U.S. patent number 3,870,375 [Application Number 05/259,591] was granted by the patent office on 1975-03-11 for powder spray system.
This patent grant is currently assigned to Nordson Corporation. Invention is credited to Lane S. Duncan, Charles H. Riedy, Simon Z. Tamny.
United States Patent |
3,870,375 |
Duncan , et al. |
March 11, 1975 |
POWDER SPRAY SYSTEM
Abstract
A coating apparatus with a powder supply system for use in a
device for electrostatically spraying powder material onto the
surface of an article or substrate to be coated. The system
includes a powder reclaiming and recycling system which
pneumatically retrieves the unused powder from the spray booths and
filters the powder from the air. The filter system includes plural
modules, each capable of accommodating a given number of spray
guns. An automatic filter shaking system releases the powder from
the filters upon command by sequentially shutting down the filter
modules, one at a time, while the system is in operation. An
additional filter module is provided so that adequate filtering
capability is maintained while the filter shaking operation
proceeds. The powder released from the filters is blown from the
filters to a feeder section through a sieve which mixes new powder
with the reclaimed powder under automatic control which replenishes
the powder supply to the feeder. The feeder employs a fluidizing
bed from which (a plurality of) plural module feeders are fed. The
feeders are positioned beneath the bed and draw powder through
elongated standpipes for improved powder flow control. This
configuration shows complete drainage of the bed and prevents
"puffing" associated with conventional fluidized bed feeders. The
feeders are quickly and easily detachable from the system and can
be quickly and easily replaced or disassembled for cleaning when
material or color change is desired.
Inventors: |
Duncan; Lane S. (Elyria,
OH), Tamny; Simon Z. (Lorain, OH), Riedy; Charles H.
(Lakewood, OH) |
Assignee: |
Nordson Corporation (Amherst,
OH)
|
Family
ID: |
26890438 |
Appl.
No.: |
05/259,591 |
Filed: |
June 5, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
194830 |
Nov 2, 1971 |
3746254 |
Jul 17, 1973 |
|
|
Current U.S.
Class: |
406/127; 406/138;
239/695; 406/144 |
Current CPC
Class: |
B05B
5/1683 (20130101); B05B 7/1454 (20130101); B05B
14/48 (20180201); B05B 7/1445 (20130101); B05B
7/1477 (20130101); Y02P 70/10 (20151101) |
Current International
Class: |
B05B
5/00 (20060101); B05B 5/16 (20060101); B05B
15/12 (20060101); B05B 7/14 (20060101); B65g
053/40 () |
Field of
Search: |
;302/42,45,47,51-53,55,57,59 ;222/195 ;239/15 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Blunk; Evon C.
Assistant Examiner: Carson; W. Scott
Attorney, Agent or Firm: Wood, Herron & Evans
Parent Case Text
This is a continuation-in-part of U.S. application Ser. No. 194,830
filed Nov. 2, 1971, now U.S. Pat. No. 3,746,254 which issued on
July 17, 1973.
Claims
Whaving described our invention, we claim:
1. A feeder for feeding a powder-air mixture comprising:
a fluidizing bed including a fluidizing chamber, a generally
horizontal porous floor for said chamber and means for directing
air through said floor into said chamber to fluidize powder
therein;
a venturi pump having at least one small diameter air inlet opening
into a large diameter expansion chamber, a powder inlet and an
outlet;
means connecting said powder inlet of said venturi pump to said
fluidizing chamber of said fluidizing bed so as to enable said
venturi pump to draw powder from said fluidizing bed into said
expansion chamber of said pump,
said connecting means comprises an elongated vertical passage
having an inlet connected to the bottom of said fluidizing bed
chamber and an outlet located vertically beneath said elongated
passage inlet, said elongated passage outlet being connected to
said powder inlet of said venturi pump for communicating powder
from said bed to said venturi pump expansion chamber,
said connecting means comprising an elongated vertical pipe, said
inlet of said elongated vertical passage being located above and
out of the horizontal plane of said generally horizontal porous
floor,
said elongated vertical pipe being horizontally spaced and
separated from said generally horizontal porous floor by a
non-porous portion of said floor.
2. The feeder of claim 1 further comprising:
a remotely controlled valve near the inlet of said passage.
3. The feeder of claim 1 further comprising:
an automatic valve operable to open in response to actuation of
said venturi pump, said automatic valve being located near the
outlet of said passage.
Description
The present invention relates to coating systems and particularly
to those for supplying powder through electrostatic spray
devices.
The practice of electrostatic spraying of liquid materials is now
well established and quite commonly practiced commercially.
Recently, however, there has been a great deal of interest and some
commercial activity in electrostatic spraying of solid particulate
materials. Such systems enable solid paints or other coating
materials to be applied to a substrate without a liquid carrier of
solvent. They therefore have the advantage of eliminating the cost
of the liquid carrier or solvent which has always heretofore been
required. Such systems also have the advantage of ease of
application and control, less expensive application equipment, a
wide range of film thicknesses is obtainable, and the problem of
controlling exhaust to atmosphere is minimized or eliminated.
Electrostatic powder spray systems operate on the principle of
tranporting a finely divided powder, generally on the order of from
10 to 50 micron (150 mesh) to a spray gun or spray head while
entrained in an air or gaseous stream. The powder is subsequently
transferred from the gun to the substrate by an electrostatic
charge applied to the powder and an opposite charge on the
substrate. Once applied to the substrate, the powder is generally
adhered as a film by heat fusion.
It is difficult in existing powder spray systems to convert from
one powder to another or from one color powder to another because
of the difficulty of purging the system of the first powder. Liquid
spray systems overcome the problem by solvent prior to spraying the
second liquid material. Dry powder systems, though, cannot tolerate
a liquid in the system so that the problem of purging the system of
a first spray prior to initiation of a cycle spraying a second
material is relatively severe. The problem is particularly acute
when changing from one color material to another in which case even
a minute amount of the first material discolors the second.
One of the sections of a powder spray system which is most
difficult to disassemble and clean is the feeder section. This
section includes an intricate manifold containing venturi pumps
with small precision orifices. Two types of feeder systems are
customarily employed. Both utilize venturi pumps which generate the
airpowder mixture to the spray guns. One such type is fed by a
vibratory hopper positioned above the venturi pump. A second type
incorporates a fluidizing bed having the venturi pump positioned
within the fluidizing chamber of the bed. With the second type of
feeder, the pump section is most difficult to remove before
cleaning.
It has therefore been one objective of this invention to provide a
feeder unit for a powder spray system which can be easily changed
or removed for cleaning so that the system may be easily converted
from one color or material to another in a minimum of time. This
objective has been accomplished by, and one aspect of this
invention is predicated upon, the concept of providing a feeder
system which in combination with a fluidizing bed is mounted
external thereto. This configuration allows the feeder mechanism to
be rapidly removed and allows the fluid bed portion of the system
to be interchanged if desired for off-line storage of powders of
different types of colors. The manifold of the feeder which carries
the venturi pumps is provided with a quick change connection to the
fluidizer bed assembly. The input and output manifolds through
which lines are connected to the pump manifold are also easily and
quickly removable therefrom for disassembly, change of parts, and
cleaning.
In systems of this type, it is also important that the feeder
section have the capability of providing a highly controllable
mixture of powder and the air. It is therefore another objective of
the present invention to provide such a feeder in which material
can be drawn from the hopper to the feeder in a smoothly flowing
and easily controllable manner. Accordingly, the present invention
is further predicated in part upon the concept of providing
elongated passages between the fluidizing portion of the fluidizer
bed and the feeder venturi pumps to facilitate the smooth and
uniform flow of powder therethrough. This concept has the advantage
that it is consistent with the above objective of providing a quick
change feeder system in that it provides a feeder fed by a
fluidizing bed having the feeder pumps positioned externally of the
fluidizing bed where they are more accessible for quick change and
cleaning.
Another important consideration in feeders of this type is the
elimination of a phenomenon known as puffing. This phenomenon
occurs, in one instance, upon the restarting of a pump after it has
been previously used and turned off. The puffing occurs when powder
settles in the feeder section or in the input ports to the feeder
pump where it becomes de-fluidized and compact in this region. When
the pump is restarted, this powder is ejected at high density into
the spray booth and an uneven and uncontrolled deposit of material
results on the object to be coated. It has been an objective of the
present invention to overcome this problem by provision of a valve
arrangement in the passages connecting to the feeder.
It has further been found that superior performance results when
certain precise dimensional relationships are maintained in the
passages within the feeder, and those connecting the feeder with
the fluidizing bed. Accordingly, the present invention provides a
feeder having such dimensions.
Another important consideration involved in efficiently employing
powder spray systems arises from the fact that with such systems a
significant portion, and in many cases, a major portion, of the
powder sprayed into the booth does not adhere to the substrate
surface of the article being coated. Most of this powder will
either settle to the bottom of the booth, or remain suspended in
the air within the booth. To efficiently operate such a powder
system, it is important to reclaim and reuse this powder. The
reclaiming is typically done in existing systems by exhausting,
through pneumatic means, the powder from the booth and passing the
air carrying the powder through separators or filter systems.
Sometimes, cyclone separators are used which can effectively
recover roughly in the area of three-fourths of the unused powder.
Such separators can operate continuously while the system is in
operation. A more effective method of retrieving the powder
involves the use of a filter section, as for example, one employing
bag filters. Whereas, nearly 100 percent of the powder can be
trapped by the filters in this manner, the use of such filters has
required the shutting down of the system to recover the filtered
powder from the bags.
It is a further objective of the present invention to provide an
efficient filter system which will permit the retrieving of the
extracted powder from the filters while the system is in operation,
thus avoiding the need to shut down the system or interrupt the use
of the system while a changing or purging of the filters is taking
place. This is extremely important in that these filters will fill
quite rapidly and the shutting down of the system to empty the
filters results in a significant amount of down-time for the
system.
Accordingly, the present invention is further predicated in part
upon the concept of providing a modular bag filter arrangement
having a sufficient number of modules so that when one of the
modules is shut down, the system can continue to operate utilizing
the filter capacity of the other modules. The reclaiming of the
powder from the filters is achieved by automatic means which
respond to the pressure drop across the filters which occurs when
the filters are filled with powder. During this operation, the
individual modules of the filter section are sequentially
de-activated and shaken to cause the powder to drop into a
reclaiming receptacle. Such a shake-down procedure can be performed
while the remaining modules of the system are in operation.
The present invention further provides an automatic control system
which pneumatically feeds the powder retrieved from the filters
from the filter receptacles and returns it to a sieve which
occupies the feeder. Further automatic controls are provided to
operate a make-up hopper to supply the system with new powder in
proportion to the amount that is consumed in the booths.
A further aspect of the invention resides in the manner in which
the reclaimed powder returned to the feeder is extracted from the
air which carries it. This feature utilizes the concept of
directing this reclaimed air down through the powder bed to utilize
the powder itself as a diffuser to decelerate the powder to thereby
collect it in the hopper to the feeder. This conveying air may be
exhausted from the feeder hopper at a point immediately above the
fluidized region and returned to the filters before being passed to
the atmosphere.
A further aspect of the invention resides in the provision for
removing electrostatic charges from the powder out of the feeders
to the guns. This change develops by mechanical action of the
powder through the feeder and, when an opposite charge of that is
to be applied by the electrostatic gun, will cause adhesion,
lumping, and irregular spray within the booths. The means include
grounded conductors in the hose between the feeders and guns to
remove the charge.
These and other objectives and advantages of the present invention
will be more readily apparent from the following detailed
description of the drawings illustrating a powder spray system
embodying principles of the present invention and in which:
FIG. 1 is a block and schematic diagram of the system embodying the
concepts of the present invention;
FIG. 2 is a side cross-sectional view illustrating the interior of
the filter module section of the system of FIG. 1;
FIG. 3 is a front elevation view illustrating one of the four-pump
feeder modules of the system of FIG. 1;
FIG. 4 is a cross-section view drawn to scale of the feeder of FIG.
3 taken along line 4--4 thereof;
FIG. 5 is an enlarged view of the feeder pump section of FIG. 4
drawn to twice the scale of FIG. 4;
FIG. 6 is a front elevational view of a second modification of an
attachment for securing the manifold block to the fluidized bed
assembly;
FIG. 7 is a cross sectional view taken on line 7--7 of FIG. 6.
The diagrammatic drawing of FIG. 1 represents a powder spray system
embodying the principals of the present invention. This system
includes a conveyor 10 which carries hooks 11 suspended therefrom
for conveying workpieces 12 through the powder spray station 13.
The spray station 13 includes a series of booths 14 which are
illustrated as four modular booths 14-1 through 14-4 so arranged as
to provide a continuous passageway for the workpieces 12 passing
therethrough. Each of the booths is provided with a pair of powder
spray guns 16 which direct electro-statically charged powder into
the booth environment which collects on the workpieces 12 which are
oppositely charged so that the powder will be attracted to the
surfaces of the workpieces 12. Only a portion of the powder sprayed
will generally adhere to the workpieces 12. The rest will remain
suspended in the air of the booths 14. This powder is collected and
recirculated by way of exhaust ducts 21 connected to the bottoms of
the booths 14.
The exhaust ducts 21 connect to inputs 22 of a bag filter section
25. The bag filter section 25 includes a plurality of bag filter
modules 26. Five of these modules 26-1 through 26-5 are
interconnect to form a single filter unit which makes up the
section 25. Each of these modules is provided with one of the
inputs 22, and each is sufficient to reclaim the powder from one of
the booths 14. The number of bag filter modules 26 is one more than
the number of spray booths 14 so that one of the modules may be
shut down to reclaim the powder trapped therein without interfering
with the capacity of the filter unit 25 to reclaim the powder from
all of the booths 14. In FIG. 1, the outputs 21 of the four booths
14 are connected to inputs of only four of the bag modules 26, the
module 26-4 having its input capped and unused. However, all of the
modules are interconnected in such a way that powder entering any
one of the inputs 22 may be filtered out through any one of the bag
module units 26 by virtue of interconnecting passages 28 between
each of the respective modules 26.
Each of the bag modules includes three banks 31 of nine filter
bags. These filters are arranged to divide the modules 26 into two
chambers, the first powder-receiving chamber 32 below the bag bank
31 communicates with the inputs 22 from the booths 14. The upper
chamber 33 is the exhaust air chamber which is positioned above the
filter bags and communicates through an exhaust air port 34 to a
common exhaust duct 35. The exhaust duct 35 of each of the booths
26 is connected to a single exhaust fan 38 which exhausts air into
an exhaust unit 39. The unit 39 muffles the sound of the exhausted
air and provides a final filter so that the air exhausted will be
clean when passed to the atmosphere. The fan modules 38 may be more
than one module as required to provide the exhaust capacity for the
number of filter modules 26 used or fans of various sizes may be
used.
The powder-laden air from the booths 14 passes through the ducts 21
to the input ports 22 and into the chambers 32 beneath the bag
modules 31. The air from the chambers 32 passes through the bag
filter modules 31 where the powder is trapped by the filters and
will adhere to the outer surfaces thereof. This air is drawn by the
fan 38 through the filters into the chamber 33 and out ports 34
through the duct 35 and out of the exhaust unit 39.
Each of the bag filter modules 26 is provided with a fluidized
powder sotrage section 41 which temporarily holds the powder
filtered by the bag modules 31 to the system. Each of these storage
sections 41 terminates into a venturi pump 42 which exhausts the
powder back into the system through a reclaiming duct 43. The bag
cleaning operation proceeds whenever the pressure drop across the
bag units 31 reaches a predetermined level indicating that the bags
are essentially saturated with reclaimed powder. The cleaning
operation is performed by first sealing the exhaust port 34 by
closing a valve which is designed to block that port. This valve 45
of a given module is open when that module is in use as illustrated
in connection with modules 26-1, 3, 4 and 5, but when the valve 45
is closed, as a particular module 26 is being cleaned, for example,
shown in connection with the module 26-2 of the system of FIG.
1.
As shown in FIG. 1, the module 26-2 is being cleaned. This cleaning
is done, as stated above, by first closing the valve 45 to block
the port 34 thereby to prevent the drawing of any powder-laden air
into filters 31 of that respective module 26. At the same time, and
by means which will be explained in more detail below, the bag
filter module 31 is shaken so that the powder will drop into the
lower region 41 of the unit 26. When the level controller 90 in the
feeder bed 65 senses a lower powder level, the venturi pump 42 of
the respective unit is then actuated to pump this powder into the
line 43.
As this reclaimed powder proceeds along the line 43, it enters a
sieve section 51 through an input manifold 52. In this section, the
reclaimed powder entering manifold 52 is mixed with new powder from
a make-up hopper 55. The air carrying the powder passes through the
sieve 51 into the feeder where the powder already in the bed 65
acts as a diffuser to decelerate and remove the reclaimed powder
from the air. The low velocity air may then be exhausted from the
bed 65 and fed through the filters to the exhaust. The powder from
the make-up hopper 55 is pumped by a venturi device 51 to the sieve
input port where it mixes with the reclaimed powder. The venturi 54
is actuated to pump new powder from the make-up hopper 55 whenever
the powder level in the filter chamber 32 is sensed by level
sensors 92 in sufficient amount to maintain the powder level to the
feeders as sensed by level sensor 90. Motor 57 turns the sieve
blades 58 which cause the powder to be sifted through a mesh screen
59 and drop into the feed hopper 61. The sieve unit 51 is a
conventional commercially available type.
The output from the sieve drops through hopper 61 into the feeder
module sections 63 which feed a powder-air mixture to the guns 16
in the spray booths 14.
The feeder sections 63 each include a fluidizer bed portion 65
which includes the fluidizing chamber 66 and an air chamber 67.
Interconnecting the chambers 66 and 67 is a porous wall 68 through
which air injected into the chamber 67 through port 69 passes to
fluidize the powder collecting in the chamber 66. In the preferred
embodiment, this fluidized powder passes through standoff tubes 71
which communicate through the air chamber 67 to a modular feeder
73. In an alternative embodiment, the porous floor 68 is sloped and
the standpipes 71 connect at the side of the chamber 67 through a
short nonporous sloped extension of the floor. Each feeder 73 is
adapted to supply four guns with powder to be sprayed. In the
eight-gun system illustrated in FIG. 1, two four-gun modular
feeders are required, each fed by a separate fluidized bed 65
interconnected by a pipe so that the fluidized powder levels
therein will be about equal in both beds 65. Each of these feeders
73 is provided with four hoses or outputs 75, each of which
communicates through line 76 with a different one of the guns 16
positioned within the booths 14. The feeders 73 are provided with
air inputs which control both the quantity and the density of the
mixture being passed through the hoses 75 to the guns 16. The
feeder modules 73 contain completely independent feeder sections
for each of the hoses 75, each of which is controlled by one of a
set of density control lines 81 and one of a set of volume control
lines 82. The air on these lines 81 and 82 is controlled through
solenoid valves represented diagrammatically as 84 which regulate
the air to the control lines from an air supply line 85. The valves
are controlled through an electrical console 87 which is provided
at some location convenient for operation by the system operator.
The discussion below sets forth the structural details and
operation of certain portions of the system, particularly the
filter section 25 and the feeder section 63.
The controls for the bag shaking sequence include a pair of
pressure sensors 46 and 47, a pressure difference detector 48, and
a shaker sequence control 49. The pressure sensor 46 is positioned
in the reclaiming duct 35 to measure the exhaust pressure, and the
pressure sensor 47 is positioned within the passage 28 to measure
the pressure therein. When the filters have become excessively
clogged, the pressure difference between the sensors 46 and 47 will
increase. Typically, the critical pressure may be 4 or 5 inches of
water column. The pressure difference detector 48 will generate a
signal when this pressure has been reached to initiate the shaker
sequence control cycle which is determined by the control module
49. This module will sequence the shaker operation at each of the
bag units 31 one at a time for approximately one minute each. The
shaker control 49 operates means which will be explained in
connection with the discussion of FIG. 2 below.
The reclaiming cycle control is automatic and is provided with
means which include level sensors in the fluidizer bed and in each
of the reclaiming chambers 41 of the filter module 25. The reclaim
control includes a control solenoid operated valve 89 which
operates the venturi pumps 42 by connection to an air supply upon
command. Normally, this command will be responsive to a signal
supplied by a powder level sensor 90 positioned near the bottom of
the fluidizer bed 65 to signal when additional powder is needed.
This will initiate the venturi pumps 42 to draw reclaiming powder
from the modules 25 and make-up hopper 55. If the module 25 is
excessively full, this level is detected by sensors 92 positioned
in the regions 41 of each of the modules 26. This control
deactivates the make-up hopper venturi pump and the feed hopper 66
receives powder only from the filter sections 25. This control is
provided by logic represented by AND-gate 94.
Referring to FIG. 2, a portion of the bag module section 25 is
illustrated in cross-section. Shown are a plurality of the bag
modules 26 interconnected to form the multiple module unit 25.
Referring to each of the modules 26 in FIG. 2, the reclaimed powder
inputs 22 is illustrated terminating at points 101 within the lower
chamber 32. The bag unit section 31 includes nine bags 102 inserted
about mesh or helical spring supports 103 attached to a supporting
mount plate 104. The mount plate 104 is a solid plate having holes
105 therein communicating with the interiors of the bags 102. The
plate 104 is mounted through brackets 107 to the housing 109 of the
unit 26 through elastic mounts 110. The mounts 110 are designed in
such a way that the support 104 and thus the bags 102 can be
vibrated with respect to the housing 109. A set of manually
operated toggle clamps or automatic pneumatic clamps 111 is
provided to firmly lock the plate 104 against the mounts 110, and
thus, immobilize it with respect to the housing 109. These
quick-acting clamps also allow the bag cartridges to be rapidly
removed from the unit and interchanged or thoroughly cleaned when
changing color.
Above the bag module 31 is the chamber 33 defined by the plate 104
and the housing 109. At the upper end of this chamber 33 is the
exhaust port 34 which commuticates through an opening 120 in the
housing 109. The valve 45 is comprised of a vertically movable
valve plate 121 which is supported upon a linearly actuatable shaft
122 of a piston and cylinder (not shown) so that it may move
vertically to seal or open the opening 120. In the centermost
module of FIG. 2, this plate 121 is shown in its opened condition.
In the leftmost module this valve plate 121 is shown in the closed
condition.
Each of the modules 26 is joined so that the lower chambers 32 form
a common chamber so that air may pass freely to any one of the
filter units 31. For the endmost of these modules 26, a plate 125
is provided to seal the opening which would otherwise form the
interconnection chamber between the adjacent modules.
Each of the modules 26 is provided with a bag shaker mechanism 130.
This shaker mechanism 130 includes a reciprocating pneumatic piston
131 contained within a cylinder 132 fixed to the housing 109. The
piston is connected to a rod 133 to the plate 104.
In operation, with reference first to the center module of FIG. 2,
the filtration operation proceeds with the powder-laden air from
the ducts 22 from the booths 14 entering through the ports 101 of
the center module and into the chambers 32 defined therebelow. The
air is drawn through the bag filters 102 where the powder collects
on the outer surfaces thereof allowing the filtered air to pass
through the openings 105 into the upper chambers 32 and out through
the openings 120 and the ducts 34 where it will proceed toward the
exhaust unit 39 under the power provided by the fan 37 (FIG. 1).
When the bag pressure drop across the filters becomes excessive,
the bag cleaning operation will proceed as follows:
First, the valve plate 121 of that module is closed to seal the
opening 120 as shown in the leftmost module of the figure. At the
same time, the pneumatic vibrator 130 will operate to shake the
plate 104 to cause the powder to fall from the bag modules 102 to
the bottom 41 (FIG. 1) of the chamber 32. The actuation of the
shaker mechanism 130 occurs automatically immediately after the
closing of the valve plate 121. This shaking will continue for a
specified amount of time until the powder has been shaken from the
bags 102. When this is completed, the shaker will stop, and the
valve plate 121 will reopen to permit reuse of the filter. The
clamps 111 can also be automatically actuated to release in
synchronism with the shaking sequence.
By the modular filter construction, the filter modules may be
designed to accommodate the requirements of one of the booths 14.
Thus, as the system is expanded by the addition of more booths, an
equivalent number of bag modules may be added to accommodate the
system. One additional bag module is provided to allow the
operation of the filter section 25 with adequate capacity when one
of the modules 26 is shut down to reclaim the powder. Thus, the
powder reclaiming operation may provide for each module 26 one at a
time while the system is in operation.
The feeder mechanism 63 is illustrated in detail in FIGS. 3, 4 and
4A. Referring to FIG. 3, one of the two four-gun feeder modules 73
is illustrated. The feeder module 73 is removably secured through
knurled headed bolts 151 to a feeder mounting block 152 rigidly
secured to the base of the air chamber 67. The feeder module 73
includes four hose connectors 154 which constitute the outputs 75
which connect to the hoses 76 which feed the guns 14 (FIG. 1). The
fluid bed 65, positioned above the air chamber 67 opposite the
porous plate 68, has attached through its forward wall a knob 155,
which operates linear actuators to open or close ports whhich allow
the powder flow to the respective feeder sections. This is
discussed more fully in connection with FIg. 4 below which is a
cross-section through one of the units of the feeder 73 and the air
chamber 67 and the fluid bed portion 65. The drawing of FIG. 4 is
to scale, and the dimensions illustrated therein have been found
effective in providing results which are far superior to prior art
devices, and accordingly, the use of these dimensions are
preferred.
Referring now to FIg. 4, the fluid bed 65 includes a closed wall
portion 161 which is connected to the sieve hopper 61 (FIG. 1).
This wall is bolted to the porous plate 68 through a bolt 162 and a
nut 163. The wall 161 defines the fluidizing chamber 66. At the
center of the porous plate 68 is provided a rectangular solid metal
plate 165 having four holes therein, one provided for each one of
the units of the feeder module 73. The powder from the sieve 51
collects in the chamber 66 while air injected through the air
chamber 67 propagates upwardly through the porous plate 68 to cause
the formation of a fluidized layer in the chamber 66 above the
plate 68. This fluidized powder is communicated off to the feeder
73 through standpipes 71 which communicate from the hole 164 in the
plate 165 downwardly through the air chamber 67 to the feeder 73.
The non-porous plate 165 prevents the incidents of fluidizing air
in the area immediately surrounding the hole 164, and thus,
eliminates turbulent flow in this region to thereby allow more
precise control of the fluidized powder mixture into the standpipe
71. The standpipes 71 are threaded at both ends. At the upper end,
they are threaded into tapped holes in the base of brackets 171
which are thereby secured to the plate 165.
The flow of fluidized powder into the standpipes 71 may be turned
off for servicing through actuation of ball valves 167 which seat
in the upper ends 168 of the standpipes 71. These balls 167 have
connected thereto hooks 169 which surround the end of a lever arm
link 170 pivotally attached to the bracket 171. The level 170 is
brought under the control of the actuator arm 172 which is slidably
mounted in a bushing 173 secured in the hole 174 in the wall 161.
The end of the arm 172 terminates in the knob 155.
The ball valve 167 may be in the form illustrated or may
alternatively be in the form of a slide valve positioned
approximately at point 175 on the standpipe 71. The choice of this
valve position is such as will eliminate the collection of powder
when the respective feeder unit is shut off. Powder collected at
this point will cause an effect known as puffing when the system is
re-energized. This effect is defined as that phenomenon wherein a
burst of powder collected in the system is dumped from the gun at
the instant of turn-on. This is undesirable in that it causes
unevenly mixed spray of powder and air into the booth area.
Further, to eliminate this effect, the feeder may be provided with
an elastic diaphragm-type valve 176 positioned at the base of the
standpipe 71. This is illustrated more clearly in FIG. 5 as being
in the form of a gasket-type washer 176 with an X slit 177 in the
center thereof which will open under the influence of the pressure
gradient applied at this point. The air powder mixture passing
through this opening 177 enters the feeder section and is drawn
therein by the venturi action of the feeder section 73. It has been
found that the system performs optimally when the dimensions are as
illustrated in FIG. 4. With this set of dimensions, it has been
found that the length of the standpipe 71 should be at least the
41/4 inch length from the ball seat at 168 to the gasket 176 as
shown. The feed mechanism 73 is described in detail in FIG. 4A.
FIG. 4A is drawn to a scale twice that of FIG. 4.
The feeder 73, as was explained above, was designed so that it can
be easily removed from the rest of the system. This easy removal is
provided through the screws 151 which cause the feeder portion 73
to separate from the air chamber mounting block 152 at the gasket
176. It is highly desirable that the feeder be easily removed from
the rest of the system, particularly in that it is essential to
clean the system of powder before replacing it with another powder
which may be of a different type or of a different color.
Typically, the feeder section 73 will be that portion of the system
which is most expensive, and for this reason, quick removal and
replacement of the feeder section with the spare section will allow
for interchange of fluid bed hoppers for rapid color or powder type
change. One fluid bed is used for each color or powder type.
The feeder section itself is also designed so that it can be
cleaned with a minimum of time and effort. To so clean the feeder
73, it has been designed so that it is made up of a three part
manifold. These three parts include the main venturi manifold
section 181, an input manifold section 182, and an output manifold
section 183. Each of these manifolds can be quickly detached from
one another. For example, the input manifold 182 is mounted against
the venturi manifold 181 and retained thereagainst through knurled
headed screws 185. Loosening and removal of these screws will allow
for quick removal of the input manifold section 182 from the
venturi manifold section 181. Similarly, the output manifold
section 183 can be removed from the venturi manifold section 181 by
loosening of the screws 159 (FIG. 3) which hold these two manifold
sections together.
Referring now to FIG. 4A, the input manifold 181 is provided with
eight air input ports, two for each of the feeder sections. Only
one feeder section is shown in the cross-section views of FIGS. 4
and 4A. Associated with each feeder section is a density control
air input port 191 and a volume control air input port 192. Each of
these ports is threaded to receive a threaded air hose connector.
The connectors at the ports 191 connect to the density control air
hoses 81 (FIG. 1) while the connectors at port 192 connect with the
volume control air hoses 82 (FIG. 1). The input port 191 tapers to
a very small air orifice 193 of a diameter of approximately 103
inches. The input port 192 terminates at a larger opening 194 which
communicates with an orifice provided within the manifold 181.
The venturi manifold 181 is provided with a density control air
chamber 201 which is cylindrical in shape and positioned coaxially
with the standpipe 71. This chamber 201 is communicated with the
orifice 193 of the density air control input port 191 through an
opening 202 in the wall of the manifold 181. An enlarged portion
203 of the chamber 201 is provided at the upper end thereof to
receive an O-ring 204 which seals the chamber 201 against the
gasket 176. At the lower end of the chamber 201 is provided a
narrowed throat 207 which connects the chamber 201 to a horizontal
bore 209 which contains the venturi feeder pump. Within the throat
207 is positioned a teflon sleeve 211 which has a lower reduced
diameter section 212 adapted to slipfit into the throat 207 and a
larger diameter upper section 213 thereby forming a step portion
215 which rests on the lower edge of the chamber 201 to limit the
downward movement of the sleeve 211 as it is inserted into the
throat 207.
The sleeve 211 has a conical chamber 219 at the upper end thereof
having its wider end communicating with the slit 177 and the gasket
176. The collar 211 fits snugly against the gasket 176 in an
airtight relationship except in regions in which a pair of opposing
slots 220 are provided which communicate between the chamber 219
and the chamber 201 in the manifold housing 181. The lower end of
the collar 211 is provided with an output chamber 222 which
communicates with the bore 209 in the venturi pump section of the
feeder.
The bore 209 communicates between the volume control air input 192
and the output connector 154. This bore is provided with an airjet
sleeve insert 231 at the control input 192. This sleeve 231 has a
smaller outside diameter region 232 of a diameter equal to that of
the bore 209 so that it may be inserted in slipfit fashion within
the bore 209. The bore 209 also has a larger diameter section 234
at the juncture with the input manifold 182. Similarly, the sleeve
231 has a larger outside diameter collar in this region and will
slip into and securely and positively position itself within the
opening of the bore 209 adjacent the volume control input port 192.
Concentrically positioned at the center of the sleeve 131 is a
control air input orifice 236 of 106 inch diameter which
communicates at one end with the narrow portion 194 of the input
port 192 and at the other end with an expansion chamber 241 within
the bore 209 which communicates with the output end 222 of the
sleeve 211.
This chamber 241 is formed within a teflon sleeve 243 which is
inserted within a metal sleeve 244 which is in turn inserted within
the bore 209. Each of the sleeves 243 and 244 are adapted to
slipfit on each other and into the bore 209.
The sleeve 243 is provided with a notch 246 in the upper surface
thereof in the region adjacent the chamber 241 to communicate with
the opening 222 of the sleeve 211. The lower portion 212 of the
sleeve 211 is adapted to extend downwardly into the chamber 241 so
as to serve as a lock pin to prevent rotation of the sleeve 243
within the bore 209.
The end 248 of the sleeve 243 is dimensioned to abut the base of
the collar 231 to limit the inward motion of the sleeve into the
bore 209. The sleeves 243 and 244 are held to this centermost
position by the output manifold 183 when it is secured in position.
The manifold 183 has mounted therein the threaded output hose
connector 154 which communicates with the output hoses. These
connectors have an outlet port 251 which communicates with a
tapered portion 252 of the bore 253 of the sleeve 243. The nylon
hose connector 154 is provided with a taper 256 adjacent the
manifold 181 to receive an O-ring 257 to seal between the manifolds
181 and 183. The O-ring 257 fits in a groove 258 in the metal
sleeve 244 to trap the sleeve in position when the manifolds 181
and 183 are connected together.
When the three manifolds are disassembled or detached from each
other and the feeder is removed from the assembly, all of the parts
of the system can be easily removed from the feeder 73 and either
replaced or reclaimed with maximum ease.
In the operation of the feeder 73, the powder is fed into the
chamber 219 of the sleeve 211. Density control air is injected into
the inlet port 191 and through the orifice 193 and through the
opening 202 into the chamber 201 where the air will turbulently
circulate until it passes through the slits 220 into the chamber
219 wherein it is mixed with the powder mixture being fed
therethrough, thereby determining the density of air-to-powder
ratio in this area. The volume control air is injected through
inlet port 192 through passage 194 and orifice 236 at high velocity
into and through the chamber 241 within the sleeve 243. This air
will pass through the opening 253 and the conical tapered portion
252 thereof to the outlet 251 and through the outlet hose connector
154. The chambers 236, 241 and 253 define a venturi tube which
generates low pressure at the outlet 222 of the sleeve 211 to draw
the air-powder mixture from the sleeve 211 into the chamber 241 to
cause it then to flow through the output 251 with the air entered
from inlet 192. By regulating the amounts of air to inlets 191 and
192, the volume and density of the powder mixture at the outlet 251
is precisely controlled. The dimensions of the passages, except
those in which the dimensions are specifically given above are as
illustrated to scale in the scale drawings of FIGS. 4 and 4A. FIGS.
6 and 7 illustrate alternative connection means for securing the
manifolds of the feeder to the air chamber fluidizier bed assembly.
These means are essentially cam-actuated clamps which snap quickly
into and out of engagement to lock the feeder or release the feeder
to and from the assembly. Referring to FIG. 6, this clamp means
includes a lever 261 attached to a shaft 262 to which are mounted
cams 263. When the lever is rotated to the position, the cams urge
the feeder manifold 181 against the gasket 176 and the feeder
mounting block 152. When the lever 261 is rotated by approximately
180.degree. the cam 263 is released to loosen the block and permit
its being slid away from the unit assembly. This can be seen in
FIG. 76 as the direction of the arrow 268. A trackway 269 is formed
as structure rigidly attached to the block 152 to receive the
feeder 73 for slidable movement in the horizontal direction. The
trackway is provided with a stop 270 to limit the motion and
properly register the feeder with respect to the rest of the
assembly to which it is attached.
Means are also provided to remove electrostatic charges from the
powder mixture out of the outlets 251 of the feeders 73. This means
is shown in two embodiments in FIGS. 4 and 4A. In FIG. 4, an outlet
hose 75 is shown as constructed of conductive material which is
electrically grounded. This hose extends from the feeder to the
guns 16 in the booths 14. In FIG. 4A, a non-conductive hose 75A is
shown having a grounded wire conductor 275 extending for several
feet within it. The conductor should be sufficiently long so that
substantially all of the particles of powder will be freed of
charge as the mixture turbulently flows through the line 75A.
While we have described only a single preferred embodiment of our
invention, persons skilled in the art to which this invention
pertains will readily appreciate numerous changes and modifications
which may be made without departing from the spirit of our
invention. For example, we have described the system as one in
which air is the fluid medium employed for transporting the powder
from the hopper to the gun. Obviously, though, other gases which
are inert with the powder may be employed with equal facility.
Therefore, the terms "air" and "pneumatic" are intended and are
used throughout the specification and claims in a generic sense to
include all suitable gases. Other changes and modifications will
also readily come to mind in the case of persons skilled in this
art. Therefore, we do not intend to be limited except by the scope
of the following appended claims.
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