Note: Descriptions are shown in the official language in which they were submitted.
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POWDER DELIVERY SYSTEM
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This invention relates to systems for
supplying air entrained solid particulate powder
material to powder spray guns or dispensers. More
particularlyj this invention relates to an improved
system for supplying an even flow of powder from a
fluidized powder source to a powder spray gun or
dispenser. ~
Characteristically, powder is supplied to a
powder spray gun through a pneumatic conveyor line
within which there is a powder pump containing a low
pressure venturi pumping chamber. This chamber is
intersected by a powder supply passage through which
powder is supplied to the pump from a fluidized bed
hopper. In order to meter or control the rate of flow
of powder from the fluidized bed into the venturi
pumping chamber, such pumps conventionally include a
metering air flow passage operable to inject a
controllefl flow of air into the powder supply passage.
The pressure of this metering air flow controls the
amount of air which is mixed with the powder entering
the pump, and consequently the rate of flow of powder
from the pump.
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One of the shortcomings of all powder spray
systems, including systems incorporating powder p`umps
of the type described hereinabove, is that the powder
ejected from the spray gun of the system commonly
flows unevenly from the gun. There are periodic puEfs
or clouds of powder ejected from the gun and periodic
reductions in the density of powder ejected from the
gun. Such periodic increases or decreases in powder
density sprayed from the gun result in uneven
application of powder to a target substrate to which
the powder is applied. Consequently, such random
changes in powder density are very undesirable.
There have been numerous attempts ~o
minimize or reduce these random changes of powder
density sprayed from a powder spray gun. Such
attempts have taken the form of changes in the design
of the powder spray gun, changes in the design and
configuration of the powder pump, etc. Most of these
changes have improved the situation somewhat, but have
not cured the problem.
It has been an objective of this invention
to provide an improved powder spray system wherein
inadvertent or random changes in the flow rate of
powder dispensed from a powder spray gun or dispenser
of the system are minimized or eliminated.
This invention is in part predicated upon
the discovery that one source of uneven flow of powder
from a powder spray gun or dispenser of a powder spray
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system is the configuration of the system between the
fluidized bed source of powder and the dispensing gun.
That portion of the system has heretoore simply
consisted of a siphon tube for supplying powder from
the fluidized bed to a powder pump, the pump, and a
long supply hose connecting the pump to the gun. It
has therefore been an objective of this invention to
eliminate powder flow variances which have heretofore
been attributable to the configuration of this portion
of the system.
These objectives are achieved, and this
invention is predicated in part upon the concept of
supplying powder from the powder pump through a hose
to an auxiliary fluidized bed of powder located near
the dispensing gun, and then supplying the powder to
the gun from the auxiliary fluidized bed through an
auxiliary powder pump and a relatively short hose. By
utilizing an auxiliary fluidized bed and an auxiliary
powder pump located near the dispensing gun outlet of
the system, erratic powder flow heretofore
attributable to the relatively long length of hose
betwéen the pump and the gun, and to a varying level
of powder within the fluidized bed source of powder,
have been reduced or completely eliminated.
I have found that a substantial portion of
the flow variances within a conventional prior art
powder spray system are attributable to two sour~es.
These sources are the relatively long hose between the
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pump and the gun and the varying level of powder in
the fluidized bed source of powder to the system`. A
long hose between the pump and the gun creates flow
variances as a result of loops and curves which
inevitably occur in such long hoses. Powder collects
in these loops or curves and eventually restricts flow
through the hose until a pressure build-up behind the
powder restriction breaks the restriction away and
causes a resulting puff of powder to be dispensed from
the gun while simultaneously causing a ~pressure
3 increase in the hose and a resulting increase in the
flow of powder to the gun. Thereafter, the powder
again begins to collect in the curve or loop of t~e
hose from which it had just broken away, until it
forms a restriction in the hose, breaks free, causes
another puff of powder, etc.
The other primary source of varying flow
from a conventionally configurated prior art powder
flow system, the varying level of powder contained in
the fluidized bed source of powder, cause~ flow
variances as a result of differing pressures being
required to draw powder into the powder pump as the
powder level changes in the fluidized bed. In fact
though, the vacuum within the pump tending to draw
powder into the pump does not change with the
differing level of powder in the fluidized bed hopper.
Instead, the vacuum pressure remains the same but the
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quantity of powder drawn into the pump changes as the
level of powder in the hopper changes.
According to the practice of this invention,
the powder spray system comprises a primary fluidized
bed hopper source of powder and a smaller capacity
auxiliary fluidized bed hopper located adjacent or
near the powdér dispensing guns. A venturi style pump
and a connecting hose transport powder from the
primary hopper to the auxiliary hopper and an
auxiliary venturi style powder pump and connecting
hose transport the powder from the auxiliary hopper to
a dispensing gun. There is an ovexflow pipe which
extends between the auxiliary hopper and the primar~
hopper and which functions to maintain a fixed level
of powder in the auxiliary hopper.
The practice of this invention with its use
of an auxiliary fluidized bed hopper and an auxiliary
venturi pump located closely adjacent the powder spray
gun of a powder spray system enables both of the above
identified sources of powder flow variances to be
eliminated. Any flow variances which occur in the long
hose between the primary hopper and the auxiliary
hopper do not affect the flow rate between 'the
auxiliary powder pump and the spray gun. Furthermore,
the use of an overflow pipe between the auxiliary
fluidized bed hopper and the primary fluidized bed
hopper enables the level of powder in the auxiliary
hopper to be maintained at a fixed level so long as an
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excess amount of powder is supplied to the auxiliary
fluidized bed. Thereby, flow variances attribut`able
! to the changing level of powder in the supply hopper
are eliminated.
These and other objects and advantages~of
this invention will be more readily apparent rom the
following description of the drawings in which:
Fig. 1 is a schematic view of a powder spray
system incorporating the auxiliary powder hopper and
auxiliary powder pump of this invention~
Referring now to the figure, there is
illustrated a powder spray system 10 for dispensing
solid particulate powder material from a plurality ~
spray guns 12. Three guns 12 are illustrated but the
system i5 equally applicable to the spraying of powder
from a single gun or from a substantially greater
number of guns 12. The guns 12 per se form no part of
the invention of this application and are well known
in the prior art. One such gun which is suitable for
use in this application is illustrated and described
in U. S. Patent No. 4,380,320 of Thomas E. Hollstein,
et al for "Electrostatic Powder Spray Gun Nozzle",
assigned to the assignee of this application.
The system 10, in addition to the guns 12,
comprises a primary or supply hopper 14, an auxiliary
hopper 16, as well as a primary pneumatic pump 18 for
pumping powder from the primary hopper 14 to the
auxiliary 16, and a plurality of auxiliary pneumatic
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pumps 20 for pumping powder from the auxiliary hopper 16 to
the guns 12. The pneumatic pumps 18 and 20 are conventional
powder pumps which per se form no part of the invention of
this application. One such pump which is suitable for use
in this application is illustrated and described in U.S.
Patent No. 3,746,254 of Lane S. Duncan, et al for "Powder
Spray System", assigned to the assignee of this application.
Another, and a preferred pump, useful in this system is
illustrated and described in co-pending Canadian patent
application Serial No. 489,024, filed August 20, 1985 and
entitled "Improved Venturi Powder Pump", also assigned to the
assignee of this application.
The hoppers 14 and 16 are also conventional
fluidizing bed hoppers and per se form no part of the inven-
tion of thi~ application. Both of these hoppers 14, 16 have
an enclosed chamber 24 in the ba~e of the hopper and an air
pervious ceiling 26 in the chamber. When high pressure air
is admitted into the inlet 28 of the chambers 24, such air
passes through the ceiling 26 of the closed chamber 24
and is operative to fluidize powder 30 contained in the
hopper above the closed chamber 24.
The two hoppers differ only in that the auxiliary
hopper is much smaller in size and capacity than is the
supply hopper 14. In one preferred embodiment wherein the
auxiliary hopper 16 supplies powder to eight guns 12, the
auxiliary hopper 16 has a
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volume equal to approximately l/16th the volume of the
supply hopper 14.
The two hoppers 14 and 16 also differ in
that the supply hopper 14 has a vent 34 in its top
wall while the auY~iliary hopper has no such vent.
Instead, the auxiliary hopper 16 is vented ~ia an
overflow tube 36 which extends from the interior of
the au~iliary hopper 16 downwardly through the closed
chamber 24 of the hopper 16 and through ~he top wall
38 of the supply hopper 14. As explained more fully
hereinafter, this overflow tube 36 functions to vent
the auxiliary hopper 16 as well as to transport all
excess powder from the auxiliary hopper 16 back to the
supply hopper. This overflow tube also functions to
maintain a fixed level of fluidized powder within the
auxiliary hopper 16.
The powder pumps 18 and 20 are all identical
except that the powder pumps 20 of the auxiliary
hopper may be of smaller capacity than the pump 18 of
the supply hopper 14. Each of these powder pumps has
an inlet port 40, an outlet port 42, and an atomizi~g
air inlet port 44. Additionally, each of these pumps
has a powder flow passage 46 therein through which
powder is drawn into a venturi pumping chambex 4~ of
the pump via a siphon tube 50 which connects the inlet
52 of the powder flow passage 46 to the fluidized bed
30 of powder from which the pump draws powder. The
supply hopper pump 18 draws powder from the hopper 14
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g
and pumps it into the auxiliary hopp~r 16 via a
transfer conduit 54 while the auxiliary hopper p`~mps
20 draw powder from the auxiliary hopper 16 and pump
it to the dispensing guns 12 via short transfer hoses
56.
The inlet ports 40 of the pumps 18, 20 are
connected via air lines 58 to a source of high
pressure air 60 while the atomizing air inlet ports 44
of the pumps are connected to the same high pressure
air source via air lines 62. Internally oE each pump
there is a small air orifice through which the high
pressure air from the source 60 flows into the ventùri
pumping chamber 48 so ar. to create a low pressu~e
within that venturi pumping chamber. That low
pressure is operative to draw powder via the siphon
tubes 50 upwardly into the venturi pumping chambers 48
of the pumps such that the powder can then be
transported via the hose 54 from the pump 18 to the
hopper 16, or in the case of the pumps 20, via the
hoses 56 to the dispensing guns 12.
As is explained more fully in the above
identified U. S. Patent No. 3,746,254, or in my
co-pending application Serial No. ~ , the
pressure o~ air supplied to the port 40 controls the
quantity of powder drawn upwardly through the siphon
tube into.the venturi pumping chamber 48 of the pump,
and the pressure of air supplied to port 44 controls
the ratio of air to powder mix within the pump.
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Typically, each of the air lines 58, 62 contains a
pressure regulator (not shown) through which the air
pressure supplied to the inlet ports 44 may be
adjusted so as to control the amount of vacuum drawn
within the venturi pumping chamber 48 of the pump and
the relative air to powder mix supplied to the venturi
chamber through the powder flow passage 46 of the
pump.
In operation of the powder dispensing system
10, high pressure air is supplied from the source 60
to the inlet ports 40, 44 of the powder pumps 18, 20,
and to the inlet ports 28 of the air chambers 24 of
the hoppers 14 and 16. The high pressure air supplied
to the inlet port 28 of the hoppers 14, 16 is
operative to fluidize all of the powder 30 contained
in the supply hopper 14 and the auxiliary hopper 16.
The fluidized powder 30 in the supply hopper 14 is
drawn via the siphon tube 50 upwardly into the venturi
pumping chamber 48 of the pump 18. This powder is
then transported from the supply hopper pump 18 via
the relatively long transfer hose 54 to the powder
inlet 68 of the auxiliary hopper 16. The fluidiæed
powder in the auxiliary hopper 16 is in turn pumped by
the auxiliary pump 20 to the dispenser guns 12 via~the
relatively short hoses 56. In practice, an excess
quantity of powder is pumped from the primary or
supply hopper 14 to the auxiliary hopper 16, which
excess is greater than the capacity of all of the
pumps ~0. As a result, excess fluidized powder flows
through the inlet 70 of the over-flow tube 36 back to
the supply hopper 14. The level of powder within the
auxiliary hopper 16 is thus always maintained at a
fixed level, that of the top edge of the inlet 70 of
the overflow tube.
A powder pump 72 may be associated with the
overflow line 36 in the event that gravity is
insufficient to carry the overflow powder to the
primary~ hopper. Such a pump may be required in
installation where there is substantial distance
between the two hoppers or where the primary hopper is
not located beneath the auxiliary hopper~ In the eve~t
that a powder pump 72 is associated with the overflow
line 36, a vent (not shown) would be provided in the
top of the auxiliary hopper in order to maintain
ambient pressure in the auxiliary hopper.
Prior to this invention, it has been the
practice to pump powder directly from the supply or
primary hopper 14 to the guns 12. There was no
intermediate or auxiliary hopper 16 in the system. I
have found that the long hoses which hereto extended
from the supply hopper 18 to the guns, as well as the
constantly changing level of powder within the supply
hopper 14, both contributed to and created a problem
of varying powder flow from the guns. Specifically, I
have found that a long hose extending from the pump of
the supply hopper to the gun had numerous curved or
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looped sections wherein powder collected and tended to
restrict flow through the long hose. This restri~cted
flo~ in turn caused a pressure drop in the hose to the
gun with a resultant drop in the ~uantity o~ powder
being pumped from the supply hopper to the gun.
Periodically through, the pressure behind the powder
created restriction built up to the point that it
caused the restriction to break, thereby causing a
high density puff of powder to be dispensed from the
gun. This in turn resulted in a temporary in~crease in
the flow of air and powder from the pump to the gun
because of the sudden increase in air flow through the
hose. Then the restriction would again build up ~n
the hose at the same point at which it had just broken
free and the process was repeated.
I have found that by utilizing the auxiliary
hopper 16 between the supply hopper and the guns, and
preferably close to the guns, the erratic powder flow
from the guns created by these powder created
restrictions in the hose are minimized or
substantially eliminated. I have also found that the
use of the auxiliary hopper 16 assists in maintaining
an even flow of powder from the guns 20 by maintaining
a fixed level of powder in the hopper from which
powder is supplied to the guns 20. The level of
powder in the supply hopper is subject to change, and
that change, prior to this invention, causes changes
in the powder flow from the guns 20. These changing
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powder flows were the result of the changing ~ir
pressur~ required to draw powder from the fluid`ized
bed of powder into the venturi pumping chamber 48 of
the pump~ As the level of powder in the fluidized bed
iB lowered a greater vacuum is required to pull powder
from that bed into the venturi chamber or as the level
is raised a lesser vacuum is required. But, the
vacuu~ in the venturi pumping chamber of the pump does
not change with changing levels of powder in the
fluidized bed. Instead, the powder flow from the pump
varies. By utilizing the invention of this
application, with the fixed level of powder in the
auxiliary hopper, this source of varying powder 1bw
from the gun is eliminated.
~ hile I have described only a single
preferred embodiment of my invention, persons skilled
in the art to which this invention pertains will
appreciate numerous changes and modifications which
may be made without departing from the spirit of my
invention. Therefore, I do not intend to he limited
except by the scope of the following appended claims:
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