Apparatus And Method For Converting A Pressure-supplied Spray Gun Into An Electrostatic Spray Gun

Abstract

The invention described relates to an attachment to or adaptation of an existing spray gun which converts it into an electrostatic spray gun, by providing an electrically insulating extension of the original gun and an electrostatic supply thereto.

Description

This invention relates to spraying apparatus and more particularly to spraying apparatus for paint spraying using the airless electrostatic system.

Previously proposed systems for airless electrostatic spraying have necessitated the purchase of entirely new equipment, and conversion from airless, i.e., purely pressurized, spraying to electrostatic airless spraying has involved considerable expense.

The present invention seeks to provide apparatus in the form of an attachment for a conventional airless pressure-atomizing spray gun which will readily convert it into an electrostatic airless spray gun, the only additional apparatus required apart from the attachment being the electrostatic generator.

According to the invention, apparatus for such conversion comprises a first body of electrically insulating material having a longitudinal bore therethrough, one end of the body being adapted for attachment to an existing spray gun in place of the usual nozzle and the other end of the body having a spray nozzle thereon supplied by the bore, and a second body attached to the first body and of electrically insulating material, the second body having a high voltage cable passing therethrough adapted to be connected at one end to a high voltage source and at the other end to a discharge probe which extends into the vicinity of the spray emerging from the spray nozzle.

Preferably the end of the first body adapted for attachment to the spray gun is provided with a hollow bolt which is passed through the nozzle retaining nut on the spray gun and screwed into the first body to retain the nozzle retaining nut thereon, the nozzle retaining nut then being screwed back onto the spray gun to attach the attachment thereto.

One embodiment of the invention will now be described by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of the attachment of the invention attached to a conventional airless spray gun; and

FIG. 2 is a side sectional view of the attachment shown in FIG. 1.

Referring to the drawings, there is shown a spray paint gun 1 having a connection 2 with a pipeline 3 for the pressurized supply of paint (or supply of other sprayable material to be sprayed). At the outlet of the gun 1 there is provided in place of the usual atomizer jet nozzle, deemed to have been removed, a hollow bolt 4.

This hollow bolt 4 has threaded into it the retaining nut 5 of the spray gun 1 and is screwed into the original gun thereafter being locked by the nut 5. The bolt 4 is also screwed into an electrically insulating body 7, preferably of plastics, and is locked thereto by a nut 6. The body 7 has a central bore 8 communicating at one end with the bore of the hollow bolt 4, and at the other end with a bored double threaded member 9, of which one end screws into the bore 8. A locking nut 10 is provided to lock the member 9 to the body 7.

On to the other end of the member 9 is screwed a nozzle retaining nut 11 retaining on the outer end of the member 9 an atomizing nozzle 12 and a washer 13, the vicinity of this nozzle being subjected to an electrostatic field so that the liquid sprayed is influenced thereby. The nozzle 12 can be of any suitable form and may in fact be the nozzle which was originally used with the spray gun 1.

Attached to the body 7 by any suitable means such as adhesion, strapping, soldering, or other convenient means (not shown) is a second body 14; the body 14 may be made integral with the body 7. This second body 14 is bored and contains a high voltage cable 15 which is connected to an electrostatic generator (not shown). The cable 15 is connected to a current limiting resistor 16, which for this purpose is held against the cable end by a spring 17, the spring and resistor being retained in the body 14 by a screw cap 18 provided with a socket 19 into which an electrostatic probe unit 20 fits.

The probe unit consists of an electrically insulating body 21, connector 22 which fits into the socket 19 and a probe 23 having a needle point 24 and electrical insulation 25. As can be seen, the probe is positioned so that its point 24 is adjacent to and spaced from the outlet of the nozzle 12. The nozzle 12, as is usual, has a diametric groove or slot in which the point 24 may be located.

To adapt a conventional spray gun, the following procedure is carried out:

The bolt 4 is removed from the body 7, after slacking the nut 6. The retaining nut 5 on the gun is unscrewed and the nozzle (which may be the nozzle 12) is removed therefrom. Next, the nut 5 having been threaded on the bolt 4, the bolt 4 is screwed into the body 7, and a locking nut 6 having been threaded on the bolt 4 is tightened on the bolt, to lock it in the body 7. The bolt 4 having been screwed into the body 7, the nut 5 is tightened back against the body 7, thus providing locked connection between the original spray gun and the attachment.

Next, the retaining nut 11 is unscrewed and the nozzle 12, which may have been removed from the original spray gun, is placed therein and retained on the member 9 by screwing up the nut 11. The electrode 24 is now adjusted into its required position with respect to the nozzle 12.

The apparatus is then ready for use as soon as it is supplied with paint via the pipeline 3 and with a high voltage via the cable 15.

To revert to the original gun, the reverse procedure is adopted.

It will be understood that various modifications can be made to the above-described embodiment without departing from the scope of the invention. For example, the two bodies 7 and 14 can be made as one integral unit. Full adjustment may be provided for the probe so as to produce optimum performance in widely varying conditions. Sometimes it may be found desirable to have the probe some 3 to 4 inches from the spray nozzle opening. This is useful when spraying paints of low electrical resistance since it prevents an unnecessary voltage drop along the paint line.

The attachment may be provided with a switch operable for example by the original trigger mechanism of the gun 1, illustrated in FIG. 1, for controlling the energization of the probe.

Claims

I claim:

1. A method of converting an existing pressure-supplied spray gun, having an original spray nozzle and retaining means for attaching said original spray nozzle to said existing spray gun, into an electrostatic spray gun, comprising:

providing a first electrically insulative body having a bore extending from one end thereof to the other end thereof, attachment means at said one end, and means for mounting nozzle means at said other end, a second body attached to said first body having an electrical lead housed therein, and an electrically conductive probe supported by one of said first and second bodies and extending into the vicinity of said nozzle means when said nozzle means is attached to said other end;

disengaging said retaining means and removing said original spray nozzle from said existing spray gun;

engaging said attachment means with said retaining means for attaching said first body to said retaining means in lieu of said original spray nozzle; and

engaging said nozzle means with said mounting means to attach said nozzle means to said other end of said first body.

2. A method according to claim 1, wherein said nozzle means is said original spray nozzle.

3. A method of converting an existing pressure-supplied spray gun, having an original spray nozzle and retaining means for attaching said original spray nozzle to said existing spray gun, into an electrostatic spray gun, comprising:

providing an electrically insulative body having a bore extending from one end thereof to the other end thereof, attachment means at said one end, and means for mounting nozzle means at said other end, and means supporting an electrically conductive probe extending into the vicinity of said nozzle means when said nozzle means is attached to said other end;

disengaging said retaining means and removing said original spray nozzle from said existing spray gun;

engaging said attachment means with said retaining means for attaching said body to said retaining means in lieu of said original spray nozzle; and

engaging said nozzle means with said mounting means to attach said nozzle means to said other end of said body.

4. A method as claimed in claim 1, in which the first body and the second body are made as one integral unit.

5. A method according to claim 1, in which the second body contains a current-limiting resistor in series with the electrical lead.

6. A method according to claim 1, in which said nozzle means comprises a jet nozzle opening, and said probe is between 3 inches and 4 inches from said jet nozzle opening.

7. A method according to claim 1, in which said attachment means comprises a hollow bolt having screw threads engageable with screw threads provided on said retaining means to bring said bore into communication with sprayable material supplied by said existing gun.

8. A method according to claim 7, in which said bore is provided with threads at said other end for engagement with threads on said nozzle means.

9. A method according to claim 1, in which said second body includes means providing a cable conduit for said electrical lead and means connecting said electrical lead through a current-limiting resistor to said probe.

10. A method according to claim 1, in which said electrically conductive probe is supported by said second body.