US3737099A

US3737099A - Electrostatic spray coating apparatus

Info

Publication number: US3737099A
Application number: US00193960A
Authority: US
Inventors: P Shaffer
Original assignee: Binks Sames Corp
Current assignee: Binks Sames Corp
Priority date: 1971-10-29
Filing date: 1971-10-29
Publication date: 1973-06-05
Anticipated expiration: 1990-06-05
Also published as: CA965943A

Abstract

Electrostatic spray coating apparatus including means for mechanically atomizing coating materials and means for electrostatically charging and depositing the atomized material onto articles, characterized by the features, individually and collectively, of improved means including an improved charging electrode for the efficient and effective charging of the material, and enhanced overall construction for greater service life, more reliable and safe operation, and economy.

Description

United States Patent 1191 [111 3,737,099 Shaffer 51 June 5, 1973 541 ELECTROSTATIC SPRAY COATING 3,425,625 2/1969 Probst ..239/15 APPARATUS 3,667,674 6/1972 Parsons et al. .....239/ 15 [75] n ento Patr ck D shatte P ospect 3,635,400 1/1972 Nord et al. ..239/l5 Helghts I Primary Examiner-M. Henson Wood, Jr. [73] Assignee: Binks Manufacturing Company, Assistant Lfrqrninq-Michaelliiar 7 u q Franklin Park, 111. Attorney Lee J Gary, Thomas R. Juettner and [22] Filed: Oct 29, 1971 Charles F. Plgott, Jr., et al.

21 Appl. No.: 193,960 57 ABSTRACT Electrostatic spray coating apparatus including means [521 [1.8. CI. ..239/15 for mechanically atomizing coating materials and 1 Cl. means for elect ostaticany charging and depositing he Fleld of Search "239/15, 3 atomized material onto articles characterized the features, individually and collectively, of improved [56] References Cited means including an improved charging electrode for UNITED STATES P E I the efficient and effective charging of the material, and enhanced overall construction for greater service 3,344,992 10/1967 Norris ..239/l5 X life, more reliable and safe operation, and economy. 3,292,860 12/1966 Williams et a1 ..239/l5 8 Claims, 3 Drawing Figures M Z4 Z0 2 2.3 10 1m &z @z @w sm.w. 9- J@49 willmmmrmmmmrumumwa a W, f 4////////////////////////////////////i:5;/7; X .4i--"--s\ M, I'/ I "I I" I '4: Q 4.. 4F' /////////////////////A7/////////,;,FZ1 "s* 6 a j? 40 9.- g; I? 3'5 ELECTROSTATIC SPRAY COATING APPARATUS BACKGROUND OF THE INVENTION Manual and automatic spray guns for mechanical atomization and electrostatic deposition of coating materials such as paint, lacquer, varnish and the like are known from such previously issued U.S. Pats. Nos. as 2,805,642; 3,048,498; 3,169,882; 3,169,883; 3,251,551; 3,253,782; 3,268,171; 3,583,632; etc. In general, the material is atomized from a nozzle either by forcing the material through an appropriately shaped nozzle under adequate hydraulic pressure (hydraulic or airless atomization) or by impinging streams of air on a stream of the material (air'atomiz ation) as shown for example in U.S. Pat. No. 3,583,632 issued to Duane Krohn and me. Atomization may also be effected by centrifugal force and by electrostatic forces. As the material is atomized, an electrostatic charge is imparted to the coating material which causes the charged particles' of atomized material to be attracted to work pieces or articles which are purposely deposited on the work.

SUMMARY OF THE INVENTION A primary object of this invention is to provide improved means for electrostatically charging the coating material, especially to insure effective charging of each particle in a hydraulically atomized spray to enhance its attraction to the grounded work.

Another object is to provide optimum safety in use and operation of airless electrostatic spray guns.

A further object is to provide an improved airless spray gun of great reliability and serviceability.

Other objects and advantages will become apparent from the drawings and the following description, which are given for the purpose of acquainting those skilled in the art with the manner of making and using my invention, and especially with the best mode presently contemplated by me of carrying out the invention.

THE DRAWINGS FIG. 1 is a vertical longitudinal section of a manually operated, hydraulic atomizing, hand spray gun e'm- DESCRIPTION The hydraulic or airless hand gun of the invention is comprised of an electrically conductive handle portion 10, an insulating ,barrel portion 20, and a nozzle assembly 30 which is electrically insulating to the extent feasible in an airless gun.

The handle is of conventional configuration, the same being formed of metal or other electrically conductive material and including a hollow hand grip 11, a forwardly projecting main or body portion 12 to which the hand grip is bolted at 13, and a pivotally mounted trigger 14. The main or body portion 12 is provided forwardly of the trigger with a depending fluid or material inlet section 15, which may appropriately be equipped with a depending hose fitting l6 and a filter or strainer 17 for the supply of coating material to the gun. The inlet section is provided with a first longitudinal passage or port 18 for the coating material to be sprayed and the body portion 12 is provided with a second longitudinal passage or port 19 for reception of electrostatic charging components.

The barrel 20 is formed of insulating material capable of withstanding the high pressures normally employed in hydraulic or airless spraying, i.e., in the order of up to about 2,000 p.s.i. The barrel has a pair of

longitudinal bores

21 and 22 therein aligned respectively with and constituting continuations of the bores 18 and 19. The bores 19 and 22 are lined with a continuous sleeve 23 of insulating material, preferably material having both high physical strength and high dielectric strength. The sleeve receives therein, with close tolerance, a resistor 24 having conductive caps at its opposite ends. The purpose and function of the resistor are described in detail in U.S. Pat. No. 3,048,498, and also U.S. Pat. No. 3,169,883. The bore 22 is dead ended adjacent the forward end of the barrel 20, the sleeve 23 extends to the end of the bore and a compression spring 25 is confined between the end of the bore and the inner conductive end of the resistor. Rearwardly of the resistor, the sleeve 23 is adapted for reception of a conductive probe 26 provided on the end of a high voltage power supply cable 27 which is extended through the hollow hand grip 11 to the rearward end of the sleeve. Details of the probe are shown in U.S. Pat. No. 3,583,632.

A microswitch 28 is mounted within the hand grip 11 for actuation by the trigger 14 for controlling the supply of high voltage to the gun. Low voltage control leads 29 extend from the switch to the cable 27 and extend back through the cable to the high voltage source for performing a control function at the source, whereby high voltage is supplied to the gun only when the gun trigger is depressed.

The nozzle assembly 30 comprises a carbide or other wear-resistant spray tip 31 of conventional construction, an electrically insulating plastic holder 32 for the tip and a cap or collar 33 of electrically insulating plastic material for detachably mounting the holder on the forward end of the barrel 20 with the tip 31 aligned with the material bore or passage 21'. The cap 33 is con' ventional, having screw threads therein for detachable coupling to a complementary external thread provided at the forward end of the barrel 20. If desired, a preorifice insert 34 may be used with the tip 31 as described in U.S. Pat. No. 3,000,576; and the tip is sealed to the barrel 20 by washers 34a.

Mounted within and projecting through the tip holder 32 is a charging needle 35 which extends from the rear face of the holder downwardly and forwardly into contact with the spray tip 31 and then forwardly from the holder and tip into a position proximate to the spray pattern of atomized particles emanating from the spray tip when the gun is in operation. The particular relation of the charging needle to the spray orifice and spray pattern is described in detail in U.S. Pat. No. 3,169,883.

The charging needle 35 contacts the spray tip 31 in the illustrated embodiment because the tip is formed of tungsten carbide which is electrically conductive. If electrically insulating materials are developed from which airless spray tips can be made, it will not be necessary for the needle to contact the tip. However, when the tip is conductive, contacting the needle with the tip provides a safety feature in that it eliminates a gap therebetween within which an extraneous and undesirable electrical charge could develop, especially when spraying conductive coating materials.

To conduct the electrostatic charging current from the power cable 27 and safety resistor 24 to the needle 35, a conductive screw 36 is extended through the barrel from the forward face of the barrel into contacting engagement with the resistor biasing spring 25.

Heretofore, in spray guns of the general character, it has been conventional to contact the needle 35 directly with the screw or conductor 36, with the consequent disadvantage that the spray tip and holder could have only a single rotational disposition relative to the gun body or barrel. When spraying with a tip producing a fan-shaped spray pattern, the fan pattern could appear only in the same vertical plane as the gun barrel and hand grip, which imposed limitations on the operator in use of the gun pursuant to the wide variety of techniques conventionally employed in the spray painting industry. Also, in assembly of tips and holders, the tip always had to have a precise rotational disposition relative to the needle.

These disadvantages of the prior art are overcome pursuant to this invention by the provision of an electrically conductive washer 37 between the holder 32 and the forward face of the barrel 20, whereby the needle can contact the washer at any rotationally offset position relative to the screw 36 and still be in electrical contact with said screw. Thus, the spray tip and holder can be set at any desired rotational disposition relative to the gun body or barrel without diminution or loss of electrostatic charging power.

The novel washer 37 is shown in FIG. 3 in its preferred form as being a unitary annular body comprised of an outer annular band or ring 37a of electrically conductive (preferably silver impregnated) polytetraflouroethylene and an inner annular band or ring 37b of regular or insulating polytetraflouroethylene. By forming the washer of the two bands or rings, the capacitive effect thereof in the circuit is greatly diminished. By forming the same from polytetraflouroethylene, the washer also provides a supplemental seal between the nozzle and the gun body.

For controlling the flow of coating material to the spray nozzle, the barrel 20 is provided at the forward end of the bore or passage 21 with a control valve 40 comprising a valve seat member 41 and a valve ball 42. The valve seat comprises a tubular stainless steel body or carrier 43 inserted in a reduced section at the forward end of the bore 21 and a tungsten carbide seat insert 44 provided'with a conical seating surface and inserted in a counter-bore in the rearward end of the carrier 43. The ball 42, which engages the conical surface of the seat insert 44 to close off the port through the seat and the carrier, is mounted on the forward end of an extension 45 which is screw threaded into the forward end of an elongate valve stem or rod 46 so as to be detachable therefrom to accommodate replacement of the ball.

The valve stem or rod 46 is formed of insulating material and extends rearwardly from the valve 40 to a sealing gland 47 mounted in a counter-bore in the rearward end of the bore or passage 21. The rod 46 is there joined with a metallic valve stem wire 48 which extends through another packing assembly or gland 49 mounted within the inlet section 15 and including an adjusting nut or screw 50 threaded into the rearward end of the passage 18. Rearwardly of the gland 49, the wire is joined to a short metallic extension 51 which is detachably connected to a metallic plunger 52 that is reciprocably mounted within a bore in the rearward part of the body portion 12 of the gun. At its rearward end, the plunger 52 has a reduced extension adapted to actuate the blade of the control switch 28.

A compression spring 53 disposed between the nut or screw and a shoulder on the extension 51 normally biases the valve stem components forwardly so as to seat the valve ball 42 on its seat 44, thereby to close the material passage 18-21, and to cause the switch 28 to be in open circuit position.

Intermediate its ends, the valve stem plunger 52 is provided with an annular depression or groove 54 adapted for reception therein of a transverse block or slide 55 carried by the trigger l4 and extending immediately below the plunger. The block 55 has a cutout 56 inits upper surface medially of its ends and the block is slidably mounted on the trigger for transverse movement to selectively move the cutout 56 into and out of alignment with the plunger 52. When the cutout is aligned with the plunger, as shown in FIG. 1, the block or slide will not be engaged in the groove in the plunger and thus actuation of the trigger will not produce any .movement of the plunger or the remainder of the valve stem. This provides a safety feature for protection of the operator when he is changing nozzles or otherwise is not actively engaged in a spray painting operation.

When it is desired to effect spray painting, the operator merely shifts the slide 55 sideways to move the slide into engagement in the groove 54. Then, when the trigger 14 is depressed or moved rearwardly, the plunger 52 and the remainder of the valve stem are moved rearwardly to open the valve 40 and to close the control switch 28. Thereupon, coating material is fed at high pressure throughthe inlet fitting 16, the filter 17 and the passages 18 and 21, past the valve 40 and through the spray tip 31 and atomized into a mist of finely divided particles. As the finely divided particles emanate from the spray tip 31, a high voltage electrostatic charge is efficiently and effectively imparted to them by the tip and the needle 35, whereby the particles will be attracted to and deposited on a grounded article to be coated.

As will be appreciated, the electrostatic coating material charging components of this gun consist of the tip 31 and the charging needle 35. If desired, the needle 35 could be omitted so long as the tip 31 is electrically conductive and has good electrical connection with the power supply terminal 36. Alternatively, if the tip were made non-conductive and/or not used with conductive paint, the needle alone could perform the charging function. However, in the present state of the art, 1 prefer to employ the combination of the two. The two members are directly coupled to the high tension conductor 27 and are otherwise widely insulated from the remaining metal components of the gun. Paint entering and passing through the gun contacts the tip 31 and is atomized in the presence of the charging needle 35, whereby essentially all of the discrete particles of the spray are efficiently and effectively charged to high electrostatic potential for efficient deposition on a grounded article of work.

At the same time, the operator is afforded optimum safety by virtue of electrical grounding of all components with which he may come in contact. Specifically,

the gun handle and body portion 12, and the grounding shield on the power supply cable 27 (which is connected to the hand grip 11) are commonly grounded. Also, the material to be sprayed is grounded at the main body 12. The gun operator is thus grounded through the gun handle where he does not and cannot become a capacitative influence in the electrostatic system.

In this manner, we have provided an extremely useful and highly efficient airless electrostatic hand spray gun of great safety, long service life, light weight, convenient handling and aesthetically pleasing design.

The same and/or comparable features can also be embodied in automatic spray guns. For example, the trigger and hand grip could be replaced by an automatic operating mechanism for the valvestem and control switch in much the same manner as disclosed in U.S. Pat. No. 3,583,632, and as will be apparent to those reasonably skilled in the art.

Thus, the objects and advantages of the invention have been shown to be achieved in a convenient, economical and practical manner.

While I have shown and described what I regard to be the preferred embodiment of my invention, it is to be appreciated that various changes, rearrangements and modifications may be made therein without departing from the scope of the invention, as defined by the appended claims.

I claim:

1. In electrostatic spray apparatus having a body including a material passage terminating in an outlet orifice at an end face of the body, nozzle means on said end face of said body communicating with said orifice, electrically conductive means in said nozzle means for imparting an electrostatic charge to the material emanating from said nozzle means, and means for conducting an electrostatic charge to the electrically conductive means in said nozzle means, the improvement comprising conducting means having a terminal spaced from said outlet orifice at said end face of said body, electrically conductive means in said nozzle means having a terminal at the end face of said nozzle means juxtaposed to said body end face, and means disposed between said end faces having an electrically conductive area spanning said terminals for electrically connecting said terminals to one another despite relative offset of said terminals, the means disposed between said end faces comprising a washer having a unitary body formed of concentric rings of conductive and nonconductive material.

2. In electrostatic spray apparatus having a body including a material passage terminating in an outlet orifice at an end face of the body, nozzle means on said end face of said body communicating with said orifice, electrically conductive means in said nozzle means for imparting an electrostatic charge to the material emanating from said nozzle means, and means for conducting an electrostatic charge to the electrically conductive means in said nozzle means, the improvement comprising conducting means having a terminal spaced from said outlet orifice at said end face of said body, electrically conductive means in said nozzle means having a terminal at the end face of said nozzle means juxtaposed to said body end face and a needle projecting from said nozzle terminal through said nozzle means to a position forwardly thereof and proximate to the material emanating from the nozzle means, and means disposed between said end faces having an electrically conductive area spanning said terminals for electrically connecting said terminals to one another despite relative offset of said terminals.

3. In the apparatus of claim 2, said nozzle means including an electrically conductive spray tip in electrically conductive contact with said needle.

4. In electrostatic spray apparatus having an electrically insulating body including a material passage terminating in an outlet orifice at an end face of the body, nozzle means rotatably mounted on said end face of said body concentric to and in communication with said orifice, electrically conductive means in said nozzle means for imparting an electrostatic charge to the material emanating from said nozzle means, and means for conducting an electrostatic charge tothe electrically conductive means in said nozzle means, the improvement comprising conducting means having a terminal spaced radially from said outlet orifice at said end face of said body, electrically conductive means in said nozzle means comprising a terminal at the end face of said nozzle means juxtaposed to said body end face and disposed at approximately the same radial spacing from said outlet orifice and a needle projecting from said terminal on said nozzle means through said nozzle means to a position forwardly thereof and proximate to the material emanating from said nozzle means, and a washer disposed between said end faces having an annular electrically conductive area encircling said orifree at the same radial spacing from said orifice as said terminals for electrically connecting said terminals to one another irrespective of the rotational offset of said terminals.

5. In the apparatus of claim 4, said nozzle means including an electrically conductive spray tip in electrically conductive contact with said needle.

6. Electrostatic spray apparatus comprising an electrically conductive operator section, an elongate electrically insulating barrel projecting forwardly from said section and having a material passage therein terminating in an outlet orifice, a nozzle assembly detachably mounted on the forward end of the barrel in communication with said orifice, said nozzle assembly being in the main electrically insulating and including therein electrically conductive means for imparting an electrostatic charge to the material emanating from said nozzle assembly, means for carrying a high electrostatic charge to said electrically conductive means including a conductor receiving passage extending through said operator section and said barrel generally parallel to said passage and including means for grounding said operator section, a valve in said passage at said orifice for opening and closing said orifice, a valve stem extending rearwardly through said passage from said valve to said operator section, said valve stem being electrically insulating between said valve and said operator section and being electrically conductive at said operator section, a control switch in said operator section connected with said electrostatic charge carrying means and having an actuator in the path of movement of said valve stem, and means for moving said valve stem rearwardly to open said valve and close said switch and for moving said valve stem forwardly to close said valve and open said switch.

7. Apparatus as set forth in claim 6, said means for moving said valve stem comprising a trigger and a bar slidably mounted on said trigger having means for selective engagement with and disengagement from said valve stem, the latter means when disengaged from the valve stem preventing actuation of both said valve and said switch.

8. Apparatus as set forth in claim 6, said valve comprising a valve ball detachably mounted on said valve

Claims

1. In electrostatic spray apparatus having a body including a material passage terminating in an outlet orifice at an end face of the body, nozzle means on said end face of said body communicating with said orifice, electrically conductive means in said nozzle means for imparting an electrostatic charge to the material emanating from said nozzle means, and means for conducting an electrostatic charge to the electrically conductive means in said nozzle means, the improvement comprising conducting means having a terminal spaced from said outlet orifice at said end face of said body, electrically conductive means in said nozzle means having a terminal at the end face of said nozzle means juxtaposed to said body end face, and means disposed between said end faces having an electrically conductive area spanning said terminals for electrically connecting said terminals to one another despite relative offset of said terminals, the means disposed between said end faces comprising a washer having a unitary body formed of concentric rings of conductive and non-conductive material.

4. In electrostatic spray apparatus having an electrically insulating body including a material passage terminating in an outlet orifice at an end face of the body, nozzle means rotatably mounted on said end face of said body concentric to and in communication with said orifice, electrically conductive means in said nozzle means for imparting an electrostatic charge to the material emanating from said nozzle means, and means for conducting an electrostatic charge to the electrically conductive means in said nozzle means, the improvement comprising conducting means having a terminal spaced radially from said outlet orifice at said end face of said body, electrically conductive means in said nozzle means comprising a terminal at the end face of said nozzle means juxtaposed to said body end face and disposed at approximately the same radial spacing from said outlet orifice and a needle projecting from said terminal on said nozzle means through said nozzle means to a position forwardly thereof and proximate to the material emanating from said nozzle means, and a washer disposed between said end faces having an annular electrically conductive area encircling said orifice at the same radial spacing from said orifice as said terminals for electrically connecting said terminals to one another irrespective of the rotational offset of said terminals.

8. Apparatus as set forth in claim 6, said valve comprising a valve ball detachably mounted on said valve stem and a valve seat removably inserted in said outlet orifice, said seat comprising a tubular carrier and a cylindrical insert of wear resistant material on which the ball seats.