GB2108868A - Spray guns - Google Patents

Abstract

A miniature spray gun for paint or dye has the flexibility of an air brush but avoids the use of valves for either the paint or the air. Air issues constantly from an air jet, and control is achieved merely by moving that air jet into and out of an operative zone immediately over a capillary paint nozzle. The control ranges from an air- only spray, with the air jet remote from the paint nozzle, progressively to maximum colour intensity as the air nozzle is moved closer to the paint nozzle. <IMAGE>

Description

SPECIFICATION Spray guns The invention relates to spray guns for producing a fine controlled spray of paint or dye in a spray pattern small enough to enable the spray gun to be used as an artist's tool. Such spray guns will be referred to herein as miniature spray guns.

There already exists a class of miniature spray guns know as Air Brushes, which are shaped rather similarly to a pen, with inlets for air from a compressed air source and for paint or dye (hereinafter simply 'paint') from a small can or reservoir. An air brush has two valves for control by the artist. One is an air valve for varying or interrupting the supply of air, and one is a needle valve for regulating the amount of paint being sprayed. On some models the two valves are controlled by a single control trigger, depending on whether it is moved axially laterally or both. On other models the two valves have separate controls although this means that the user must stop spraying and use both hands to adjust the amount of paint being sprayed.

Air brushes are internal mix miniature spray guns, in that the air and paint are mixed together internally of the unit before issuing as a mist spray.

There also exists a class of external mix miniature spray guns in which a spray is generated by blowing the air over a fine-tipped capillary nozzle for the paint. These external mix miniature spray guns are less expensive than the air brushes, in particular because they do not require the use of a sophisticated needle valve for the paint. Instead, the paint supply is adjustable, rather empirically, by screwing the capillary paint nozzle into or away from the path of the air jet.

The invention provides an external mix miniature spray gun which is more economical to manufacture than the external mix miniature spray guns described above, and yet is more flexible in use and attains some of the versatility of the most expensive air brushes.

The spray gun of the invention is an external mix miniature spray gun in which a spray is obtained by directing a jet of air from a compressed air source over a capillary paint nozzle, wherein control of the amount of paint sprayed is achieved without the use of control valves for the paint or the air by having an air nozzle for the jet of air mounted on a movable member that is resiliently biased to bring the jet of air out of operative relationship with the capillary paint nozzle but is movable under finger pressure to bring the jet of air progressively into the said operative relationship.

It is surprising that an acceptable degree of accuracy of the spray can be obtained when the air nozzle is mounted on a movable member. At first sight it appears that the artist using the spray gun would be unable to direct the spray with sufficient accuracy, and yet this surprisingly is not the case. The reasons are twofold. First, the movable member can be designed so as to be controlled with the forefinger, so that the user is effectively pointing his forefinger at all times in the direction of spraying. Secondly, the extent of movement to bring the air nozzle from its rest position above and out of operative relationship with the paint nozzle into such operative relationship is extremely small, possibly only 2 to 3 mm.

In use, the spray gun of the invention enjoys a striking advantage over conventional external mix miniature spray guns and over some air brushes.

This advantage lies in the ease with which the spray gun can be used to direct a jet of air at the work without simultaneously spraying paint. This particular mode of use is of benefit when a sprayed area has to be dried or can be used to create special effects on the artwork by chasing droplets of paint over the article being sprayed.

With conventional external mix miniature spray guns the 'air only' mode can be established, if at all, only by screwing the capillary paint nozzle down into its holder to its maximum extent, which takes time. Also, to revert to normal spraying the paint nozzle must be screwed back to its original level and an acceptable intensity of spray must be re-set by the empirical method of alternately spraying a test area and adjusting the paint nozzle.

Even with some air brushes a rather similar sequence of stopping spraying, screwing down the needle valve and resuming spraying under 'air only' conditions must be followed. To perform this function using a spray gun according to the invention, all that is necessary is to release the finger pressure on the movable member to aliow it to move to its rest position away from the capillary paint nozzle. From this 'air only' mode the user has full control of the colour intensity by gradual depression of the movable member to bring the air jet closer to the paint nozzle. The maximum colour intensity that can be sprayed can be varied, if desired, by raising or lowering the paint nozzle or by raising or lowering a stop defining the lower limit of movement of the movable member.A further advantage of not using an on/off switch is improved suitability for use with the continuousiy running type of compressor and the elimination of back pressure and/or the use of a bleeder valve.

The movable member may if desired be urged to the above rest position under the sole bias of its own resilience. To this end the movable member may be a resilient hollow tubular plastics member, secured fast at one end to a support and carrying at its other end the air nozzle. If desired the air nozzle may be movable axially of the direction of spraying over a limited distance, to vary the spray pattern.

Drawing The drawing is a side elevation, partly in section, of a spray gun according to the invention attached to a paint container 2. The attachment is via a lid portion 4 of the spray gun, which is a screw fit over the paint container 2. Fast to the lid portion 4 is a handle and paint nozzle moulding 6 which comprises a base portion 6a, an upstanding tubular portion 6b for mounting a paint nozzle, and a rearwardly extending elongate handle portion 6c intended to be held in the manner of a pen to direct the spray in use. A paint nozzle 8 is screwthreaded into the tubular portion 6b, with a compression spring 10 between a shoulder on the paint nozzle and a spaced shoulder on the tubular portion 6b to provide a frictional resistance against any accidental turning of the paint nozzle 8 which would move the nozzle 8 axially across of the lid 4.From the bottom of the paint nozzle 8 there extends a narrow bore tube 1 2 which extends into the paint container 2 through an aperture in the lid portion 4, to supply paint to the nozzle 8.

Rigidly fastened as a force-fit to a rear end of the handle portion 6c is a length of stiff but resilient plastics tubing 14. Into a forward end of the plastics tubing 14 is fitted an air nozzle 16, and into a rearward end of the plastics tubing is fitted a flexible tube 1 8 for connection to a source of compressed air (not shown). The plastics tubing 14 is also threaded through apertures in a trigger moulding 20 which is shaped to sit over the top of the handle portion 6c in the manner of a saddle.

The resilience of the tube 1 8 maintains the trigger 20 slightly above the handle portion 6c, but this resilience can be overcome by finger pressure, which has the effect of pivoting the trigger moulding about a pivot zone generally at the rear end of the handle portion 6c.

In the rest position of the trigger as shown in the drawing, the axis of the air nozzle 1 6 is about 0.2 mm above the top of the paint nozzle 8, which is a spacing sufficient to ensure that no paint is entrained in the jet of air issuing from the nozzle 1 8. Depression of the trigger 20 brings the air nozzle 1 6 progressively closer to the top of the paint nozzle 8, to cause progressively more paint to become entrained as a spray in the air jet. The maximum colour intensity is obtained when the trigger 20 fully depressed, with a lower face 22 of the trigger abutting the handle portion 6c, but this maximum colour intensity can itself be varied by screw adjustment of the paint nozzle 8.

Axial movement of the air nozzle 1 8 may be allowed for, as this affects the spray pattern achieved.

A forward portion 24 of the trigger 20 is angled downwardly so that it lies alongside a corresponding portion 26 of the handle portion 6c.

The location of these two portions is such that in use an operator's thumb straddles the trigger 20 and handle portion 6c, and provides the operator with a far greater 'feei' and control of the extent of depression of the trigger 8 than if a simple straight trigger has been provided.

There is a tendency for a small amount of paint to run down the side of the paint nozzle 8 and tubular portion Sb in use, particularly if the paint nozzle is set too high. A small well 28 is therefore formed in the base portion 6a, immediately forward of the tubular portion Sb, for collecting any paint that runs down the side of the tubular portion. An aperture at the bottom of the well 28 communicates with the interior of the paint container, so that air can pass to the inside of the container to replace the quantity of paint sprayed through the paint nozzle 8. Any paint collecting in the well 28 is thus drawn back into the container by this air flow.

In use the spray gun is used with a continuous supply of compressed air, for example from a small compressor. Depression of the trigger 20 against the bias of the resilient tube 1 8 causes the paint to be sprayed as above described, whereas release of the trigger results in the delivery of a jet of 'clean' or paint-free air which can be used for drying an area already painted or for creating special effects on areas previously sprayed.

Claims (8)

1. An external mix miniature spray gun in which a spray is obtained by directing a jet of air from a compressed air source over a capillary paint nozzle, wherein control of the amount of paint sprayed is achieved without the use of control valves for the paint or the air having an air nozzle for the jet of air mounted on a movable member that is resiliently biased to bring the jet of air out of operative relationship with the capillary paint nozzle but is movable under finger pressure to bring the jet of air progressively into the said operative relationship.

2. A spray gun according to claim 1 , wherein resilient bias urging the movable member to bring the jet of air out of operative relationship with the capillary paint nozzle is provided by the inherent resilience of the movable member.

3. A spray gun according to claim 2, wherein the movable member is hollow and tubular, with one end secured fast to a support and the other end carrying the air nozzle.

4. A spray gun according to any preceding claim, wherein the axes of the air nozzle and the capillary paint nozzle lie in the same plane at all times.

5. A spray gun according to claim 4, wherein the air nozzle is adjustable towards and away from the capillary paint nozzle.

6. A spray gun according to claim 4 or claim 5, wherein the capillary paint nozzle is adjustable axially.

7. A spray gun according to any preceding claim, wherein beneath the capillary paint nozzle is a drip tray for any paint running down the side of the paint nozzle, and a passage for returning any paint collecting in the drip tray back to a paint reservoir.

8. An external mix miniature spray gun substantially as described herein with reference to the drawing.