US3459374A

US3459374A - Electrostatic coating apparatus

Info

Publication number: US3459374A
Application number: US470144A
Authority: US
Inventors: Richard O Probst
Original assignee: Ransburg Corp
Current assignee: Ransburg Corp
Priority date: 1965-07-07
Filing date: 1965-07-07
Publication date: 1969-08-05
Anticipated expiration: 1986-08-05
Also published as: DE1577913B2; GB1159364A; DE1577913A1; GB1159363A

Description

Aug. 5, 1969 Filed July 7, 1965 ll u I R. 0,. PROBST ELECTROSTATIC COATING APPARATUS 2 Sheets-Sheet 1 Aug. 5, 1969 R. o. PRoBsT 3,459,374

ELECTROSTATIC COATING APPARATUS Filed July 7, 1965 2 Sheets-Sheet. 2

Unted States Patent O 3,459,374 ELECTROSTATIC COATlN-G APPARATUS Richard 0. Probst, Indianapolis, Ind., assignor to Ransburg Electro-Coating Corp., a corporation of Indiana Filed July 7, 1965, Ser. No. 470,144 Int. Cl. Bb 5/02 US. Cl. 239- 8 Claims ABSTRACT 0F THE DISCLOSURE A hydrostatic, electrostatic paint spray hand gun with an elongated barrel and a Valve at the front thereof. A liner in a coating material passage through the barrel provides the strength necessary to withstand the high hydrostatic pressures used and permits inexpensive fabrication of the barrel. A Valve actuator extends rearwardly through the coating material passage and a sealing gland to a trigger. The valve seat, actuator and barrel are demountable for cleaning, and the gland body is held in the barrel by the handle, eliminating threaded joints which require sealing for the high pressure coating material. A sleeve of plastic insulating material surrounds the end of the high voltage cable and the voltage dropping resistor in a second passage through the barrel and handle. The trigger is connected with the valve actuator by a latch which is disengageable when the gun is not 1n use.

rlhis invention relates to a spray coating apparatus and more particularly to an apparatus which utilizes hydrostatic atomization of a liquid coating material and electrostatic charging and deposition of the spray particles on an article to be coated.

In co-pending Probst application Ser. No. 272,615 filed Apr. 12, 1963, and assigned to the assignee of this invention, there is shown and claimed a commercial ernbodiment of an apparatus utilizing hydrostatic atomization of coating material and electrostatic charging and deposition of coating material particles. The apparatus shown in such application operates satisfactorily, has excellent efficiency in the use of coating material and deposits a high quality coating on the articles. Certain structural features of the apparatus, however, contribute to a high manufacturing cost and to servicing problems, which make it impractical to perform certain servicing procedures in the field. The present application is concerned with modifications of the structure of the earlier application which obviate these problems.

The combination of hydrostatic atomization and electrostatic charging and deposition of the coating material impose certain physical and electrical requirements on the apparatus which contribute to the problems of cost and servicing diiiiculty. The electric field for electrostatic charging and deposition of coating material particles requires a voltage of several thousand volts, preferably at least of the order of 40,000 to 50,000 volts, as about 60,000 volts. In a hand held electrostatic spray apparatus, a conductive, grounded handle is utilized, which must be insulated from the high voltage circuit. A charging electrode, physically located adjacent the coating material discharge orifice, must have an appropriate spacing from the grounded handle to establish a voltage gradient in the vicinity of the area of spray formation, sufficient to charge the particles adequately for eiiicient transfer to the articles being coated. Furthermore, the high voltage circuit includes a series resistance of several megohms. One or more resistors which provide the series resistance are preferably mounted Within the barrel of the gun, as close to the charging electrode as possible and protected from physical damage. The high voltage resistors have a minimum length for the resistance required and the voltages to which they are subjected. The physical size of the resistors and the electrode-to-handle spacing are limiting factors in determining the barrel length.

In a hand held device, as the sray gun of the previous and the present applications, balance is an important factor. A production worker cannot perform efficiently if he is required to work with a poorly balanced tool.

In the interests of balance, it is preferable for the high voltage cable and coating material conduits, both of which are exible to enter the gun at the rear, as through or adjacent the grip element. On the other hand, the valve is a hydrostatic atomization spray device should be as close to the nozzle as possible so that control of the coating material is effected with only a small amount of coating material conduit enters the gun at the rear and the valve is at the front, an elongated valve actuator extends rearwardly through the coating material passage to a trigger mechanism at the rear. A gland structure carries a seal surrounding the valve actuator to prevent leakage of thhe coating material. The valve seat, the valve actuator and the gland structure should be demountable so that the parts may be cleaned, checked, and replaced with a minimum of effort.

In the apparatus disclosed in the prior application, the entire barrel structure is machined from a homogeneous block of plastic material. It was found impractical to mold or cast the barrel shape as such castings of suitable insulating material have voids or areas of nonhomogeneity which might fail under the high pressures of the coating material. Furthermore, in the gun of the prior application, the bland body is threaded into the rear end of the barrel and received in a passage in the metallic rear body portion. It is necessary to remove the gland body from the body in order to open the barrel for cleaning. The joint between the gland housing and the body is sealed with O-rings which require precise adjustment to withstand the high pressures of the coating material. It is impractical to perform the assembly in the field. Accordingly, when it was necessary to replace the valve or to clean the valve actuator, the entire apparatus had to be sent to a service center. This is obviously undesirable.

One object of the present invention is the provision of a gun in which the requirement for physical strength of the barrel is reduced. This permits at least rough casting of the barrel of a plastic insulating material, greatly reducing its cost.

Another object of the invention is to simplify the mounting of the valve actuator gland body so the gun may be disassembled to service the valve actuator without removing the gland body from the grip.

One feature of the invention is that the coating material passage of the barrel is provided with a tubular liner having one end forming a coating material inlet for connection with the source of coating material under pressure and the other end connected with a discharge nozzle. Another feature is that the barrel liner is of a homogeneous plastic material. Yet a further feature is that the barrel liner is a resin impregnated fibrous material.

The apparatus includes a valve in the coating material passage and has a valve actuator extending rearwardly therefrom through the barrel passage. Another feature of the invention is that a sealing gland body for the valve actuator has a rearwardly facing surface which bears against a forwardly facing surface of the handle secured to the rear of the barrel. The connection between the barrel and the handle holds these two parts together supporting the gland body. The forward portion of the gland body ex` tends into a recess in the rear surface of the barrel and has a sliding fit therewith. The barrel itself may be removed from the handle and gland body without removing the gland body from the handle.

The high voltage circuit includes a resistor in a passage through the barrel. A further feature is that a plug of conductive ceramic material is sealed with the barrel at the front of the passage and forms a portion of the high voltage circuit between the resistor and the spray charging electrode.

Still another feature is that the valve actuator is connected with a trigger through a disengageable latch for movement of the trigger independent of the valve.

Further features and advantages of the invention will readily be apparent from the following specification and from the drawings in which:

FIGURE 1 is an elevation of a hydrostatic, electrostatic hand gun embodying the invention;

FIGURE 2 is a fragmentary longitudinal section through the forward portion of the gun;

FIGURE 3 is a fragmentary longitudinal section through the connection between the trigger and the valve actuator;

FIGURE 4 is a broken transverse section taken generally along line 4 4 of FIGURE 3; and

FIGURE 5 is an enlarged fragmentary section, similar to a portion of FIGURE 4, showing the trigger latch engaged with the valve actuator.

The hydrostatic gun illustrated in the drawings has an elongated body which extends forwardly from a grounded conductive handle or pistol grip 11. The forward or barrel portion 12 of the body is molded or cast of a plastic insulating material, as Delrin an acetal resin manufactured by E. I. du Pont de Nemours & Co., and has a central part with a generally oval cross-section, terminating in a cylindrical section 12a at the front of the barrel and a circular flange 12b at the rear thereof. Coating material is discharged from an orifice at the front of the barrel and the particles are charged by a field extending from electrode 13. The rear portion 15 of the body is of a conductive material, as aluminum, and has the conductive handle 11 secured to the rear thereof. A trigger 16 is pivoted to body portion 15 and, as will appear, may be actuated to operate a valve controlling the discharge of coating material. The trigger also operates a switch which controls the high votlage so that the gun is charged only when the coating material valve is open.

A cylindrical boss 17 extends downwardly from the rear body portion immediately adjacent the rear of the barrel 12 and has a coating material supply conduit 18 connected therewith through a swivel fitting 19. The boss 17 houses a suitable filter (not shown) for the coating material. Hose 18 is connected with a source of coating material under a high pressure, for hydrostatic atomization of the coating material upon discharge from a small orifice. The pressure of the coating material may Vary, depending on the physical characteristics, as viscosity, of the coating material and the size and shape of the discharge orifice, and the desired rate of delivery of the coating material. With present coating materials, pressures may range from 400 to 3000 pounds per square inch; and in most applications, the pressure is preferably of the order of 800 to 1000 pounds per square inch.

A high voltage cable 20 enters the gun through the base of grip 11 and, as will appear, is connected with charging electrode 13 which extends forwardly from the front of barrel 12. The high voltage cable is connected with a suitable source of high votlage, to establish a voltage gradient that will impart to the atomized coating material particles an electrostatic charge and establish a field from the hand gun to the grounded article being coated, resulting in the eicient transfer of coating material to the article. In a typical installation, the average field gradient is of the order of at least 3 kilovolts and preferably of the order of 5 to 10 kilovolts per inch. A total voltage from the power supply should be at least 40 to 50 kilovolts and preferably is about 60 kilovolts. Where the discharge apparatus is supported mechanically rather than by hand, a higher voltage, i.e., kilovolts, may be used.

Turning now to FIGURE 2 of the drawings, it will be seen that the barrel portion 12 of the body 10 has a pair of vertically spaced

passages

21, 22 extending therethrough and aligned with

similar passages

23, 24, respectively, extending through conductive body portion 15.

At the forward end of barrel portion 12, cylindrical forward end 12a is formed concentrically with lower passage 22. The upper passage 21 has an offset section 21a. A plastic valve housing 25 is secured to the front end of barrel 12 by a plastic collar 26. A nozzle holder 27 is mounted on the valve housing 25 by a plastic collar 28.

The

upper passages

23, 21, 21a through rear portion 15 of the body 10 and through the barrel 12 carry the high voltage circuit. High voltage cable 20 extends through the conductive handle and rear body portion and terminates in a conductive button 31 which engages the rear terminal of a high voltage series dropping resistor 32. A grounded conductive sheath (not shown) on cable 20 is connected with conductive grip 11 and effectively grounds it and the operator who holds it. A sleeve 33 of plastic insulating material, as polyethylene, surrounds resistor 32 and the end of the high voltage cable. The thickness and length of the polyethylene tube is such that the high voltage cannot arc over to the conductive elements of the gun, either directly through the tube or along the inner surface to the rear thereof. The forward end of resistor engages a connector spring 35 in offset passage portion 21a. A second series dropping resistor 36 extends forwardly from the spring. A plug 37 of conductive ceramic material is sealed with auxiliary passage 21a by O-ring 38, blocking coating material from the resistor passage.

A suitable material for plug 37 is a ceramic sold by American Lava Corporation under the trademark Alsimag No. 193. It has sucient conductivity to complete the high voltage circuit, without adding appreciably to the effective electrical capacity.

A conductive button 40 in the rear face of valve holder 25 contacts plug 37 and is connected through a wire 41 in the valve holder and a conductive ink coating on the rear surface of nozzle holder 27 with the charging electrode 13.

Extending through the lower passage 22 of plastic barrel 12 is a high strength tubular liner 44. Coating material under high pressure flows through filter housing 17 and upwardly through port 45 into an annular chamber 46 and the interior bore 47 of gland body 48. The gland body is positioned in passage 24 of the conductive body 15 and is sealed therewith by O-rings 50, 51. The end of gland body 48 projects forwardly from body 15 into a recess 53 formed in the rear face of plastic barrel 12 and surrounds the rear end of liner 44, to which it is sealed by O-ring 54. The forward end of liner 44 extends into a recess 55 on the rear surface of valve holder 25 and is sealed therewith by O-ring 56. A valve seat 57 is carried by the valve holder and cooperates with ball valve 58 to control the flow of coating material through the gun. The ball valve is supported in a carrier 59 at the forward end of a valve stem or actuator 62 which extends rearwardly through the coating material liner tube and has a wire rod portion 63 extending outwardly through sealing members 64 and packing nut 64a for connection with trigger 16.

The nozzle holder 27 mounted on the forward end of the valve holder has a nozzle 27a with a small, preferably elongated, orifice therein through which the coating material is discharged in an expanding film-like spray. Further details of the orifice, spray characteristics and electrode may be found in Iuvinall Patent 3,169,883 issued Feb. 16, 1965.

Barrel 12 is preferably molded or cast of a suitable plastic material, as Delrin. It is common for this material to mold with nonhomogeneous sections, as voids or the like, which would fail under the high pressure of the coating material, or might break down if subjected to the high voltage of the charging circuit. It is possible to use this type of barrel construction, which may be inexpensively manufactured, as the coating material passage 22 is lined with tube 44 having sufficient physical strength to hold the coating material pressure. This tube may be machined from a homogeneous Delrin rod, or may be manufactured from an even stronger material as epoxy bonded fiber glass. The high voltage circuit is contained within polyethylene tube 33, preventing arcing. Thus, the plastic barrel 12 serves primarily as a cover and mounting for the high voltage and coating material passages and need not have sucient physical strength to contain the coating material pressure, or dielectric strength to prevent high Voltage arcing. The manufacturing cost of the barrel is greatly reduced by eliminating the need for machining thevarious irregular surfaces from a solid block.

In the prior model of the gun, the gland body is threaded into the rear of the barrel. This requires that when the barrel is removed from the rear portion of the gun body, the gland be removed also. The O-ring seals between the gland and the rear portion of the body are extremely critical and require factory-trained personnel for servicing. This makes it difficult to remove the barrel for cleaning the coating material passage or servicing the valve actuator in the field. In the present construction, the gland body has a sliding fit into recess 53 at the rear face of body 12. The gland body 48 has a shoulder 65 which faces rearwardly and engages a forwardly facing surface 66 of rear body portion 15, surrounding passage 24. As the barrel is secured directly to the rear body, the gland body is held in posiiton without further mechanical interconnection. With this construction, rbarrel 12 may be slipped forwardly off gland body 48 without disturbing the positioning of the gland body in the rear body portion 15. The coating material passage liner 44 can easily be removed for cleaning the passage or the valve stem or to replace the tube should it become damaged or contaminated fith hardened or conducting paint. Replacement of the tube is, of course, much less expensive than replacing the entire barrel.

When the operator is not handling the gun, it is desirable that accidental opening of the valve and energization of the high voltage circuit be prevented. This is accomplished by providing a disengageable connection between the trigger and the valve actuator. In FIGURE 3, it is seen that the wire rod actuator portion 6-3 extends outwardly from packing nut 64a and is connected with an extension rod 68. The rear portion 69 of rod 68 projects into handle 11 where it actuates high Voltage control switch 70.

Trigger 16 includes a pair of spaced

side wall portions

71 and 72 which extend generally parallel with the longitudinal axis of the gun on either side of actuator extension 68 and are connected with body portion 15 by screws 73, for pivotal movement of the trigger parallel with the longitudinal axis of the gun. A latch plate 75 is slidably mounted between the

trigger wall portions

71 and 72 for movement at right angles to the longitudinal plane of the gun body. Latch plate 75 has one portion 76 which has a configuration matching the outer surface of valve actuator extension 68 and which when aligned with the actuator extension as shown in FIGURE 4, is spaced from it. In this position of latch plate 75, the trigger is disengaged from the valve actuator and movement of the trigger has no effect on the valve. If the latch plate is shifted to the right, as shown in FIGURE 5, portion 77 is located in a slot 78 in the undersurface of actuator extension 68. Operation of the trigger moves the latch plate into engagement with the rod extension, opening the valve and energizing the high voltage circuit. When the gun is not in use, latch plate 75 is shifted to the left, as shown in FIGURE 4, disconnecting the trigger from the valve. A

pin 79 mounted on trigger wall 71 extends into a slot 80 in the latch plate, limiting its movement.

I claim:

1. Apparatus for hydrostatic atomization and electrostatic deposition of coating material on a surface to lbe coated, comprising: a barrel of lmolded plastic material subject to weakening voids and nonhomogeneous sections, said 'barrel having a pair of passages therethrough; a conductive handle connected with the rear of said barrel and having a pair of passages therein forming continuations of the passages of the barrel; a tubular liner extending through one of said passages in the barrel and in contact with the barrel throughout the length thereof, the end of the liner extending from the rear of said barrel toward the handle, forming a coating material inlet; high potential circuit means in the other of said barrel and handle passages; a sleeve of plastic insulating material surrounding the circuit means within said other passage, extending through the lbarrel and into the handle; a discharge nozzle connected with the other end of said liner and through which coating material is discharged to form a spray of particles for deposition on an article to be coated; and a conductive charging electrode connected with said circuit means and operably associated With the discharge from said orifice for electrostatically charging the atomized particles of coating material discharged therefrom.

2. Apparatus of the character described for hydrostatic atomization of coating material, comprising: an elongated barrel of a molded plastic material having a passage extending therethrough; a tubular liner in said passage having one end forming a coating material inlet a discharge nozzle connected with the other en-d of said tubular liner and through which coating material is discharged as a spray of particles for deposition on an article to be coated; and a valve in said passage and including a valve seat adjacent the other end of said tubular liner ahead of said nozzle, and a valve member operably associated with said seat and carried by a valve actuator which extends rearwardly through said liner said other end of the liner projecting outwardly beyond the forward end of said barrel and said valve seat `being mounted on a valve seat carrier with a rear face having a recess slidably received over the projecting end of said liner.

3. Apparatus for hydrostatic atomization and electrostatic deposition of coating material on a surface to be coated, comprising: a barrel of insulating material, having a pair of passages therethrough; a conductive body connected with the rear of said barrel and having a pair of passages therein forming continuations of the passages of the barrel; a tubular liner extending through one of said barrel passages, the end of the liner at the rear of said barrel forming a coating material inlet; high potential circuit means in the other of said passages of said barrel and the body passage associated therewith; a discharge nozzle connected with the other end of said liner and through which coating material is discharged to fonm a spray of particles for deposition on the surface to be coated; a conductive charging electrode connected with said circuit means and operably associated with the discharge from said orice for electrostatically charging the atomized particles of coating material discharged therefrom; a 'valve in said coating material passage and including a valve seat adjacent the forward end of said tubular liner, ahead of said nozzle, and a valve member operably associated with said seat and carried lby a valve actuator which extends rearwardly through said passage and a sealing gland body for said valve actuator, said body extending into the rear of the coating material passage in said 'barrel and having a rearwardly facing surface which bears against a forwardly facing surface of said conductive body, said valve actuator extending outwardly from the rear of said barrel, through said gland body.

4. The coating apparatus of claim 3 in which the rear end of said barrel has a recess therein and said gland body has a sliding t within said recess.

5. The coating apparatus of claim 3 wherein the forward end of said gland body surrounds the rear end of said liner.

6. The coating apparatus of claim 5 wherein an O-ring seals the joint between said liner and gland tbody.

7. Apparatus for hydrostatic atomzation and electrostatic deposition of coating material on a surface to be coated, comprising: a barrel of molded plastic material subject to weakening voids and nonhomogeneous sections, said barrel having a pair of passages therethrough; a conductive handle connected with the rear of said barrel and having a pair of passages therein forming continuations of the passages of the barrel; a tubular liner extending through one of said passages in the barrel, the end of the liner at the rear of said barrel forming a coating material inlet; high potential circuit tmeans in the other of said barrel passages; a sleeve of plastic insulating material surrounding the circuit means within said other passage; a discharge nozzle connected with the other end of said liner and through which coating material is discharged to form a spray of particles for deposition on an article to be coated; a conductive charging electrode connected with said circuit means and operably associated with the discharge from said orifice for electrostatically charging the atomized particles of coating material discharged therefrom; a valve in said passage and including a valve seat adjacent the other end of said tubular liner ahead of said nozzle, and a valve member operably associated with said seat and carried by a valve actuator which extends rearwardly through said liner; and a sealing gland body for said valve actuator, said body extending into the rear of the passage in said barrel and having a rearwardly facing surface which bears against a forwardly facing surface of said handle, said valve actuator extending outwardly from the rear of said barrel, through said gland body.

8. Apparatus for hydrostatic atomization and electrostatic deposition of coating material on a surface to be coated, comprising: a barrel of insulating material, having a pair of passages therethrough; a conductive body connected with the rear of said barrel and having a pair of passages therein forming continuations of the passages of the barrel; means at the rear of said barrel connected with one of said barrel passages, forming a coating material inlet; high potential circuit means in the other of said passages of said barrel and the body passage associated therewith; a discharge nozzle connected with the other end of said one barrel passage and through which coating Imaterial is discharged to form a spray of particles for deposition on the surface to be coated; a conductive charging electrode connected with said circuit means and operably associated with the discharge from said orice for electrostatically charging the atomized particles of coating material discharged therefrom; a valve in said coating material passage and including a valve seat adjacent the forward end thereof, ahead of said nozzle, and a Valve member operably associated with said seat and carried by a valve actuator which extends rearwardly through said coating material passage; and a sealing gland body for said valve actuator, said gland body extending into the rear of said coating material passage in said barrel and having a rearwardly facing surface which bears against a forwardly facing surface of said conductive tbody, said valve actuator extending outwardly from the rear of said barrel, through said gland body.

References Cited UNITED STATES PATENTS 1,800,451 4/1931 Jenkins 239-527 2,926,106 2/1960 Gauthier 239-3 X 2,989,241 6/1961 Badger 239-15 3,048,498 8/1962 Juvinall et al. 239-3 X 3,169,882 2/1965 Juvinall et al 239-15 X 3,169,883 2/1965 Juvinall 239-15 X 3,253,782 5/1966 Fischer et al 239-499 X EVERETT W. KIRBY, Primary Examiner U.S. Cl. X.R. 239-3 UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No` 3,459, 374 August 5 1969 Richard O. Probst It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2 line l2, "flexible, should read flexible line 14, "is" should read in line 17 after "material" insert between the valve and the nozzle. Where the coating material n; line 22 "thhe" should read the line 33 "bland" should read gland Column 4 lines 30 and 3l after "resistor" insert 32 Column 5 line 41 "fith" should read with Signed and sealed this 15th day of September 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer WILLIAM E. SCHUYLER, JR.

Commissioner of Patents