US3539103A - Electrostatic spray gun - Google Patents

Description

I United States Patent [72] Inventor James C. Marsh [56] References Cited Toledo, Ohio UNITED STATES PATENTS [2U P g g'i 2,350,367 6/1944 Peters et a1. 174/47X [221 PM 3,169,882 2/1965 .luvinall et al. 239 15x [45] Patented Nov. 10,1970

3,233,831 2/1966 Fraser 239/15 [731 By 3 234 317 2/1966 Henderson 174/41x Champion Spark Plug Company TM 0M0 3,265,856 8/1966 Cecil 174/47X jmmnuon Delaware. 3,324,225 6/1967 Throstrup 174/47 Primary Examiner-Robert B. Reeves Assistant Examiner-H. S. Lane Attorney0wen and Owen [54] ELECTROSTA'UC SPRAY GUN ABSTRACT: An air atomizing electrostatic spray gun having 2 Chin! 9 Draw!" I the charging wire to the spray gun carriedwithin the air hose [52] [1,3, (I 239/15, and physically shielded thereby. Provision is made at the 174/47 source of high electrostatic voltage to introduce the insulated [51] lnt.Cl. 1305b 5/00, i charging wire into the air line to the spray gun. Within the H011: 3/16 i spray gun itself the air is diverted into a valved air passage [50] Field of Search 239/15, 3; while the insulated charging wire is separately directed into a 174/47; 1 18/629 passage to the electrostatic charging system.

POWE R HI- OUTLET A111 fl SUPPLY I-I II-(MHM IHL Patented Nov. 10, 1 970 Sheet 1 v INVENTOR. JAMES 5. MAR SH POWE R OUTLET Sheet INVENTOR. JAMES E. MARSH.

ATTYS' ELECTROSTATIC SPRAY GUN BACKGROUND OF THE INVENTION In presently known air atomizing spray guns there are two hoses extending to the gun, one of which carries the fluid to be sprayed and the other of which is an air line to introduce atomizing and, in some instances pattem-shaping air, into the spray gun. When such spray guns are made to incorporate electrostatic charging of the atomized particles, a third line for the charging voltage must be added. Because the charging voltage to the gun amounts to several thousand volts, care must be taken to protect the wire against physical damage which might result in a distressing shock if an operator touched an exposed wire on which this high voltage is imposed. At the present time, then, a third heavy cable or line extends to the spray gun which significantly reduces the maneuverability and increases the difficulty of operation of the spray gun.

The current carried by the charging wire to the gun is, even with presently known relatively electrically inefficient guns, only a few milliamperes so that the charging wire itself may be very small. The required insulation for the wire thus essentially determines the cable size. We have found that by utilizing the physical protection afforded by the air hose only a small insulated wire is required to supply the charging voltage to an electrostatic spray gun. Further, the elevated air pressure in the air hose affords additional protection against sparking.

BRIEF SUMMARY OF THE INVENTION The invention includes the combination of means associated with the source of high voltage for an air atomizing electrostatic spray gun to introduce an insulated wire carrying the charging voltage into the air line to the spray gun, and means at the spray gun to connect the air line into a valved air passage while separately directing the insulated wire into a passage within the gun leading to the electrostatic charging system for the gun.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a diagrammatic view of an electrostatic spray gun system embodying the present invention;

FIG. 2 is a cross-sectional view of a power supply for a spray gun, with parts indicated diagrammatically, the section being taken on line 2-2 of FIG. 1', 7

FIG. 3 is a fragmentary sectional view taken on line 3-3 of FIG. 2;

FIG. 4 is a sectional view taken on line 4-4 of FIG. 3;

FIG. 5 is a sectional view taken on line 5-5 of FIG. 3;

FIG. 6 is a sectional view taken on line 6-6 of FIG. 3;

FIG. 7 is a cross-sectional view of a spray gun constructed in accordance with the present invention, with parts in full;

FIG. 8 is an end elevation of the spray discharge end of the spray gun shown .in'FIG. 7; and

FIG. 9 is a sectional view taken on line 9-9 of FIG. 7.

Referring to the drawings and particularly to FIG. 1, an electrostatic spray gun system incorporating the present invention includes a spray gun 10, a power supply 11 and a paint pressure pot l2.

The power source for the electrostatic system is connected to any convenient outlet through a power cord 14. A casing for the power supply includes a bottom canister 15 and a bonnet 16 attached thereto. In the form shown in the drawings the bonnet need not be hermetically sealed, but as hereinafter described, certain modifications of the invention may require this expedient.

Within the bonnet I6 there is an air conductor and control unit 18 (FIGS. 2. 3, 4, 5 and 6) comprising a body 19 preferably made from an insulating material and formed with various chambers and passages as hereinafter described. One wall of the body is open and is covered by a diaphragm 20 hermctically sealing the body I9 and held in place by a cover 21 Ill which is fastened to the body l9 by a series of screws 22. The body 19 has an inlet air compartment 23 and an outlet air compartment 24 formed therein, and separated by walls that are sealed by the diaphragm 20. Air enters the inlet compartment 23 from an air supply hose 25 leading from any suitably regulated source of air pressure, and preferably from a moisture removal device 26. Air passes from the inlet compartment 23 to the outlet compartment 24 through a restrictive slot 27 (FIG. 5) so that whenever the spray gun is operating the pressure in the outlet compartment 24 is lower than the pressure in the inlet chamber 23 by an amount equal to the pressure drop caused by flow across this restriction. When the spray gun is not operating the pressure in the two chambers comes to balance very quickly. I

Also within the conductor and control unit 18 is a diaphragm operated switch 30 (FIGS. 3 and 5). The switch 30 is a conventional normally open microswitch, and is disposed in its own chamber 31 in the body 19. A disk 32 overlies the operating button of the microswitch and is engaged by the diaphragm 20. As best shown in FIG. 6 one side of the diaphragm 20 is exposed to pressure in the inlet compartment 23 by communication through a bypass passage 33 while the opposite side thereof is exposed to the pressure in the outlet compartment 24 through a passage 34 (FIGS. 3 and 6) formed in the wall of the switch chamber 31. Thus, when the spray gun is operating and there is a higher pressure in the inlet compartment 23 than in the outlet compartment 24 there will be a higher pressure on the top of the diaphragm 20 than on the bottom thereof and the switch 30 will be closed. When the pressures on the two sides of the diaphragm 20 are balanced the microswitch assumes its normally open position. Switch 30 is connected in the input line to the power transformed as hereinafter described.

As above noted, air enters the air conductor and control unit 18 through an air line 25 and flows from the inlet compartment through restriction 27 into the outlet compartment 24. The air is removed from the latter compartment by an air hose 40 attached by a gland nut 41 to a tubular extension 42 from the body 19 of the air conductor and control unit. The gland nut 41 seats against a shoulder 43 of a tubular member 44 having a series of air openings 45 in a wall thereof through which air can flow from the outlet compartment 24 into the air hose 40 and to the spray gun.

The tubular member 44 has an O-ring seal 46 engaging the wall of a bore 47 in the block I9. An insulating tube 48 is threaded to the lower end of the member 44 and is movable therewith as a unit. The assembly of the tubular member 44 and tube 48 is received in the bore of a high tension bushing 50 and a spring contact 52 on the tube 48 connects with a high tension wire 54 which is the high voltage charging wire for the electrostatic spray gun 10. The spring contact 52 engages a stationary high tension contact 56 extending through the lower wall of the bushing to engage a connecting strap 58 from the output side of a high voltage supply 60. It will be seen that the high tension charging wire 54 thus extends through the tubular elements 44 and 48 into the interior of the air hose 40 leading to the spray gun 10. The high tension charging wire 54 is thus protected against abrasion, kinking, and other physical damage by the wall of the air hose 40.

The canister 15 may be oil-filled and it is therefore desirable to insert a packing 61 around the wire 54 between the tubular member 44 and the insulating tube 48. This packing may be tightened in the usual manner by the threaded connection that attaches the two tubular elements together.

The air how 40 with the electrostatic charging wire 54 nowhoused therein is taken to the spray gun 10 where the air is diverted into the normal air passages in the metallic spray gun body designated 10a in FIG. 7. At the spray gun end, the air hose-wire combination is provided with a fitting 65 having a shoulder 66 that bears against a suitably formed shoulder on the bottom of the handle of the spray gun. The fitting is received in a bore 67 in the spray gun handle and has spaced sealing grooves 68 and 69 thereon in which conventional O- rings are disposed to cooperate with the walls of the bore 67. Between the seals thus provided the fitting 65 has a plurality of radial air holes 70 through which air passes from the hose 40. The wire 54 continues on axially from the fitting 65 and the point of egress is sealed by conventional packing placed under compression by a gland nut 71. The fitting 65 is held in place in any suitable manner as by a set screw 72.

Air from the fitting holes 70 passes through an opening 73 into a handle passage 74. The flow of air from this passage is controlled by a valve 75 actuated to its open position by the conventional gun trigger 76 and biased to closed position by a spring 78. When the valve 75 is open air flows to the front of the spray gun body through a passage 79 which passage is also used to carry the electrostatic charging wire 54. At the front of the spray gun body the air enters an annular chamber 80 and from this chamber the air flows to the front of the gun through a passage 81 in an insulated body extension 82 to an air cap 83.

The air cap may take any of several forms depending on the configuration of the spray desired. For example, as shown in FIG. 7 the air cap 83 may contain a helically channeled insert 84 which imparts a whirling motion to the air and this air emerges from an annular air orifice 85 directed axially of the gun. The air cap is held in place against the channeled insert 84 and to the gun body extension 82 by a suitable insulating gland nut 86.

The electrostatic charging wire 54 terminates in a spring contact 88, having been taken through the annular air chamber 80 at the front of the spray gun body into a separate passage 89 in the insulated nozzle extension. The insulated nozzle extension itself is held against the metallic spray gun body a by a gland nut 90 threaded to the spray gun body and having an internal shoulder 91 bearing against a shoulder 92 within the gun as indicated in FIG. 7.

A fluid tip 99 of the spray gun 10 receives paint from a conventional paint hose 100 having a fitting threaded into the metallic spray gun body 10a in its normal position and from which paint passes through a center passage 101 in the nozzle extension. At the fluid tip, the paint reaches a valve seat 102 and beyond the valve seat flows into a cylindrical chamber 103 formed in the fluid tip 99. The fluid tip itself is threaded over an internal extension 104 of the insulating gun body 82. An insert 105 in the fluid tip cooperates with the interior of the chamber 103 to form an annular fluid orifice 106. The fluid issuingfrom the orifice is atomized by air from the annular air orifice 85 into a fine spray.

The fluid is-charged by conductivity from an internal electrode 110 which receives its charging voltage from the wire 54 through the spring contact 88. The electrode is spaced sufficiently far to the rear of the fluid orifice that there is no possibility of sparking when the fluid column is absent or when the passage between the electrode and the fluid orifice 106 is filled with paint.

The flow of fluid from the paint supply hose 100 and the center channel 101 is controlled by an elongated needle valve 112 the front of which is made of insulating material and which is controlled by the gun trigger 76 in the normal manner. The needle valve 112 seats against the valve seat 102 when the trigger is pulled against the force of its conventional seating spring 113. While the fluid needle valve 112 has an insulating forward section which seats on the valve seat 102, the rear portion thereof which is normally contained within the metallic gun body 10a may be made of metal as in a normal nonelectrostatic spray gun.

If the air operated switch 30 is eliminated, and the charging voltage turned on and off by the other means, the entire interior of the bonnet 16 will contain air under pressure so that this part must be hermetically sealed to the canister 15. g

The wiring diagram for the electrical system is shown in FIGS. 2 and 4. As shown the power cord 14 is a three wire cord having a neutral supply wire 115, a hot or power wire 116 and an equipment ground wire 117. An off-on toggle switch 118 has one of its terminals connected directly to the power wire 116 and its other terminal connected to one terminal of the air-operated switch 30. The other terminal of the air operated switch 30 is connected to the primary of the power transformer 60 and, in parallel, to an indicator pilot light 120. The neutral wire of the power line 114 is connected to the pilot light 120 and to the primary of the power transformer 60. An equipment ground is established through wire 117 which is fastened to any convenient part of the power supply 11 as by a nut 121. The air hose 40 is of a conventional braided type with one of the strands being of metal so that the spray gun 10 is grounded through the air hose to the power supply and ultimately to wire 117. A micrometer 122 is connected between the secondary output and ground to read the total current in the system.

Iclaim:

1. An electrostatic spray gun having a coating material conduit, an air hose and a high voltage charging wire all connected thereto, a high voltage source connected to said charging wire, said charging wire being inserted into said air hose in a fitting adjacent said high voltage source, and a switch adjacent said source to apply voltage to said charging wire only whenever air flows in said air hose to said spray gun.

2. An electrostatic spray gun having a coating material conduit, an air hose and a high voltage charging wire all connected thereto, a high voltage source connected to said charging wire, said charging wire being inserted into said air hose in a fitting adjacent said high voltage source, and an air actuated switch adjacent said source to apply voltage to said charging wire only whenever air flows in said air hose to said spray gun.

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