U.S. patent application number 14/172067 was filed with the patent office on 2014-06-19 for dense phase pump for dry particulate material.
This patent application is currently assigned to Nordson Corporation. The applicant listed for this patent is Nordson Corporation. Invention is credited to Edwin Jeroen Beuk, Terrence M. Fulkerson, Andreas Kleineidam, Ulf Kleineidam.
Application Number | 20140169990 14/172067 |
Document ID | / |
Family ID | 34636517 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140169990 |
Kind Code |
A1 |
Fulkerson; Terrence M. ; et
al. |
June 19, 2014 |
DENSE PHASE PUMP FOR DRY PARTICULATE MATERIAL
Abstract
A dense phase pump for particulate material includes a pump
chamber wherein material flows into the pump chamber under negative
pressure and flows out of the pump chamber under positive pressure.
A plurality of pinch valves are provided to control flow of
material into and out of the pump chamber. The pinch valves are
operated independent of each other and of the pump cycle rate. A
modular design of the pump is provided.
Inventors: |
Fulkerson; Terrence M.;
(Brunswick Hills, OH) ; Beuk; Edwin Jeroen;
(Hamont-Achel, BE) ; Kleineidam; Ulf; (Hamburg,
DE) ; Kleineidam; Andreas; (Elmshorn, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nordson Corporation |
Westlake |
OH |
US |
|
|
Assignee: |
Nordson Corporation
Westlake
OH
|
Family ID: |
34636517 |
Appl. No.: |
14/172067 |
Filed: |
February 4, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13680316 |
Nov 19, 2012 |
8678777 |
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14172067 |
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|
12963969 |
Dec 9, 2010 |
8333570 |
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13680316 |
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12407929 |
Mar 20, 2009 |
7997878 |
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12963969 |
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10711429 |
Sep 17, 2004 |
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12407929 |
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60524459 |
Nov 24, 2003 |
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Current U.S.
Class: |
417/65 |
Current CPC
Class: |
B05B 14/48 20180201;
B05B 7/1459 20130101; F04F 5/48 20130101 |
Class at
Publication: |
417/65 |
International
Class: |
F04F 5/48 20060101
F04F005/48 |
Claims
1. A pump for dry particulate material, comprising: a pump chamber
defined in part by a gas permeable member disposed in a pressure
chamber; wherein during pump operation material flows into said
pump chamber under negative pressure and material flows out of said
pump chamber under positive pressure during a pump cycle; wherein
flow rate of material from the pump is adjustable independent of
the pump cycle duration.
2. The pump of claim 1 comprising a suction pinch valve and a
delivery pinch valve that control flow of material in and out of
the pump chamber respectively, said pinch valves having open/closed
times that are separately controllable from the pump cycle
time.
3. The pump of claim 1 comprising a control circuit that adjusts
duration of time that the negative pressure is applied to the
pressure chamber to adjust flow rate.
4. The pump of claim 3 comprising a suction valve and a delivery
valve that control flow of material in and out of the pump chamber
respectively, said valves having open/closed times that are
separately controllable with respect to the negative pressure
duration time.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of U.S. Non-Provisional
patent application Ser. No. 13/680,316 filed on Nov. 19, 2012, for
DENSE PHASE PUMP FOR DRY PARTICULATE MATERIAL, which is a
continuation of U.S. Non-Provisional patent application Ser. No.
12/963,969 filed on Dec. 9, 2010, for DENSE PHASE PUMP FOR DRY
PARTICULATE MATERIAL, which is a continuation of U.S.
Non-Provisional patent application Ser. No. 12/407,929 filed on
Mar. 20, 2009, for DENSE PHASE PUMP WITH SINGLE ENDED FLOW AND
PURGE, now U.S. Pat. No. 7,997,878, which is a divisional of U.S.
Non-Provisional patent application Ser. No. 10/711,429 filed on
Sep. 17, 2004, for DENSE PHASE PUMP FOR DRY PARTICULATE MATERIAL,
now abandoned, which claims the benefit of U.S. Provisional patent
application Ser. No. 60/524,459 filed on Nov. 24, 2003, for PINCH
PUMP WITH VACUUM TUBE, now expired, the entire disclosures of which
are fully incorporated herein by reference.
TECHNICAL FIELD OF THE INVENTION
[0002] The invention relates generally to material application
systems, for example but not limited to powder coating material
application systems. More particularly, the invention relates to a
pump that reduces cleaning time, color change time and improves
convenience of use.
BACKGROUND OF THE INVENTION
[0003] Material application systems are used to apply one or more
materials in one or more layers to an object. General examples are
powder coating systems, other particulate material application
systems such as may be used in the food processing and chemical
industries. These are but a few examples of a wide and numerous
variety of systems used to apply particulate materials to an
object.
[0004] The application of dry particulate material is especially
challenging on a number of different levels. An example, but by no
means a limitation on the use and application of the present
invention, is the application of powder coating material to objects
using a powder spray gun. Because sprayed powder tends to expand
into a cloud or diffused spray pattern, known powder application
systems use a spray booth for containment. Powder particles that do
not adhere to the target object are generally referred to as powder
overspray, and these particles tend to fall randomly within the
booth and will alight on almost any exposed surface within the
spray booth. Therefore, cleaning time and color change times are
strongly related to the amount of surface area that is exposed to
powder overspray.
[0005] In addition to surface areas exposed to powder overspray,
color change times and cleaning are strongly related to the amount
of interior surface area exposed to the flow of powder during an
application process. Examples of such interior surface areas
include all surface areas that form the powder flow path, from a
supply of the powder all the way through the powder spray gun. The
powder flow path typically includes a pump that is used to transfer
powder from a powder supply to one or more spray guns. Hoses are
commonly used to connect the pumps to the guns and the supply.
[0006] Interior surface areas of the powder flow path are typically
cleaned by blowing a purge gas such as pressurized air through the
powder flow path. Wear items that have surfaces exposed to material
impact, for example a spray nozzle in a typical powder spray gun,
can be difficult to clean due to impact fusion of the powder on the
wear surfaces. Pumps also tend to have one or more wear surfaces
that are difficult to clean by purging due to impact fusion.
Conventional venturi pumps can be purged in the direction of the
gun, but are difficult to reverse purge back to the supply.
[0007] There are two generally known types of dry particulate
material transfer processes, referred to herein as dilute phase and
dense phase. Dilute phase systems utilize a substantial quantity of
air to push material through one or more hoses or other conduit
from a supply to a spray applicator. A common pump design used in
powder coating systems is a venturi pump which introduces a large
volume of air under pressure and higher velocity into the powder
flow. In order to achieve adequate powder flow rates (in pounds per
minute or pounds per hour for example), the components that make up
the flow path must be large enough to accommodate the flow with
such high air to material (in other words lean flow) otherwise
significant back pressure and other deleterious effects can
occur.
[0008] Dense phase systems on the other hand are characterized by a
high material to air ratio (in other words a "rich" flow). A dense
phase pump is described in pending U.S. patent application Ser. No.
10/501,693 filed on Jul. 16, 2004 for PROCESS AND EQUIPMENT FOR THE
CONVEYANCE OF POWDERED MATERIAL, the entire disclosure of which is
fully incorporated herein by reference, and which is owned by the
assignee of the present invention. This pump is characterized in
general by a pump chamber that is partially defined by a gas
permeable member. Material, such as powder coating material as an
example, is drawn into the chamber at one end by gravity and/or
negative pressure and is pushed out of the chamber through an
opposite end by positive air pressure. This pump design is very
effective for transferring material, in part due to the novel
arrangement of a gas permeable member forming part of the pump
chamber. The overall pump, however, in some cases may be less than
optimal for purging, cleaning, color change, maintenance and
material flow rate control.
[0009] Many known material application systems utilize
electrostatic charging of the particulate material to improve
transfer efficiency. One form of electrostatic charging commonly
used with powder coating material is corona charging that involves
producing an ionized electric field through which the powder
passes. The electrostatic field is produced by a high voltage
source connected to a charging electrode that is installed in the
electrostatic spray gun. Typically these electrodes are disposed
directly within the powder path, adding to the complication of
purging the powder path.
SUMMARY OF THE INVENTION
[0010] The invention provides apparatus and methods for improving
the cleanability and serviceability of a pump for particulate
material, such as, for example but not by way of limitation, powder
coating material. The invention also contemplates apparatus and
methods for improving material flow rate control using a dense
phase pump. The invention further contemplates methods and
apparatus for dense phase transfer with a pump concept that can be
reverse or upstream purged to the source as well as forward or
downstream purged to an applicator. In accordance with another
aspect of the invention, method and apparatus for a dense phase
pump are contemplated that provide more than one purge function,
such as for example, a soft purge and a hard purge, both optionally
applied in a forward or reverse purge direction.
[0011] Cleanability of the pump refers to reducing the quantity of
material that needs to be purged or otherwise removed from interior
surfaces that define the material flow path through the pump, as
well as simplifying the purging process by making the material flow
path more amenable to purge cleaning Improving cleanability results
in faster color change times, for example, by reducing
contamination risk and shortening the amount of time needed to
remove a first color powder from the pump prior to introducing a
second color powder.
[0012] In accordance with another aspect of the invention, interior
surface areas are reduced so as to reduce the amount of surface
area exposed to the flow of material. In one embodiment, the
reduced surface areas result from the use of a pump that transfers
or moves material in dense phase.
[0013] In accordance with another aspect of the invention, a dense
phase pump is contemplated that is easier to purge by providing a
material flow path that has minimal dead space and straight through
purging. In one embodiment, a pump chamber is provided that is
generally cylindrical with a first open end through which material
enters and exits the pump chamber, and a second open end through
which purge air can be introduced to purge the pump chamber along
the entire length thereof. In a specific embodiment the purge air
is introduced at the second end of the cylindrical pump chamber
axially opposite the first end. This provides straight through
purging of the pump chambers. This arrangement also facilitates the
ability to forward purge through to the spray applicator and also
to reverse purge the pump, even back to the supply.
[0014] In accordance with another aspect of the invention,
cleanability and serviceability are facilitated by providing
replaceable wear parts that have interior surfaces that form part
of the material flow path in the pump. On one embodiment, the wear
parts are realized in the form of Y-blocks that are releasably
retained in a solid body for easy access and replacement.
[0015] In accordance with a further aspect of the invention,
cleanability and serviceability are further enhanced by a modular
pump design. In one embodiment, a modular dense phase pump is
provided that is characterized by a number of modular elements such
as a manifold body, a valve body and one or more material flow path
bodies that include one or more wear surfaces. The modular elements
are secured together such as by bolts. By locating the wear parts
in separate modular elements, they can be easily replaced or
serviced when normal purging alone is not sufficient to clean the
surfaces. In accordance with another aspect of the invention, a
modular construction is contemplated by which all pneumatic energy
is supplied to the pump via a manifold body. In one embodiment, the
manifold body provides pneumatic ports on a single surface to
receive pressurized air from corresponding ports formed in a single
surface of a supply manifold. The manifold body also optionally
accommodates a purge function. In accordance with still another
aspect of the invention, pressurized air needed for pneumatic
valves in the pump is routed internally to the valve body from the
manifold body.
[0016] In further accordance with another aspect of the invention,
interior surface areas are reduced by designing the pump to operate
with high material density low air volume material feed. In the
context of a powder coating material pump, high density means that
the powder supplied by the pump to an applicator has a
substantially reduced amount of entrainment or flow air in the
powder flow as compared to conventional low density or dilute
powder flow systems. Low air volume simply refers to the use of
less volume of flow air needed to move or transfer powder due to
its higher density in the powder flow.
[0017] By removing a substantial amount of the air in the powder
flow, the associated conduits, such as the powder path through the
pump, a powder feed hose and a powder feed tube, can be
substantially reduced in diameter, thereby substantially reducing
the interior surface areas.
[0018] In accordance with another aspect of the invention, a dense
phase pump is provided that provides improved control and selection
of the material flow rate from the pump by providing a scalable
flow pump arrangement. In one embodiment, the pump includes a pump
chamber that is at least partially defined by a gas permeable
member. The gas permeable member is disposed in a pneumatic
pressure chamber of the pump so that material flows into and out of
the pump chamber in response to the application of negative and
positive pressure applied to the pressure chamber. Flow of material
into and out of the pump chamber is controlled by operation of two
or more pinch valves. Material flow rate control is provided, in
accordance with one aspect of the invention, by providing separate
and independent control of each of the pinch valves with respect to
each other. Optionally, control of the pinch valves can be
independent of the pump cycle rate which refers to the cycle time
for applying positive and negative pressure to the pump chamber. In
one embodiment, the pinch valves are realized in the form of
flexible members that are open and closed by pneumatic pressure
applied to an outside surface of the flexible member. This avoids
the need for a control member such as a piston, rod or other device
to open and close the pinch valves, and also facilitates
independent timing of the pinch valve operation. The use of air
pressure to open and close the flexible members greatly simplifies
the overall pump design and further facilitates use of the modular
embodiment when needed.
[0019] In an alternative embodiment of a scalable material flow
rate control process, flow rate control is effected independent of
the pump cycle rate by controlling the suction time portion of the
pump cycle rate. This allows for control of the flow rate with or
without independent control of the suction and delivery pinch
valves. In accordance with another aspect of the invention, flow
rate control by use of the suction time, in combination with
control of the pinch valves, allows the suction time to be adjusted
so as to occur during the middle of the pump cycle to prevent
overlap between the suction and delivery valve on times, thereby
reducing the amount of pressurized air needed to operate the
pump.
[0020] In accordance with another aspect of the invention, the
above described arrangement of a single pump chamber and two pinch
valves can be optionally modified to include a second pump chamber
and two additional pinch valves. The second pump chamber operates
out of phase with the first pump chamber to provide a smooth
delivery of material from the pump. In one embodiment, the one pump
chamber fills with material while the other empties and vice-versa
in an alternating manner. Material flow rate control and
consistency of flow can be optimized by providing independent
timing of each of the four pinch valves with respect to each other
and/or with respect to the cycle time of the pump. Such flow
control can be useful, for example, with a pump that supplies
material to a spray applicator. In another embodiment, the
invention contemplates a transfer pump that is used to move powder
from a powder recovery system back to a supply. In a transfer pump
embodiment, consistency of flow is not usually of concern because
the material is simply being transferred to a receptacle. Volume of
flow is typically of primary interest, therefore, independent
timing control of all the pinch valves is not necessary.
[0021] These and other aspects and advantages of the present
invention will be apparent to those skilled in the art from the
following description of the exemplary embodiments in view of the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a simplified schematic diagram of a powder coating
material application system utilizing the present invention;
[0023] FIGS. 2A-2C are assembled and exploded isometric views of a
pump in accordance with the invention;
[0024] FIGS. 2D-2G are elevation and cross-sectional views of the
assembled pump of FIG. 2A;
[0025] FIGS. 3A and 3B are an isometric and upper plan view of a
pump manifold;
[0026] FIGS. 4A and 4B illustrate a first Y-block;
[0027] FIGS. 5A and 5B are perspective and cross-sectional views of
a valve body;
[0028] FIGS. 6A and 6B illustrate in perspective another Y-block
arrangement;
[0029] FIG. 7 is an exploded perspective of a supply manifold;
[0030] FIG. 8 is an exemplary embodiment of a pneumatic flow
arrangement for the pump of FIG. 2A;
[0031] FIGS. 9A and 9B are an isometric and exploded isometric of a
transfer pump in accordance with the invention;
[0032] FIG. 10 is an exemplary embodiment of a pneumatic flow
arrangement for a transfer pump;
[0033] FIG. 11 is an alternative embodiment of a pneumatic circuit
for the transfer pump;
[0034] FIG. 12 is a representation of material flow rate curves for
a pump operating in accordance with the invention; and
[0035] FIG. 13 is a graph depicting powder flow rates versus pinch
valve open duration for two different pump cycle rates.
DETAILED DESCRIPTION OF THE INVENTION AND EXEMPLARY EMBODIMENTS
THEREOF
[0036] The invention contemplates a number of new aspects for a
dense phase pump for particulate material. The pump may be used in
combination with any number or type of spray applicator devices or
spray guns and material supply.
[0037] By "dense phase" is meant that the air present in the
particulate flow is about the same as the amount of air used to
fluidize the material at the supply such as a feed hopper. As used
herein, "dense phase" and "high density" are used to convey the
same idea of a low air volume mode of material flow in a pneumatic
conveying system where not all of the material particles are
carried in suspension. In such a dense phase system, the material
is forced along a flow path by significantly less air volume as
compared to a conventional dilute phase system, with the material
flowing more in the nature of plugs that push each other along the
passage, somewhat analogous to pushing the plugs as a piston
through the passage. With smaller cross-sectional passages this
movement can be effected under lower pressures.
[0038] In contrast, conventional flow systems tend to use a dilute
phase which is a mode of material flow in a pneumatic conveying
system where all the particles are carried in suspension.
Conventional flow systems introduce a significant quantity of air
into the flow stream in order to pump the material from a supply
and push it through under positive pressure to the spray
application devices. For example, most conventional powder coating
spray systems utilize venturi pumps to draw fluidized powder from a
supply into the pump. A venturi pump by design adds a significant
amount of air to the powder stream. Typically, flow air and
atomizing air are added to the powder to push the powder under
positive pressure through a feed hose and an applicator device.
Thus, in a conventional powder coating spray system, the powder is
entrained in a high velocity high volume flow of air, thus
necessitating large diameter powder passageways in order to attain
usable powder flow rates.
[0039] Dense phase flow is oftentimes used in connection with the
transfer of material to a closed vessel under high pressure. The
present invention, in being directed to material application rather
than simply transport or transfer of material, contemplates flow at
substantially lower pressure and flow rates as compared to dense
phase transfer under high pressure to a closed vessel. However, the
invention also contemplates a dense phase transfer pump embodiment
which can be used to transfer material to an open or closed
vessel.
[0040] As compared to conventional dilute phase systems having air
volume flow rates of about 3 to about 6 cfm (such as with a venturi
pump arrangement, for example), the present invention may operate
at about 0.8 to about 1.6 cfm, for example. Thus, in the present
invention, powder delivery rates may be on the order of about 150
to about 300 grams per minute. These values are intended to be
exemplary and not limiting. Pumps in accordance with the present
invention can be designed to operate at lower or higher air flow
and material delivery values.
[0041] Dense phase versus dilute phase flow can also be thought of
as rich versus lean concentration of material in the air stream,
such that the ratio of material to air is much higher in a dense
phase system. In other words, in a dense phase system the same
amount of material per unit time is transiting a flow path
cross-section (of a tube for example) of lesser area as compared to
a dilute phase flow. For example, in some embodiments of the
present invention, the cross-sectional area of a powder feed tube
is about one-fourth the area of a feed tube for a conventional
venturi type system. For comparable flow of material per unit time
then, the material is about four times denser in the air stream as
compared to conventional dilute phase systems.
[0042] With reference to FIG. 1, in an exemplary embodiment, the
present invention is illustrated being used with a material
application system, such as, for example, a typical powder coating
spray system 10. Such an arrangement commonly includes a powder
spray booth 12 in which an object or part P is to be sprayed with a
powder coating material. The application of powder to the part P is
generally referred to herein as a powder spray, coating or
application operation procedure or process, however, there may be
any number of control functions, steps and parameters that are
controlled and executed before, during and after powder is actually
applied to the part.
[0043] As is known, the part P is suspended from an overhead
conveyor 14 using hangers 16 or any other conveniently suitable
arrangements. The booth 12 includes one or more openings 18 through
which one or more spray applicators 20 may be used to apply coating
material to the part P as it travels through the booth 12. The
applicators 20 may be of any number depending on the particular
design of the overall system 10. Each applicator can be a manually
operated device as with device 20a, or a system controlled device,
referred to herein as an automatic applicator 20b, wherein the term
"automatic" simply refers to the fact that an automatic applicator
is mounted on a support and is triggered on and off by a control
system, rather than being manually supported and manually
triggered. The present invention is directed to manual and
automatic spray applicators.
[0044] It is common in the powder coating material application
industry to refer to the powder applicators as powder spray guns,
and with respect to the exemplary embodiments herein we will use
the terms applicator and gun interchangeably. However, it is
intended that the invention is applicable to material application
devices other than powder spray guns, and hence the more general
term applicator is used to convey the idea that the invention can
be used in many particulate material application systems other than
the exemplary powder coating material application system described
herein. Some aspects of the invention are likewise applicable to
electrostatic spray guns as well as non-electrostatic spray guns.
The invention is also not limited by functionality associated with
the word "spray". Although the invention is especially suited to
powder spray application, the pump concepts and methods disclosed
herein may find use with other material application techniques
beyond just spraying, whether such techniques are referred to as
dispensing, discharge, application or other terminology that might
be used to describe a particular type of material application
device.
[0045] The spray guns 20 receive powder from a supply or feed
center such as a hopper 22 or other material supply through an
associated powder feed or supply hose 24. The automatic guns 20b
typically are mounted on a support 26. The support 26 may be a
simple stationary structure, or may be a movable structure, such as
an oscillator that can move the guns up and down during a spraying
operation, or a gun mover or reciprocator that can move the guns in
and out of the spray booth, or a combination thereof.
[0046] The spray booth 12 is designed to contain powder overspray
within the booth, usually by a large flow of containment air into
the booth. This air flow into the booth is usually effected by a
powder overspray reclamation or recovery system 28. The recovery
system 28 pulls air with entrained powder overspray from the booth,
such as for example through a duct 30. In some systems the powder
overspray is returned to the feed center 22 as represented by the
return line 32. In other systems the powder overspray is either
dumped or otherwise reclaimed in a separate receptacle.
[0047] In the exemplary embodiment herein, powder is transferred
from the recovery system 28 back to the feed center 22 by a first
transfer pump 400, an exemplary embodiment of which in accordance
with the invention is described hereinafter. A respective gun pump
402 is used to supply powder from the feed center 22 to an
associated spray applicator or gun 20. For example, a first gun
pump 402a is used to provide dense phase powder flow to the manual
gun 20a and a second gun pump 402b is used to provide dense phase
powder flow to the automatic gun 20b. Exemplary embodiments of the
gun pumps 402 in accordance with the invention are described
hereinafter.
[0048] Each gun pump 402 operates from pressurized gas such as
ordinary air supplied to the gun by a pneumatic supply manifold
404. The present invention provides a pump and manifold arrangement
by which the pump 402 is mounted to the supply manifold 404 with a
gasket or other seal device therebetween. This eliminates
unnecessary plumbing between the manifold 404 and the pump 402.
Although schematically illustrated in FIG. 1 as being directly
joined, it is contemplated that in practice the manifolds 404 will
be disposed in a cabinet or other enclosure and mounted to the
pumps 402 with a wall of the cabinet therebetween. In this manner,
the manifolds 404, which may include electrical power such as
solenoid valves, are isolated from the spraying environment.
[0049] The supply manifold 404 supplies pressurized air to its
associated pump 402 for purposes that will be explained
hereinafter. In addition, each supply manifold 404 includes a
pressurized pattern air supply that is provided to the spray guns
20 via air hoses or lines 405. Main air 408 is provided to the
supply manifold 404 from any convenient source within the
manufacturing facility of the end user of the system 10. Each pump
402 supplies powder to its respective applicator 20 via a powder
supply hose 406.
[0050] In the FIG. 1 embodiment, a second transfer pump 410 is used
to transfer powder from a supply 412 of virgin powder (that is to
say, unused) to the feed center 22. Those skilled in the art will
understand that the number of required transfer pumps 410 and gun
pumps 402 will be determined by the requirements of the overall
system 10 as well as the spraying operations to be performed using
the system 10.
[0051] Although the gun pump and the transfer pumps may be the same
design, in the exemplary embodiments there are differences that
will be described hereinafter. Those differences take into account
that the gun pump preferably provides a smooth consistent flow of
powder material to the spray applicators 20 in order to provide the
best coating onto the objects P, whereas the transfer pumps 400 and
410 are simply used to move powder from one receptacle to another
at a high enough flow rate and volume to keep up with the powder
demand from the applicators and as optionally supplemented by the
powder overspray collected by the recovery system 28.
[0052] Other than the pumps 400, 410 and 402, the selected design
and operation of the material application system 10, including the
spray booth 12, the conveyor 14, the guns 20, the recovery system
28, and the feed center or supply 22, form no necessary part of the
present invention and may be selected based on the requirements of
a particular coating application. A particular spray applicator,
however, that is well suited for use with the present invention is
described in pending International patent application number
PCT/US04/26887 for SPRAY APPLICATOR FOR PARTICULATE MATERIAL, filed
on Aug. 18, 2004, the entire disclosure of which is incorporated
herein by reference. However, many other applicator designs may be
used as required for a particular application. A control system 34
likewise may be a conventional control system such as a
programmable processor based system or other suitable control
circuit. The control system 34 executes a wide variety of control
functions and algorithms, typically through the use of programmable
logic and program routines, which are generally indicated in FIG. 1
as including but not necessarily limited to feed center control 36
(for example supply controls and pump operation controls), gun
operation control 38 (such as for example, gun trigger controls),
gun position control 40 (such as for example control functions for
the reciprocator/gun mover 26 when used), powder recovery system
control 42 (for example, control functions for cyclone separators,
after filter blowers and so on), conveyor control 44 and material
application parameter controls 46 (such as for example, powder flow
rates, applied film thickness, electrostatic or non-electrostatic
application and so on). Conventional control system theory, design
and programming may be utilized.
[0053] While the described embodiments herein are presented in the
context of a dense phase pump for use in a powder coating material
application system, those skilled in the art will readily
appreciate that the present invention may be used in many different
dry particulate material application systems, including but not
limited in any manner to: talc on tires, super-absorbents such as
for diapers, food related material such as flour, sugar, salt and
so on, desiccants, release agents, and pharmaceuticals. These
examples are intended to illustrate the broad application of the
invention for dense phase application of particulate material to
objects. The specific design and operation of the material
application system selected provides no limitation on the present
invention except as otherwise expressly noted herein.
[0054] While various aspects of the invention are described and
illustrated herein as embodied in combination in the exemplary
embodiments, these various aspects may be realized in many
alternative embodiments, either individually or in various
combinations and sub-combinations thereof. Unless expressly
excluded herein all such combinations and sub-combinations are
intended to be within the scope of the present invention. Still
further, while various alternative embodiments as to the various
aspects and features of the invention, such as alternative
materials, structures, configurations, methods, devices, software,
hardware, control logic and so on may be described herein, such
descriptions are not intended to be a complete or exhaustive list
of available alternative embodiments, whether presently known or
later developed. Those skilled in the art may readily adopt one or
more of the aspects, concepts or features of the invention into
additional embodiments within the scope of the present invention
even if such embodiments are not expressly disclosed herein.
Additionally, even though some features, concepts or aspects of the
invention may be described herein as being a preferred arrangement
or method, such description is not intended to suggest that such
feature is required or necessary unless expressly so stated. Still
further, exemplary or representative values and ranges may be
included to assist in understanding the present invention however,
such values and ranges are not to be construed in a limiting sense
and are intended to be critical values or ranges only if so
expressly stated.
[0055] Even from the general schematic illustration of FIG. 1 it
can be appreciated that such complex systems can be very difficult
and time consuming to clean and to provide for color change.
Typical powder coating material is a very fine particulate and
tends to be applied in a fine cloud or spray pattern directed at
the objects being sprayed. Even with the use of electrostatic
technology, a significant amount of powder overspray is inevitable.
Cross contamination during color change is a significant issue in
many industries, therefore it is important that the material
application system be able to be thoroughly cleaned between color
changes. Color changes however necessitate taking the material
application system offline and thus is a significant cost driver.
The present invention is directed to providing a pump that is
easier and faster to clean. Additional features and aspects of the
invention are applicable separately from the concern for
cleanability.
[0056] With reference to FIGS. 2A, 2B and 2C there is illustrated
an exemplary embodiment of a dense phase pump 402 in accordance
with the present invention. Although the pump 402 can be used as a
transfer pump as well, it is particularly designed as a gun pump
for supplying material to the spray applicators 20. The gun pumps
402 and transfer pumps 400 and 410 share many common design
features which will be readily apparent from the detailed
descriptions herein.
[0057] The pump 402 is preferably although need not be modular in
design. The modular construction of the pump 402 is realized with a
pump manifold body 414 and a valve body 416. The manifold body 414
houses a pair of pump chambers along with a number of air passages
as will be further explained herein. The valve body 416 houses a
plurality of valve elements as will also be explained herein. The
valves respond to air pressure signals that are communicated into
the valve body 416 from the manifold body 414. Although the
exemplary embodiments herein illustrate the use of pneumatic pinch
valves, those skilled in the are will readily appreciate that
various aspects and advantages of the present invention can be
realized with the use of other control valve designs other than
pneumatic pinch valves.
[0058] The upper portion 402a of the pump is adapted for purge air
arrangements 418a and 418b, and the lower portion 402b of the pump
is adapted for a powder inlet hose connector 420 and a powder
outlet hose connector 422. A powder feed hose 24 (FIG. 1) is
connected to the inlet connector 420 to supply a flow of powder
from a supply such as the feed hopper 22. A powder supply hose 406
(FIG. 1) is used to connect the outlet 422 to a spray applicator
whether it be a manual or automatic spray gun positioned up at the
spray booth 12. The powder supplied to the pump 402 may, but not
necessarily must, be fluidized.
[0059] Powder flow into an out of the pump 402 thus occurs on a
single end 402b of the pump. This allows a purge function 418 to be
provided at the opposite end 402a of the pump thus providing an
easier purging operation as will be further explained herein.
[0060] If there were only one pump chamber (which is a useable
embodiment of the invention) then the valve body 416 could be
directly connected to the manifold because there would only be the
need for two powder paths through the pump. However, in order to
produce a steady, consistent and adjustable flow of powder from the
pump, two or more pump chambers are provided. When two pump
chambers are used, they are preferably operated out of phase so
that as one chamber is receiving powder from the inlet the other is
supplying powder to the outlet. In this way, powder flows
substantially continuously from the pump. With a single chamber
this would not be the case because there is a gap in the powder
flow from each individual pump chamber due to the need to first
fill the pump chamber with powder. When more than two chambers are
used, their timing can be adjusted as needed. In any case it is
preferred though not required that all pump chambers communicate
with a single inlet and a single outlet.
[0061] In accordance with one aspect of the present invention,
material flow into and out of each of the pump chambers is
accomplished at a single end of the chamber. This provides an
arrangement by which a straight through purge function can be used
at an opposite end of the pump chamber. Since each pump chamber
communicates with the same pump inlet and outlet in the exemplary
embodiment, additional modular units are used to provide branched
powder flow paths in the form of Y blocks.
[0062] A first Y-block 424 is interconnected between the manifold
body 414 and the valve body 416. A second Y-block 426 forms the
inlet/outlet end of the pump and is connected to the side of the
valve body 416 that is opposite the first Y-block 424. A first set
of bolts 428 are used to join the manifold body 414, first Y-block
424 and the valve body 416 together. A second set of bolts 430 are
used to join the second Y-block 426 to the valve body 416. Thus the
pump in FIG. 2A when fully assembled is very compact and sturdy,
yet the lower Y-block 426 can easily and separately be removed for
replacement of flow path wear parts without complete disassembly of
the pump. The first Y-block 424 provides a two branch powder flow
path away from each powder chamber. One branch from each chamber
communicates with the pump inlet 420 through the valve body 416 and
the other branch from each chamber communicates with the pump
outlet 422 through the valve body 416. The second Y-block 426 is
used to combine the common powder flow paths from the valve body
416 to the inlet 420 and outlet 422 of the pump. In this manner,
each pump chamber communicates with the pump inlet through a
control valve and with the pump outlet through another control
valve. Thus, in the exemplary embodiment, there are four control
valves in the valve body that control flow of powder into and out
of the pump chambers.
[0063] The manifold body 414 is shown in detail in FIGS. 2B, 2E,
2G, 3A and 3B. The manifold 414 includes a body 432 having first
and second bores therethrough 434, 436 respectively. Each of the
bores receives a generally cylindrical gas permeable filter member
438 and 440 respectively. The gas permeable filter members 438, 440
include lower reduced outside diameter ends 438a and 440a which
insert into a counterbore inside the first Y-block 424 (FIG. 4B)
which helps to maintain the members 438, 440 aligned and stable.
The upper ends of the filter members abut the bottom ends of purge
air fittings 504 with appropriate seals as required. The filter
members 438, 440 each define an interior volume (438c, 440c) that
serves as a powder pump chamber so that there are two pump powder
chambers provided in this embodiment. A portion of the bores 434,
436 are adapted to receive the purge air arrangements 418a and 418b
as will be described hereinafter.
[0064] The filter members 438, 440 may be identical and allow a
gas, such as ordinary air, to pass through the cylindrical wall of
the member but not powder. The filter members 438, 440 may be made
of porous polyethylene, for example. This material is commonly used
for fluidizing plates in powder feed hoppers. An exemplary material
has about a 40 micron opening size and about a 40-50% porosity.
Such material is commercially available from Genpore or Poron.
Other porous materials may be used as needed. The filter members
438, 440 each have a diameter that is less than the diameter of its
associated bore 434, 436 so that a small annular space is provided
between the wall of the bore and the wall of the filter member (see
FIGS. 2E, 2G). This annular space serves as a pneumatic pressure
chamber. When a pressure chamber has negative pressure applied to
it, powder is drawn up into the powder pump chamber and when
positive pressure is applied to the pressure chamber the powder in
the powder pump chamber is forced out.
[0065] The manifold body 432 includes a series of six inlet
orifices 442. These orifices 442 are used to input pneumatic energy
or signals into the pump. Four of the orifices 442a, c, d and f are
in fluid communication via respective air passages 444a, c, d and f
with a respective pressure chamber 446 in the valve block 416 and
thus are used to provide valve actuation air as will be explained
hereinafter. Note that the air passages 444 extend horizontally
from the manifold surface 448 into the manifold body and then
extend vertically downward to the bottom surface of the manifold
body where they communicate with respective vertical air passages
through the upper Y-block 424 and the valve body 416 wherein they
join to respective horizontal air passages in the valve body 416 to
open into each respective valve pressure chamber. Air filters (not
shown) may be included in these air passages to prevent powder from
flowing up into the pump manifold 414 and the supply manifold 404
in the event that a valve element or other seal should become
compromised. The remaining two orifices, 442b and 442e are
respectively in fluid communication with the bores 434, 436 via air
passages 444b and 444e. These orifices 442b and 442e are thus used
to provide positive and negative pressure to the pump pressure
chambers in the manifold body.
[0066] The orifices 442 are preferably, although need not be,
formed in a single planar surface 448 of the manifold body. The air
supply manifold 404 includes a corresponding set of orifices that
align with the pump orifices 442 and are in fluid communication
therewith when the supply manifold 404 is mounted on the pump
manifold 414. In this manner the supply manifold 404 can supply all
required pump air for the valves and pump chambers through a simple
planar interface. A seal gasket 450 is compressed between the faces
of the pump manifold 414 and the supply manifold 404 to provide
fluid tight seals between the orifices. Because of the volume,
pressure and velocity desired for purge air, preferably separate
purge air connections are used between the supply manifold and the
pump manifold. Although the planar interface between the two
manifolds is preferred it is not required, and individual
connections for each pneumatic input to the pump from the supply
manifold 404 could be used as required. The planar interface allows
for the supply manifold 404, which in some embodiments includes
electrical solenoids, to be placed inside a cabinet with the pump
on the outside of the cabinet (mounted to the supply manifold
through an opening in a cabinet wall) so as to help isolate
electrical energy from the overall system 10. It is noted in
passing that the pump 402 need not be mounted in any particular
orientation during use.
[0067] With reference to FIGS. 4A and 4B, the first Y-block 424
includes first and second ports 452, 454 that align with their
respective pump chamber 434, 436. Each of the ports 452, 454
communicates with two branches 452a, 452b and 454a, 454b
respectively (FIG. 4B only shows the branches for the port 452).
Thus, the port 452 communicates with branches 452a and 452b.
Therefore, there are a total of four branches in the first Y-block
424 wherein two of the branches communicate with one pressure
chamber and the other two communicate with the other pressure
chamber. The branches 452a, b and 454a, b form part of the powder
path through the pump for the two pump chambers. Flow of powder
through each of the four branches is controlled by a separate pinch
valve in the valve body 416 as will be described herein. Note that
the Y-block 424 also includes four through air passages 456a, c, d,
f which are in fluid communication with the air passages 444a, c, d
and f respectively in the manifold body 414. A gasket 459 may be
used to provide fluid tight connection between the manifold body
414 and the first Y-block 424.
[0068] The ports 452 and 454 include counterbores 458, 460 which
receive seals 462, 464 (FIG. 2C) such as conventional o-rings.
These seals provide a fluid tight seal between the lower ends of
the filter members 438, 440 and the Y-block ports 452, 454. They
also allow for slight tolerance variations so that the filter
members are tightly held in place.
[0069] With additional reference to FIGS. 5A and 5B, the valve body
416 includes four through bores 446a, 446b, 446c and 446d that
function as pressure chambers for a corresponding number of pinch
valves. The upper surface 466 of the valve body includes two
recessed regions 468 and 470 each of which includes two ports, each
port being formed by one end of a respective bore 446. In this
embodiment, the first recessed portion 468 includes orifices 472
and 474 which are formed by their respective bores 446b and 446a
respectively. Likewise, the second recessed portion 470 includes
orifices 476 and 478 which are formed by their respective bores
446d and 446c respectively. Corresponding orifices are formed on
the opposite side face 479 of the valve body 416.
[0070] Each of the pressure chambers 446a-d retains either an inlet
pinch valve element 480 or an outlet pinch valve 481. Each pinch
valve element 480, 481 is a fairly soft flexible member made of a
suitable material, such as for example, natural rubber, latex or
silicone. Each valve element 480, 481 includes a central generally
cylindrical body 482 and two flanged ends 484 of a wider diameter
than the central body 482. The flanged ends function as seals and
are compressed about the bores 446a-d when the valve body 416 is
sandwiched between the first Y-block 424 and the second Y-block
426. In this manner, each pinch valve defines a flow path for
powder through the valve body 416 to a respective one of the
branches 452, 454 in the first Y-block 424. Therefore, one pair of
pinch valves (a suction valve and a delivery valve) communicates
with one of the pump chambers 440 in the manifold body while the
other pair of pinch valves communicates with the other pump chamber
438. There are two pinch valves per chamber because one pinch valve
controls the flow of powder into the pump chamber (suction) and the
other pinch valve controls the flow of powder out of the pump
chamber (delivery). The outer diameter of each pinch valve central
body portion 482 is less than the bore diameter of its respect
pressure chamber 446. This leaves an annular space surrounding each
pinch valve that functions as the pressure chamber for that
valve.
[0071] The valve body 416 includes air passages 486a-d that
communicate respectively with the four pressure chamber bores
446a-d. as illustrated in FIG. 5B. These air passages 486a-d
include vertical extensions (as viewed in FIG. 5B) 488a-d. These
four air passage extensions 488a, b, c, d respectively are in fluid
communication with the vertical portions of the four air passages
444d, f, a, c in the manifold 414 and the vertical passages 456d,
f, a, c in the upper Y-block 424. Seals 490 are provided for air
tight connections.
[0072] In this manner, each of the pressure chambers 446 in the
valve body 416 is in fluid communication with a respective one of
the air orifices 442 in the manifold body 414, all through internal
passages through the manifold body, the first Y-block and the valve
body. When positive air pressure is received from the supply
manifold 404 (FIG. 1) into the pump manifold 414, the corresponding
valve 480, 481 is closed by the force of the air pressure acting
against the outer flexible surface of the flexible valve body. The
valves open due to their own resilience and elasticity when
external air pressure in the pressure chamber is removed. This true
pneumatic actuation avoids any mechanical actuation or other
control member being used to open and close the pinch valves which
is a significant improvement over the conventional designs. Each of
the four pinch valves 480, 481 is preferably separately controlled
for the gun pump 402.
[0073] In accordance with another aspect of the invention, the
valve body 416 is preferably made of a sufficiently transparent
material so that an operator can visually observe the opening and
closing of the pinch valves therein. A suitable material is acrylic
but other transparent materials may be used. The ability to view
the pinch valves also gives a good visual indication of a pinch
valve failure since powder will be visible.
[0074] With additional reference to FIGS. 6A and 6B, the remaining
part of the pump is the inlet end 402b formed by a second Y-block
end body 492. The end body 492 includes first and second recesses
494, 496 each of which is adapted to receive a Y-block 498a and
498b. One of the Y-blocks is used for powder inlet and the other is
used for powder outlet. Each Y-block 498 is a wear component due to
exposure of its internal surfaces to powder flow. Since the body
492 is simply bolted to the valve body 416, it is a simple matter
to replace the wear parts by removing the body 492, thus avoiding
having to disassemble the rest of the pump.
[0075] Each Y-block 498 includes a lower port 500 that is adapted
to receive a fitting or other suitable hose connector 420, 422
(FIG. 2A) with one fitting connected to a hose 24 that runs to a
powder supply and another hose 406 to a spray applicator such as a
spray gun 20 (FIG. 1). Each Y-block includes two powder path
branches 502a, 502b, 502c and 502d that extend away from the port
500. Each powder path in the second Y-blocks 498 are in fluid
communication with a respective one of the pinch valves 480, 481 in
the pinch valve body 416. Thus, powder that enters the pump at the
inlet 420 branches through a first of the two lower Y-blocks 498
into two of the pinch valves and from there to the pump chambers.
Likewise powder from the two pump chambers recombine from the other
two pinch valves into a single outlet 422 by way of the other lower
Y-block 498.
[0076] The powder flow paths are as follows. Powder enters through
a common inlet 420 and branches via paths 502a or 502b in the lower
Y-block 498b to the two inlet or suction pinch valves 480. Each of
the inlet pinch valves 480 is connected to a respective one of the
powder pump chambers 434, 436 via a respective one branch 452, 454
of a respective path through the first or upper Y-block 424. Each
of the other branches 452, 454 of the upper Y-block 424 receive
powder from a respective pump chamber, with the powder flowing
through the first Y-block 424 to the two outlet or delivery pinch
valves 481. Each of the outlet pinch valves 481 is also connected
to a respect one of the branches 502 in the lower Y-block 498a
wherein the powder from both pump chambers is recombined to the
single outlet 422.
[0077] The pneumatic flow paths are as follows. When any of the
pinch valves is to be closed, the supply manifold 404 issues a
pressure increase at the respective orifice 442 in the manifold
body 414. The increased air pressure flows through the respective
air passage 442, 444 in the manifold body 414, down through the
respective air passage 456 in the first Y-block 424 and into the
respective air passage 486 in the valve body 416 to the appropriate
pressure chamber 446.
[0078] It should be noted that a pump in accordance with the
present invention provides for a proportional flow valve based on
percent fill of the powder pump chambers, meaning that the flow
rate of powder from the pump can be accurately controlled by
controlling the open time of the pinch valves that feed powder to
the pump chambers. This allows the pump cycle (i.e. the time
duration for filling and emptying the pump chambers) to be short
enough so that a smooth flow of powder is achieved independent of
the flow rate, with the flow rate being separately controlled by
operation of the pinch valves. Thus, flow rate can be adjusted
entirely by control of the pinch valves without having to make any
physical changes to the pump.
[0079] The purge function is greatly simplified in accordance with
another aspect of the invention. Because the invention provides a
way for powder to enter and exit the pump chambers from a single
end, the opposite end of the pump chamber can be used for purge
air. With reference to FIGS. 2A, 2C, 2E and 2G, a purge air fitting
504 is inserted into the upper end of its respective pump chamber
438, 440. The fittings 504 receive respective check valves 506 that
are arranged to only permit flow into the pump chambers 438, 440.
The check valves 506 receive respective purge air hose fittings 508
to which a purge air hose can be connected. Purge air is supplied
to the pump from the supply manifold 404 as will be described
hereinbelow. The purge air thus can flow straight through the
powder pump chambers and through the rest of the powder path inside
the pump to very effectively purge the pump for a color change
operation. No special connections or changes need to be made by the
operator to effect this purging operation, thereby reducing
cleaning time. Once the system 10 is installed, the purging
function is always connected and available, thereby significantly
reducing color change time because the purging function can be
executed by the control system 39 without the operator having to
make or break any powder or pneumatic connections with the
pump.
[0080] Note from FIGS. 1 and 2A that with all four pinch valves
480, 481 in an open condition purge air will flow straight through
the pump chambers, through the powder paths in the first Y-block
424, the pinch valves themselves 480, 481, the second Y-block 498
and out both the inlet 420 and the outlet 422. Purge air thus can
be supplied throughout the pump and then on to the spray applicator
to purge that device as well as to purge the feed hoses back to the
powder supply 22. Thus in accordance with the invention, a dense
phase pump concept is provided that allows forward and reverse
purging.
[0081] With reference to FIG. 7, the supply manifold 404
illustrated is in essence a series of solenoid valves and air
sources that control the flow of air to the pump 402. The
particular arrangement illustrated in FIG. 7 is exemplary and not
intended to be limiting. The supply of air to operate the pump 402
can be done without a manifold arrangement and in a wide variety of
ways. The embodiment of FIG. 7 is provided as it is particularly
useful for the planar interface arrangement with the pump, however,
other manifold designs can also be used.
[0082] The supply manifold 404 includes a supply manifold body 510
that has a first planar face 512 that is mounted against the
surface 448 of the pump manifold body 414 (FIG. 3A) as previously
described herein. Thus the face 512 includes six orifices 514 that
align with their respective orifices 442 in the pump manifold 414.
The supply manifold body 510 is machined to have the appropriate
number and location of air passages therein so that the proper air
signals are delivered to the orifices 514 at the correct times. As
such, the manifold further includes a series of valves that are
used to control the flow of air to the orifices 514 as well as to
control the purge air flow. Negative pressure is generated in the
manifold 404 by use of a conventional venturi pump 518. System or
shop air is provided to the manifold 404 via appropriate fittings
520. The details of the physical manifold arrangement are not
necessary to understand and practice the present invention since
the manifold simply operates to provide air passages for air
sources to operate the pump and can be implemented in a wide
variety of ways. Rather, the details of note are described in the
context of a schematic diagram of the pneumatic flow. It is noted
at this time, however, that in accordance with another aspect of
the invention, a separate control valve is provided for each of the
pinch valves in the valve body 414 for purposes that will be
described hereinafter.
[0083] With reference to FIG. 8, a pneumatic diagram is provided
for a first embodiment of the invention. Main air 408 enters the
supply manifold 404 and goes to a first regulator 532 to provide
pump pressure source 534 to the pump chambers 438, 440, as well as
pattern shaping air source 405 to the spray applicator 20 via air
hose 406. Main air also is used as purge air source 536 under
control of a purge air solenoid valve 538. Main air also goes to a
second regulator 540 to produce venturi air pressure source 542
used to operate the venturi pump (to produce the negative pressure
to the pump chambers 438, 440) and also to produce pinch air source
544 to operate the pinch valves 480, 481.
[0084] In accordance with another aspect of the invention, the use
of the solenoid control valve 538 or other suitable control device
for the purge air provides multiple purge capability. The first
aspect is that two or more different purge air pressures and flows
can be selected, thus allowing a soft and hard purge function.
Other control arrangements besides a solenoid valve can be used to
provide two or more purge air flow characteristics. The control
system 39 selects soft or hard purge, or a manual input could be
used for this selection. For a soft purge function, a lower purge
air flow is supplied through the supply manifold 404 into the pump
pressure chambers 434, 436 which is the annular space between the
porous members 438, 440 and their respective bores 434, 436. The
control system 39 further selects one set of pinch valves (suction
or delivery) to open while the other set is closed. The purge air
bleeds through the porous filters 438, 440 and out the open valves
to either purge the system forward to the spray gun 20 or reverse
(backward) to the supply 22. The control system 39 then reverses
which pinch valves are open and closed. Soft purge may also be done
in both directions at the same time by opening all four pinch
valves. Similarly, higher purge air pressure and flow may be used
for a hard purge function forward, reverse or at the same time. The
purge function carried out by bleeding air through the porous
members 438, 440 also helps to remove powder that has been trapped
by the porous members, thus extending the useful life of the porous
members before they need to be replaced.
[0085] Hard or system purge can also be effected using the two
purge arrangements 418a and 418b. High pressure flow air can be
input through the purge air fittings 508 (the purge air can be
provided from the supply manifold 404) and this air flows straight
through the powder pump chambers defined in part by the porous
members 438, 440 and out the pump. Again, the pinch valves 480, 481
can be selectively operated as desired to purge forward or reverse
or at the same time.
[0086] It should be noted that the ability to optionally purge in
only the forward or reverse direction provides a better purging
capability because if purging can only be done in both directions
at the same time, the purge air will flow through the path of least
resistance whereby some of the powder path regions may not get
adequately purged. Fir example, when trying the purge a spray
applicator and a supply hopper, if the applicator is completely
open to air flow, the purge air will tend to flow out the
applicator and might not adequately purge the hopper or supply.
[0087] The invention thus provides a pump design by which the
entire powder path from the supply to and through the spray guns
can be purged separately or at the same time with virtually no
operator action required. The optional soft purge may be useful to
gently blow out residue powder from the flow path before hitting
the powder path with hard purge air, thereby preventing impact
fusion or other deleterious effects from a hard purge being
performed first.
[0088] The positive air pressure 542 for the venturi enters a
control solenoid valve 546 and from there goes to the venturi pump
518. The output 518a of the venturi pump is a negative pressure or
partial vacuum that is connected to an inlet of two pump solenoid
valves 548, 550. The pump valves 548 and 550 are used to control
whether positive or negative pressure is applied to the pump
chambers 438, 440. Additional inputs of the valves 548, 550 receive
positive pressure air from a first servo valve 552 that receives
pump pressure air 534. The outlets of the pump valves 548, 550 are
connected to a respective one of the pump chambers through the air
passage scheme described hereinabove. Note that the purge air 536
is schematically indicated as passing through the porous tubes 438,
440.
[0089] Thus, the pump valves 550 and 552 are used to control
operation of the pump 402 by alternately applying positive and
negative pressure to the pump chambers, typically 180.degree. out
of phase so that as one chamber is being pressurized the other is
under negative pressure and vice-versa. In this manner, one chamber
is filling with powder while the other chamber is emptying. It
should be noted that the pump chambers may or may not completely
"fill" with powder. As will be explained herein, very low powder
flow rates can be accurately controlled using the present invention
by use of the independent control valves for the pinch valves. That
is, the pinch valves can be independently controlled apart from the
cycle rate of the pump chambers to feed more or less powder into
the chambers during each pumping cycle.
[0090] Pinch valve air 544 is input to four pinch valve control
solenoids 554, 556, 558 and 560. Four valves are used so that there
is preferably independent timing control of the operation of each
of the four pinch valves 480, 481. In FIG. 8, "delivery pinch
valve" refers to those two pinch valves 481 through which powder
exits the pump chambers and "suction pinch valve" refers to those
two pinch valves 480 through which powder is fed to the pump
chambers. Though the same reference numeral is used, each suction
pinch valve and each delivery pinch valve is separately
controlled.
[0091] A first delivery solenoid valve 554 controls air pressure to
a first delivery pinch valve 481; a second delivery solenoid valve
558 controls air pressure to a second delivery pinch valve 481; a
first suction solenoid valve 556 controls air pressure to a first
suction pinch valve 480 and a second suction solenoid valve 560
controls air pressure to a second suction pinch valve 480.
[0092] The pneumatic diagram of FIG. 8 thus illustrates the
functional air flow that the manifold 404 produces in response to
various control signals from the control system 39 (FIG. 1).
[0093] With reference to FIGS. 9A and 9B, and in accordance with
another aspect of the invention, a transfer pump 400 is also
contemplated. Many aspects of the transfer pump are the same or
similar to the spray applicator pump 402 and therefore need not be
repeated in detail.
[0094] Although a gun pump 402 may be used as a transfer pump as
well, a transfer pump is primarily used for moving larger amounts
of powder between receptacles as quickly as needed. Moreover,
although a transfer pump as described herein will not have the same
four way independent pinch valve operation, a transfer valve may be
operated with the same control process as the gun pump. For
example, some applications require large amounts of material to be
applied over large surfaces yet maintaining control of the finish.
A transfer pump could be used as a pump for the applicators by also
incorporating the four independent pinch valve control process
described herein.
[0095] In the system of FIG. 1 a transfer pump 400 is used to move
powder from the recovery system 28 (such as a cyclone) back to the
feed center 22. A transfer pump 410 is also used to transfer virgin
powder from a supply, such as a box, to the feed center 22. In such
examples as well as others, the flow characteristics are not as
important in a transfer pump because the powder flow is not being
sent to a spray applicator. In accordance then with an aspect of
the invention, the gun pump is modified to accommodate the
performance expectations for a transfer pump.
[0096] In the transfer pump 400, to increase the powder flow rate
larger pump chambers are needed. In the embodiment of FIGS. 9A and
9B, the pump manifold is now replaced with two extended tubular
housings 564 and 566 which enclose lengthened porous tubes 568 and
570. The longer tubes 568, 570 can accommodate a greater amount of
powder during each pump cycle. The porous tubes 568, 570 have a
slightly smaller diameter than the housings 564, 566 so that an
annular space is provided therebetween that serves as a pressure
chamber for both positive and negative pressure. Air hose fittings
572 and 574 are provided to connect air hoses that are also
connected to a source of positive and negative pressure at a
transfer pump air supply system to be described hereinafter. Since
a pump manifold is not being used, the pneumatic energy is
individually plumbed into the pump 400.
[0097] The air hose fittings 572 and 574 are in fluid communication
with the pressure chambers within the respective housings 564 and
566. In this manner, powder is drawn into and pushed out of the
powder chambers 568, 570 by negative and positive pressure as in
the gun pump design. Also similarly, purge port arrangements 576
and 578 are provided and function the same way as in the gun pump
design, including check valves 580, 582.
[0098] A valve body 584 is provided that houses four pinch valves
585 which control the flow of powder into and out of the pump
chambers 568 and 570 as in the gun pump design. As in the gun pump,
the pinch valves are disposed in respective pressure chambers in
the valve body 584 such that positive air pressure is used to close
a valve and the valves open under their own resilience when the
positive pressure is removed. A different pinch valve actuation
scheme however is used as will be described shortly. An upper
Y-block 586 and a lower Y-block 588 are also provided to provide
branched powder flow paths as in the gun pump design. The lower
Y-block 588 thus is also in communication with a powder inlet
fitting 590 and a powder outlet fitting 592. Thus, powder in from
the single inlet flows to both pump chambers 568, 570 through
respective pinch valves and the upper Y-block 586, and powder out
of the pump chambers 568, 570 flows through respective pinch valves
to the single outlet 592. The branched powder flow paths are
realized in a manner similar to the gun pump embodiment and need
not be repeated herein. The transfer pump may also incorporate
replaceable wear parts or inserts in the lower Y-block 588 as in
the gun pump.
[0099] Again, since a pump manifold is not being used in the
transfer pump, separate air inlets 594 and 596 are provided for
operation of the pinch valves which are disposed in pressure
chambers as in the gun pump design. Only two air inlets are needed
even though there are four pinch valves for reasons set forth
below. An end cap 598 may be used to hold the housings in alignment
and provide a structure for the air fittings and purge
fittings.
[0100] Because quantity of flow is of greater interest in the
transfer pump than quality of the powder flow, individual control
of all four pinch valves is not needed although it could
alternatively be done. As such, pairs of the pinch valves can be
actuated at the same time, coincident with the pump cycle rate. In
other words, when the one pump chamber is filling with powder, the
other is discharging powder, and respective pairs of the pinch
valves are thus open and closed. The pinch valves can be actuated
synchronously with actuation of positive and negative pressure to
the pump chambers. Moreover, single air inlets to the pinch valve
pressure chambers can be used by internally connecting respective
pairs of the pressure chambers for the pinch valve pairs that
operate together. Thus, two pinch valves are used as delivery
valves for powder leaving the pump, and two pinch valves are used
as suction valves for powder being drawing into the pump. However,
because the pump chambers alternate delivery and suction, during
each half cycle there is one suction pinch valve open and one
delivery pinch valve open, each connected to different ones of the
pump chambers. Therefore, internally the valve body 584 the
pressure chamber of one of the suction pinch valves and the
pressure chamber for one of the delivery pinch valves are connected
together, and the pressure chambers of the other two pinch valves
are also connected together. This is done for pinch valve pairs in
which each pinch valve is connected to a different pump chamber.
The interconnection can be accomplished by simply providing
cross-passages within the valve body between the pair of pressure
chambers.
[0101] With reference to FIG. 10, the pneumatic diagram for the
transfer pump 400 is somewhat more simplified than for a pump that
is used with a spray applicator. Main air 408 is input to a venturi
pump 600 that is used to produce negative pressure for the transfer
pump chambers. Main air also is input to a regulator 602 with
delivery air being supplied to respective inputs to first and
second chamber solenoid valves 604, 606. The chamber valves also
receive as an input the negative pressure from the venturi pump
600. The solenoid valves 604, 606 have respective outputs 608, 610
that are in fluid communication with the respective pressure
chambers of the transfer pump.
[0102] The solenoid valves in this embodiment are air actuated
rather than electrically actuated. Thus, air signals 612 and 614
from a pneumatic timer or shuttle valve 616 are used to alternate
the valves 604, 606 between positive and negative pressure outputs
to the pressure chambers of the pump. An example of a suitable
pneumatic timer or shuttle valve is model S9 568/68-1/4-SO
available from Hoerbiger-Origa. As in the gun pump, the pump
chambers alternate such that as one is filling the other is
discharging. The shuttle timer signal 612 is also used to actuate a
4-way valve 618. Main air is reduced to a lower pressure by a
regulator 620 to produce pinch air 622 for the transfer pump pinch
valves. The pinch air 622 is delivered to the 4-way valve 618. The
pinch air is coupled to the pinch valves 624 for the one pump
chamber and 626 for the other pump chamber such that associated
pairs are open and closed together during the same cycle times as
the pump chambers. For example, when the delivery pinch valve 624a
is open to the one pump chamber, the delivery pinch valve 626a for
the other pump chamber is closed, while the suction pinch valve
624b is closed and the suction pinch valve 626b is open. The valves
reverse during the second half of each pump cycle so that the pump
chambers alternate as with the gun pump. Since the pinch valves
operate on the same timing cycle as the pump chambers, a continuous
flow of powder is achieved.
[0103] FIG. 11 illustrates an alternative embodiment of the
transfer pump pneumatic circuit. In this embodiment, the basic
operation of the pump is the same, however, now a single valve 628
is used to alternate positive and negative pressure to the pump
chambers. In this case, a pneumatic frequency generator 630 is
used. A suitable device is model 81 506 490 available from Crouzet.
The generator 630 produces a varying air signal that actuates the
chamber 4-way valve 628 and the pinch air 4-way valve 618. As such,
the alternating cycles of the pump chambers and the associated
pinch valves is accomplished.
[0104] FIG. 12 illustrates a flow control aspect of the present
invention that is made possible by the independent control of the
pinch valves 480, 481. This illustration is for explanation
purposes and does not represent actual measured data, but a typical
pump in accordance with the present invention will show a similar
performance. The graph plots total flow rate in pounds per hour out
of the pump versus pump cycle time. A typical pump cycle time of
400 milliseconds means that each pump chamber is filling or
discharging during a 400 msec time window as a result of the
application of negative and positive pressure to the pressure
chambers that surround the porous members. Thus, each chamber fills
and discharges during a total time of 800 msec. Graph A shows a
typical response if the pinch valves are operated at the same time
intervals as the pump chamber. This produces the maximum powder
flow for a given cycle time. Thus, as the cycle time increases the
amount of powder flow decreases because the pump is operating
slower. Flow rate thus increases as the cycle time decreases
because the actual time it takes to fill the pump chambers is much
less than the pump cycle time. Thus there is a direct relationship
between how fast or slow the pump is running (pump cycle time based
on the time duration for applying negative and positive pressure to
the pump pressure chambers) and the powder flow rate.
[0105] Graph B is significant because it illustrates that the
powder flow rate, especially low flow rates, can be controlled and
selected by changing the pinch valve cycle time relative to the
pump cycle time. For example, by shortening the time that the
suction pinch valves stay open, less powder will enter the pump
chamber, no matter how long the pump chamber is in suction mode. In
FIG. 12, for example, graph A shows that at pump cycle time of 400
msec, a flow rate of about 39 pounds per hour is achieved, as at
point X. If the pinch valves however are closed in less than 400
msec time, the flow rated drops to point Y or about 11 pounds per
hour, even though the pump cycle time remains at 400 msec. What
this assures is a smooth consistent powder flow even at low flow
rates. Smoother powder flow is effected by higher pump cycle rates,
but as noted above this would also produce higher powder flow
rates. So to achieve low powder flow rates but with smooth powder
flow, the present invention allows control of the powder flow rate
even for faster pump cycle rates, because of the ability to
individually control operation of the suction pinch valves, and
optionally the delivery pinch valves as well. An operator can
easily change flow rate by simply entering in a desired rate. The
control system 39 is programmed so that the desired flow rate is
effected by an appropriate adjustment of the pinch valve open
times. It is contemplated that the flow rate control is accurate
enough that in effect this is an open loop flow rate control
scheme, as opposed to a closed loop system that uses a sensor to
measure actual flow rates. Empirical data can be collected for
given overall system designs to measure flow rates at different
pump cycle and pinch valve cycle times. This empirical data is then
stored as recipes for material flow rates, meaning that if a
particular flow rate is requested the control system will know what
pinch valve cycle times will achieve that rate. Control of the flow
rate, especially at low flow rates, is more accurate and produces a
better, more uniform flow by adjusting the pinch valve open or
suction times rather than slowing down the pump cycle times as
would have to be done with prior systems. Thus the invention
provides a scalable pump by which the flow rate of material from
the pump can be, if desired, controlled without changing the pump
cycle rate.
[0106] FIG. 13 further illustrates the pump control concept of the
present invention. Graph A shows flow rate versus pinch valve open
duration at a pump cycle rate of 500 msec, and Graph B shows the
data for a pump cycle rate of 800 msec. Both graphs are for dual
chamber pumps as described herein. First it will be noted that for
both graphs, flow rate increases with increasing pinch valve open
times. Graph B shows however that the flow rate reaches a maximum
above a determinable pinch valve open duration. This is because
only so much powder can fill the pump chambers regardless of how
long the pinch valves are open. Graph A would show a similar
plateau if plotted out for the same pinch valve duration times.
Both graphs also illustrate that there is a determinable minimum
pinch valve open duration in order to get any powder flow from the
pump. This is because the pinch valves must be open long enough for
powder to actually be sucked into and pushed out of the pump
chambers. Note that in general the faster pump rate of Graph A
provides a higher flow rate for a given pinch valve duration.
[0107] The data and values and graphs provided herein are intended
to be exemplary and non-limiting as they are highly dependent on
the actual pump design. The control system 39 is easily programmed
to provide variable flow rates by simply having the control system
39 adjust the valve open times for the pinch valves and the
suction/pressure times for the pump chambers. These functions are
handled by the material flow rate control 672 process.
[0108] In an alternative embodiment, the material flow rate from
the pump can be controlled by adjusting the time duration that
suction is applied to the pump pressure chamber to suck powder into
the powder pump chamber. While the overall pump cycle may be kept
constant, for example 800 msec, the amount of time that suction is
actually applied during the 400 msec fill time can be adjusted so
as to control the amount of powder that is drawn into the powder
pump chamber. The longer the vacuum is applied, the more powder is
pulled into the chamber. This allows control and adjustment of the
material flow rate separate from using control of the suction and
delivery pinch valves.
[0109] Use of the separate pinch valve controls however can augment
the material flow rate control of this alternative embodiment. For
example, as noted the suction time can be adjusted so as to control
the amount of powder sucked into the powder chamber each cycle. By
also controlling operation of the pinch valves, the timing of when
this suction occurs can also be controlled. Suction will only occur
while negative pressure is applied to the pressure chamber, but
also only while the suction pinch valve is open. Therefore, at the
time that the suction time is finished, the suction pinch valve can
be closed and the negative pressure to the pressure chamber can be
turned off. This has several benefits. One benefit is that by
removing the suction force from the pressure chamber, less
pressurized process air consumption is needed for the venturi pump
that creates the negative pressure. Another benefit is that the
suction period can be completely isolated from the delivery period
(the delivery period being that time period during which positive
pressure is applied to the pressure chamber) so that there is no
overlap between suction and delivery. This prevents backflow from
occurring between the transition time from suction to delivery of
powder in the powder pump chamber. Thus, by using independent pinch
valve control with the use of controlling the suction time, the
timing of when suction occurs can be controlled to be, for example,
in the middle of the suction portion of the pump cycle to prevent
overlap into the delivery cycle when positive pressure is applied.
As in the embodiment herein of using the pinch valves to control
material flow rate, this alternative embodiment can utilize
empirical data or other appropriate analysis to determine the
appropriate suction duration times and optional pinch valve
operation times to control for the desired flow rates. During the
discharge or delivery portion of the pump cycle, the positive
pressure can be maintained throughout the delivery time. This has
several benefits. By maintaining positive pressure the flow of
powder is smoothed out in the hose that connects the pump to a
spray gun. Because the suction pinch valves can be kept closed
during delivery time, there can be an overlap between the end of a
delivery (i.e. positive pressure) period and the start of the
subsequent suction period. With the use of two pump chambers, the
overlap assures that there is always positive pressure in the
delivery hose to the gun, thereby smoothing out flow and minimizing
pulsing. This overlap further assures smooth flow of powder while
the pinch valves can be timed so that positive pressure does not
cause back flow when the suction pinch valves are opened. Again,
all of the pinch valve and pressure chamber timing scenarios can be
selected and easily programmed into the control system 39 to effect
whatever flow characteristic and rates are desired from the pump.
Empirical data can be analyzed to optimize the timing sequences for
various recipes.
[0110] The invention contemplates a dense phase pump that is highly
efficient in terms of the use of pressurized process air needed to
operate the pump. As noted above, the suction pressure optionally
can be turned off as part of the pump flow rate control process
because the pinch valves can be separately timed. This reduces the
consumption of process air for operating the venturi pump that
produces the negative suction pressure. The use of dense phase
transport allows for smaller powder flow path geometries and less
air needed to transport material from the pump to the gun. Still
further, the pinch valves operate in a normally open mode, thus
there is no need for air pressure or a control member or device to
open the pinch valves or to maintain them open.
[0111] Thus, the invention contemplates a scalable material flow
rate pump output by which is meant that the operator can select the
output flow rate of the pump without having to make any changes to
the system other than to input the desired flow rate. This can be
done through any convenient interface device such as a keyboard or
other suitable mechanism, or the flow rates can be programmed into
the control system 39 as part of the recipes for applying material
to an object. Such recipes commonly include such things as flow
rates, voltages, air flow control, pattern shaping, trigger times
and so on.
[0112] The invention has been described with reference to the
preferred embodiment. Modifications and alterations will occur to
others upon a reading and understanding of this specification and
drawings. The invention is intended to include all such
modifications and alterations insofar as they come within the scope
of the appended claims or the equivalents thereof.
* * * * *