Patent Publication Number: US-5289977-A

Title: Electrostatic spray gun power supply connection

Description:
BACKGROUND OF THE INVENTION 
     Electrostatic spray guns are useful in applying coatings with a high transfer efficiency. Such spray guns usually have a high voltage power supply located within the barrel of the gun which in turn typically contacts a metallic member to transfer voltage to the needle electrode. 
     Such spray guns have been sold by Graco Inc., the assignee of the instant invention under the trademark PRO GUN. That product had a spring which extended from the front end of the power supply and in turn contacted a conductive member within the barrel. Such a spring has either been in contact with the member directly or is contained within a rubber boot while contacting the member. 
     Such a construction, to a greater or lesser extent still allows some air to exist within the barrel of the gun in the presence of high voltage electric fields. The presence of this air can lead to the production of ozone which in turn can chemically attack the barrel of the gun and lead to electrical breakdown of the barrel. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of this invention to provide an improved construction which limits the capacitance and amount of air in the front end of the gun and hence the amount of ozone that will be produced. 
     It is further an object of this invention to provide a front end construction of the electrostatic spray gun which is reliable and easily and inexpensively manufactured. 
     The front of the power supply (such as that shown in the aforementioned Graco PRO GUN spray guns and more explicitly set forth in U.S. Pat. Nos. 4,219,865, 4,290,091, 4,377,838 and 4,978,075, the contents of which are incorporated by reference) is provided with a small flange at the front end thereof which surrounds a contact. A rubber boot snaps over the flange and contains therein a conductive rubber pin. The flange and boot are symmetrical in nature and do not need to be oriented in any particular direction. 
     Because the rubber pin completely fills the cylindrical cavity within the boot, air in the front end of the gun is almost completely eliminated as when the power supply boot and pin are placed within the gun, the boot is compressed in the mating barrel which it seals by conforming to the barrel cavity and the power supply. The small energy flow path of the conductive rubber pin minimizes volume or capacitive energy storage in the front end of the gun. 
     The boot and pin are also manufactured from ozone resistive material such that by eliminating the air the production of damaging ozone is almost completely eliminated. 
     These and other objects and advantages of the invention will appear more fully from the following description made in conjunction with the accompanying drawings wherein like reference characters refer to the same or similar parts throughout the several views. 
    
    
     A BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the prior art device construction. 
     FIG. 2 shows a cross-section of a spray gun utilizing the instant invention. 
     FIG. 3 shows the boot and plug of the instant invention in non-assembled condition. 
     FIG. 4 shows the front end of the gun in an assembled position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The instant invention, generally designated 10 is designed for use in a spray gun 12 having a power supply 14 located in the barrel 16 thereof. A lead 18 from multiplier 20 in power supply 14 extends to the front end of power supply 14 and is surrounded by a flange 22. 
     Shown in FIG. 3 are the portions of the connector which are comprised generally of a boot 24 having a notch 26 in one end thereof which engages flange 22 on power supply 14 and a cylindrical interior passage 28 which contains cylindrical, flexible connector plug 30. 
     As can also be seen in FIG. 3, when in its free standing unassembled state, plug 30 does not extend the full length of passage 28, however when assembled, in barrel 16, boot 24 is compressed axially such that the end of conductive pin 30 is approximately even with the end of boot 24. 
     The end of pin 30 contacts conductive member 32 which then carries the charge to the front of the gun where it is applied to the paint or other coating material. By providing compression of boot 24, air in that area of the gun is completely forced out thereby preventing the build-up of ozone which can harm the barrel and cause electrical breakdown. 
     It is contemplated that various changes and modifications may be made to the power supply connection without departing from the spirit and scope of the invention as defined by the following claims.