GB2061768A - Spray guns - Google Patents

Abstract

A spray gun is controlled by supplying air to inlet 16 to move piston 10 backwards to open air valve 12, 13; needle valve 28, carried by the piston 10 and controlling the spray material, at first remains biased closed (by spring 24) but on further movement of the piston 10 is opened. Thus at start of spraying, atomised air is supplied to the head before the needle valve 28 opens and persists at the end of spraying after the needle valve 28 closes. This is achieved because of the lost motion connection between the forked end 25 of the operating piston 10 and the needle collar 30. Preferably, no rubber compounds are used for the various spray gun seals so that the spray gun can be safely cleaned with paint solvents if required. <IMAGE>

Description

SPECIFICATION Spray guns This invention relates to air atomised spray guns.

In previous proposals, spray guns for paint or other fluid materials suitable for dispersion by atomisation comprises a piston operable to pen a spray gun nozzle valve in response to the application of air pressure applied to the piston. The piston surrounds a needle of a needle valve arranged to open a spray gun noule so as to allow air and fluid to leave the spray gun. In such proposals, and as is desired, the guns are arranged so that the release of fluid is later than the application of air pressure providing atomisation of the fluid and cut-off of the fluid is before the removal of the atomising air supply to the nozzle to prevent projection of non-atomised fluid.

It is an object of the invention to provide an improved spray gun.

According to the invention there is provided an air atomised spray gun having a body including an air operated piston arranged to move backwards on the application of air pressure, an air valve, formed between an outer surface of the piston and an inner surface of said body, which opens whenever said piston moves towards its backward position to allow the air to pass to a spray head valve a spray valve opening member mechanically coupled to a forward end of said piston arranged such that on movement of said piston the air valve opens before the spray head valve whenever the piston moves backwards and the spray head valve closes before the air valve closes when the piston moves forwards.

An air atomised spray gun according to the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a part sectioned view of the gun; Figure 2 is a schematic view of the air passage in the gun; and Figure 3 is an isometric view of a coupling between the end of a piston in the gun and a spray valve opening member.

Referring to the drawing, a piston 10, mounted in a spray gun body 11, has a shoulder 12 which contacts with a carbon filled P.T.F.E. seat 13, to form an air valve.

The piston 10 is provided with P.T.F.E. seals 14 and is urged by a spring 1 5 to close the air valve. Two air inlets 16 and 17, in the body 11, are arranged so that inlet 1 6 supplies air through a diecast spacer 1 8 to act on the piston 10 to open the air valve, thus allowing air from inlet 1 7 to pass through a diecast spacer 1 9 and the air valve towards the sprayhead 20 via two air passages (see Fig. 2) in the body 11. Incorporated into these air passages are two variable valves 21 and 22 which independently regulate the two air supplies to the sprayhead 20. An auxiliary piston 23 within piston 10 is biased by a spring 24 towards the forked end 25 (see Fig.

3) of the piston 10.

The sprayhead 20 is provided with stainless steel fluid inlets 26, a spray nozzle 27 and an air cap 31. A needle valve 28 extends from the spray nozzle 27 through a spring loaded, self adjusting P.T.F.E. packing and needle support 29 to the forked end 25 of piston 10 where the needle 28 is provided with a collar 30 which is loosely held by the forked end 25.

In use, air is supplied to inlet 1 6 which moves piston 10 backwards to open the air valve. Air from inlet 1 7 flows through the diecast spacer 1 9 and past the seating 12 of the piston 10 towards the spray head 20. In the initial stages of the movement of piston 10, the needle 28 remains stationary so that the spray nozzle 27 remains closed. After the piston has moved about .060", the forked end 25 engages the collar 30 thereafter movement of piston 10 causes needle 28 to move and open the spray nozzle 27. Air passes through the body into the sprayhead 20 and out between the spray nozzle 27 and the air cap 31 to atomise the fluid supplied via inlets 26 as it passes out through the spray nozzle 27.The rate of flow of the paint through the spray nozzle 27 is regulated by the amount of movement of needle 28 which in turn is controlled by an adjustable piston stop mechanism 32 at the back of the spray gun body.

When it is required to stop spraying the supply of air is removed from inlet 1 6 and the piston moves forwards urged by the spring 14. As the auxiliary piston 23 is also urging the needle 28 forwards, the collar 30 being held against the forked end 25 during spraying, the needle valve 28 moves towards and closes the spray nozzle 27 thus stopping the flow of fluid. The piston 10 continues to move forwards under the influence of the spring 1 5 and closes the air valve cutting off the supply of air from inlet 1 7 to the sprayhead 20.It will be noted that once the spray nozzle 27 is closed, the spring force of the spring 24 acts to declerate the piston 10 thus reducing the impact of the shoulder 1 2 onto the seating 1 3. This tends to extend the working life of the air valve and provide one advantage of the described embodiment.

It will thus be appreciated that the spray nozzle is opened after the application of atomising air to the spray head and closes before the supply of atomising air ceases.

Another advantage is that air passing through the air valve during operation of the gun is contained within the body 11. In earlier guns where the needle passed through the centre of the piston air could be lost past the seal fitted between the needle and the piston. If that seal were made more effective to prevent air leakage, there was a tendency of preventing relative movement of the piston and the needle and cause the needle to move out of sequence unless its closing spring load were substantially increased. This tends to slow down the operating speed of the piston and hence, the operating speed of the spray gun.Such an increase in the spring load also means an increase in air pressure as required to operate the spray gun and consequent increases in all of the operating forces, acting on the construction of the spray gun tending to reduce the operating life between mainte nance periods.

Supporting seals for the piston and the needle valve 28 including packing 29, are formed of PTFE material. The construction and mode of operation of the spray gun according to the invention allows for progres sive overcoming of the static friction resulting from the seals. The mass of the piston is substantially greater than that of the needle so providing a momentum sufficient to overcome the needle seal friction enabling rapid acceler ation of the needle to the open position.

Preferably, the weight of the piston 10 is at least eight times the weight of needle 28. The described gun has been found to offer im proved operating speeds compared to an equivalent gun, having a centrally supported needle movable within the body of the piston.

Taking a full operating cycle from turn on to turn off, the described gun operates up to 30% more quickly.

The piston 10 and needle 28 are on the same axis. It is possible and using a spring biassed coupling between the piston 10 and the needle 28 to arrange for the needle to be on an axis displaced from the axis of the piston. Such an arrangement may be required where the spray valve is placed out of line of the axis of the piston.

The control valves 21 and 22 are separately variable and independently control of the air available via ports 27A for the atomisation of the fluid and the air available via ports 33 for the control and formation of the pattern of the deposition of the fluid. Thus, where fluids require a different ratio of air for these func tions adjustment is possible to adjust the air flows separately.

All moving parts are lubricated by the natu ral action of the P.T.F.E. seals provided and the initial grease of compounds used during the manufacturing processes. No external lu brication source is required thus prolonging the intervals between service and replacement of parts. Further in earlier guns where dry air is used as is required when spraying powders fsuch as epoxy paint powders, lubrication in the seals tended to be removed by the dry air.

Guns made according to the present invention which require no lubrication in use, are suit able for spraying with dry air and so can be used satisfactorily for spraying powder onto work pieces.

Claims (9)

1. An air atomised spray gun having a body including an air operated piston arranged to move backwards on the application of air pressure, an air valve, formed between an outer surface of the piston and an inner surface of said body, which opens whenever said piston moves towards its backward position to allow the air to pass to a spray head valve a spray valve opening member mechanically connected to a forward end of said piston arranged such that on movement of said piston the air valve opens before the spray head valve whenever the piston moves backwards and the spray head valve closes before the air valve closed when the piston moves forwards.

2. An air atmoised spray gun according to Claim 1, including spring biassing means urging against said piston to bias said valve opening member to close said spray nozzle.

3. An air atomised spray gun according to Claim 1 or Claim 2, in which said piston has a mass substantially greater than said valve opening member.

4. An Air atomised spray gun according to any of Claims 1 to 3, in which said piston and said valve operating member are positioned on at least substantially the same axis.

5. An air atomising gun according to any of Claims 1 to 4, in which piston support surfaces are formed at least in part of P.T.F.E.

material.

6. An air atomising gun according to any of Claims 1 to 5, in which a packing and support for said valve opening member is formed of P.T.F.E. material.

7. An air atomised spray gun according to any of Claims 1 to 6, in which the said air valve is formed of P.T.F.E. material filled with mica or carbon.

8. An atomising spray gun according to any of Claims 1 to 7, including two variable air valves respectively in air passages between the air valve and atomising air outlets and pattern forming air outlets, which air valves are independently variable.

9. An air atomised spray gun substantially as herein described with reference to the accompanying drawings.