Note: Descriptions are shown in the official language in which they were submitted.
21 15205
FLAME SPRAY GUN
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to applicator devices useful for
flame spraying heat fusible, powdered plastic or metal
coatings onto a substrate, and more particularly, to a flame
spray gun corlprising means disposed within the gun for
instantaneously controlling the powder feed rate through the
gun.
2. Description of Related Art
Many flame spray guns, spray nozzles, torches and the
like have previously been disclosed in prior art patents such
as United Statcss Patent Nos. 2,125,764; 2,404,590; 2,436,335;
2,544,259; 2,594,222; 2,643,955; 2,794,677; 2,804,337;
2,961,335; 3,073,528; 3,171,599; 3,441,215; 3,460,764;
3,565,345; 4,632,309; 4,835,022; 4,865,252; and 4,934,595.
Some flar~ie spray systems that are useful for coating
objects with ~~ thin layer of heat fusible plastic or metal
powder employ ~~ hopper having an eductor nozzle disposed at or
near its base. Compressed air or another pressurized gas is
directed throu~~h the eductor nozzle, where it entrains powder
drawn from the hopper, and conveys the powder through a flow
line to an applicator device such as a flame spray gun.
In various prior art devices, the powder feed rate has
been controlled in different ways. U.S. 4,934,595, for
example, discloses a pilot valve that is mounted on the hopper
body and controls the flow of compressed air through the
eductor. The pilot valve is operated by a switch disposed on
the flame spray gun. A disadvantage of this system is that
once the pilot valve is closed by operating the switch on the
applicator device, the flow of pressurized air through the
eductor is blocked, and powder is permitted to settle in the
flow line between the hopper and the gun. This can in turn
_ 21 15205
2
contribute to undesirable powder surging when the pressurized
air supply to the eductor is subsequently reestablished.
The applicant has appreciated an improved flame spray
system is disclosed that utilizes a powder control mechanism
comprising a valve disposed in the base of the hopper above
the eductor. The valve is operated by a switch disposed on
the applicator device, and controls the powder flow into the
eductor area independently of the compressed air flow through
the eductor. This control system enables the operator to turn
off the powder feed and purge the flow line of powder prior to
turning off the air flow through the eductor. Although this
system avoids the powder surging problems associated with the
device disclo:~ed in U.S. 4,934,595, it still suffers the
disadvantage of a delay between the time the powder valve is
closed and thE: time that the last powder in the flow line
clears the flame spray gun. The delay between operation of
the switch controlling the powder valve and the cessation of
powder flow through the flame spray gun is proportional to the
length of the flow line.
Other prior art devices such as those disclosed, for
example, in U.S. 3,441,215 and in FIGS. 3 and 4 of 4,835,022
utilize an intE:grated powder delivery system in which a powder
hopper is attached to the top of the applicator device.
Powder is gravity fed into the applicator device through a
hand operated valve. A principal disadvantage of these
systems is that the powder hopper must be located above and
adjacent to the applicator device.
A powder :Feed system and applicator device are therefore
needed that comprise a remote powder storage container and
means for providing real time control of powder flow and the
powder feed :rate through the applicator device. Such
apparatus is disclosed herein.
21 15205
3
SUMMARY OF THE INVENTION
According to one embodiment of the invention, a flame
spray applicat~~r device for heat fusible powdered materials is
provided that comprises a body having a pistol grip handle and
a powder nozzle containing an eductor through which
pressurized conveying air passes and draws fluidized powder
from a remote source to be heated by a combusting mixture of
air or other o:~cygen-containing gas and fuel gas as the powder
is discharged from the distal end of the device. A trigger-
operated valve is preferably disposed in the flow path of the
pressurized air upstream of the eductor so that the operator
can continuously control the supply of pressurized air to the
eductor and thereby effectively and substantially
instantaneously control the rate at which powder is discharged
from the powder nozzle of the device.
According to one preferred embodiment of the invention,
a flame spray gun is provided that comprises a body having a
pistol grip handle, a powder nozzle disposed in a cylindrical
bore within tree body, an eductor disposed in a cylindrical
bore within tree powder nozzle, a first connector means for
providing pressurized air to the body from a remote source, an
air flow path between the pressurized air connection and the
inlet end of th.e eductor, a trigger-operated valve controlling
air flow through the air flow path, and a second connector
means for pro~aiding fluidized powder from a remote powder
source to the cylindrical bore of the body at a point adj acent
to the outlet end of the eductor at a relatively lower
pressure than that of the pressurized air. According to a
particularly preferred embodiment of the invention, another
manually adjustable valve is provided in the air flow path
between the trigger-operated valve and the eductor for use in
regulating the air flow rate to the eductor independently of
the trigger-operated valve. According to another particularly
preferred embodiment of the invention, a second pressurized
21 15205
4
air flow path is provided between the first connector means
and an annular space around the powder nozzle in the
cylindrical bore of the body, and another manually adjustable
valve is provided in the air flow path between the first
connector means and the annular space.
In another aspect, the present invention resides in an
apparatus for applying a flame-sprayed coating of a heat-
fusible powdered material to a substrate, the apparatus
comprising a flame spray gun having a body, a powder nozzle
disposed inside the body, an eductor nozzle extending inside
the powder nozale and having an inlet and outlet, a fluidized
powder supply port within the powder nozzle adjacent to the
eductor nozzle outlet, a first passageway supplying a flow of
pressurized conveying gas to the eductor nozzle inlet, a
trigger-operated valve disposed inside the body for
selectively controlling the flow of conveying gas through the
first passageway, an annulus around the powder nozzle, a
second passageway providing fluid communication between the
annulus and the first passageway at a point in the first
passageway that: is upstream of the trigger-operated valve, the
second passageway supplying a flow of pressurized combustion
gas to the annulus, and a valve controlling the flow of
combustion gay; through the second passageway, wherein the
powder nozzle comprises a radially extending flange blocking
the annulus, and a plurality of orifices in the flange
permitting the pressurized combustion gas to flow past the
flange through the annulus.
In a further aspect, the present invention resides in an
apparatus for applying a flame-sprayed coating of a heat-
fusible powdered material to a substrate, the apparatus
comprising a flame spray gun having a body, a powder nozzle
disposed inside the body, an eductor nozzle extending inside
the powder noz;~le and having an inlet and outlet, a fluidized
2~ ~5ao5
powder supply port within the powder nozzle adjacent to the
eductor nozzle outlet, a first passageway supplying a flow of
pressurized conveying gas to the eductor nozzle inlet, and a
trigger-operated valve disposed inside the body for
selectively controlling the
flow of conveying gas through the first passageway, wherein
the body of the flame spray gun further comprises a second
passageway for supplying fluidized powder to the powder supply
port of the powder nozzle and means for maintaining a
predetermined rotational alignment between the powder nozzle
and the body.
F3RIEF DESCRIPTION OF THE DRAWINGS
The apparatus of the invention is further described and
explained in relation to the following figures of the drawings
in which Figures 1, 3, 4 and 5 are shown together and wherein:
FIG. 1 is a perspective view of a preferred embodiment of
the flame spray gun of the invention;
FIG. 2 is cross-sectional side elevation view taken along
line 2--2 of FIG.1;
FIG. 2A _-''_s an enlarged view of the powder nozzle and
eductor portions of the flame spray gun of FIG. 2.
FIG. 3 is a perspective view of the sealing diaphragm of
the invention;
FIG. 4 is cross-sectional plan view taken along line 4--4
of FIG. 1; and
FIG.5 is an enlarged front perspective view of the powder
nozzle of the invention.
Like reference numerals are used to indicate like parts
in all figures of the drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIGS. 1-5, flame spray gun 10 of the
invention preferably comprises metal body 12 having a pistol
21 X5205
6
grip handle, and a metal hood 14 that threadedly engages the
forwardly extending end of body 12. Upwardly extending hanger
plate 16 of body 12 comprises aperture 18, and provides a
convenient mea:zs for hanging flame spray gun 10 from a support
hook or the like when not in use. Alternatively, it will be
apparent that a ring or hook can be attached to body 12 in
place of hanger plate 16 for use in hanging flame spray gun 10
from a rack, bf~lt, or the like. Body 12 preferably comprises
a centrally disposed axial bore 44 (Figure 2) that
communicates with fluid passageways 54,56 and a forwardly
facing annulus 55 (figure 2A) that communicates with fluid
passageway 58. Diaphragm 50 is preferably located between
body 12 and hood 14. Fuel gas supply line 20 (Figure 1)
having valve ~?8 disposed at or near its end is releasably
joined to boc.y 12 by fitting 26, and communicates with
passageway 58 of body 12. A preferred fuel gas for use in
flame spray gun 10 is propane. Pressurized combustion gas
supply line 22 having valve 32 disposed at or near its end is
releasably joined to body 12 by fitting 30, and communicates
with passageway 56 of body 12. A preferred pressurized
combustion gas for use in flame spray gun 10 is compressed
air. Fluidized powder supply line 24 is releasably joined to
body 12 by f:_tting 40 (Figure 2), and communicates with
passageway 72 of body 12. Although not shown in the drawings,
it will be ap~~arent that a conventional hand operated valve
can also be provided at or near the end of powder supply line
24, although such a valve may not be needed for reasons
discussed belo~N in relation to the operation of the invention.
A preferred powder for use in flame spray gun 10
comprises a major portion of a cryogenically ground ethylene-
methacrylic acid (EMAA) polymer. It will also be understood
to those of ordinary skill in the art upon reading this
disclosure that powders comprising other thermoplastic
polymers, mi~saures of thermoplastic and thermosetting
21 1505
7
polymers, finE:ly divided metals, finely divided ceramics,
glass beads, and the like, can also be satisfactorily applied
using an applicator device as disclosed herein. Where the
powder to be applied comprises a major portion of a
thermoplastic resin, the powder should be heated to at least
its softening point by the flame at the outlet end of flame
spray gun 10. Metal and ceramic powders are generally applied
as an overcoat to a thermoplastic layer with the apparatus of
the invention, and need only be heated sufficiently upon
exiting flame ;pray gun 10 that the particles will soften the
preexisting pl,~stic surface to facilitate bonding between the
particles and the surface. Where the plastic surface is
already softens=d to some extent by preheating with flame spray
gun 10, very minor heating of the metal or ceramic particles
may be needed in order to effectuate the desired degree of
bonding.
Powder no;azle 46 is disposed inside bore 44, and eductor
nozzle 48 is preferably threaded into the upstream end of
stepped internal bore 45 of powder nozzle 46. As shown in
FIG. 2A, educe=or nozzle 48 preferably comprises centrally
disposed axial bore 82 having a smaller diameter than the
diameter of passageway 54.
Valves 3~~, 42 are adapted to control flow through
passageway 54 and valve 36 is adapted to control flow through
passageway 56.. Passageway 56 preferably provides fluid
communication between a point upstream of valve 42 in
passageway 54 <~nd annulus 88 (Figure 2A) around powder nozzle
46. Valves 34, 36 are preferably operated by adjustment knobs
98, 100 (Figure 40, respectively, and valve 42 is preferably
operated by trigger 38 to facilitate continuous and
substantially instantaneous control by the operator.
Powder no ~zle 46 is preferably held in place when hood 14
is threaded onto body 12 by flange 74 (Figure 5) that seats in
recess 51 (Figure 2) of body 12. One function of diaphragm 50
2~ X5205
8
is to serve as a sealing gasket between the facing and
otherwise con~~acting portions of hood 14 and body 12.
Diaphragm 50 is preferably made of an elastomeric material
such as rubber, and most preferably, is made of NEOPRENE°
rubber having a durometer of about 90. It is understood,
however, that other materials such as soft metals or synthetic
compositions may also be suitable for use as diaphragm 50 in
some application.
Referring to FIGS. 2, 2A and 5, powder nozzle 46
preferably further comprises thicker-walled body section 90
having outwardly facing annular groove 80 adapted to receive
O-ring 78. Similarly, eductor nozzle 48 preferably comprises
a thicker wall body section having outwardly facing annular
groove 94 adapted to receive O-ring 92. Passageway 72 of body
12 communicates with stepped cylindrical bore 45 of powder
nozzle 46 through orifice 84 in body section 90. Recess 96
between flange 74 and body section 90 cooperates with bore 44
of body 12 to define annular space 88 which communicates with
passageway 56. Circumferentially spaced orifices 76 in flange
74 permit pres;~urized combustion gas entering annulus 88 from
passageway 56 to flow past flange 74 and outwardly through
centrally disp~~sed bore 66 of hood 14.
Referring to FIGS. 2 and 2A, hood 14 preferably further
comprises inwardly facing annulus 57 (defined by recess 158)
that is coaxially aligned with annulus 55 (defined by recess
102) of body 12. Referring to FIGS. 2A and 3, a portion of
diaphragm 50 partially partitions annulus 57 from annulus 55,
and thereby helps distribute the fuel gas flow evenly around
annulus 55. An. array of circumferentially spaced orifices 64,
65 are preferably provided to allow the fuel gas to flow past
diaphragm 50 and into annulus 57. Although it will be
appreciated th;~t the number, diameter and spacing of orifices
64, 65 can be changed depending upon factors such as, for
example, the pressure, temperature, desired flow rate and type
z~ ~~zo5
9
of fuel gas being used, eight orifices spaced about 45 degrees
apart are depicted in FIG. 3.
Referring to FIG. 3, according to a particularly
preferred embodiment of the invention, diaphragm 50 comprises
discrete orifices 64 that are alternated with orifices 65
having slots 6'7 extending radially inward from orifices 65 to
centrally disp~~sed aperture 86. Slots 67, while not required
to operate flame spray gun 10, are believed to improve
performance b5r directing a minor portion of the flow of
compressed air passing axially through annulus 88 radially
outward into crifices 65. These radially directed flows of
compressed air are believed to assist in balancing the flow of
fuel gas into annulus 57 and also to assist in mixing the fuel
gas with combu:~tion gas. Aperture 86 preferably has an inside
diameter greater than the outside diameter of powder nozzle
46 to permit a:cial flow through annulus 88. Most preferably,
the diameter o:E aperture 86 is about equal to the diameter of
bore 44.
Bore 66 o:E hood 14 and surface 68 near the outlet end of
stepped internal bore 45 of powder nozzle 46 are preferably
tapered so as to provide a slightly increasing bore diameter
in the flow direction. This slight flaring near the outlet of
flame spray gu:n 10 is also believed to enhance the mixing of
combustion aiz- flowing through annulus 88 with fuel gas
flowing through circumferentially spaced orifices 60, 62 in
hood 14 and to enhance the coverage pattern of the powder
particles discharged through powder nozzle 46.
Similarly, in the preferred embodiment depicted in FIGS.
2 and 2A, circumferentially spaced, axially directed ports 60
are alternated. with inwardly directed oblique ports 62 to
provide converging flow paths for fuel gas discharged from
annulus 57 through hood 14. Circumferentially spaced,
radially extending orifices 52 are preferably provided in the
forwardly extending, open section of hood 14 to allow ambient
21 152 0 5
9a
air to be drawn radially inward as powder, pressurized air and
fuel gas are discharged through centrally disposed bore 66 and
ports 60, 62 oi_ hood 14. This flow of ambient air adjacent to
interiorly facing sidewall 112 of hood 14 is believed to
assist in keeping hood 14 cool during use of flame spray gun
10.
Powder nozzle 46 and body 12 preferably further comprise
cooperative means for placing powder nozzle 46 in a
predetermined rotational alignment inside bore 44 so that
orifice 84 of powder nozzle is aligned with passageway 72 of
body 12. One preferred means for achieving this rotational
alignment is p=_n 70 that extends through orifice 71 (Figure 5)
in flange 74 ar..d into a cooperatively aligned cylindrical bore
102 in body 12.
Referring to FIGS. 1-5, flame spray gun 10 is operated by
first connecting lines 20, 22 and 24 to suitable sources of
fuel gas, pre;~surized gas (preferably compressed air), and
powder, respectively. Although the fuel gas and compressed
air are supplied to flame spray gun 10 at pressures
significantly greater than atmospheric pressure, the powder
supplied to flame spray gun 10
21 15205
to
through line 24 is preferably at about atmospheric pressure as it approaches
the
gun in line 24. According to one preferred embodiment of the invention, the
powder is supplied from a fluidized bed powder source entrained in flow of
gas,
preferably air, at a, pressure sufficiently greater than atmospheric to offset
the
pressure drop that occurs due to friction within line 24. This pressure drop
can
vary for a particular powder depending upon the length and diameter of line
24.
When flame spray gun 10 is used for the first time, valves 28, 32, 34, 36
and 42 are preferably closed, and lines 20, 22, 24 are connected to flame
spray
gun 10 by means of fittings 26, 30 and 40, respectively. Valve 32 is then
opened, permitting compressed air to flow upward into passageways 54, 56 until
it is blocked by valves 42, 36, respectively. Valve 36 is opened sufficiently
to
establish a desired rate of flow of combustion air into annulus 88. Valve 28
is
then opened to allow fuel gas to flow through passageway 58 into annulus 55,
through orifices 64., 65 into annulus 57, and through ports 60, 62 into the
open
end of hood 14. If diaphragm 50 contains slot 67, some of the compressed air,
which is preferabl~r at a slightly higher pressure than the fuel gas, passes
axially
through annulus 8f~, through orifices 76 in flange 74 of powder nozzle 46, and
radially outward tr~rough slots 67 into orifices 65 of diaphragm 50, where it
is
mixed with the fuel gas prior to being discharged through ports 60, 62 in hood
14. The remainder of the compressed air flowing through passageway 56 and
annulus 88 is discharged through tapered bore 66 of hood 14 as combustion air.
As the fuel gas anti combustion air are discharged under pressure from face
110
of hood 14, they mix to form a combustible mixture that is lighted to create a
flame. The flame is then adjusted by operating valves 28, 36 as needed.
Once the fl;~me is ignited, flame spray gun 10 is desirably moved back and
forth across the su'~bstrate to be coated in order to preheat and drive
moisture off
of the surface. (Tlhis assumes that the surface has already been cleaned and
prepared for the application of a flame sprayed coating as disclosed in the
prior
art.) Once the surface is ready, powder is injected into the flame by opening
valve 34 and depressing trigger 38 to open valve 42 against the pressure of
spring
108 from the position shown in FIG. 2 to position 106 shown in phantom
outline.
~21 15205
11
Opening valves 34;, 42 allows compressed air to flow upwardly through
passageway 54, into eductor nozzle 48 and outwardly through bore 82 of eductor
nozzle 48 as shown in FIG. 2A. Because bore 82 has a restricted diameter, a
significant pressure drop is experienced at the point where the compressed air
exits bore 82 into bore 45 of powder nozzle 46. This pressure drop creates a
vacuum or "negative pressure" over orifice 84, causing powder to be drawn up
into bore 45 out of line 24. The powder is then entrained in the flow of
conveying air, whi~~h is discharged past tapered surface 68 of powder nozzle
46
and through the open end of hood 14. As the flow of powder and conveying air
exits hood I4, the ;powder particles are heated by the surrounding flame prior
to
being blown onto the surface being coated.
A significant feature of the apparatus of the invention is the provision of
trigger operated valve 42 in combination with inductor nozzle 48 and powder
supply orifice 82 in powder nozzle 46 so that the operator can continuously
control the powder feed rate by controlling the flow of conveying air through
passageway 54. Once valve 34 is initially opened to the extent desired for a
particular powder, compressed air pressure and application, subsequent control
of
the powder feed rake is achieved by varying the extent to which trigger 38 is
depressed. By simply releasing trigger 38, the operator can almost
instantaneously hall: the flow of powder through powder nozzle 46. Because no
powder remains in flame spray gun 10, plugging is not a problem and there are
no slugs of powder when powder flow is reestablished by again depressing
trigger
38. If a greater powder flow rate is desired that can be achieved by fully
opening
valve 34 and by fully depressing trigger 38, one can increase the regulated
pressure of the compressed air supplied through line 22.
Other alterations and modifications of the invention will likewise become
apparent to those o:f ordinary skill in the art upon reading the present
disclosure,
and it is intended that the scope of the invention disclosed herein be limited
only
by the broadest interpretation of the appended claims to which the inventors
are
legally entitled.
