The one or more electrodes is preferably grounded
when corona
charging is not used. Alternatively, the one or more electrodes may have a
positive or
1 o negative charge in the range of about 0 to about 100 KV, and more
preferably in the range of
about 60 to about 80 KV to effect corona charging in addition to the
tribocharging effect.
This provides a spray gun nozzle that incorporates directed air tribocharging
with corona
charging. The corona charging preferably is done at the same polarity as the
powder is
charged by the tribocharging material. The tribocharging lowers the voltage
level required
s5 from the high voltage power source to achieve the same effective transfer
ratio of the powder;
also reducing back ionization and permitting better coverage in areas that
would otherwise be
difficult to spray, such as for example, areas having Faraday Cage effects. A
particularly well
suited negative tribocharging material in this example is Delrin AF although
other materials
as set forth hereinabove and others may alternatively be used. As a further
alternative, the
2 o tribocharging and corona charging may be done with a positive polarity. By
using a corona
charging polarity that is the same as the tribocharging polarity, the corona
field not only may
be used to charge the powder but also will discharge or neutralize surface
charge build-up on
the tribocharging surface, thus eliminating in some applications the need for
a grounding or
discharge pin.
z 5 As shown in Figure 7, the electrode may be positioned within an electrode
holder
490. The electrode holder 490 has an outer surface 492 made of the materials
described for
the internal passageway 412 of the nozzle described above. However, it is
important to note
that other electrode configurations are possible such as for example, a ground
ring, or a blunt
or sharp tipped conductive pin. If a conductive pin is used, it may be
positioned at a right
3 o angle to the fluid passageway anywhere in the nozzle 400. The electrodes
are positioned
upstream within about 2 inches of the air jet impingement on the wall. For
corona charging
enhancement, the electrode 460 preferably though not necessarily will be a
sharp pointed pin
or sharp edged ring, to name two examples.
In a preferred embodiment of the nozzle 400 for non-corona enhanced
tribocharging,
35 the electrode is grounded and positioned upstream of 2 pairs of aligned,
opposed air jets
which are laterally spaced one diameter apart. The air jets are angled at 60
degrees with


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respect to the longitudinal axis.
IV. TRIBO-CHARGING COMPONENTS OF POWDER DELIVERY SYSTEMS
The invention further provides tribocharging powder contact surfaces in
various
components throughout a powder delivery system which can be used to
tribocharge the
powder to the same polarity as the corona powder supply. Tribocharging at
several areas
along the delivery system incrementally increases the charge on the powder as
it passes
through each tribocharging area. This benefits corona gun systems with
increased transfer
1 o efficiency. This idea can also be used with tribocharging gun systems. The
tribocharging
areas of the powder supply system tribocharge the powder to the same polarity
as is used in
the triboguns of the system.
As shown in FIG. 9, a typical powder spray system 500 includes a spray gun 510
connected by a powder supply hose 540 to a hopper 520, through a powder pump
530
s5 mounted on top of the hopper. The spray gun 510 is, for example a negative
charging corona
type powder spray gun, but may alternatively be a positive charging corona
gun, or a negative
or positive tribo-charging powder spray gun.
An electrical line 544 is connected to the gun 510 from control system 550
which
regulates air pressure to pump 530 and the voltage of the corona electrode in
gun 510. Within
2 o the powder hopper 520, a diffuser plate 521 is configured to extend over a
cross-sectional
area within the hopper, and is formed of a porous material through which air
passes to fluidize
the powder. Because the hopper sidewalls 522 and the diffuser plate 521 are
high contact
areas of the powder, the invention includes constructing the plate 521 and
sidewalk 522 out
of the negative tribo pre-charging materials selected from the group
consisting of polyamides,
2 5 particularly nylon 6/6, a polyamide blend, fiber reinforced polyamide
resin, acetal polymer,
aminoplastic resin or mixtures thereof. Thus contact of the powder with the
diffuser plate 521
and sidewalls within the hopper 520 pre-charges the powder negatively before
it is
transported to negative corona gun 510.
The pump 530, shown in cross-section in Figure 8, includes a body 531 with a
3 o powder inlet tube 532 leading to a cavity 533 which is intersected by an
ejector or venturi
nozzle 534 and a venturi throat 535. The venturi throat 535 is held in the
pump body 531 by a
throat holder 536 which extends out of the pump body to provide an attachment
fitting 537
for a hose. Within the attachment fitting 537 is a wear sleeve 538, also
referred to as a wear
tube, downstream of the pump throat. The wear sleeve prevents impact fusion on
the inside
3 5 wall of the throat holder. An atomizing air inlet 539 intersects with the
throat holder 536 to
provide air flow which j oins the powder air mixture from the venturi throat.
This area in the powder delivery system is thus a suitable site for use of one
of the


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described pre-charging materials. Thus it is desired that the venturi throat
535, wear sleeve
538, pump suction tube 532, and powder hose (not shown) be coated with or
fabricated from
the materials selected from the group consisting of a polyamide, polyamide
blend, fiber
reinforced polyamide resin, acetal polymer, aminoplastic resin or mixtures
thereof, as
described in more detail above, to precharge the powder triboelectrically with
a negative
polarity. It is additionally preferred that the length of the venturi throat
535 and the throat
holder 536 be extended by, for example, from one to five inches beyond the
edge of the pump
body. Optimally, this extended length provides for substantial additional
negative
tribocharging of powder at this region of the powder delivery system.
1 o Powder pre-charged in the powder delivery system in the hopper and/or pump
as
described in this section flows through the hose to arrive at the gun with a
pre-established
negative charge. This pre-charging augments the additional negative charge
applied at the
gun by the corona electrode.
V. UNIPOLARITY POWDER COATING SYSTEM INCLUDING CORONA AND
TRIBOCHARGING GUNS
As shown in Figure 9, a corona gun 510 is shown together in use with a tribo-
charging powder spray gun 10 of the invention, which has been described in
detail, above.
2 o The corona gun 510 and the tribocharging gun 10 have the same polarity.
This unique
combination allows for the tribocharging gun 10 to be used as a touch up gun,
for example, to
penetrate the corners or hard to reach parts that the corona gun 510 has not
effectively coated.
This exemplary combination of a negative corona gun 510 and a negative tribo-
charging gun
10 is preferably connected to a common powder delivery system 520, which pre-
charges the
2 5 powder negatively as described above. I Alternatively, the tribocharging
gun may comprise
the short barrel gun 200 (not shown) which is described in more detail, above.
This novel
combination of one or more negative corona guns with one or more negative
tribo guns,
optimally with a negative pre-charging powder delivery system, used to coat
different parts of
the same workpiece is one important embodiment of this invention.
VI. TRIBOCHARGING GUN WITH AIR JETS
As shown in Figure 10, a novel tribocharging gun 600 is provided which
comprises a
powder feed section 610, a powder charging section 620, and a spray nozzle 630
located at
the outlet of the gun. The powder charging section 620 of the tribocharging
gun 600 further
3 5 comprises a cylindrically shaped body 622 having an internal bore 623 for
housing the
internal components of the gun. Housed within the bore 623 of the body 622 is
a powder tube
connector 612 having an internal bore 626a. A first end 616 of the connector
612 is


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connected to a powder supply tube (not shown) for supplying fluidized powder
to the powder
flow passageway 626a,b,c of the gun 600. The second end 618 of the powder tube
connector
612 is connected to an inlet air entry 640. The inlet air entry 640 has an
internal passageway
626b and one or more angled holes or air jets 642 which are connected to an
air manifold 628
located in the body 622 for supplying pressurized air to the air jets 642 in
order to increase the
velocity and induce turbulence of the fluidized powder entering the gun.
Connected to 'the
inlet air entry 640 is an outer wear tube 650 which has an internal passageway
which is part
of the powder flow passageway 626 of the gun. The outer wear tube 650 further
comprises
one or more air jets 652. Pressurized air is provided to the air jets 652 via
passageway 654
1 o which is in fluid communication with air manifold 628. The gun 600 may
further be provided
with an optional inner wear surface 660 which forms an annular powder flow
path. As shown
in a cross sectional view in Figure 10A, a plurality of air jets 652 are
arranged in an opposed
configuration at one or more longitudinal stations. Preferably the air jets
652 comprise an
angle y ( as measured counterclockwise from the longitudinal axis) preferably
in the range of
about 90 to about 135 degrees. The air jet velocity is preferably high enough
to induce
turbulence and cause the powder flowing through passageway to contact the wall
opposite the
air jet, in order to increase the tribocharging of the powder. It is preferred
that the air jet
velocity be in the range of about 100 to about 1,000 feet/second and more
preferably in the
range of about 400 to about 800 feet/second.
2 o In order to provide tribocharging of the powder, the powder contact
surfaces of the
gun such as the internal surface of the powder flow passageway 626a-c, the
nozzle 630 and
the outer surface of the inner charge tube 660 are constructed from or coated
with a
tribocharging material. For a positive polarity tribocharging gun the powder
contact surfaces
are preferably selected from the group consisting of: fluoropolymers
particularly PTFE. For a
negative polarity tribocharging gun the powder contact surfaces are preferably
selected from
the group consisting of: nylon, particularly nylon 6/6, a polyamide blend, a
fiber reinforced
polyamide resin, an acetal polymer, an aminoplastic resin or mixtures thereof.
In yet another embodiment of the invention as shown in Figure 11, the
tribocharging
gun is the same as described above, except for the following differences.
First, no inner
s o charge tube 660 is utilized. Second, the air jets 652 of the tribocharging
gun 600 located
within the outer wear tube 650 are arranged in a helical pattern about the
longitudinal axis as
shown in Figures 11 and 1 1A. Optionally, the air jets 652a located on the
upper portion of
the tube 650 can have a different angular orientation than the air jets 652b
located on the
lower portion of the tube 650 (not shown). The air jets 652a, 652b when
configured in this
3 5 manner, are designed to impact the fluidized powder against the opposite
wall in a staggered
or wave fashion in order to increase the tribocharging of the powder. It is
preferred that there


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be 3-4 sets of holes arranged in the configuration, with each set comprising 2
or more holes.
This helical configuration functions to induce turbulence and swirl the
fluidized powder in a
helical fashion so that the relatively heavier powder is spun or induced to
impact the wall via
centrifugal forces into contact with the passageway wall.
An advantage of this embodiment is that to cause each powder particle to
impact the
charging surface numerous times and thereby increase the charge on the powder,
instead of
forming mechanical waves on the charging surface such as shown in the Figure 1
gun, the
charging surface is a straight cylinder which is easy to manufacture, while
the air jets 652
cause the powder particles to take a turbulent route through the flow passage
626a,b,c,
1 o impacting the surface many times to increase the triboelectrically induced
charge on the
powders.
With reference to Fig. 12, another embodiment of the short barrel
tribocharging gun
200 of Fig. 2 is illustrated. In the embodiment of Fig. 12, the modified gun
200' includes a
gun body 210' that retains a powder conduit insert 800 that is somewhat
different from the
15 insert 220 in Fig. 2. The insert 800 includes a powder feed inlet 802 and
an optional diffuser
air inlet 804. Diffuser air may be used as required to increase the velocity
of the powder
through the gun 200'. This increased velocity increases the tribocharge
charging effect on the
powder, and also helps diffuse the powder, and also may be used to affect the
spray pattern.
Diffuser air however is not required in all situations, and depends on several
factors among
2 o which are notably the velocity and pressure of the powder entering the gun
200' from the
powder supply hose 540 and related powder supply components (see Fig. 9 and
the discussion
herein related thereto) as well as how much additional diffusion of the powder
is required, if
any, through the gun. In many cases where the air jets are incorporated into a
tribocharging
type gun, the pressure drop created by the air flow through the air jets may
be sufficient to
25 obviate the use of diffuser air. This is particularly the case when the air
jets are forwardly
angled to direct a significant air flow in the axially forward direction
through the gun, thereby
inducing a suction effect at the powder inlet end of the gun. Reducing overall
air use in a
spray gun is usually beneficial as it reduces operating costs associated with
shop air, impact
fusion and wear. Reducing impact fusion helps speed up color change and
cleaning
3 0 operations.
The inner end 800a of the powder conduit insert 800 slideably receives a first
end of a
charging tube 806. The charging tube 806 is preferably made of any one of the
various
materials described herein to apply either a positive or negative charge to
the powder as
desired for a particular application. The charging tube inlet 806a may include
an optional
3 5 internal diametric reduction or neck down 808 which serves to increase
powder velocity
(without needing to increase diffuser air volume or pressure) and also to re-
center the powder


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in the central volume of the charging tube 806 before the powder enters the
main portion of
the charging tube.
A solid or hollow shaft 810 is longitudinally and preferably coaxially
positioned
within the charging tube 806. This shaft 810 is preferably but not necessarily
cylindrical in
shape, and includes an optional taper to a conical end 810a to facilitate
discharge of the shaft
810. The charging tube 806 includes a metallic discharge or grounding ring 812
that is
connected to a grounded discharge pin 814. The pin 814 permits the charging
tube 806 and
the shaft 810 to self discharge during a spraying operation as charge builds
up on the
tribocharging surfaces. A bore 816 is provided to receive a grounded pin or
wire (not shown)
1 o that contacts the grounding ring 812.
The body 210' includes an air inlet port 250' much in the same manner as the
port
250 in the embodiment of Fig. 2 herein. This port 250' opens into an annulus
817. The
annulus 817 is in fluid communication with and surrounds another annulus 818
that is
generally defined by the space between the outer circumference of the shaft
810 and the inner
surface of the charging tube 806. The annulus 818 preferably forms a rather
narrow gap
between the charging tube 806 and the shaft 810. A series of air jets 240' are
provided
through the wall of the charging tube 806, in a manner similar to the
embodiment of Fig. 2
herein, and pressurized air flows from the outer annulus 817 to the inner
annulus 818
therethrough. The exact location, number, angle and orientation of the jets
240' may be
2 o determined based on various factors as previously described herein. In
accordance with one
aspect of the invention, the smaller annulus 818, as compared, for example to
the diameter of
the tubular insert 220 in Fig. 2, significantly reduces the travel distance
for powder particles
that are forced by air from the jets 240' toward the shaft 810. Thus, less air
is required to
cause the powder to impact the tribocharging surface of the shaft 810 at a
comparable velocity
2 5 to the embodiment of Fig. 2. This not only reduces the air requirements,
but also reduces
impact fusion effects. Additionally, use of the shaft 810 substantially
increases the total
surface area of tribocharging material to which the powder particles are
exposed, because the
powder will impact both the surface area of the shaft 810 as well as the inner
surface area of
the charging tube 806. The air jets 240' may be angled forwardly and radially
as in Fig. 12
3 0 (relative to the longitudinal axis of the gun 200') or may also be offset
to create a spinning air
movement around the shaft 810, as previously described herein. The narrower
annulus 818
also permits conventional tribocharging effects on the powder as it passes
through the gun
200', much in an analogous manner that a prior art tribocharging gun uses a
tortuous or wavy
path for the powder to pass through. By way of example, the annulus 818 may
vary from
3 5 about 0.02 inches to about 0.5 inches, although the exact dimensions
selected will depend on
the overall performance characteristics and requirements of each gun design.


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The shaft 810 is positioned and held in the charging tube 806 by any
convenient
mechanism, such as for example centering pins (not shown). Furthermore, in the
embodiment
of Fig. 12, the insert 800, the charging tube 806 and the nozzle 820 form the
gun barrel and
may all be made of the various materials described herein to produce positive
or negative
charging of the powder particles as desired, as will the shaft 810 be made of
such
tribocharging materials. The embodiment of Fig. 12 uses a conventional flat
spray nozzle 820
having a slot 821 but any suitable nozzle design may be used.
With reference to Fig. 13, an alternative embodiment of the Fig. .12 version
is
illustrated. Like parts are given like reference numerals and the description
thereof is not
s o repeated. In the embodiment of Fig. 13, the charging tube 822 and the
shaft 824 have been
modified at their forward ends to cooperate with a corresponding configuration
of a nozzle
body 826 to define a tribocharging parallel wave path 828 that is downstream
of the annulus
818. The wave path 828 is realized in the form of an hourglass type reduced
diameter in the
nozzle body cavity 820. The shaft 824 is formed with a corresponding geometry,
and the
charging tube 822 forward end simply abuts the backward end of the nozzle body
826 to form
a smooth continuous contour. A spider 830 is centered and supported in the
nozzle body 826
cavity by a plurality of radial legs 832. The spider 830 may be joined or
assembled with the
shaft 824 if so required, by a pin insert 834, and at its forward end the
spider 830 may be used
to support a conventional conical nozzle 836. The spider 830 preferably is
made of a suitable
2 o tribocharging material such as those described herein. In this embodiment
then, the gun 200"
operates with both the air jets 240', the charging tube 822 and the shaft 824
initially charging
the powder, as well as a tribocharging post-charge function produced by the
parallel wave
path 828. Although in the embodiment of Fig. 13 the tribocharging section 828
is illustrated
as a parallel wave pattern, such illustration is intended to be exemplary in
nature and should
2 5 not be construed in a limiting sense. Those skilled in the art will
readily appreciate that the
tribocharging section may be realized utilizing any number of known
tribocharging
arrangements.
Fig. 14 illustrates another modification of the gun 200' in Fig. 12. In this
version, the
shaft 810 is installed in a slightly axially forward position as compared to
the shaft 810 in Fig.
3 0 12. This has the effect of positioning the conical rearward tip 810a of
the shaft 810 nearer the
grounding pin 814. This significantly increases the ease with which the shaft
810 may
discharge during a spraying operation.
Fig. 14 further includes the concept of incorporating both an initial air jet
assisted or
induced tribocharging function and an additional tribocharging function into
the gun 200'.
35 Note in Fig. 14, as compared for example to Fig. 13, that the air jets 240'
are positioned aft of
the shaft 810. This places the air jet induced tribocharging function first,
followed by a


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subsequent tribocharging function in the annulus 818. The air jets apply
sufficient energy to
the powder particles to cause impact against the charging tube and shaft
surfaces to charge the
powder. The air flow produced by the air jets is sufficient to allow a
tribocharging effect
downstream via the annulus 818 without needing a tortuous, wavy or other
conventional
s tribocharging path, although such tribocharging techniques and
configurations may be used if
so required.
With reference next to Fig. 15, another gun embodiment is illustrated. The
basic
concept illustrated in this drawing is referred to herein as an "inside-out"
gun because, as
compared to the embodiments previously described herein, the flow direction of
the air jets is
z o reversed. Thus the prior embodiments herein can for convenience be
referred to as "outside-
in" gun configurations. In the embodiment of Fig. 15 then, the gun 840
includes a gun body
842 that has a rearward end 842a and a forward end 842b. The rearward end 842a
includes a
counterbore that slideably receives and retains a powder conduit insert 844.
The powder
insert 844 supports a powder tube connection nipple 846 and an air inlet
connector 848. The
15 insert 844 receives and supports a first end of a charging tube 850 that is
made of a suitable
tribocharging material as previously described herein. The charging tube 850
extends through
the gun body 842 to a nozzle assembly 852. The particular design of the nozzle
assembly 852
may be selected as required for a specific spray pattern. In the example of
rig. 15, the nozzle
assembly 852 includes a nozzle body 852a that retains a spider 852b which at
one end
2 o supports a conventional conical nozzle 852c. The spider 852b may include
radial legs 852d
or other suitable elements to such as pins to support the spider 852b within
the nozzle body
852a.
The insert 844 receives and supports a first or inlet end of an air tube 854
which in
this example is realized in the form of a hollow shaft. The air tube 854
includes one or more
2s air jets 856 that are formed at appropriate angles and orientations as
described herein before
with respect to the other embodiments herein. In the example of Fig. 15, the
air jets 856
produce a forward air flow towards the front of the gun 840, but are radially
angled to direct
powder against the inner surface 858 of the charging tube 850. The inlet end
854a of the air
tube 854 is in fluid communication with the air inlet coupling 848. Therefore,
pressurized air
~ o fed into the air inlet 848 via an air hose (not shown) enters the air tube
854 and exits through
the various air jets 856. The air tube 854 generally coextends with the
charging tube 850 and
has a forward end 854b of the air tube 854 is closed and supported by the
spider 852a.
As compared to the embodiments, for example, of Figs. 2, 7, 3A-3D, 4A-4H, and
11,
the concept of the inside-out gun is that the powder particles have a
substantially shorter
3 5 travel distance under the influence of the pressurized air from the air
jets 856 before the
particles impact the tribocharging surface of the charging tube 850. This
reduces the amount.


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of air to achieve adequate impact velocity to effect adequate charging of the
powder and also
reduces the amount of lost energy from the particles traveling down the gun.
The air tube 854
may be also made of tribocharging material to further increase the
tribocharging effect of the
design. Another advantage of the inside-out design is that the gun is simpler
to manufacture
s as it uses fewer parts.
Fig. 16 shows a variation of the inside-out gun of Fig. 15. In Fig. 16, the
gun 840'
has a central gun body 860 that also functions as the charging tube. The
powder insert 844' is
attached at an inlet end of the body and a nozzle assembly 852' is attached at
an opposite end
of the gun body 860. The nozzle assembly 852' may be similar to that shown in
Fig. 15 or
1 o may be of some other suitable design.
In both Figs. 15 and 16, a grounding pin 862 extends through the gun body
842/860
to discharge the tribocharging surfaces and components inside the guns. The
pin 862 is
illustrated in Fig. 16 with the pin omitted in Fig. 15 to illustrate the pin
bore 862a.
Fig. 17 illustrates an embodiment of the invention in a hand operated gun
is configuration. Previous embodiments herein are illustrated as automatic gun
configurations
such as are mounted on gun supports and gun movers, although the main elements
of those
embodiments may be incorporated into a manual gun handle, as exemplified in
Figs. 17 and
18.
In Fig. 17 then, the gun 870 includes a handle portion 872 having a trigger
874 or
2 0 other control device for controlling the flow of powder through the gun
870. A gun body 876
supports a powder feed hose connector. 878 to which a powder feed hose (not
shown) may be
connected. Powder flows down a powder extension tube 880 which may be made of
tribocharging material. The extension tube 880 is supported within a gun body
extension 882
that at an opposite end supports a nozzle assembly 883. The extension tube 880
is generally
25 concentrically mounted within the gun body 876 and extension 882 to provide
an annulus
884. This annulus 884 receives pressurized air through an air fitting 886 that
is connected to
an air line 886a extending up through the handle 872. A diffuser air
passageway 888 is
formed through the wall of the powder extension tube 880. The passageway 888
is sized so
as to effect a desired balance between diffuser air entering the powder
extension tube 880 and
3 o air that will travel down the annulus 884 to the charging portion 890 of
the gun 870.
The charging portion 890 in this example is in the form of an outside-in gun,
and
includes a charging tube 892 that is inserted at one end into the forward end
of the powder
extension tube 880. The forward end of the charging tube 892 is assembled to
the nozzle
assembly 883. The charging tube 892 is supported by ribs or legs 894 that
include or permit
s 5 the air from the annulus 884 to pass through a series of air jets 896. The
air entering the
charging tube 892 directs the powder particles to impact the tribocharging
surface 892a of the


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charging tube 892 as in the earlier described embodiments. It is contemplated
that the
extension tube 880 and the nozzle assembly 882 may also be made of suitable
tribocharging
materials to enhance the charging effect of the gun 870. The use of the
internal diffuser air
passageway 888 requires only a single air supply to the gun 870 for both
diffuser air and air
s for the jets 896, thus eliminating any need for a second air port into the
side of the gun at the
portion 890. Although not shown in Fig. 17, a shaft similar in concept to the
shaft 810 in Fig.
15 may be used in the gun configuration of Fig. 17.
The embodiment of Figure 17 has a ground pin 893 which is connected to the
extension 882 which is electrically conductive. The extension 882 is in turn
connected to a
z o grounding screw 885 which is electrically grounded by a ground wire 887.
Placing the
ground pin 893 at a location just behind, or upstream, of the location where
tribocharging air
assist jets 896 first impact the charging surface is preferred in that in this
location the surface
charge which builds up on the tribocharging surface due to the tribocharging
of the powder
can be readily discharged by ground pin 893 to promote tribocharging of the
powder. If the
15 ground pin is placed too far upstream from the point of air jet
impingement, the surface
charge which builds up on the surface will not be discharged by the ground
pin. If the ground
pin is placed in front of, or downstream of, the place where the tribocharging
air jets impinge
on the charging surface, the powder charged by impinging that surface will be
discharged by
the ground pin as the powder flows downstream over the ground pin.
2 o In a typical tribocharging gun, extending the length of the gun barrel
downstream of
the tribocharging portion tends to cause a loss of charge before the powder is
ejected through
the nozzle. In Figs. 18A-D we illustrate an alternative arrangement wherein
for different gun
lengths, the air jet induced tribocharging portion 890 is kept positioned
closer to the nozzle,
therefore the charge loss is minimized. In all of these embodiments, it is
preferred that the
2 s ground pin or other ground element (not shown) be placed at a location
just behind the place
where tribocharging air assist jets first impact the charging surface as is
done in the Figure 17
embodiment.
With reference next to Fig. 19, a spray gun is illustrated that incorporates
the concept
of an inside-out gun in a hand held manual spray gun configuration. The gun
900 includes a
3 o gun body 902 that has a handle 904. The handle 904 may include
conventional trigger
mechanisms 906 for controlling the flow of powder into the gun 900. The body
902 supports
a charging tube 908 within a body extension 910. The charging tube 908 is made
of a suitable
tribocharging material as set forth hereinabove. At a rearward end of the gun
body 902 is
attached a powder inlet cap assembly 912, that in a manner similar to the
embodiments of
3 s Figs. 1 S and 16, includes a powder hose connector 914 and an air fitting
916 (the air and
powder supply lines being omitted from Fig. 19 for clarity). The air inlet 916
is in fluid


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communication with an air tube 918 that extends longitudinally through the gun
900 from the
inlet head 912 to a nozzle assembly 920. In this embodiment, the nozzle
assembly includes a
flat spray nozzle 922 within which is installed a spider 924 that may be
similar in design to
the spider 852b of Fig. 15 herein. The spider 924 supports the forward end of
the air tube
918. The air tube extends generally concentrically through the gun 900, thus
providing an
annulus 926 between the outer surface of the air tube 918 and the inner
surface 908a of the
charging tube 908. In a portion 928 of the gun 900 a number of air jets 930
are provided
through the wall of the air tube 918 which are directed towards the forward
end of the gun
near the nozzle. The number, location, orientation and angles of the various
air jets 930 may
1 o be selected for a particular gun design as explained hereinabove. The air
j ets 930 also need
not be all at the forward end of the gun 900 but may also be located more
towards the gun
handle.
Powder enters the gun 900 through the coupling 914 and passes down the annulus
926. Appropriate sizing of the annulus 926 may be used to provide a
tribocharging precharge
to the powder before it reaches the portion 928 of the gun 900. Pressurized
air flow from
inside the air tube 918 out to the annulus 926, causing powder particles to
impact the
tribocharging surface of the charging tube 908. The air tube 918 may also be
constructed of
tribocharging material to increase the charging effect on the powder. Although
the gun 900 is
illustrated as having a charging tube 918 disposed within a gun extension 910,
these two
2 o elements may if required be a single tube, as in the embodiment of Fig. 16
herein.
As in the previous embodiments, a ground pin 931 is placed at a location just
behind
the place where tribocharging air assist jets 930 first impact the charging
surface. The
grounding pin 931 is connected to the extension 910 which is electrically
conductive. The
extension 910 is grounded through a ground screw 933 to a ground wire 935.
2 5 Another advantage of the inside-out gun configurations illustrated herein
is that if
impact fusion should occur along portions of the charging tube surface, it is
a straightforward
operation to simply rotate the air tube 918 through an angle sufficient to
reorient the air jets
930 towards "clean" tribocharging surface areas where there is no impact
fusion. This
exposes clean charging surface to the impacting powder particles and will
improve the
3 o charging efficiency as the gun is used. Alternatively, the relative axial
position between the
air jets 930 and the tribocharging surfaces could be adjusted to expose clean
charging surface
to the powder, or both the relative axial and rotational positions could be
changed.
Fig. 20 illustrates another embodiment of the invention that combines the
inside-out
configuration with an outside-in configuration in a single gun. In this
embodiment, the gun
3 5 940 includes a gun body 942 that supports at one end a powder inlet cap
assembly 944 and at
an opposite end a nozzle assembly 946. The nozzle assembly 946 is illustrated
to be a conical


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nozzle type with a nozzle 948 supported by a spider 950 in a manner similar to
other
embodiments described herein.
The inlet assembly 944 includes a powder hose fitting 952 and an air fitting
954. The
air fitting 954 is in fluid communication with an air tube 956 that extends
through the gun to
the nozzle assembly 946 and is supported at the forward end by the spider 950.
A charging
tube 958 is also supported inside the gun body 942 and concentrically
surrounds the air tube
956 to form a second or outer annulus 960 therebetween. The air tube 956
includes a
plurality of inside-out air jets 957 that allow air to pass from inside the
air tube into the
annulus 960. The charging tube 958 is sized with a diameter that is less than
the diameter of
s o the gun body 942, thereby providing an air passageway or second outer
annulus 962. The
charging tube 958 is also provided with a number of air jets 964 such that the
charging tube
958 also functions as an outside-in air tube. Pressurized air flows from the
second or outer
annulus 962 through the charging tube air jets 964 into the first or inner
annulus 960. Powder
from the inlet 952 flows into the inner annulus 960 and is then entrained in
the air flow
1s produced by the air jets 957 and 964. The two sets of air jets, one outside-
in and the other
inside-out significantly increases the turbulence of the powder and causes
impact with both
the charging tube surface 958a and the air tube outer surface 956a. A
grounding pin 966 is
provided as previously described hereinabove.
Pressurized air enters the gun through the air fitting 954 and flows through
the air
2 o tube 956. In addition, an air passageway 968 is provided that directs part
of the air into the
outer annulus 962. In this manner only a single air input is needed to the
gun. If required, a
portion or the air may also be directed into the inner annulus 960 to function
as diffuser air,
however this is unlikely to be needed as the volume of moving air from all the
air jets will in
most cases adequately diffuse the powder. The gun 940 may also include
additional powder
2 s flow lengths prior to the charging operation to incorporate a tribocharge
pre-charge or post-
charge effect.
Figures 21-24 show another embodiment of the invention. In this embodiment, an
electronically conductive extension 972 supports a nozzle 974 having a slot
976. A charge
sleeve 978 is installed between the nozzle 974 and a charge sleeve holder 980.
The powder
3 o feed tube 982 is inserted into the charge sleeve holder 980 and is
connected to a powder feed
hose 984. A ground pin 986 is connected to the extension 972. The extension
972 is
connected through a ground screw 988 to a ground wire 990. The charge sleeve
holder 980
includes air jets 981 which enhance the tribocharging ability of the gun. The
jets 981 impinge
upon the inside surface 979 of the charge sleeve 978 which is constructed from
a
3 5 tribocharging material such as those described above. The ground pin 986
is positioned just
behind the place where tribocharging air assist jets 981 impact the charging
surface 979.


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Figures 22 and 23 show the charge sleeve holder 980 in more detail. As shown
in
Figure 23, the air jets 981 are disposed at 90 degree intervals around the
circumference of the
charge sleeve holder 980. The passage 992 for the ground pin 986 is shown in
Figure 23 as
disposed between two of the air jets 981.
Figure 24 shows a view of the charge sleeve 978 assembled to the charge sleeve
holder 980. A locating pin 996 is fractionally received within the holder 980.
When the
charge sleeve 978 is assembled to the holder 980, the locating pin 996 is
received within a
slot 994 formed within the exterior surface of the sleeve 978. This permits
the sleeve 978 to
assume a particular positional orientation in the holder 980 (hereinafter
referred to as a first
orientation). In this first orientation, a certain portion of the interior
surface 979 of the sleeve
978 is impacted by the air jets 981 and worn away by the frictional charging
of the powder.
In order to be able to expose different parts of the interior surface 979 to
the air jets 981 a
number of such slots are formed on the exterior of sleeve 978. To reorient the
sleeve in
holder 980 in a different positional orientation, the sleeve 978 would be
pulled out of the
holder 980 and rotated to align a different slot formed in the exterior of
sleeve 978 with the
pin 996 and the sleeve 978 would then be pushed back into holder 980. In this
way a new
portion of the charging surface 979 would be impacted by air jets 981 to be
used for
frictional, or triboelectric, charging of the powder without the need for
replacing the charge
sleeve 978. In addition, the sleeve 978 is symmetrical so that its orientation
within the holder
2 0 90 can be reversed with the opposite and of sleeve 978 being inserted into
holder 980. This
doubles the number of different orientations the sleeve can assume within
holder 980 to
permit an even greater portion of the surface to be used for triboelectric
charging before the
sleeve 978 must be replaced.
Consequently, among the advantages of this embodiment is the employment of a
2 5 novel concept in triboelectric gun of designing one or more components of
the gun, which are
used as a triboelectric charging surface, to be assembled into the gun in more
than one
orientation so that more of the surface can be used for tribocharging the
powder before the
component is replaced with a new component. This saves the customer money by
enabling
the customer to more fully utilize the component before replacing it.
3 o A further cost savings is provided to the customer by forming the
triboelectric
charging assembly in two pieces as a charge sleeve and a charge sleeve holder.
By
constructing this component as a two piece assembly, only the charge sleeve
holder, which
includes the air jets and is more complicated to manufacture, does not have to
be replaced.
Thus the charge sleeve 978 is a much simpler part to manufacture and replace
than a charge
s 5 sleeve such as the one shown in Figure 17 which includes the air jets as
well as the charging
surface.


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Note also that in the Figure 21-24 embodiment all of the air jets 981 are in a
single
vertical plane. This produces a number of advantages. The charge sleeve can be
shorter than
charge sleeves with sets of air jets provided along the length of the charge
sleeve. Also, any
air introduced from the back of the gun will feed all the air jets uniformly,
which produces
more even charging of the powder. Further, all powder impact areas within the
sleeve are
close to the ground pin. In addition, a lower pressure can be used for air
jets in a single plane,
which reduces energy requirements, since there is no pressure drop between the
first set of air
jets and the second set of air jets.
In accordance with another aspect of the invention then, various combinations
of air
so jet assisted tribocharging and tribocharging techniques can be implemented
in a spray gun.
These include but are not necessarily limited to: air jet assisted
tribocharging followed by
tribocharging; tribocharging followed by air jet assisted tribocharging; an
inside-out air jet
assisted tribocharging followed by tribocharging; tribocharging followed by an
inside-out air
jet assisted tribocharging; inside-out air jet assisted tribocharging followed
by an outside-in
air jet assisted tribocharging; and inside-out air jet assisted tribocharging
combined with
outside-in air jet assisted tribocharging. Various tribocharging material
combinations may
also be used in a gun, including positive and negative charging materials as
required. A
significant advantage of the air jet assisted tribocharging guns is that their
short length design
makes them suitable for coating the insides of pipes and other enclosed
surfaces. The short
2 o gun length allows the gun to travel through a pipe that even has bends of
various angles,
which is difficult for prior art spray guns of significant length.
The present invention further contemplates apparatus and method for shaping
and
directing the flow of powder sprayed through a spray nozzle of an
electrostatic spray gun. In
general, the nozzle may be provided with openings that produce a desired shape
or pattern to
2 5 the powder spray. The powder spray pattern may also be shaped and directed
by deflector
devices that are mounted on the nozzle to shape and/or influence the powder
spray pattern.
These nozzle features may be used individually or in any suitable combination,
and may be
incorporated into any powder spray nozzle including but not limited to nozzles
for corona
spray guns and triboguns with the latter including without limitation
conventional
3 o tribocharging spray guns or unconventional tribocharging spray guns as
described herein.
With reference to Figs. 25-28, a first embodiment of a spray nozzle 700 in
accordance
with the invention is illustrated. The nozzle 700 includes a generally
cylindrical body 702
having a central axial passageway in the form, for example, of a bore 705
therein that extends
from a powder inlet end 702a to an outlet end 702b. A first plurality of
openings or slots 704
3 5 are provided at a rounded front end 700a of the nozzle 700. This first set
of slots 704 are used
to form a primary powder spray pattern indicated by the directional arrows PS
on Fig. 26.


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The front end 700a need not be rounded but may have other suitable shapes to
produce a
desired pattern. The slots 704 therefore need not be arcuate as illustrated in
the exemplary
embodiment.
Each slot 704a and 704b is angled with respect to the longitudinal axis LA of
the
s nozzle 700. In this exemplary embodiment, the nozzle 700 includes two
arcuate slots 704a
and 704b respectively aligned at angles 6a and6b with respect to the
longitudinal axis LA.
Preferably but not necessarily the angles 9a and 6b are substantially equal.
The values of ~a
and 6b are selected based on the desired characteristics of the spray pattern.
In one example,
Ba and 6b are about 15 degrees to form an included angle between the slot 704a
and 704b of
1 o about 30°. Other angles may be selected as required but it is
contemplated that the angles 9a
and eb will be other than zero degrees (i.e., parallel to the axis LA). By
having the slots
angled relative to the axis LA, powder flowing through the slots 704 is
directed to converge
and impinge each other as indicated by the intersection of the arrows PS. This
convergence
causes a decrease in the velocity of the powder spray and produces a wider
powder spray
1s pattern with better more uniform dispersion or distribution of the powder
particles within the
spray pattern as compared to single slot nozzles or parallel slot nozzles.
The angled slots 704 have additional benefits. Because of the angled
orientation, it is
less likely that powder particles could pass straight through the nozzle 700
and out one of the
slots 704 without impacting an interior surface area of the nozzle body 702.
By increasing
2 o impact or surface contact of the powder against the nozzle 700, the
tribocharging effect can be
enhanced. Thus it is preferred although not necessary that the nozzle 700 or
at least the
impact surfaces within the nozzle 700 be made of a suitable tribocharging
material of the
same polarity as the spray gun to which the nozzle 700 is attached. For
example, if the nozzle
700 is used with a corona gun or an unconventional negative tribogun as
described herein, the
2 5 nozzle may be made of DelrinTM or other suitable negative polarity
tribocharging materials.
If the nozzle is being used with a positive tribogun, the nozzle may be made
of any suitable
positive tribocharging materials such as PTFE for example. The angled slots
704 also
increase the impact surface area of powder before the powder is ejected from
the nozzle.
The angles 6a and 6~ typically will be within a useful range. If the angle 8
is too
3 o shallow, backpressure will be reduced and powder could flow through the
nozzle 700
unimpeded. If the angle 8 is too steep there may develop too much backpressure
and too low
a powder flow rate through the slots 704.
The angled slots 704 also cause backpressure to build within the nozzle body
702,
thus slowing down the velocity of the powder spray and increasing collisions
of the powder
3 5 particles with each other and impact with the nozzle interior
tribocharging surfaces, thereby
enhancing the tribocharging effect of the nozzle. The number of slots used is
a matter of


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choice.
The slots 704 are shaped so as to produce a somewhat flat fan-like spray
pattern.
Because powder particles vary in size and mass, the spray pattern produced by
the slots 704
alone may not exhibit a desired powder distribution within the spray pattern.
In many cases,
use of the angled slots 704 alone will be sufficient. However, if so required
or desired, the
nozzle 700 is provided with a second set of openings or vents 706. In this
example there are
two vents 706a and 706b but alternatively a single vent may be used or more
than two may be
used.
As best illustrated in Fig. 27, the vents 706 are preferably although not
necessarily
z o positioned between the slots 704 near the end portions thereof. Other
locations may be used.
The vents are also each angled outwardly relative to the longitudinal axis LA
at respective
angles as and a,,. In one embodiment the angles c~ and a,, are equal but they
need not be. A
suitable angle is about 30° to form an included angle between the vents
of about 60°, however
other angles may be used to achieve a desired effect on the spray pattern.
The vents 706 may be used for a number of different purposes. The vents
provide
pressure relief to reduce or control the backpressure within the nozzle 700 by
venting air.
Also, some powder will also be vented and will tend to flow about the
peripheral region or
envelope of the spray pattern thus increasing the amount of powder particles
in that region
(which typically includes a significant amount of fines). The outward envelope
of air flow
2 o and powder also helps slow down the resultant powder spray and help to
direct the powder
spray in a forwardly direction (recognizing that the convergent powder streams
from the
nozzle slots 704 will cause some powder to deflect at angles away from a
generally forward
direction; the flow from the vents 706 assists in constraining such powder
into the generally
forward moving spray pattern.)
2 s Note that depending on the desired spray pattern the slots 704 and vents
706 may
individually be either converging or diverging and may have various shapes and
orientations.
The nozzle body 702 may include a suitable extension 708 with seal grooves 710
so
that the nozzle can be press fit or otherwise installed at a forward end of a
spray gun.
In some spraying applications, a generally circular spray pattern is desired.
Such
s o spray patterns are conunonly produced by the use of a diffuser such as the
conical nozzle 836
illustrated in Fig. 13 herein. However, such arrangements require multiple
parts such as the
nozzle 836, spider 830 and holder 826.
With reference to Figs. 29-32 a second embodiment of a spray nozzle 712 in
accordance with the invention is illustrated. This nozzle 712 may be used with
any powder
3 s spray gun including but not limited to corona and triboguns. Preferably
although not
necessarily the nozzle 712 is made of a tribocharging material that
electrostatically charges


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-39-
powder with the same polarity as the spray gun, similar to the nozzle 700
described herein.
The nozzle 712 includes a body 714 having a central longitudinal bore 716
therein.
The bore 716 extends from an inlet end 716a to an outlet end 716b. The outlet
end 716b
includes an interior surface 718 that tapers radially outward at an angle (31,
relative to the
longitudinal axis LA2 of the nozzle 712.
A deflector in the form of a cone 720 is disposed at the outlet end 716b of
the nozzle
712. This cone 720 is used to produce a conical deflection of the powder flow
exiting the
nozzle bore 716 to cause the powder spray pattern to be generally circular
(the spray cloud
itself being generally conical). The cone 720 is preferably although not
necessarily centered
1 o with respect to the outlet end 716b of the nozzle. The cone angle X32 may
be selected to be any
angle that produces the desired size spray pattern. For example, 55° is
a suitable angle in
many applications. The cone angle biz may be selected such that the value
(32/2 is about equal
to ail. However this need not be the case in all applications.
In the exemplary embodiment, the cone 720 is attached to the nozzle 712 by a
number
of ribs 722. Although three ribs are illustrated, other numbers may be used.
The ribs 722 are
equidistantly spaced about the cone circumference (120° increments for
3 ribs) to stabilize the
cone 720 during spraying. The ribs 722 connect an outer surface 724 of the
cone 720 to the
tapered nozzle surface 718 although other locations and attachment techniques
may be used.
Preferably but not necessarily the cone 720, ribs 722 and nozzle body 714 are
integrally
2 o formed either by machining or molding. Alternatively, the cone 720 may be
a separate part
suitably attached to the nozzle body 714. The cone 720 or at least the cone
surface 724 may
be made of a suitable tribocharging material.
The cone 720 and the tapered nozzle end 718 thus are appropriately spaced
apart to
form a conical nozzle orifice or path 726. The dimensions and angles of the
orifice 726 may
2 5 be selected to effect a desired spray pattern size. If so desired, vents
(not shown) may be used
with the conical nozzle 712 as described herein with the embodiment of Figs.
25-28. The
nozzle 712 may also be provided with a mounting extension 728 similar to the
extension 708
previously described herein (Fig. 25).
For the generally circular spray nozzle 712 embodiment, although a wider more
3 o uniform spray pattern is produced, in some applications it may be desired
to constrain the
powder spray pattern and also to assist in the forward movement of the spray
pattern. In
accordance within this aspect of the invention, a device may be attached to
the nozzle and
function as a deflector or shroud to shape and direct the powder spray
pattern. The device
may also function as a velocity brake to further assist in reducing the
forward velocity of the
3 5 spray pattern.
In a first embodiment of Figs. 33 and 34, such a device is realized in the
form of a


CA 02460374 2004-03-18
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-40-
deflector or shroud 730. The deflector 730 includes a sleeve portion 732
adapted to slip fit
over the outside of a spray nozzle (Fig. 35). The sleeve 732 may include a
seal groove 733
that retains an o-ring (not shown) or other suitable part that provides a seal
and helps keep the
deflector 730 on the nozzle. It should be noted that the deflector 730 may be
used with other
powder spray nozzles including but not limited to the generally flat spray
pattern nozzle 700
herein.
As best illustrated in Figs. 34 and 35, the deflector 730 includes a shroud-
like cone
portion 734 that envelops the forward end of the spray nozzle 712. The cone
734 flares at ari
appropriate angle to produce the desired spray pattern size and shape. The
cone 734 includes a
lip 736 at its forward end. This lip 736 may be used to assist in constraining
the size of the
spray pattern and also to direct the spray pattern forwardly. The deflector
730 is particularly
but not singularly suited for larger spray patterns. The conical shape and the
lip 736 also
function to brake the velocity of the powder spray from the nozzle 712. A
conical shape is
not required however and any suitable shape may be selected to produce a
desired spray
pattern. The deflector 730 can even be selectively "decoupled" by sliding it
backward to a
position where it no longer envelops or influences the spray pattern, without
requiring
complete disassembly thereof.
Figs. 36-38 illustrate another embodiment of a device used to shape a powder
spray
pattern. In this embodiment, a deflector 740 includes a central base 742 that
allows the
2 o deflector 740 to be slip fit onto a nozzle (Fig. 38). The base may include
a groove 744 that
retains a seal such as an o-ring in a manner similar to the above-described
embodiment of
Figs. 33-35.
In this example, the deflector 740 includes a flared cone or shroud portion
746 that
outwardly flares along its entire length. By omitting an end lip, the
deflector 740 allows for a
2 5 spray pattern having a higher velocity with smaller spray pattern sizes,
particularly useful for
spraying into corners and small parts. Again, adjusting the axial position of
the deflector on
the nozzle allows an operator to change the spray pattern size and the
influence of the
deflector on the spray pattern.
Note that the deflectors 730, 740 may be made of an appropriate tribocharging
3 o material to enhance electrostatic charging of the powder spray, as
described herein above.
With reference to Figs. 35 and 38, in some applications it may be desired to
have the
operator grounded at the same potential as the feedback ground of the
tribogun. To
accommodate this, the handle 872 may include an electrically conductive shell
750. This
shell 750 is electrically in contact with a grounding lug 752 inside the
handle 872. A ground
3 5 wire 754 is attached at one end to the grounding lug 752 and at its other
end to a second
grounding lug 756. The second ground lug 756 is electrically connected to a
ground pin 758


CA 02460374 2004-03-18
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which in turn is electrically connected to the conductive extension 760 of the
gun, which is
used to bleed off charge via the ground pin 986 from the tribocharging
surfaces as described
hereinbefore. A second ground wire 762 is routed from the ground lug 756 to
earth ground
through the handle 872.
With reference again to Fig. 18A-D and 21, the gun length may be changed by
changing the length of the tubular gun extension 870/972. The gun extension
870/972 is a
conductive member such as made out of a suitable metal, for example, aluminum.
The
extension 870/972 is conductive so as to provide a feedback ground path to
bleed off charge
buildup on the tribocharging surfaces, such as are readily produced on the
impact surfaces of
s o the charging portion 890/970. These charges or ions may be grounded to the
extension 972
via the ground pin 986 (Fig. 21).
In order to facilitate rapid gun extension length changes, as illustrated in
Figs. 39-42,
the extension has been modified to include a splice or coupling 770. The
splice 770 is press
fit inserted into a rearward end 722a of a barrel extension 772 to form an
extension assembly
15 773. The splice 770 may include one or more seal grooves 774 to retain
respective o-rings or
similar seals. The seals (not shown) provide a seal function and also help to
secure the
assembly 770, 772 in the gun body 876. The free end of the splice 770 is slip
fit inserted into
the forward end 972a of the gun extension 972 (Fig. 41) such that the forward
end of the
extension 972 abuts the back end 772a of the added barrel extension assembly
773.. A
2 o forward end 772b of the barrel extension assembly 773 slideably receives
the charge sleeve
portion 890 with a nozzle 974 mounted thereto such that the front end 772b of
the barrel
extension assembly 773 abuts a shoulder 775 of the nozzle 974. Note that the
grounding pin
986 makes contact with the newly added barrel extension 772 to insure
discharge of the
tribocharging surfaces in the charge sleeve 980.
25 The overall gun length therefore has been increased (or decreased by
opposite steps)
by simple slip fit connections while maintaining overall smooth outer contour
of the gun.
Thus, the gun length can be quickly and easily changed with two simple slip
fit disconnects
(Figs. 41 and 42) and reconnects of the extension 772 at the ends thereof (to
effect size
changes exemplified in Figs. 18A-D). An operator can therefore quickly change
gun length
3 o with minimal downtime during a spraying operation. The barrel extension
concept and
"length change on the fly" may be implemented with any suitable nozzle design
or gun body
design.
The gun body 876 and gun extension assembly 773 form an outer wall of the air
annulus or manifold 884 that receives air from the air fitting 886. This air
manifold 884 is
35 used to provide pressurized air to the air jets 981.
Gun length adjustment on the fly is facilitated by the simple press fit
assembly of the


CA 02460374 2004-03-18
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-42-
two ends 773a, 773b of the gun extension assembly 773 (Fig. 42). Because the
charging
portion 970 remains at the forward end of the spray gun, the extension 772 may
be made any
length without adversely affecting the tribocharging capability of the gun or
the feedback
grounding feature. Note that the length of the powder inlet tube 982/880 must
also be
changed commensurate with any change in the length of the extension assembly
773. This
can be accomplished by simply adding or removing slip-fit interconnected
powder tube
extension pieces 880 as illustrated in Figs. 18A-D. The back end 880a of the
extension 880
includes a socket 880b that slideably receives the nose portion 982a of the
powder inlet tube
982. A front or nose portion 880c slip fits into a socket 980a at the back end
of the sleeve
s o holder 980, or alternatively a socket at the baclc end of another powder
tube extension (not
shown in Fig. 42). Each slip fit connection may include appropriate seals as
required.
The designs illustrated in Figs. 18A-D, 21 and 41, 42 include the feature of
positioning or aligning the air jets 981 with reference to a single vertical
plane (relative to the
spray gun longitudinal axis) and proximate the discharge pin 986. This
maintains a more
uniform air distribution to the air jets and positions the pin 986 (near
impact areas) at a
location to best bleed off residual charge produced by the tribocharging
process in the
primary charging portion 970 of the gun.
The various aspects of the invention described herein including but not
limited to the
gun extension (length change), angled and conical nozzle slots and vents, and
deflectors may
2 o be used individually or any combination thereof as required for a
particular spraying
procedure.
VII. COMBINATION TRIBOCHARGING AND CORONA CFIARGING
As previously described herein, corona charging and tribocharging technologies
may
be combined to achieve additional benefits over using only one or the other
alone. This is
2 5 particularly, although not exclusively, the case when the unconventional
tribocharging
materials described herein are used in the tribocharging section.
Figure 43 illustrates this aspect of the invention in a rotary atomizing
powder spray
gun. The basic corona spray gun details are described in United States Patent
No. 6,105,886
(the "' 886 patent") issued to Hollstein et al., the entire disclosure of
which is fully
3 o incorporated herein by reference. In Figure 43, the primed (') reference
numerals correspond
to the reference numerals and description in the '886 patent (see Fig. 2 of
the '886 patent and
the related discussion therein), and such description need not be repeated
herein for a
complete understanding and practice of the present invention.
In accordance with the present invention, the rotary atomizing powder spray
gun of
35 the '886 patent is modified to include a tribocharging section by using
tribocharging material
for some or all of the components that powder contacts passing through the
spray gun. Thus,


CA 02460374 2004-03-18
WO 03/031076 PCT/US02/31820
-43-
one or more or all of the powder hose 49', the non-rotating tube member 48',
the spindle 31'
and the nozzle/distributor 39' are made of suitable tribocharging materials,
such as but not
limited to the tribocharging materials identified hereinabove. Alternatively,
the powder
contacting surfaces of these components may be coated or otherwise provided
with
s tribocharging material.
Because the powder path of the rotary atomizing spray gun comprises
tribocharging
material, a ground or discharge pin P may be appropriately positioned (shown
in an
exemplary manner in Figure 43) to discharge the surface of the tribocharging
material. The
pin P or other suitable conductive member is preferably grounded as indicated
by the line Q
s o in Figure 43. Since the spindle 31' is rotating, the pin P also will
rotate and its ground
connection can be made through a brush, slip ring or other suitable structure.
The exemplary spray gun of Figure 43 uses a tribocharging section that
tribocharges
the powder first, followed by a corona charging section that in this exemplary
embodiment
corona charges the powder as it exits the nozzle/distributor 39'. Note that
the corona
2s electrodes 77' need not be integrally combined with the spray gun body 11'
as in the
embodiment of Figure 43, but alternatively may be a separate assembly or
separate corona
gun with electrodes appropriately positioned. Alternatively, the corona
charging electrode
may be positioned internal to the spray gun (analogous to the embodiment of
Figure 7 herein).
In such an alternative case, the corona electrode not only charges the powder
but also
2 o discharges the tribocharging surface, thereby obviating the need for a
ground or discharge pin.
This discharge effect enhances the effectiveness of the triboelectric
charging.
As a further alternative embodiment to Figure 43, the tribocharging section
may
include a directed air tribocharging feature. By directed air is simply meant
the air jet assisted
tribocharging concepts described hereinbefore by which pressurized air is
directed through
25 one or more air jets to produce a turbulence in the powder flow and direct
the powder against
the tribocharging material in the powder path. Thus in the embodiment of
Figure 43, one or
more air jets or other suitable directed air mechanisms may be incorporated
into the spray gun
to provide the air jet assisted function. The gun would be further modified to
include an
appropriate pressurized air source to feed air to the air jets. Preferably the
air jets would be
3 o positioned just downstream of the discharge pin P.
The combination of corona charging and tribocharging may be further
facilitated by
providing a switch arrangement such as a switch selector device associated
with the spray
gun. Figure 44 illustrates such an arrangement in accordance with the
invention. The spray
gun of Figure 44 is basically the same directed air tribocharging gun 970
described
3 5 hereinabove with respect to Figure 21. The gun 970 however has been
modified to include a
switch arrangement that allows an operator to select a desired charging mode
depending on a


CA 02460374 2004-03-18
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-44-
particular spraying operation. For example, depending on the type of powder or
the article or
area thereof being sprayed, an operator may need tribocharging only, directed
air
tribocharging only, corona charging only, corona charging with tribocharging,
or corona
charging with directed air tribocharging. Although the exemplary embodiment of
Figure 44
illustrates directed air tribocharging, those skilled in the art will
appreciate that the invention
may be realized using a tribocharging spray gun and corona charging without
the directed air
tribocharging feature.
In accordance with this aspect of the invention, a two or three position
switch 1000 is
incorporated into the spray gun handle. The number of positions available for
the switch
1000 will be selected depending on how many charging mode options are to be
made
available to the operator. It should be noted that other mode selection
techniques besides a
manual switch may also be provided as an alternative to the switch 1000. For
example, a
remote switch or a software based control switch could be used to name just
two examples.
In the embodiment of Figure 44, a three position switch is provided to allow
selection
or changing of one of three charging modes, such as, for example, directed air
tribocharging
alone, directed air tribocharging with corona charging, or corona charging
alone. Other
charging modes may be realized as required by using additional switching
options. For
example, the spray gun could be operated in a tribocharging and corona
charging mode
without air assist, or a tribocharging mode alone without air assist or corona
charging. Thus
2 o the embodiment of Figure 44 is intended to be exemplary in nature and not
limited to the
specific charging mode options illustrated.
The three position switch 1000 produces a switch signal on signal line 1002
which is
detected by a suitable logic circuit 1004 corresponding to the selected
charging mode.
Preferably, but not necessarily, the switch 1000 is co-actuated with actuation
of the trigger
z 5 1006 used to start a spraying operation. Alternatively, the switch 1000
may be actuated
independently of the trigger 1006, and further still ma be located other than
on the spray gun
itself.
The logic circuit 1004 controls operation of a high voltage supply 1008 that
charges
an electrode 1010 or alternatively a number of electrodes, which electrode
functions as the
3 o corona charging section. The electrode 1010 may be positioned exterior the
nozzle 974 or
interior the nozzle. If positioned exterior the nozzle, the electrode 1010 may
be mounted on
the gun body or separately supported nearby. 'The electrode 1010 corona
charges powder
sprayed through the nozzle 974. As an example, the logic circuit 1004 may
simply control an
on/off signal 1012 of the supply 1008 when corona charging is selected, or
alternatively could
s 5 control a higher voltage output level to the electrode 1010 when corona
charging alone is
selected, or a lower voltage output level when tribocharging (directed air or
non-directed air)


CA 02460374 2004-03-18
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-45-
is used with the corona charging.
The logic circuit 1004 also generates an appropriate powder spray control
signal 1014
to a powder control unit 1016. The powder control unit 1016 activates a powder
feed 1018,
such as, for example, a powder pump, to start a spraying operation. The powder
control unit
1016 may further be used to control an on/off function of a pressurized air
source 1020 to an
air fitting 1022 corresponding to whether or not directed air tribocharging is
selected.
By appropriate actuation of the switch mechanism 1000, an operator may select
or
change the charging mode of the spray gun without changing any parts or
connections. The
switching arrangement may be conveniently mounted on the spray gun either
separately or in
z o combination with the trigger.
While the invention has been described with reference to a preferred
embodiment, it
should be understood by those skilled in the art that various changes may be
made and
equivalents may be substituted for elements thereof without departing from the
scope of the
invention. In addition, many modifications may be made to adapt a particular
situation or
material to the teachings of the invention without departing from the
essential scope thereof.
Therefore, it is intended that invention not be limited to the particular
embodiment
disclosed as the best mode contemplated for carrying out this invention, but
that the invention
will include all embodiments falling within the scope of the appended claims.

Representative Drawing
A single figure which represents the drawing illustrating the invention.
Administrative Status

For a clearer understanding of the status of the application/patent presented on this page, the site Disclaimer , as well as the definitions for Patent , Administrative Status , Maintenance Fee  and Payment History  should be consulted.

Administrative Status

Title Date
Forecasted Issue Date Unavailable
(86) PCT Filing Date 2002-10-04
(87) PCT Publication Date 2003-04-17
(85) National Entry 2004-03-18
Dead Application 2007-10-04

Abandonment History

Abandonment Date Reason Reinstatement Date
2006-10-04 FAILURE TO PAY APPLICATION MAINTENANCE FEE

Payment History

Fee Type Anniversary Year Due Date Amount Paid Paid Date
Application Fee $400.00 2004-03-18
Maintenance Fee - Application - New Act 2 2004-10-04 $100.00 2004-08-17
Registration of a document - section 124 $100.00 2004-08-19
Registration of a document - section 124 $100.00 2004-08-19
Registration of a document - section 124 $100.00 2004-08-19
Registration of a document - section 124 $100.00 2004-08-19
Maintenance Fee - Application - New Act 3 2005-10-04 $100.00 2005-08-09
Owners on Record

Note: Records showing the ownership history in alphabetical order.

Current Owners on Record
NORDSON CORPORATION
Past Owners on Record
LADER, HARRY J.
MESSERLY, JAMES W.
REHMAN, WILLIAM R.
SANNER, MICHAEL R.
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.
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Document
Description 
Date
(yyyy-mm-dd) 
Number of pages   Size of Image (KB) 
Claims 2004-03-18 4 129
Abstract 2004-03-18 2 93
Drawings 2004-03-18 30 1,064
Description 2004-03-18 45 2,966
Representative Drawing 2004-05-17 1 21
Cover Page 2004-05-17 1 67
PCT 2004-03-18 8 312
Correspondence 2004-05-13 1 27
Assignment 2004-03-18 3 102
Assignment 2004-08-19 5 152