U.S. patent number 3,870,233 [Application Number 05/394,422] was granted by the patent office on 1975-03-11 for color change of electrostatic spray apparatus.
This patent grant is currently assigned to Nordson Corporation. Invention is credited to Donald R. Hastings, William W. Lyth, Frederick R. Wilhelm.
United States Patent |
3,870,233 |
Wilhelm , et al. |
March 11, 1975 |
Color change of electrostatic spray apparatus
Abstract
An electrostatic spray system for spraying multiple colors of
material or multiple materials through a single common gun,
including apparatus for spraying solvent through the gun between
color or material changes. The system includes a dump valve for
connecting the spray gun to a waste tank upon a color change so
that the old color plus a solvent for purging the system of the old
color may be pumped to the waste tank upon a color change. The dump
valve is mounted directly upon the spray gun and is made from
non-metallic, low capacitance material so that it does not store an
electrical potential sufficient to create a dangerous condition in
a spray environment and so that it does not leak or bleed excessive
electrical potential from the system and thereby destroy its
deposition efficiency.
Inventors: |
Wilhelm; Frederick R. (Avon
Lake, OH), Hastings; Donald R. (Elyria, OH), Lyth;
William W. (Cleveland, OH) |
Assignee: |
Nordson Corporation (Amherst,
OH)
|
Family
ID: |
23558891 |
Appl.
No.: |
05/394,422 |
Filed: |
September 12, 1973 |
Current U.S.
Class: |
239/692; 239/70;
239/124; 251/61.2; 239/112; 239/305; 251/368 |
Current CPC
Class: |
B05B
12/14 (20130101); B05B 15/55 (20180201); B05B
12/088 (20130101); B05B 12/087 (20130101); B05B
5/16 (20130101); B05B 12/149 (20130101) |
Current International
Class: |
B05B
12/08 (20060101); B05B 12/00 (20060101); B05B
12/14 (20060101); B05B 15/02 (20060101); B05B
5/00 (20060101); B05B 5/16 (20060101); B05b
005/02 (); B05b 007/24 (); B05b 015/02 () |
Field of
Search: |
;239/15,70,112,113,124,127,305 ;251/61.2,368 ;118/302 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Wood, Jr.; M. Henson
Assistant Examiner: Kashnikow; Andres
Attorney, Agent or Firm: Wood, Herron & Evans
Claims
Having described our invention, we claim:
1. An electrostatic spray system for selectively spraying any one
of a plurality of spray materials from a common spray gun, which
system comprises
a spray gun having a spray material flow passage terminating in an
outlet orifice and a selectively operable valve for controlling the
emission of spray material from said orifice,
means including a high voltage power supply for applying an
electrical charge to spray material as it is emitted from said
spray gun,
a plurality of spray material reservoirs and a solvent
reservoir,
means including an electrical control circuit for selectively
connecting any one of said reservoirs to said spray gun so as to
enable spray material to be supplied from a selected reservoir to
said gun,
a dump tank, and
a dump valve operatively connected to the spray material flow
passage of said gun and operable when opened to bypass spray
material from said flow passage to said dump tank, said dump valve
being positioned immediately adjacent said gun and made from
components which have a capacitance sufficiently low as to preclude
said dump valve from storing a potentially dangerous electrical
charge,
said dump valve comprising a valve housing, said housing having an
inlet port and an outlet port interconnected by a dump flow
passage, and
a needle valve element located within said dump flow passage and
operable to control the flow of spray material through said dump
valve.
2. The electrostatic spray system of claim 1 in which said dump
valve is physically attached to and supported from said spray
gun.
3. The electrostatic spray system of claim 1 in which said
components of said dump valve are all made from non-metallic
materials.
4. The electrostatic spray system of claim 1 in which all of said
components of said dump valve which are exposed to contact with
said spray material are made from non-metals.
5. The electrostatic spray system of claim 1 in which said dump
valve includes a fluid motor for controlling positioning of said
needle valve element within said dump flow passage.
6. The electrostatic spray system of claim 5 in which said needle
valve element is mounted within a piston, said piston being
slideable within said dump valve passage.
7. The electrostatic spray system of claim 6 in which said fluid
motor includes a flexible diaphragm and a fluid motor chamber, said
diaphragm being located between and sealingly separating said dump
flow passage from said fluid motor chamber of said dump valve.
8. The electrostatic spray system of claim 7 in which said dump
valve includes a valve seat located within said dump flow passage,
said piston including a section in slideable contact with a wall
section of said dump flow passage of said dump valve, said section
of said piston being shaped as a sector of a sphere so as to enable
said piston mounted needle valve element to be self-centering
within said valve seat.
9. The electrostatic spray system of claim 8 in which said dump
valve is physically attached to and supported from said spray
gun.
10. The electrostatic spray system of claim 9 in which said
components of said dump valve are all made from non-metallic
materials.
11. The electrostatic spray system of claim 10 in which said dump
valve housing and said piston are made from a plastic material and
in which said needle valve and needle valve seat are made from a
ceramic material.
12. The electrostatic spray system of claim 11 in which said
diaphragm biases said piston and needle valve to a normally closed
position.
13. The electrostatic spray system of claim 7 in which said
components of said dump valve are all made from non-metallic
materials.
14. A dump valve for use in an electrostatic spray system for
selectively spraying any one of a plurality of spray materials from
a common spray gun, which dump valve comprises
a valve housing having an inlet port and an outlet port
interconnected by a dump flow passage,
a movable valve element located within said dump flow passage and
operable to control the flow of spray material through said dump
valve,
said dump valve being made from components which have a capacitance
sufficiently low as to preclude said dump valve from storing a
potentially dangerous electrical charge so that said dump valve is
adapted to be positioned immediately adjacent the common spray gun
of said system.
15. The dump valve of claim 14 in which said dump valve further
includes means for attaching said housing to and supporting it from
an electrostatic spray gun.
16. The dump valve of claim 15 in which the components of said dump
valve are all made from non-metallic materials.
17. The dump valve of claim 15 in which all of the components of
said dump valve which are exposed to contact with said spray
material are made from non-metals.
18. The dump valve of claim 14 in which said dump valve includes a
fluid motor for controlling positioning of said valve element
within said dump flow passage.
19. The dump valve of claim 18 in which said valve element is
secured to and mounted upon a piston, said piston being slideable
within said dump valve passage.
20. The dump valve of claim 19 in which said fluid motor includes a
flexible diaphragm and a fluid motor chamber, said diaphragm being
located between and sealingly separating said dump flow passage
from said fluid motor chamber of said dump valve.
21. The dump valve of claim 20 in which said diaphragm biases said
piston mounted needle valve to a closed position.
22. The dump valve of claim 19 which further includes a valve seat
located within said dump flow passage, said movable valve element
being a needle valve element and said piston including a section in
slideable contact with a wall section of said dump flow passage of
said dump valve, said section of said piston being shaped as a
sector of a sphere so as to enable said piston mounted needle valve
element to be self-centering within said valve seat.
23. The dump valve of claim 22 in which said dump valve housing and
said piston are made from a plastic material and in which said
needle valve element and valve seat are made from a ceramic
material.
24. The dump valve of claim 23 in which said fluid motor includes a
flexible diaphragm and a fluid motor chamber, said diaphragm being
located between and sealingly separating said dump flow passage
from said fluid motor chamber of said dump valve.
25. The dump valve of claim 24 in which said diaphragm biases said
piston mounted needle valve element to a normally closed
position.
26. The dump valve of claim 14 which further includes a valve seat
located within said dump flow passage, said movable valve element
being a needle valve element mounted upon a movable piston, said
piston including a section in slideable contact with a wall section
of said dump flow passage of said dump valve, said section of said
piston being shaped as a sector of a sphere so as to enable said
piston mounted needle valve element to be self-centering within
said valve seat.
27. The dump valve of claim 26 in which said dump valve housing and
said piston are made from a plastic material and in which said
needle valve element and valve seat are made from a ceramic
material.
Description
The invention of this application relates to a quick-change color
system for use with a single spray gun operable to selectively
discharge different coating materials, such as paints of different
color, or varnishes, waxes, protective coating materials or other
surface treating liquids upon a substrate. More particularly, the
present invention relates to a quick color change electrostatic
spray system in which the paint or other material is sprayed or
discharged from the nozzle, is electrostatically charged with an
electrical charge of one polarity and deposited upon a substrate or
object of the opposite polarity. The present invention is
specifically directed to such a quick-change spray system for
changing from one color or material to another without the
previously used old color or material contaminating the new color
or material when it is sprayed.
Throughout the application, we shall refer to the invention as
being applicable to a color change system or a system for quickly
changing from one color material to another to be sprayed from a
common gun. It should be appreciated though that the reference to
color change is for convenience only and that the reference is used
in a generic sense to encompass and include changes of materials,
as for example changes from one wax, varnish, paint or other
material to another material.
The increased use of automated painting and coating apparatus such
as in assembly lines in automobile plants or for coating a series
of objects to be painted or otherwise coated as the objects pass a
spray station, and in which these objects typically require the
applications of different coatings and colors, have resulted in an
increased demand for multiple color paint spray systems. The
utility of systems wherein a single apparatus having a single
discharge nozzle, or single set of nozzles, as the requirement may
be, for spraying the plurality of coating liquids one at a time has
resided in the ability of the color change system to change from
one color to another quickly and with a minimum waste of paint and
solvent. Typically, these systems employ a manifold to which the
plurality of coating liquids is connected and through which one of
the plurality of coating liquids is selectively connected to the
spray gun. When changing from one coating material to another, it
is necessary to purge the manifold, the feedline connecting the
manifold to the spray gun, and the spray gun itself of the old
coating color prior to the injection of a new color. Commonly, the
solvent material is injected into the system to force the old color
out of the system through a dump valve and to flush the system of
the old color. Commonly, the duration of the injection of solvent
into the system has either been controlled manually or by an
automatic timer circuit. In general, irrespective of which method
was employed, a manual or an automatic one, the objective was
always to minimize the quantity of paint and solvent required to
effect a color change and the time required to make the changeover.
Two patents which disclose automatic systems for effecting the
color change are U.S. Pat. No. 3,672,570, issued June 27, 1972, and
U.S. Pat. No. 3,450,092, issued June 17, 1969.
One of the factors which affects the time period for making a
changeover from one color to another is the length of line which
must be purged of the old paint by means of a solvent and then
replaced with a new paint. In general, this length of line or
conduit is that which extends between the distribution manifold and
the spray gun and between the spray gun and the dump valve. In the
case of electrostatic spray systems, these lengths of hoses are
dictated by safety and spray efficiency conditions which require
that the manifold be located a specified minimum distance or
"standoff" from the spray gun and that the dump valve similarly be
located a specified minimum distance from the electrostatically
charged gun. At the present time, these minimum distances are
required to prevent leakage of electrical charge or current from
the gun back through the paint to and through the manifold to
ground, or from the gun through the conduit to the dump valve and
subsequently to ground. If the manifold or the dump valve is
located too close to the electrostatically charged gun and is
grounded, escessive voltage losses occur through leakage to the
manifld or dump valve with the result that the system sprays
inefficiently, i.e. with less than optimal deposition of the paint
onto the objective or substrate. Alternatively, if the manifold and
dump valve are ungrounded, a safety hazard can be created if a
leaked charge is stored on the manifold or dump valve and is
subsequently discharged by contact with some grounded object so as
to create a spark in a volatile spray booth atmosphere.
One objective of this invention has been to shorten the length of
conduit required to be located between the dump valve and the spray
gun so as to minimize the wasted paint required to be purged from
the line in the event of a color or spray material change without
creating a condition of spray loss of efficiency or of a safety
hazard.
Another objective of this invention has been to provide a color
change electrostatic spray system in which the dump valve may be
physically attached to the spray gun so as to eliminate all conduit
between the gun and the dump valve and without creating a safety
hazard or an inefficient electrostatic spray system.
These objectives are accomplished and this invention is partially
predicated upon the concept of utilizing a dump valve located
closely adjacent or attached to the spray gun but one which is
incapable of either leaking current to ground through the dump
valve or of storing a potentially dangerous electrical charge. To
this end the dump valve utilized in the system of this invention is
made from electrically non-conductive and very low or practically
zero capacitance such that the valve may be mounted directly upon
the electrostatic spray gun and thereby eliminates any need of an
electrical "standoff" in the paint conduit between the valve and
the electrostatically charged gun.
Another objective of this invention has been to provide an improved
dump valve which is not subject to clogging and which may be made
from very low or for practical purposes zero capacitance materials.
In the preferred embodiment the dump valve is made from a plastic
housing within which there is a ceramic valve seat and needle
valve. The ceramic needle valve is mounted in a plastic piston, the
movement of which is controlled by a diaphragm type pneumatic
motor.
These and other objectives of this invention will be more readily
apparent from the following description of the drawings in
which:
FIG. 1 is a diagrammatic illustration of an electrostatic color
change spray system incorporating the invention of this
application.
FIG. 2 is a cross sectional view through the dump valve employed in
the system illustrated in FIG. 1.
Referring to the drawings, there is illustrated diagrammatically a
color change system for electrostatically spraying any one of three
different paints from a single common spray gun 10. The gun 10 is a
conventional electrostatic spray gun of the type which includes a
pneumatic cylinder 11 at the rear of the gun having a piston 12
movable therein and operatively connected to a needle 13 of the
spray gun. The needle 13 operates as a valve to open or close a
central spray material flow passage 14 through which coating
material is emitted for atomization as it is ejected from the gun.
The gun 10 depicted in the drawing is of the airless spray type,
but the invention is equally applicable to spray guns of the type
which utilize an atomizing air stream impacting with the liquid
stream to effect atomization of the spray particles as they are
ejected from the gun.
In order to increase the deposition efficiency of the gun 10, it
includes an electrostatic charge-applying needle 16 extending from
the discharge orifice 17 of the gun. This needle is supplied with a
high voltage electrical charge from a high voltage power supply 20
through a control circuit as is conventional in all electrostatic
spray guns.
To control actuation of the needle 13 and consequent emission of
spray from the gun, air from an air pressure source 21 is supplied
to the gun through a solenoid actuated valve 22. When air pressure
is supplied to an inlet port 23 of the gun through the valve 22, it
causes the piston 12 to move rearwardly against a spring bias and
thereby effects opening movement of the needle 13 relative to its
seat. Closure of the valve 22 connects the port 23 to atmosphere
and allows the spring 24 of the gun to effect closing movement of
the needle 13 relative to its seat.
Actuation of the air flow control valve 22 is controlled by the
solenoid 26. This solenoid is in turn controlled by an electrical
color set control and timer circuit indicated generally at 27. This
timer may be electrical and of the general type illustrated and
described in U.S. Pat. No. 3,450,092, or may be pneumatic as
illustrated and described in U.S. Pat. No. 3,672,570. For the sake
of simplicity, it has been illustrated as an electrical control in
the diagrammatic illustration of FIG. 1.
This same timer and color set control 27 also controls solenoids
29, 30, 31, and 32, each one of which controls opening and closing
of a liquid flow control valve 33, 34, 35, and 36 respectively.
These four valves are all located within a common manifold 37, from
which paint or solvent is supplied through a pressure regulator to
the paint flow passage 14 of the gun via a conduit 38. Paint or
solvent may be dumped from the paint or spray material flow passage
14 of the gun through a dump valve 40 and discharge conduit 41,
which conduit empties into a waste tank or reservoir 42. The dump
valve 40 is pneumatically actuated, as explained more fully
hereinafter, and is connected to the valve 22 via a pneumatic line
45. The dump valve 40 is normally closed, i.e., so long as the
valve 22 is open and air pressure is supplied to the dump valve 40
through the connecting line 45, the dump valve 40 is maintained in
a closed position.
The solvent flow control valve 33 is operable to control the flow
of solvent from a solvent supply tank 46 through the valve 33 and
the conduit 38 to the gun 10. Similarly, the valves 34, 35, and 36
are operative to control the flow of paint from three different
paint reservoirs 47, 48, and 49 through pumps associated with the
reservoirs and through the valves 34, 35, and 36 to the gun 10 via
the pressure regulator and the conduit 38.
In operation, the timer and color set control 27 is operative to
supply an electrical signal to the solenoid 26 and simultaneously
to one of the solenoids, as for example solenoid 30, so as to
connect paint from the reservoir 47 and its associated pump 47A
through the manifold 37 and conduit 38 to the material flow passage
14 of the gun 10. Simultaneously, the timer and control circuit 27
is operative to energize solenoid 26. So long as the solenoid 26 is
energized, air pressure from the source 21 is supplied via the port
23 to the pneumatic motor of the gun so as to open the needle valve
13 and cause paint to be ejected as a spray from the gun.
Simultaneously, air from the pressure source 21 is supplied through
the open valve 22 to the dump valve 40 so as to hold the dump valve
40 in a closed position and preclude the flow of paint through the
dump valve.
At the conclusion of a color cycle and upon signal for a new color
or type of material, the timer and color set control 27 is
operative to de-energize the solenoid associated with the valve of
the first color, in the example solenoid 30 of the valve 34, so as
to disconnect the first paint reservoir 47 from the manifold 37 and
move the associated valve 34 to a position in which it forms a
throughway for the flow of solvent from one end of the manifold to
the other. Simultaneously, the timer and color set control 27
energizes the solenoid 29 of the valve 33 so as to move the valve
33 to a position in which solvent from the reservoir 46 is supplied
by a pump 46A to one end of the manifold 37. The solvent then is
forced through the manifold pushing all of the residual paint in
the manifold and in the line 38 and the gun ahead of it through the
dump valve 40, which is then opened as a consequence of the
solenoid 26 being de-energized by the timer set control 27. After
the solenoid valve 29 has been energized for a period of time
sufficient for solvent flow to purge the old paint from the system,
the solenoid 29 is de-energized and the solenoid associated with
the valve for a new paint, as for example solenoid 32 of valve 36,
is energized so as to enable paint from the new paint reservoir, 49
in the example, to be supplied via the pump 49A through the
manifold 37, the pressure regulator 44, and the line 38 to the
fluid passage 14 of the gun 10. When the passage 14 has been filled
with a new paint, the solenoid 26 is energized so as to open the
valve 22 and close the dump valve 40 via air pressure supplied
through the valve 22. The new paint then purges the outlet orifice
15 of the gun of the old paint so that the system is then ready for
application of the new paint to the substrate to which it is to be
applied.
Prior to the invention of this application, the dump valve 40 has
always had to be located several feet away from an
electrostatically charged gun 10 in order to preclude a potentially
dangerous electrical charge from being stored on the dump valve and
possibly creating a spark in a potentially volatile atmosphere. An
alternative which would avoid storage of a potentially dangerous
voltage in the dump valve was to ground it, but unless the dump
valve was located several feet from the gun it leaked sufficient
electrical charge through the paint to the valve and to ground as
to render the electrostatic spray system inefficient.
The dump valve 40 of this invention, which facilitates its being
mounted on the gun without either a danger of storing a potentially
dangerous charge and without leaking electrical charge to ground,
is illustrated in detail in FIG. 2. This dump valve 40 comprises a
two-piece housing 40A including a body 50 and a body closure cap
51. These two components of the housing 40A are interconnected by
non-metallic elements such as plastic bolts or closure clips (not
shown). Between the two pieces 50, 51 there is a diaphragm 52 which
serves to divide an axial chamber 53 of the body into a piston
chamber 54 and a fluid motor chamber 55. The two chambers are
sealingly separated by the diaphragm 52 and an O-ring seal 56
mounted within a groove 57 formed in the face of the body cap 51. A
passage 58 interconnects the fluid chamber 55 to an outlet port 59.
The pneumatic line 45 is threaded into this port 59.
The piston chamber 54 communicates with a axial passage 60 through
the housing body 50 and with a dump port 61. The dump port 61 is
threaded for reception of the dump conduit 41 which connects the
piston chamber to the waste tank 42.
At its upper end, the body 50 of the housing terminates in a neck
63 which has pipe threads formed over its external surface so that
it may be sealingly threaded into a correspondingly threaded port
64 of the spray gun housing. The port 64 is in fluid communication
with the main spray material flow passage 14 of the spray gun.
Located internally of the dump valve and slideably mounted within
the piston chamber 54, there is a piston 65. A piston mounted
needle valve 66 is fixedly secured within this piston and extends
upwardly into a valve seat 67 fixedly mounted within a counterbored
seat 68 formed in the interior of the body 50 at the lower end of
the bore 60. The needle valve 66 is normally biased into sealing
engagement with the seat 67 as a result of the diaphragm 52 urging
the piston 65 upwardly to a position in which the tapered nose
section 69 of the needle valve 66 enngages the lip 70 of the valve
seat. Opening of the dump valve occurs as a consequence of liquid
pressure in the bore 60 from the spray material flow passage 14 of
the gun overcoming the pneumatic pressure in the chamber 55 so as
to force the resilient diaphragm 52 downwardly. The liquid pressure
in the chamber 60 is only able to overcome the pneumatic pressure
in the line 45 when the dump valve is to be opened and the chamber
55 is connected to atmosphere through the pneumatic valve 22.
An air bleed or vent (not shown) may be provided through the
housing body 50 to open the rear side of the piston chamber to
atmospheric pressure. The necessity for such air vent or bleed hole
is determined by the fit between the piston 65 and piston chamber
53. In the preferred embodiment the fit is sufficiently loose that
air or liquid cannot become entrapped on the back side of the
piston between the piston and the diaphragm 52. However, if a tight
sliding fit is utilized, then such an air vent is preferably
provided to ensure that the piston is always free for sliding
movement within the piston chamber.
All of the components of the dump valve which enable it to be
mounted directly upon the body of an electrostatic spray gun are
made from non-metallic materials. In the preferred embodiment, both
sections 50, 51 of the housing of the dump valve are made from
either nylon or "Delrin" plastic and the piston 65 is made from
Delrin plastic. In the preferred embodiment of the invention the
diaphragm 52 is either made from Teflon or Rulon and the needle
valve 66 and valve seat 67 are made from a ceramic material.
Consequently, the dump valve cannot store an electrical charge
sufficient to create a spark and the valve cannot leak electrical
energy to ground.
The primary advantage of the invention of this application is that
it enables the dump valve to be mounted directly on the gun so that
there need be no standoff conduit between the dump valve 40 and the
body of the spray gun. Consequently, the paint required to fill
that conduit and the solvent required to fill it are saved during
each color tank spray cycle. Additionally, the time required to
remove the old paint from that conduit and replace it with solvent
and subsequently with a new paint is saved.
While we have described only a single preferred embodiment of the
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 the
invention. As an example, the dump valve 50 has been illustrated
and described as being controlled by the solenoid control valve 22,
the same valve which controls actuation of the spray gun piston 12.
In most commercial installations the dump valve 40 is controlled by
a separate solenoid actuated valve independently of the spray gun
controlled solenoid valve, but for the sake of simplicity and
clarity the two have been described in this application as being
controlled from a single common solenoid valve 22. Therefore, we do
not intend to be limited except by the scope of the following
appended claims.
* * * * *