U.S. patent number 3,815,820 [Application Number 04/272,615] was granted by the patent office on 1974-06-11 for hydrostatic atomizing apparatus.
This patent grant is currently assigned to Ransburg Electro-Coating Corp.. Invention is credited to Richard O. Probst.
United States Patent |
3,815,820 |
Probst |
June 11, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
HYDROSTATIC ATOMIZING APPARATUS
Abstract
An apparatus for atomizing liquid coating material and
electrostatically depositing the material on a surface to be coated
comprising an elongated body of insulating material having two
passages therethrough, one passage for liquid coating material and
the other passage containing resistor means connected with a source
of high electrical potential. An electrode is connected with said
resistor means for electrostatically charging atomized particles of
said coating material.
Inventors: |
Probst; Richard O.
(Indianapolis, IN) |
Assignee: |
Ransburg Electro-Coating Corp.
(Indianapolis, IN)
|
Family
ID: |
23040550 |
Appl.
No.: |
04/272,615 |
Filed: |
April 12, 1963 |
Current U.S.
Class: |
239/707;
118/626 |
Current CPC
Class: |
B05B
5/053 (20130101); B05B 5/035 (20130101) |
Current International
Class: |
B05B
5/053 (20060101); B05B 5/025 (20060101); B05B
5/035 (20060101); B05b 005/02 () |
Field of
Search: |
;239/3,15 ;118/624-632
;317/3 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ward, Jr.; Robert S.
Attorney, Agent or Firm: Hofgren, Wegner, Allen, Stellman
& McCord
Claims
I claim:
1. Apparatus for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: an elongated body of insulating material having two
passages therethrough, terminating adjacent the forward end
thereof; means connecting one of said passages with a supply of
liquid coating material under sufficient pressure to effect
discharge of said material through an orifice for hydrostatic
atomization; means for controlling the flow of coating material
through siad one passage; circuit means in the other of said
passages, connectable with a source of high potential; first means
mounted on said body, closing the other of said passages; second
means mounted on said body and extending across said one passage
and including a surface defining the orifice in communication with
said one passage; a conductive charging electrode operably
associated with the discharge from said orifice; and further
circuit means connecting said electrode through circuit means in
said other passage with said high voltage source for
electrostatically charging atomized particles of coating material
discharged from said orifice.
2. Apparatus for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: an elongated body of insulating material having two
passages therethrough, terminating at the forward end thereof;
means connecting one of said passages with a supply of liquid
coating material under sufficient pressure to effect discharge of
said material through an orifice for hydrostatic atomization of the
material; means for controlling the flow of coating material
through said one passage; resistor means in the other of said
passages, connectable with a source of high potential; first
closure means mounted on said body, closing one of said passages;
second closure means mounted on said body and closing the other of
said passages, the one of said closure means closing said resistor
passage including circuit means connected with said resistor means,
and the other of said closure means including a surface defining
said orifice in communication with said first passage, there being
a conductive charging electrode operably associated with the
discharge from said orifice and connected through said circuit
means with said high voltage source for electrostatically charging
atomized particles of coating material discharged from said
orifice.
3. Apparatus for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: an elongated body of insulating material having two
passages therethrough, terminating at the forward end thereof;
means connecting one of said passages with a supply of liquid
coating material under sufficient pressure to effect discharge of
said material through an orifice for hydrostatic atomization of the
material; means for controlling the flow of coating material
through said one passage; resistor means in the other of said
passages, connectable with a source of high potential; first
closure means mounted on said body closing the other of said
passages and retaining said resistor means therein, said first
closure means including a conductor connected with said resistor
means; and second closure means mounted on said first closure means
and including a nozzle having said orifice therein and positioned
in communication with said coating material passage, there being a
conductive charging electrode mounted on said second closure and
extending outwardly therefrom, adjacent said orifice, and connected
through said conductor with said resistor means and the source of
high voltage for electrostatically charging atomized particles of
coating material discharged from said orifice.
4. The apparatus of claim 3 wherein said first closure member has
formed therein a flow passage in communication with said coating
material passage and includes a valve seat forming part of said
flow control means.
5. The apparatus of claim 3 wherein said second closure has a
recess with a conductive nozzle insert therein, with said electrode
having a portion held in said recess by said nozzle insert, and
said nozzle is in the circuit between said electrode and said
conductor.
6. The apparatus of claim 3 wherein said second closure has a
conductive rear surface in contact with said conductor, and said
electrode and nozzle are connected with said surface.
7. The apparatus of claim 3 wherein said nozzle seats against a
conductive sealing washer carried by said first closure and
connected with said conductor, and said electrode has a portion in
contact with said nozzle.
8. A hand gun for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: an elongated body of insulating material having two
spaced passages extending longitudinally therethrough and
terminating at the forward end thereof; a handle extending from
said body at a rear portion thereof; means connecting one of said
passages with a supply of liquid coating material under sufficient
pressure to effect discharge of said material through an orifice
for hydrostatic atomization; resistor means in the other of said
passages, connectable with a source of high potential; a first
closure member mounted on said body closing the other of said
passages and retaining the resistor means therein, said first
closure member having an orifice in alignment with said one
passage; a conductor extending through said first closure member
and connecting with the forward terminal of said resistor means; a
retaining ring securing said first closure member to said body; a
valve seat in the orifice of said first closure member, said valve
seat having a flow passage therethrough; a valve member in said one
passage and engageable with said valve seat to close said one
passage; a valve stem extending rearwardly through said one
passage; spring means urging said valve stem forwardly to seat said
valve member; a valve operating trigger pivotally mounted on said
body adjacent said handle and connected with said valve stem, for
manual actuation of said valve; a second closure member mounted on
said first closure member and including a nozzle having said
orifice therein and positioned in communication with the flow
passage of said valve seat; a retaining ring securing said second
closure member to said first closure member; and a conductive
charging electrode mounted on said nozzle and extending outwardly
therefrom, adjacent the orifice therein, said charging electrode
being connected through said conductor in the first closure member
with said resistor means and the source of high voltage for
electrostatically charging atomized particles of coating material
discharged from said orifice.
9. A hand gun for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: an elongated body of insulating material having two
passages therethrough, terminating adjacent the forward end
thereof; a handle at the rear of said body; means connecting one of
said passages with a supply of liquid coating material under
sufficient pressure to effect discharge of said material through an
orifice for hydrostatic atomization; a liquid coating material
inlet housing of conductive material forming an extension of said
one passage, at the rear thereof and adjacent said handle; resistor
means in said other passage; a high voltage cable connectable with
a source of high voltage, extending through said handle into said
other passage, and connecting with a rear terminal of said resistor
means; a nozzle having said orifice in communication with said one
passage; and an electrode operably associated with said orifice and
connected with said resistor means for electrostatically charging
atomized particles of coating material discharged from said
orifice.
10. The hand gun of claim 9 wherein a valve is provided adjacent
the forward end of said coating material passage, and the spacing
between the forward end of the resistor passage and the forward end
of the coating material passage is substantially less than the
spacing between the rear ends of said passages.
11. The hand gun of claim 10 wherein a step is formed in said
resistor passage, and said resistor means is in two sections, said
step being less than the diameter of said resistor sections, the
ends of said resistors overlapping.
12. Apparatus for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: an elongated body of insulating material having two
passages therethrough, terminating at the forward end thereof;
means connecting one of said passages with a supply of liquid
coating material under sufficient pressure to effect discharge of
said material through an orifice for hydrostatic atomization, the
passages being spaced from the longitudinal axis of the body, with
at least the forward portion of the body being offset from the
remainder thereof and having a generally circular cross-section
about said coating material passage; means for controlling the flow
of coating material through said one passage; circuit means in the
other of said passages, connectable with a source of high
potential; a nozzle having said orifice in communication with said
one passage; and an electrode operably associated with said orifice
and connected with said circuit means for electrostatically
charging atomized particles of coating material discharged from
said orifice.
13. Apparatus for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: an elongated body of insulating material, said body
having a generally oval cross-section, with two passages extending
longitudinally therethrough and offset from the axis of the body,
said passages terminating at the forward end of the body; means
connecting one of said passages with a supply of liquid coating
material under sufficient pressure to effect discharge of said
material through an orifice for hydrostatic atomization, the
forward portion of the body being offset from the remainder thereof
and having a generally circular cross-section about said coating
material passage; means for controlling the flow of coating
material through said one passage; resistor means in the other of
said passages, connectable with a source of high potential; a
nozzle having said orifice in communication with said one passage;
and an electrode operably associated with said orifice and
connected with said resistor means for electrostatically charging
particles of coating material discharged through said orifice.
14. The apparatus of claim 12 wherein said nozzle is mounted in a
circular carrier held in position on said body by a threaded
retainer collar.
15. Apparatus for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: an elongated body portion of insulating material having
two passages therethrough terminating adjacent the forward end
thereof; a body portion of conductive material joined with said
body of insulating material and having two passages therethrough in
alignment with the passages of the body of insulating material; a
tubular member extending into a passage in each of said two body
portions, aligning said body portions; means connecting one of the
passages of said body portions with a supply of liquid coating
material under sufficient pressure to effect discharge of the
material through an orifice for hydrostatic atomization; high
voltage circuit means extending through the other passage of said
body portions; a nozzle having said orifice in communication with
said one passage of the insulating body; and an electrode operably
associated with said orifice and connected with said high voltage
circuit means for electrostatically charging atomized particles of
coating material discharged from said orifice.
16. The apparatus of claim 15 wherein said tubular member is a
sleeve of high dielectric material around said high voltage circuit
means and extending through the corresponding passages of the two
body portions, said passages being straight and in substantial
axial alignment.
17. The apparatus of claim 15 wherein said tubular member is a
bushing mounted in the end of the coating material passage of said
body of insulating material and extending into the corresponding
passage in said conductive body portion.
18. A hand gun for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: a body portion of insulating material having two
passages therethrough, terminating adjacent the forward end
thereof; a conductive body portion connected with the rear of said
insulating body portion, including a handle, said conductive body
portion having two passages extending at least a portion of the way
therethrough and aligned with the two passages of said insulating
body portion; means for aligning said two body portions, including
a sleeve of dielectric insulating material extending through one
pair of aligned passages of said two body portions; means
connecting the other of said passages with a supply of liquid
coating material under sufficient pressure to effect discharge of
said material through an orifice for hydrostatic atomization; a
high voltage cable connectable with a source of high voltage
extending through said handle into the sleeve in said pair of
passages; a resistor in said sleeve, connected with said cable; a
nozzle having said orifice in communication with said other
passage; and an electrode operably associated with said orifice and
connected with said resistor for electrostatically charging
atomized particles of coating material discharged from said
orifice.
19. Apparatus for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: an elongated body portion of insulating material having
a passage therethrough, terminating adjacent the forward end
thereof; a second body portion connected with the rear of said
first body portion and having a passage therethrough in alignment
with the passage of said first body portion; a bushing carried in
the passage of the first body portion and extending into the
passage of the second body portion, said bushing having a flow
passage therethrough; means connecting the flow passage of said
bushing with a supply of liquid coating material under sufficient
pressure to effect discharge of said material through an orifice
for hydrostatic atomization; and a nozzle having said orifice, at
the forward end of said body member and in communication with said
passage.
20. The apparatus of claim 19 wherein a valve is located in the
passage of the first body portion, actuated by a trigger carried on
said second body portion and including a valve rod extending
forwardly through the coating material passage and rearwardly
through a packing gland carried by said bushing.
21. Apparatus for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: an elongated body of insulating material having a
passage therethrough, terminating adjacent the forward end thereof;
a handle at the rear of said body; means connecting said passage
with a supply of liquid coating material under sufficient pressure
to effect discharge of said material through an orifice for
hydrostatic atomization; means forming a valve seat in said passage
having a flow opening therethrough, said flow opening having a
chamfered surface; a carrier mounted on said actuator and having a
recess in the end thereof; and a ball valve member received in said
recess and secured therein by cement, said ball member being
movable into seated engagement with said chamfered surface, said
valve actuator being movable to move the ball from said seat; high
voltage supply means; a nozzle having an orifice in communication
with said coating material passage; a conductive charging electrode
operably associated with said orifice; and circuit means connecting
said electrode with said high voltage supply for electrostatically
charging atomized particles of coating material discharged from
said orifice.
22. In apparatus for atomizing liquid coating material and
electrostatically depositing the material on a surface to be
coated: an elongated body of insulating material having a passage
therethrough; a source of high voltage; resistance means in said
passage and connected with said high voltage source; a sleeve of
high dielectric material intimately surrounding said resistance
means; a paste dielectric material filling the spaces in said
passage surrounding said sleeve; and an electrode connected with
said resistance means for electrostatically charging atomized
particles of said coating material.
23. Apparatus for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: an elongated body of insulating material having a
passage therethrough, terminating adjacent the forward end thereof;
means connecting said passage with a supply of liquid coating
material under sufficient pressure to effect discharge of said
material through an orifice for hydrostatic atomization; means for
controlling the flow of coating material through said passage;
resistor means connectable with a source of high potential; a
nozzle having said orifice in communication with said coating
material passage, with cooperating surfaces on said nozzle and gun
body establishing a plurality of predetermined positions of the
nozzle on the body; a conductive charging electrode operably
associated with said orifice; and circuit means connecting said
electrode through said resistance means with said high voltage
source for electrostatically charging particles of atomized coating
material discharged from said orifice.
24. The apparatus of claim 23 wherein said nozzle has an elongated
orifice, and is mounted in a carrier removably secured to said
body, there being keying surfaces on said carrier and body
establishing two positions of the nozzle relative to the body, with
the orifice displaced substantially 90.degree. between the two
positions, and said electrode is mounted on said carrier to retain
a fixed position with relation to said orifice.
25. Apparatus for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: an elongated body of insulating material having a
passage therethrough, terminating adjacent the forward end thereof;
means connecting said passage with a supply of liquid coating
material under sufficient pressure to effect discharge of said
material through an orifice for hydrostatic atomization; valve
means at a forward point in said passage, for controlling the flow
of coating material through said passage; a valve actuator rod
extending rearwardly from said valve; circuit means connectable
with the source of high potential; a nozzle having said orifice in
communication with said one passage; a conductive charging
electrode operably associated with said orifice and connected
through said circuit means with said source of high voltage; and a
switch actuated by said valve actuator rod to control said high
voltage with operation of said valve.
26. The apparatus of claim 25 for use as a hand gun having a handle
at the rear of said body and a trigger adjacent said handle and
between said valve and switch, and said valve actuator rod has a
portion extending rearwardly from said trigger for actuating said
switch.
27. The hand gun of claim 26 in which said switch is mounted in
said handle, and said handle is sealed with said body.
28. Apparatus for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: an elongated body of insulating material having two
passages therethrough, terminating adjacent the forward end
thereof; means connecting one of said passages with a supply of
liquid coating material under sufficient pressure to effect
discharge of said material through an orifice for hydrostatic
atomization; means for controlling the flow of coating material
through said one passage; circuit means in the other of said
passages, connectable with a source of high potential; first means
mounted on said body, closing the other of said passages; second
means mounted on said body and extending across said one passage
and including a surface defining the orifice in communication with
said one passage; a conductive charging electrode operably
associated with the discharge from said orifice; and further
circuit means connecting said electrode through the circuit means
in said other passage with said high potential source for
electrostatically charging atomized particles of coating material
discharged from said orifice.
29. Apparatus for hydrostatic atomization and electrostatic
deposition of coating material on a surface to be coated,
comprising: an elongated body of insulating material, said body
having two passages extending longitudinally therethrough and
offset from the axis of the body, said passages terminating at the
forward end of the body; means connecting one of said passages with
a supply of liquid coating material under sufficient pressure to
effect discharge of said material through an orifice for
hydrostatic atomization, the forward portion of the body being
offset from the remainder thereof and having a generally circular
cross-section about said coating material passage; means for
controlling the flow of coating material through said one passage;
resistor means in the other of said passages, connectable with a
source of high potential; a nozzle having said orifice in
communication with said one passage; and an electrode operably
associated with said orifice and connected with said resistor means
for electrostatically charging particles of coating material
discharged through said orifice.
Description
This invention is concerned with a hydrostatic spray coating
apparatus and more particularly with a hand gun for hydrostatically
atomizing and electrostatically depositing coating material on an
article to be coated.
Prior commercial apparatus for atomizing and electrostatically
depositing coating material commonly utilizes either electrostatic
or air atomization. In coating certain types of articles, as where
a high coating material delivery rate is desired or to penetrate
into a recess, for example, it is desirable to atomize the coating
material hydrostatically, as by projecting the coating material
through a small orifice under high pressure. The interaction of the
stream of coating material with air causes a break-up of
atomization of the coating material into small particles which may
be charged electrostatically. Hydrostatic atomization provides a
fog-like spray in which the particles do not have the persisting
high velocity possessed by particles atomized by air, nor the wide
spray pattern of centrifugal atomization. The efficiency of
deposition of the coating material on articles, and the quality of
the coating may be improved by imparting an electrostatic charge to
the spray particles.
A suitable commercial apparatus for hydrostatic atomization and
electrostatic charging of coating materials should incorporate
safety features to prevent a discharge or spark and possible fire
or explosion if the spacing between the article being coated (which
is normally grounded) and the charged gun becomes too small, and to
prevent injury to the operator where the apparatus is used as a
hand held gun. For use as a hand gun, the apparatus should be of
small size, convenient to handle and well balanced. It is also
desirable that the gun be economical to manufacture and simple in
construction to facilitate cleaning, servicing and repair. The
novel featueres of the apparatus disclosed and claimed herein
contribute to the fulfillment of these objectives.
The apparatus includes a nozzle defining an orifice through which
the coating material under high pressure is directed, to be
atomized into fine particles through interaction with air
surrounding the nozzle. Electorde means are operably associated
with the nozzle and connected with a source of high voltage to
establish an electrostatic field in the vicinity of the region of
formation of the spray particles, imparting a charge to the
particles and affecting their deposition on the article to be
coated. A valve controls the flow of paint to the orifice. The
circuit from the source of high voltage includes one or more
resistors whcih limit the current flow and provide a safety factor
by reducing the electrode voltage if the current increases. The
high voltage circuit between the resistor and electrode and
electrode means further have a small physical area and appropriate
configuration to limit the effective electrical capacity of the
system and the energy which may be stored therein and discharged
rapidly therefrom.
An electrode system with a low "effective capacity" is a system
which has such low true capacitance, such poor conductivity of the
material of which it is formed or such shape (particularly as to
"sharpness" or "bluntness" of its configuration) that, in an
electrostatic coating system of the character with which I am here
concerned, the energy contributed to a disruptive discharge between
such electrode system and an opposed "blunt" electrode, by the
electricity stored in the electrode system is insufficient to
render such discharge objectionable.
One feature of the invention is the provision of an apparatus with
an elongated body and two passages therethrough, one for the
coating material and the other for the high voltage circuit,
including resistor means. A first closure closes one of the
passages and a second closure closes the other. A further feature
is that the closure for the passage with the resistor means
includes a conductor connected with the resistor for connection
with the charging electrode means, and that the closure for the
other passage includes a nozzle with a discharge orifice for the
coating material.
Another feature is that the two passages through the body of the
apparatus are spaced apart a sufficient distance to prevent
internal arcing or other discharge from the high voltage circuit.
At the forward end of the apparatus, the voltage in the high
voltage circuit is reduced and the spacing between the high voltage
circuitry in the coating passage is reduced to minimize the bulk of
the gun.
Yet a further feature is that the passage for the coating material
through the body of the gun is substantially straight to avoid
unnecessary wear on the walls of the passage. At the forward end of
the gun, where the passage spacing is reduced, the body is provided
with an offset or eccentric configuration to have a circular
cross-section about the coating material passage.
A further feature is that a valve seat of hard, abrasion resistant
material is mounted on a carrier at the front of the body and a
valve memeber is movable longitudinally in the body, into and out
of seating engagement with the valve seat. More particularly, the
valve seat is a generally cylindrical member with an orifice
therethrough and a chamfered valve surface, and the valve member is
a ball mounted at the end of an elongated actuator rod extending
through the coating material passage.
Still another feature of the invention is that the valve actuating
mechanism operates a switch controlling the high voltage applied to
the charging electrode so that the gun is only charged when the
valve is open and coating material can flow.
Further features and advantages of the invention will readily be
apparent from the following specification and from the drawings, in
which:
FIG. 1 is a diagrammatic illustration of a system embodying the
invention;
FIG. 2 is an elevation of a hand gun embodying the invention;
FIG. 3 is a vertical section taken longitudinally through the gun
of FIG. 2 as shown by a line 3--3 of FIG. 6;
FIG. 4 is an enlarged fragmentary section of the nozzle portion of
the gun of FIG. 3;
FIG. 5 is an exploded view of the forward end of the gun;
FIG. 6 is a vertical transverse section through the gun generally
along the line 6--6 of FIG. 2;
FIG. 7 is a vertical transverse section through the gun generally
along the line 7--7 of FIG. 2;
FIG. 8 is an enlarged fragmentary section of a modified nozzle
structure; and
FIG. 9 is an enlarged fragmentary section of another modified
nozzle structure.
The embodiment of the invention illustrated herein is a gun adapted
to be held in the hand of an operator, and some of the features are
particularly suited for such use. It is to be understood, however,
that the apparatus could be mounted on a suitable structure, either
fixed or movable, and actuated from a remote location.
Turning now to the drawings, and particularly to FIG. 1, a coating
system is illustrated utilizing an apparatus embodying the
invention. Articles 10 are carried by hangers 11 from a conveyor
12, preferably at ground potential. The hydrostatic spray coating
apparatus indicated generally at 13 is illustrated as a hand gun
having a body 14, a handle portion 15 and trigger 16. A hose 17
connects the gun with a suitable source of coating material under
high pressure, as paint pump 18. Power supply 20, which is
connected with spray apparatus 13 through a cable 21, provides the
unidirectional high voltage which establishes an electrostatic
field between the spray apparatus and the articles 10. Particles of
coating material are charged in the field and are electrostatically
deposited on the articles. Trigger 16 controls the discharge of
coating material from the gun 13, and, in a preferred embodiment of
the apparatus, controls also the application of high voltage from
power supply 20.
The pressure of the coating material supplied from pump 18 depends
to some extent on the physical characteristics of the coating
material, the nature of the discharge orifice and the like. For
example, with present coating materials, pressures may range from
400 to 3,000 pounds per square inch. In a typical system, the
pressure may be of the order of 800 to 1,000 pounds per square
inch.
The voltage of power supply 20 must be sufficient to establish a
voltage gradient adequate to impart to the atomized particles an
electrostatic charge, and to establish a field from the coating
apparatus to the articles which will affect the deposition on the
articles of a substantial portion of the particles which would not
otherwise be so deposited. In a typical installation, an average
field gradient of the order of at least 3 kilovolts and preferably
of the order of 5-10 kilovolts per inch has been found
satisfactory. A total voltage from the power supply of the order of
at least 40 to 50 kilovolts, and preferably of the order of about
60 kilovolts is suitable in most hand apparatus. A higher voltage,
as of the order of 90 kilovolts, may be used with mechanically
supported guns.
The body 14 of the gun, FIG. 2, has a rear portion 22 preferably of
a suitable conductive material, as aluminum, and a forward or
barrel portion 23 preferably molded of an insulating plastic
material, as Delrin, an acetal resin sold by E. I. DuPont.
Conductive handle 15 is secured to and depends from the rear of
body portion 22 forming an angle of the order of 90.degree.
therewith, and is grounded, as will appear, to ground the operator.
Trigger 16 is pivoted at 24 to body portion 22. Hose 17 for the
liquid coating material is connected through a swivel fitting 25
with a boss 26 which extends downwardly from body portion 22 and
houses a filter. The hose connection is in front of and generally
parallel with handle 15. High voltage cable 21 enters the gun
through the base of handle 15.
The coating mateiral is discharged from an orifice at the forward
end of barrel 23, is atomized, and atomized particles are charged
in the field extending from electrode 27 to the metallic portions
at the rear of the gun and to the articles being coated. The
spacing between electrode 27 and body portion 22 is approximately
71/4 inches, establishing the field gradient in the vicinity of the
discharge from the orifice.
Referring more particularly to the FIGS. 3 and 4, body portion 22
has a passage 28 extending longitudinally through its upper portion
and a passage 29 extending longitudinally through its lower
portion. Barrel 23, which has an oval crosssection (FIG. 6), is
similarly provided with an upper passage 30 and a lower passage 31.
Barrel 23 has a flange 23a (FIGS. 2 and 6) at the rear thereof,
seated against the body portion 22 and secured thereto as by bolts
34. The upper passages 28 and 30 and the lower passages 29 and 31,
and the two body portions 22 and 23 are aligned. A closure or valve
housing 35 secured to the forward end of barrel 23 by a threaded
retaining ring or nut 36 closes the forward end of passage 30. A
second closure or nozzle carrier 37 mounted on valve housing 35 by
a threaded cap 38 closes the forward end of passage 31.
One piece handle 15 is secured to the rear of body portion 22 by
screws 40.
A bushing 41 is threaded into the enlarged rear portion 31a of
passage 31 and extends through passage 29 in body portion 22.
Coating material from hose 17 flows through swivel joint 25 and
filter housing 26 into the bore 41a of bushing 41 and to passage
31. A cylindrical valve seat 42 is carried in the bore 42 through
valve housing 35, in communication with passage 31. Nozzle 44
carried by nozzle housing 37 has an orifice 44a communicating with
the bore 43 of the valve housing which forms a portion of passage
31.
The rear face of valve seat 42 is chamfered at 42a to seal with a
ball valve member 45 carried at the forward end of a valve rod 46
which extends through the length of passage 31. A valve holder 46a
is threaded to the end of valve rod 46 and has a recess 46b in
which ball 45 is seated. The ball is cemented into the recess by a
suitable solvent resistant adhesive, as an epoxy resin, and the
periphery 46c of the mounting member is swaged around the ball.
It has been found that swaging alone is often insufficient to
secure the ball valve member to the holder, as the high pressure
coating material is forced into the space between the ball and the
holder. When the ball is seated, the force of the coating material
tends to keep the ball seated, and as the valve rod is retracted,
the ball valve member may pull from the recess rather than lifting
from the valve seat. The adhesive holds the ball valve member in
place and prevents paint from getting behind the ball to hold it
shut.
A valve rod extension 47 is brazed to a screw 48 threaded into the
rear of rod 46, extending rearwardly of the gun through packing
washers 50 and connected with valve actuator 51. The actuator is
urged forwardly of the gun by a spring 52, seating ball valve 45
against the sealing surface 42a of the valve seat. Actuator 51 is
loosely engaged with a pin 53 carried by the trigger 16. Movement
of the trigger rearwardly toward handle 15 retracts the valve rod
against the action of spring 52, opening the valve and allowing a
flow of coating material through passage 31 to nozzle 44 from which
it is discharged.
High voltage cable 21 enters the gun through the base of handle 15
and is anchored in place by a fitting 54. The cable includes a
grounded conductive outer covering 21a electrically connected with
the handle 15, grounding the conductive portions of the gun. An
inner conductor 21b, connected with the high voltage terminal of
power supply 20, is surrounded by a body 21c of dielectric
material. The dielectric body 21c and high voltage conductor 21b
extend through handle 15 and into sleeve 55 which extends through
aligned passages 28 and 30. A conductive button 56 is connected
with high voltage conductor 21b and contacts the rear terminal of
resistor 57 in the rear portion of upper passage 30 of barrel
23.
Dielectric sleeve 55 is shrunk around resistor 57 to have close
intimate contact therewith. This provides effective heat transfer
from the resistor to the sleeve through which the heat is
dissipated into the body of the gun. The space in passage 30
outside sleeve 55 is packed with a high dielectric silicone grease
30b to eliminate air pockets which would provide a relatively low
impedance discharge path, and which would impair heat transfer.
Bushing 41 and sleeve 55 serve to align the two body portions.
Bushing 41 is threaded into barrel 23. The force of the coating
material acts against packing washers 50 held by nut 50a and does
not tend to separate the two portions of the gun. Retainer screws
34 need be strong enough only to hold the parts together, and not
to withstand the force of the coating material.
At the forward end of barrel 23 there is a step in passage 30, with
the forward portion 30a thereof being offset toward passage 31. A
second resistor 58 is located in passage portion 30a and is
connected with the forward end of resistor 57 through a spring 59.
The forward end of passage 30a is closed by a sealing plug 62 which
has a conductor wire 63 extending therethrough. A loop 63a of
conductor wire is in contact with the forward end of resistor 58. A
conductor 64 extends through valve housing 35 and terminates at the
rear thereof in a recess 65 filled with a conductive cement which
is in contact with the forward end of conductor 63. The forward end
of conductor 64 is located in a recess 66 filled with a conductive
cement and in physical contact with nozzle 44 which is of an
abrasion resistant conductive material. Charging and field
establishing electrode 27 comprises a length of wire having a loop
portion 27a seated in a recess 37a of the nozzle housing and held
in place by nozzle 44.
The coating material which is discharged under high pressure
through the orifice 44a of nozzle 44 preferably issues therefrom as
a thin film. With a narrow elongated orifice 44a, as shown in the
drawing, the film of coating material is flat and fan-like, with
diverging edges, and substantially in a single plane. A nozzle with
a circular rather than an elongated orifice and having a spinner
insert, may be used to provide a hollow, diverging conical
film.
At the forward edge of the film there is a zone or area of break-up
in which the desired fine particles are formed. The electrode 27 is
desirably located outside the film, to avoid disturbing the film
and the particle formation. The forward end of electrode 27 is
preferably located adjacent or slightly to the rear of the zone of
break-up. The field, which extends from the electrode both to the
grounded body portion 22 and to the articles being coated, has a
gradient in the vicinity of the particle formation such that a
charge is imparted to the particles. The field extending from the
electrode to the articles causes the charged particles to be
attracted to the articles so that a substantial portion of the
particles which otherwise would have fallen to the floor or gone
past the articles, are deposited on the articles.
As a safety feature, it is desirable that the high voltage be
connected with the gun and the exposed electorde 27 only when
coating material is being discharged. Accordingly, means are
provided for controlling the high voltage in accordance with the
position of valve 45. Valve actautor 51 has a switch operating
portion 51a which extends rearwardly into the interior of handle
15. A voltage control switch 68 is operated by actuator portion 51a
when the trigger is retracted and valve 45 opened. Switch 68 is
connected through wires 68a, a part of cable 21, with a suitable
circuit for operating the high voltage power supply. For example
(FIG. 1), the switch may be connected in series with the coil of a
relay 69 connected across the leads 70, 71, connected with a
suitable source of power, not shown. Contacts 69a and 69b of the
relay are closed when the relay is energized, connecting the leads
70, 71 with the power supply circuitry (not shown in detail).
Limiting factors on the transverse size of the gun are the spacing
required between the high voltage circuit and portions of the
structure with which an objectionable discharge might occur, and
the physical strength of the body required to withstand the
pressure of the coating material. By objectionable discharge is
meant either excessive leakage current or a transient spark
discharge. The dielectric cable body 21b provides adeuqate
insulation for high voltage conductor 21c even though it extends
through the grounded conductive handle 15, and is in close
proximity thereto. The conductive button 56 at the forward end of
the high voltage cable is isolated from conductive gun body portion
22 and bushing 41 by sleeve 55 which has a higher dielectric
constant than body portion 23.
The spacing between passages 28 and 29, and between passages 30 and
31, aligned therewith, at the forward end of conductive body
portion 22 and the rear end of barrel portion 23 is determined by
the physical strength of the parts, and particularly by the web 23a
of the plastic barrel between passages 30 and 31, where bushing 41
is threaded into the barrel. Passage 30 is straight, aligned with
passage 28 and parallel with passage 31, to facilitate assembly of
the high voltage cable and resistor 57, which cannot be bent on
insertion. The spacing between resistor passage 30 and coating
material passage 31 is maintained throughout the major portion of
barrel 23. However, the current flow through the high voltage
circuit is sufficient to reduce the voltage at the forward end of
resistor 57 and the spacing between the high voltage circuit and
coating material passage 31 may be reduced without danger of arcing
from the high voltage circuit to other structure, as the nozzle or
valve.
The forward end 57a of resistor 57 is silver coated for good
contact with connector spring 59. The forward end 58a of resistor
58 is preferably coated with a graphite material which, while
conductive for connection with conductor 63, has an appreciable
resistance to minimize the effective capacity of the system.
The close spacing of resistor passage portion 30a and coating
material passage 31 makes it possible to reduce the diameter of the
forward end of the gun. It is desirable, however, that the forward
gun structure be circular in cross-section and symmetrical about
the forward end of the coating material passage 31. This permits
the use of threaded retainer nut 36 and nozzle cap 38, and
symmetrical valve and nozzle housings 35 and 37. In addition to the
downward step in passage 30, a slight upward step is provided in
coating material passage 31. The coating material passage 31 is
preferably substantially straight throughout the body of the gun,
to facilitate the design and operation of the valve and to
eliminate sharp corners which would increase the flow resistance
and would be subject to wear, particularly with coating materials
containing abrasive particles.
The slight step 31b in the coating material passage permits valve
stem 46 to lie against the upper surface of the passage, leaving
the lower portion of the passage free for flow of coating material.
The compact cross-section of the lower portion of the flow passage
has less flow resistance than would an annular flow passage of
equivalent area, if the valve stem were centered in the passage. In
addition, the valve stem is stabilized and guided by contact with
the passage wall. Valve 45 and the valve holder are centered in the
passage portion ahead of step 31b so taht the flow of coating
material through the valve is uniform and not concentrated in one
zone. An extension of the axis of the valve seat coincides with the
axis of valve rod 47 and the valve actuator 51.
Valve housing 35 is positioned on the forward end of barrel 23,
closing the end of resistor passage portion 30a. A pin 75 extends
into an opening 76 in the valve housing insuring alignment of
conductor 64 with conductor 63, in the high voltage circuit.
Nozzle housing 37 has a boss 77 extending rearwardly therefrom to
locate the nozzle on the valve housing. Boss 77 may be selectively
located in one of a plurality of recesses, as 78, on the forward
portion of the valve housing. In the embodiment of the invention
illustrated herein, the aperture or orifice 44a of nozzle 44 is an
elongated slot (FIG. 4). The recesses 78 on the nozzle housing are
preferably located with a spcaing of 90.degree., so that orifice
44a may be oriented either vertically or horizontally.
The valve seat 42 is of a wear resistant material, as stainless
steel or tungsten carbide. The inner diameter of valve seat 42 is
slightly less than the inner diameter of passage 43 through the
valve housing. If it should be necessary to replace the valve seat,
a tool may be inserted from the left end of the valve housing to
force the valve seat out.
Valve rod 46 has sufficient flexibility to permit ball valve member
45 to seat properly on the chamfered sealing surface 42a of the
valve seat. With the valve closed, the area of the valve supporting
structure exposed to the pressurized coating material tends to hold
the valve seated. This pressure is developed primarily on the right
hand or rear face of screw 48. The central portion of the ball
valve member 45 is not exposed to the coating material and has no
force acting against it tending to open the valve. A relatively
high initial force is required on the trigger 16 to lift ball valve
45 from its seat. As soon as coating material enters the space
between the ball and seat 42, the force tending to open the valve
is increased by the fluid force with the result that valve opens
rapidly. This eliminates any initial dribble of coating material
which might occur if the valve were held partially open or opened
slowly.
The high pressure hose line for coating material ends in a fitting
80 secured to adapter fitting 81 connected with the inner or rotary
member 82 of the swivel coupling (FIG. 7). Outer member 83 of the
swivel coupling is threaded into the filter housing 26 and is
seated against a spring 84. Inner member 82 turns on a bearing, 85,
preferably of low friction plastic, and is sealed with outer member
83 by an O-ring 86. A portion 87 of the bore of inner swivel
coupling member 82 has a tool receiving configuration, as a
hexagonal cross-section, so that the inner member may be held
securely while fitting 81 is attached thereto. Retainer nut 88
holds inner member 82 in place and has a bore similarly configured
for receiving a tool to tighten it in place.
The filter 90, which may be a sleeve of a wire mesh material, is
mounted on a base 92 held in place by spring 84 and having a
passage 92a through which the coating material flows into an
annular chamber 93 around the valve stem bushing 41. Ports 94
through the bushing provide for the flow of coating material into
bore 41a and passage 31.
With the high pressures under which the coating material is handled
in a hydrostatic apparatus, leakage is a particularly troublesome
problem. It is essential that the coating material be excluded from
the resistor passage, that leakage from the gun itself be avoided
and that solvent used in cleaning be kept from handle 15 and switch
68.
Bushing 41 is threaded into the gun body 23 and this joint is
sealed with an O-ring 96 (FIG. 3). An O-ring 97, located
immediately adjacent the ring 96, provides a seal between bushing
41 and bore 29 through gun body portion 22. A further sealing ring
99 is provided around valve stem bushing 41, rearwardly of the
paint inlet passage.
At the forward end of the barrel, valve housing 35 is sealed with
barrel extension 23b by a sealing ring 102. Any coating material
which escapes past this seal is trapped in an annular groove 103
from which it is drained through passage 104.
Nozzle 44 is seated against and seals with a resilient washer 105
received in a recess in the forward face of valve holder 35.
The interior of handle 15 is sealed by a ring 107 received in a
channel in the rear face of body member 22. O-ring 108 provides a
seal with the high voltage cable fitting 54, at the base of the
handle. O-ring 109 seals with valve actuator 51.
Closure 62, at the forward end of resistor passage 30a is sealed
with the walls of the passage by means of an O-ring 106.
The gun may readily be cleaned by removing retainer nut 36
releasing the valve housing and the nozzle housing which is carried
thereon.
If it is desired to change the nozzle, as to utilize a nozzle with
a different spray configuration, it is necessary merely to remove
nozzle cap 38, lift off nozzle housing 37 and replace it with a
housing carrying the desired nozzle.
A modified high voltage circuit in the nozzle portion of the gun is
illustrated in FIG. 8. Parts which have already been identified by
reference numeral are indicated by the same reference numeral and
will not be described in detail again. Sealing plug 62 has a
conductor 110 therethrough with a loop portion 110a in contact with
the face or terminal of resistor 58. The forward 110b of conductor
110 is coiled for resilience and contacts a body of conducting
cement filling recess 111 in the rear face of valve holder 35. A
wire 112 extends through the valve holder and has a coiled spring
portion 112a in recess 113 at the forward end of the holder. Nozzle
housing 114 has a conductive coating 115 over the rear surface
thereof which is contacted by the resilient end 112a of conductor
112. Coating 115 is applied after nozzle 44 is inserted in the
holder and makes a good electrical contact with the nozzle body.
Charging electrode 116 is press-fit in a hole in the nozzle housing
and has a portion 116a which extends along and in contact with the
edge of the nozzle. This construction eliminates difficulty
encountered with the construction of FIG. 4 where coating material
became lodged in the groove ahead of nozzle 44 and around the
looped portion 27a of electrode 27.
A further modified high voltage circuit is shown in FIG. 9. Again,
elements of the construction which have been described above and
identified by reference numeral are assigned the same numeral and
will not be described in detail again. Sealing plug 120 is of a
semi-conductive plastic material, as a plastic impregnated with
graphite particles. A central point 121 formed in the plug extends
into conductive cement filling the cavity 122 in the rear face of
valve housing 35. Conductor 123 extends forwardly through valve
housing 35 from cavity 122 to a recess in the forward surface in
which nozzle sealing washer 124 is seated. Nozzle washer 124 is of
a conductive resilient plastic material and interconnects the end
123a of conductor 123 with nozzle 44. Electrode 116 is press-fit in
the nozzle holder 114 and contacts the side of nozzle 44, as in
FIG. 8.
While I have shown and described a preferred embodiment of my
invention, it is to be understood that it is capable of many
modifications. Changes, therefore, in the construction and
arrangement may be made without departing from the spirit and scope
of my invention as disclosed in the appended claims.
* * * * *