EP0215889B1

EP0215889B1 - Improvements in or relating to gas-operated spraying equipment

Info

Publication number: EP0215889B1
Application number: EP86901976A
Authority: EP
Inventors: Jan Ilott
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-03-27
Filing date: 1986-03-27
Publication date: 1992-07-15
Anticipated expiration: 2006-03-27
Also published as: EP0215889A1; WO1986005719A1

Abstract

A nozzle (12), for use in a gas-operated spraying apparatus such as an airbush. The nozzle locates concentrically within an air cap (13) in the gas outlet of a spraying apparatus (22) and cooperates with a tapered needle (10) located in an axial passage thereof to seal the outlet of the nozzle. The needle is retractable in the nozzle to dispense a medium such as paint to be sprayed. The nozzle is made of a resilient material expandable slightly by the needle as the latter moves into sealing engagement with the nozzle outlet.

Description

This invention relates to gas-operated spraying equipment and particularly, but not exclusively, to airbrushes. airbrushes are tools used by artists and illustrators for selectively spraying coloured dyes or pigments dissolved or dispersed in an aqueous or other liquid solvent or carrier to form inks, paints or similar media (hereinafter referred to as "paint" for the sake of convenience), and are used extensively in the preparation of advertisements and like commercial artwork, although such is the skill of exponents that airbrush work is now considered a fine art form.
A definitive work detailing the history, the construction and use of airbrushes is "The airbrush Book" by Seng-gye Tombs Curtis and Christopher Hunt published by Orbis Publishing Limited, London in 1980. This reference describes in detail the various types of airbrush past and present. As fine art tools, airbrushes are relatively delicate and, moreover, they are expensive. For example, conventionally, the nozzle and/or the needle (which control the release of paint) may be made of brass, stainless steel or a platinum alloy. They are easily damaged in that, to provide a different sized nozzle, to replace a damaged nozzle or needle , or for cleaning purposes, the airbrush must be disassembled, cleaned and reassembled. During reassembly, the needle must be inserted into the nozzle to exactly the correct extent to ensure a seal and to avoid damaging the nozzle.
Fig.1 is a diagrammatic fragmentary cross-section of a known nozzle/needle combination.
The needle 10 has a tip of substantially conical shape sealingly fitting into a nozzle 12. The aperture in the nozzle 12 may be, for example, 0.2mm. The diameter of the needle may taper from 1.5mm to a point.
The angle of taper is small so that, upon retraction of the needle, a considerable movement is necessary to give an appreciable change in the flow of paint. This is desirable so as to give greater control of paint flow. However, if the angle of taper of the needle is too small, the mechanical advantage is such that on moving to the closed position, the needle tip 11 tends, in use, permanently to spread the nozzle opening. The sealing may be reduced but also the airbrush no longer has the required control characteristics in the dispensation of paint. If the needle is bent, the paint will not flow evenly. If the nozzle is bent or distorted, it will not locate concentrically with the needle or a surrounding air cap 13 and the airflow through the annulus between the nozzle and the air cap will be uneven. Uneven flow of paint or of air gives rise variously to spatter, spitting, lack of focus or asymmetrical spray pattern. In an extreme case, of course, the nozzle 12 may well be split or cracked by the needle tip 11.
The needle and the nozzle are both relatively expensive items to replace but the errors produced due to these faults and the time lost in replacement or cleaning can be more expensive.
Other forms of spraying equipment utilise concentric needle, nozzle and air cap arrangements and, to varying extents, suffer from the disadvantages above ascribed to airbrushes. The present invention relates equally to such other forms of spraying equipment.
Publication WO 81/03131 describes a spraying apparatus for spraying expoxy resins. The apparatus described includes a one-piece, moulded, expoxy container and nozzle. A plastics needle is also described. After use, the container, nozzle and needle are thrown away. The needle has a non-tapered shank which cooperates with the nozzle both to close the same and to permit spraying. A barrel on the needle serves as a closure valve, in a rest position of the needle, of the expoxy container.
An object of the present invention is the provision of an improved nozzle arrangement of low cost wherein the aforesaid disadvantages are minimised or overcome.
According to one aspect of the present invention, there is provided a nozzle, for a gas-operated spraying apparatus, having a passage for paint to be dispensed, the passage having an outlet of reduced size at its forward end arranged, in use to cooperate with a tapered needle located in the passage to form a seal, characterised in that the nozzle is made of a resiliently stretchable material arranged to be stretched slightly by the needle on movement beyond the seal-forming point but having sufficient resilient memory to return to its original shape, as the needle is retracted.
A nozzle made of such a material, for example, a plastics material resistant also to the media such as paint to be applied by the airbrush, permits the use of a needle with a lesser taper thereby giving even greater control of the flow of paint.
A nozzle made of an appropriate plastics material may be injection moulded at low cost and yet with high precision. The resilience of the material allows greater tolerances on the needle whilst still providing an excellent seal therewith and very fine control in use.
The nozzle is arranged, in use, for insertion axially in the gas outlet of a spraying apparatus. Preferably, the nozzle has its own integral seals for sealing, in use, between paint and gas passages in the spraying apparatus.
The nozzle may have grooves in the external surface thereof for cooperating, in use, with internal surfaces of the spraying apparatus to define gas passages.
Advantageously, the nozzle's integral seals include means cooperating, in use, with the internal surfaces of the spraying apparatus, for obviating the pressure difference between the gas passages and paint passages for preventing gas leaking into the paint.
It is preferred that at least a part of the external surface of the nozzle is of non-circular shape and is arranged in use, to mate with a correspondingly shaped part of the internal surfaces of a spraying apparatus to prevent rotation of the nozzle on insertion thereof into such spraying apparatus.
The nozzle's passage, at its forward end, may taper internally to the reduced outlet, the taper being in the range from 5 to 8 degrees. Alternatively, the passage, in this region, may be stepped or be tapered and stepped to give a final taper which may be as low as 0 degrees. Preferably, the passage may extend axially of the full length of the nozzle, the needle being arranged co-axially therein.
In use, the nozzle is preferably mounted in a gas-operated spraying apparatus having a retractable plunger which cooperates with the needle, the plunger being spring-loaded towards a rest position in which the needle is urged thereby into sealing engagement with the nozzle. For the finest work, it is essential that maximum control is exercised over the initial movement of the needle.
"Double independant control" of air and paint is provided by a single operating member in most high class commercially available airbrushes. The operating member is depressed to increase the flow of air and is moved in a second substantially perpendicular direction, usually rearwardly, to control the retraction of the needle and thereby the flow of paint.
Fig. 2 of the accompanying drawings is a fragmentary diagrammatic sketch of a prior art airbrush air and paint (needle) control means.
A manually operated control means comprises a button 14 depressable to move a rod 15 pivotally connected thereto whereby progressively to open an air valve (not shown). The rod slides in an aperture of the body member 17. The button stem 16 is bifurcated to straddle the needle 10. The body member 17 provides a fulcrum 18 whereabout a lever 19 may pivot. The lever 19 engages a needle support 20 and thereafter is curved forwardly to form a sliding engagement with the stem 16. Pivotal movement of the stem 16 in a clockwise direction (as seen in the drawings) pivots the lever 19 about its fulcrum and urges the needle support 20 and hence the needle 10 to the right. The needle is thereby retracted in the nozzle (not shown) to dispense the paint. The arrangement constitutes an approximately 1:4 linkage and the movement of the needle 10 corresponds substantially linearly to that of the button 14. Such movement does not give rise to the desired initial finest control mentioned above.
Described hereinafter is a control means (forming the subject of my co-pending application No. EP-A-0216845 filed simultaneously herewith and claiming priority also from UK patent application No. 8507966 filed 27th March 1985) enabling finer initial control of the movement of the needle.
The invention will be described further, by way of example, with reference to Figs. 3 to 18 of the accompanying drawings, in which:-

Fig. 3 is side elevation of a preferred form of airbrush incorporating a nozzle having the features of this invention:
Figs. 3a, 3b and 3c indicate the detached transverse sectional shape of the airbrush on the lines a-a, b-b and c-c respectively;
Fig. 4 is a diagrammatic cross-sectional view of one form of side mounted paint cup and its manner of connection to the airbrush of Fig. 3;
Fig. 5 is a diagrammatic sketch of a pumped means for supplying paint at constant pressure to an airbrush;
Fig. 6 is a fragmentary section of the tip of a needle and a nozzle according to the present invention;
Figs. 6a to 6h illustrate modifications of the arrangement shown in Fig. 6;
Fig. 7 is a vertical cross-sectional view of the nozzle end of an airbrush, showing a preferred nozzle;
Figs. 7a and 7b are detached cross-sections taken on the lines 7a-7a and 7b-7b of Fig. 7;
Fig. 8 is a vertical section, corresponding to part of Fig. 7. but showing also a needle and its operating plunger;
Figs. 9 and 10 illustrate modified forms of the needle shown in Fig. 8;
Fig. 10a illustrates a modified form of head of a needle which may be used in any of the embodiments of needles described herein;
Fig. 11 illustrates diagrammatically a modified form of nozzle and air cap of an airbrush;
Fig. 12 is a detached cross-section taken on the line 12 - 12 of Fig. 11;
Fig. 13 illustrates an alternative manner of sealing a needle operating plunger in the body of an airbrush;
Fig. 14 is a diagrammatic sketch of an operating member and its associated mechanism;
Fig. 14a is a perspective view of the operating member shown in Fig. 14;
Fig. 14b and Fig. 14c are diagrammatic sketches of a preferred biasing arrangement of the operating member of Fig. 14;
Fig. 15 is a diagrammatic sketch of an alternative pneumatically operated needle and air control mechanism;
Fig. 16 is a diagrammatic sketch of a direct manual control means for controlling airflow;
Fig. 17 is a diagrammatic view of a further air flow control arrangement; and
Fig. 18 is a partial diagrammatic view of a modification of the air control arrangement shown in Fig. 17.

As shown in Fig. 3 of the drawings, an airbrush incorporating the nozzle of the present invention, may itself be of novel shape. The airbrush comprises a body 22 preferably moulded from a plastics material of lightweight but high strength. The body 22 is symmetrical about its vertical longitudinal midplane as indicated by the cross-section sketches in Figs. 3a, 3b and 3c. The body 22 has an air cap 23 which locates the nozzle and needle assembly (described below) in the body, an operating member 24 for controlling the feed of air and paint to the nozzle, a transverse through hole 25 for receiving a paint cup 26 (Fig. 4) or a blanking plug or plugs when a pressurised paint feed is used, and an air or an air and paint connector 27 whereby air or air and paint to be sprayed may be fed to the airbrush, via a connecting pipe or pipes 28. The sockets for connector 27 and the pipes 28 thereto may be coaxial or side by side. As shown in Fig. 4a, the coupling between the airline and the airbrush comprises two axially-bored screw-threaded relatively rotatable members sandwiching therebetween a soft resilient O-ring. Screwing of the male member into the female member causes the O-ring to be deformed obturating the axial passage. In this way, a throttle valve is incorporated into the airline permitting the maximum airflow to be preset. However, it is envisaged that at least the airline connecting pipe 28 will be couplable to the airbrush by some quick-release coupling, for example, a bayonet coupling. The arrangement shown in Fig. 4a could be provided in one half of such a coupling.
If the paint to be applied by the airbrush is supplied in the side mounted cup 26, the cup has a radially extending feed pipe 29, closed at its end 30 and shaped so as to draw paint from the bottom of the cup 26. The pipe 29 has an aperture 31 adjacent the closed end 30 arranged to communicate, when inserted from either end, as desired, into the through hole 25, with a longitudinal paint feed passage 32 in the body 22.
If the paint to be sprayed is to be fed by pressure to the airbrush, it is advantageous that the pressure of the paint at the airbrush is maintained constant. Fig. 5 diagrammatically illustrates a constant pressure paint pumping device in which a pump 33 (shown here as a self-priming pump although other types of pump may be used) feeds the paint to be applied via a filtered inlet pipe 34, from a reservoir 35 and the pipe 28 to the airbrush. The paint is fed to the nozzle 12 (shown diagrammatically) and surplus returns therefrom through a cconstant pressure valve 36 via a return pipe 37 to the reservoir 35.
If the pump 33 is of the self-priming type, it is advantageous that some means of de-activating the self-priming be provided otherwise, as the reservoir 35 empties, air may be drawn through the pipe 28 to the airbrush. If a non-self-priming pump is used, its dimensions should be such that it can be received in a small container.
The constant pressure valve 36 is preferably located in the airbrush so that it operates at the same head pressure as the paint supplied to the nozzle. The valve comprises a flat plate 38 whereover a thin flexible membrane 39 is peripherally secured so as to form a paint passage therebetween. The membrane 39 acts as a false surface layer and surplus paint will pass through the valve whenever the pressure of the paint on the membrane 39 is equal to or greater than ambient pressure.
Shaft leakage of paint from the pump 33 can be returned via the return pipe 37 to the reservoir 35.
Referring now to Figs. 6 to 13 of the drawings, novel features of the needle 10, nozzle 12 of the present invention, and air cap 13 will be described. The nozzle 12 is a one piece injection moulding of a plastics material resistant to the media it is likely to encounter, may have a high dimensional stability, good fatigue resistance and a high elongation before break. A preferred material for the nozzle is an acetal resin such as the co- or homo-polymer of polyoxymethylene. Upon elongation of either of these materials, the yield point occurs above 7% elongation. Other suitable materials have yield points between 5% and 10% elongation. In its cooperation with the needle, the nozzle is intentionally stressed. It is preferred that the yield point is not exceeded in order fully to utilise the memory of the plastics material. However, it is known that some plastics materials retain most of their memory even when stressed beyond the yield point and can recover their shape upon simple warming. Certain plastics materials may perform better if they are plastically pre-strained i.e. if they are stretched beyond their yield points. This may be effected by forcing the needle into the nozzle outlet.
Depending on the use to which the airbrush is to be put, the needle 10 may be of a plastics material or of a metal such as stainless steel or tungsten or may be coated or plated with tungsten, platinum or gold or may be treated by way of nitriding to provide appropriate surface characteristics. The nozzle 12 presents, at its forward end, an outlet in a frustro-conical shaped portion, the outlet being, with the needle in its rest position, sealed to prevent the escape of paint from a substantially annular paint flow passage 40. For an airbrush, the nozzle outlet and the needle tip are microscopic in size and hence for the purposes of illustration have been enlarged and somewhat exaggerated. The needle 10 has a tip 11 of varying taper, the taper being greatest adjacent the point and lessening (to be in the range of 1 to 6 degrees) towards the region whereat it forms a seal with the nozzle. In this region, the diameter of the needle tip 11 is only slightly greater than the diameter e.g. 0.2mm, of the outlet in the nozzle whereby the latter is stretched by engagement with the needle as the needle moves slightly beyond its seal forming position. As the needle is withdrawn (moved to the right in the drawings) due to its shallow taper and due to the contraction of the plastics material of the nozzle (caused by its memory), excellent control of the dispensation of paint through the annular passage 40 therebetween is achieved because of the greater movement of needle necessary to produce a change in the quantity of paint dispensed.
The nozzle 12 locates, in use, substantially concentrically within an air cap 13 and defines therewith an annular passage 41 for the flow of air. The frustro-conical shape of the nozzle 12 presents an annular land 42 which creates a negative pressure to draw paint out of the nozzle, and enhances turbulent flow in the air stream. A fillet of paint forms a reservoir in the angle between the needle and the land. The air turbulence atomises paint from this reservoir and from the needle and the air flow is drawn over the tip 11 of the needle 10. This land may take different shapes to increase or decrease the atomisation or the suction of paint. For example, the land 42 as shown is substantially at right angles to the axis of the nozzle. It may also take the form of a convex or concave slope of constant or varying radius of curvature or may be constituted by a slope of greater taper than that of the conicity of the remainder of the frustro-conical portion.
Within the principle upon which the present invention is based and described generally in relation to Fig. 6, many variations are possible in the cooperation between the needle and the nozzle or between the nozzle and the air cap to achieve particular effects. These are exemplified by the fragmentary diagrammatic sketches forming Figs. 6a to 6h.
In Fig. 6a, the nozzle 12 is shown as having three distinct regions of external taper. A first region 12a permits internally a relatively large passage for paint terminating in a steep internal shoulder 13a. The second region 12b is steeper than the first but axially offset from the internal shoulder to strengthen the nozzle in the region of the tip. The third region 12c is of taper only slightly greater than the internal taper of the nozzle outlet to provide the nozzle tip with the necessary stretchability. It will be seen that the air cap 13 is correspondingly shaped to provide a passage for air which will create the suction necessary to suck paint. Striations are also shown at 12d in this drawing. These represent annular roughening on the surface of the needle and/or the internal surface of the nozzle tip. It will be seen that the projecting tip of the needle is smooth to prevent the build-up of paint thereon. The internal taper of the nozzle outlet and the external taper of the needle tip can be quite high whilst still retaining the feature of stretching the nozzle and consequent contraction thereof upon retraction of the needle as described above.
Fig. 6b illustrates a nozzle tip similar to that shown in Fig. 6a. However, the internal surface of the nozzle and the external taper of the needle are much less. The internal surface of the nozzle tip may be roughened. Axial or helical grooves may be provided in an initial part of this surface which contacts the needle to provide better paint flow whilst maintaining the fine control of dispensation permitted in accordance with the present invention. The internal taper of the nozzle and the taper of the needle may alternately or additionally be chosen such that, on retraction of the needle, a wedge-shaped passage for paint is formed. The angle of this wedge is arranged to encompass the particle-size range expected in a pigment-based paint to be sprayed.
Figs.6c, 6d and 6e illustrate different forms that the end of the nozzle tip can take within the scope of the invention. It is essential that the needle tip project beyond the nozzle tip to provide focus of paint sprayed. Excessive projection reduces atomisation efficiency and too little projection reduces focussing preventing fine lines from being drawn. Bearing this in mind, it is still possible to increase the angle of taper of the needle for example to 12 degrees as shown (somewhat exaggerated) in the drawings. To achieve appropriate atomisation and focus, it is then preferred to have the end of the nozzle tip sharply undercut (Fig.6c), to provide a terminal land on the nozzle tip (Figs.6d and 6e) or to provide a stepped taper on the needle tip (Fig.6e).
The nozzle/needle combination shown in Fig. 6f illustrates another advantageous feature of the present invention. If the land 42 on the nozzle is formed as a smooth convex slope, with or without a step, only a very shallow fillet of paint can locate in the angle. Even at low air flow, the tendency for paint to be stripped from this reservoir in relatively large globules is minimised as there is insufficient depth of paint in the reservoir.
Figs.6g and 6h show cooperation between the nozzle tip and the concentrically located air cap 13 to modify the airflow over the needle tip. It has been found that efficient atomisation of paint can be maintained at low air flow pressure.
As can be seen in Fig. 7, the air cap 13 serves to locate the nozzle 12 in the body 22 of the airbrush, the air cap being a screw fit into a threaded socket in the front end of the airbrush. The air cap 13 has a skirt 43 which may be flexible arranged to fit sealingly into an appropriately dimensioned bore 44 in the body 22. Internally, the air cap 13 is shaped to receive the frustro-conical shaped nozzle 12 and defines therewith narrow air passages 45 (Fig. 7a) in the surface of the nozzle 12 and/or internally of the cap 13. To achieve greater air flow, the air passages 45 may be of trapezoidal cross-section.
The nozzle 12 has a hollow central cylindrical portion 46 having the frustro-conical shape at its forward end and a tapered hollow plug 47 at its rear end. The plug 47 is a compression fit into a similarly tapered recess 48 in the body 22. An air vent ring 49 is provided in the surface of the plug 47 (Fig. 7b) or the recess 48 (Fig. 7) and an air vent 50 leads therefrom to the exterior of the body 22. In another embodiment (not shown), the plug 47 has stepped lands and the recess 48 is similarly shaped, one of the steps providing an annular air vent ring acting in the same way as the ring 49 and communicating with an air vent 50.
Air is supplied via a passage 51 in the body 22 to the space between the central cylindrical portion 46 of the nozzle 12 and the skirt 43 of the air cap 13 and thence, via the air passages 45 to the air outlet defined by the air cap 13 and the conical portion of the nozzle 12.
The nozzle 12 has a first diameter bore 52 extending from the rear to adjacent the frustro-conical portion and a second lesser diameter bore 53 tapered at its forward end, the taper (in this embodiment) being in the range of 5 to 8 degrees. The needle 10 is located in these bores as shown in Fig. 8. A spring 54 surrounds the needle. The spring 54 or the needle 10 may be coated with a release agent to prevent binding but, preferably, the spring floats clear of the internal surface of the bore 52 and the surface of the needle stem 55. The spring 54 abuts at its forward end against the shoulder defined by the change in diameter between the first and second bores 52 and 53. It is preferred however to provide a stepped or tapered shoulder 56 at this point so as to locate and hold the forward end of the spring 54. The other end of the spring engages a head 57 of the needle 10 and is compressed so as to bias the needle to the right (as shown in the drawings). The needle is held in the bores by the spring which may also assist in centering the needle wherein.
The head 57 of the needle has a self-centering recess 58 wherein an end 59 of an operating plunger 60 locates. The head 57, besides centering the needle in the bores, serves also to prevent over-insertion of the needle in the bores. The construction of the nozzle from a plastics material, in accordance with the present invention, provides a range of non-destructive sealing positions of the needle in the nozzle outlet. In most embodiments, the needle head, particularly the modified head shown in Fig. 10a, ensures that this range is not exceeded even when the needle tip has a relatively steep taper and the plunger cooperates with the needle to define a sealing position of the needle intermediate the extremes of the range. A passage for the flow of paint to be applied extends from the feed passage 32, around the head 57 of the needle and through the first and second diameter bores of the nozzle to the tip 11 of the needle.
The plunger 60 may be sealed in the body by a pressure operated skirt 61 as shown in Fig. 8. Alternatively, as shown in Fig. 13, a stuffing box seal comprising a screw 62, spring 63, washer 64 and packing material 65 such as P.T.F.E. tape may seal the plunger 60 into the body 22 against the ingress of paint. In yet another embodiment (not shown), the plunger may be sealed to the body by a diaphragm whereby to avoid sliding surfaces.
As can be seen from Fig. 9, the needle 10 may be provided with a pre-compressed spring 66 held in position on the needle stem 55 by a washer 67 and obturation 68 whereby to ensure a bias on the needle independent of the extent of insertion of the needle 10 into the nozzle 12.
Alternatively, and as shown diagrammatically in Fig. 10, an extension spring 69 secured to the needle stem 55 or having reduced diameter portion locating on a shoulder thereof and at the other end locating on shoulder 70 of the nozzle 12 may serve to bias the needle toward its retracted position. The extension spring 69 preferably has a high initial tension.
Fig. 11 shows an alternative method of locating the nozzle 12 in the air cap 13. In this embodiment, the nozzle 12 has rearwardly of its frustro-conical portion, a first diameter cylindrical portion 71 and a second diameter cylindrical portion 72. Either or both portions may be interference fits within corresponding bore portions of the air cap 13. Narrow air passages 73 are provided longitudinally and in the surface of the cylindrical portions of the nozzle 12 or of the corresponding bore portions of the air cap 13.
In another embodiment (not shown), the nozzle is a screw fit (preferably, a left hand thread) within the air cap to prevent rotation or other movement of the nozzle relative to the air cap. A seal, similar to the seal 47 shown in Fig.7, but which permits limited axial movement, is provided in this embodiment. This arrangement permits accurate location of the needle relative to the nozzle and to air cap. The air cap may then be screwed or otherwise located in the airbrush body to determine the end position of the needle. Yet another method of preventing the nozzle from rotating in the air cap is to provide the cylindrical or conical portion of the nozzle with a non-circular e.g. polygonal, cross-section. The internal surface of the mating section of the air cap is correspondingly shaped, air passages 45 being provided, as previously described, in the surface of the nozzle or in the air cap.
Another feature which may be utilised in an airbrush is shown diagrammatically in Figs. 14 and 14a. As mentioned above, greatest control is required by an operator when least paint is being dispensed. It is preferred that any movement of the needle, initially should be caused by a magnified movement of operating member 24 i.e. movement of the needle should be some reduced function of movement of the operating member 24. For example, arcuate movement of the operating member 24 may cause movement of the needle 12 in dependance, at least initially, upon the square of the arcuate movement.
As shown in Figs. 14 and 14a, the operating member 24 comprises a control lever 74 suspended by pivotal links 75, 76 in a slot 77 in the body 22 of the airbrush. The needle operating plunger 60 is slidably located in the body 22 and is urged by a spring 78 acting on a lever 79 pivotally connected to the plunger 60, to the left as seen in Fig. 14 to bias the needle to its sealing position in the nozzle.
The lever 79 also pivotally connects to the suspension link 75 which, in turn, pivotally connects an edge of a plate 80 supporting the control lever 74. At an opposite edge of the plate 80, the link 76 pivotally connects the plate 80 with an adjustable stop 81 formed by a non-rotatable captive nut 84 in the body 22 of the airbrush. The stop 81 defines the rest (sealing) position of the needle 10. The control lever 74 can be depressed (see Fig. 2 and see also Fig. 15) to operate an air valve (not shown).
Such movement has little effect on the dispensation of paint as the movement of the needle occasioned thereby is insufficient to open the annular passage between the needle tip 11 and the nozzle 12. However, if desired, effective use of this movement of the needle can be made if the rest position of the needle is preset using the captive nut 84, to provide a predetermined dispensation of paint merely upon depression of the control lever 74. On the other hand, some lost motion may be provided to prevent rearward movement of the plunger 60, and hence of the needle upon depression of the lever 74.
If the control lever 74 is moved rearwardly, its suspension ensures that a reduced motion is transferred via the linkage to the plunger 60 to move the latter to the right, as seen in the drawings, and thereby permit corresponding movement of the needle 10 under the action of its spring.
It will be appreciated that the links 75, 76 operate only in tension and could therefore be replaced by cords, wires or the like.
Figs. 14b and 14c illustrate an alternative method of biasing the control member during dispensation of paint. A spring 78' is attached to the airbrush body and to an arm of a lever 79' pivotally attached at one end to the airbrush body and, at its other end, to the pivotal connection between the plunger 60' and the links 75'. Such a biasing arrangement can be arranged to operate at a substantially constant force irrespective of the position of the control member. Alternatively, two similar springs may be used acting collectively to provide a constant force/unit extension.
Even better initial control of the needle 10 can be achieved using a servo-assisted mechanism such as that diagrammatically shown in Fig. 15. In this embodiment, the position of the needle is pneumatically controlled. The conventional air supply to and through the airbrush is controlled by a control lever 85 operating, by depression, an air valve 86 supplying air through the body to the air cap. The control member 85 is mounted on a top member of a parallelogram linkage, the bottom member of which comprises a leaf spring 87 and the two side members comprise leaf springs. The lever 85 is movable horizontally to the right (as seen in the drawing) against the spring bias.
The air valve 86 is a double valve which supplies air, on operation, also to a servo-assisted mechanism 88. Such air passes through a throttle valve 89 and, thereafter, its pressure is controlled by a vent valve 90 operated by the horizontal movement of the control lever 85.
The servo-assisted mechanism 88 comprises a reservoir 91 made of a flexible substantially inextensible material. The reservoir has opposite edges connected respectively to the plunger 60 and to an adjustable stop 81 similar to that described in relation to Figs. 14 and 14a. Air, at a pressure controlled by the vent valve 90, is fed to the reservoir 91 to inflate the latter. Initial inflation causes only a small change in the longitudinal dimension (between the connected opposite edges) of the reservoir. Further inflation causes a greater change in the longitudinal dimension and maximum change in the longitudinal dimension occurs as the reservoir 91 approaches full inflation. In this way, great control of the movement of the needle 10 (and of the consequent supply of paint) can be exercised for fine work.
In accordance with a desirable further feature of an airbrush as described herein, control of the air supply to the nozzle can be enhanced.
Referring to Fig. 16, a very simple air control valve is shown in which air is ducted along a flexible tube 92 constrained by a duct 93 in the body of the airbrush. A spring 94 is mounted in the body and is biased upwardly as shown. The spring locates under the tube 92 at a break in the duct 93 and, by its bias, pinches the tube upwardly. The spring 94 can be moved downwardly, out of engagement with the tube 92, by corresponding movement of a control lever 74' similar to the control lever described in relation to Fig. 14.
Fig. 17 shows a further form of air control in which, additionally, the control of air is dependent upon the instantaneous position of the control member in controlling the flow of paint. In the arrangement described in relation to Fig. 14, it was indicated that the control lever 74 was moved downwardly (as indicated by the arrow in that Figure) to increase the flow of air. The arrow is shown positioned at what is the point of natural rotation of the linkage 75, 80, 76. It may be desirable, in fact, to allow the instantaneous position of the lever 74, in dispensing paint, to have an effect on the control of the rate of dispensation of air. This can be achieved, in Fig. 14, by having the point of contact of the lever 74 away from the natural point of pivotal movement of the linkage 75, 80, 76.
In Fig. 17, such an arrangement is shown; albeit utilising a modified air valve. The lower element 80' of the control lever 74' is part of a linkage 75', 80', 76'. The element 80' is, in this case, a one piece moulding integral with the lever 74' and integrally connected through a moulded hinge 95 with a member 96 telescopically containing a second member 97. The member 97 extends through a first seal 98 into and through an air chamber 99 and into engagement with a resiliently deformable seal 100. Air is fed to the chamber 99 through a passage 101. Pivotal movement of the second member 97 about the first seal 98, occasioned by corresponding movement of the control lever 74' downwardly, causes deformation of the resiliently deformable seal 100 permitting air to escape therepast and to the air cap of the airbrush. It will be appreciated that the hinge 95 can be located as desired along the linkage 75, 80', 76 during design, to achieve the effect of enhanced air dispensation. Other arrangements are possible, of course, with the embodiments described in Figs. 14, 16, 17 and 18, in which the point of operation (for example, constituted by the hinge 95 in Fig. 17) can be adjustable along the linkage i.e. the element 80' in Fig. 17.
Fig. 18 shows a modified form of air valve which can be incorporated in the arrangement of Fig. 17. In this embodiment, a piston-like member 102 is connected to the control lever (not shown) and is pivotally and/or slidably mounted in a seal 103. The end of the member 102 is telescopically located in a mushroom-headed valve 104 urged by a spring 105 onto a conical seat 106. Pivotal movement of the member 102 displaces the valve 104 from the seat 106 allowing air to be fed via the passage 101' and the chamber 99' to the air cap (not shown) of the airbrush.
In a modification of the embodiment shown in Fig.18, the valve 104 is flat-headed and is pivotally connected at its stalk end to a lever pivoted similarly to the piston 102. Pivotal movement of the lever rocks the valve on its flat head to permit the passage of air.
Throughout this description, the terms "air" and "paint" have been used. It will be appreciated that any relatively inert gas, such as Freon, may be used instead of air. Similarly, the term "paint" has been used merely for the sake of simplicity as it is known to spray both acqueous and non-acqueous based dyes or pigments.
The invention may be applied to existing airbrushes or other micro-spraying or spraying equipment or to novel airbrushes, for example, as shown in Fig. 3. It will be appreciated that many variations are possible of the integers described herein, and the description and drawings hereof are not to be considered in any way limitative thereof.

Claims

A spraying apparatus,particularly a gas-operated spraying apparatus, comprising a nozzle (12) of a plastics material having a passage (40) for medium to be dispensed, the passage having an outlet of reduced size at its forward end, a needle (10) located in the passage (40) and arranged, in use, to cooperate with the outlet to form a seal, characterised in that the nozzle (12) is made of a plastic material able to be stretched by the needle (10), the needle (10) is tapered and has a first position in which it forms a seal with the nozzle outlet but is movable to a second, rest position, beyond the seal-forming first position, in which the nozzle outlet is expanded, the nozzle material having sufficient resilient memory to return to its unstretched shape as the needle is retracted, in use to dispense medium, from the second position towards and beyond the first position.
An apparatus as claimed in claim 1 characterised in that the nozzle (12) is injection moulded from a plastics material resistant also to media to be dispensed.
An apparatus as claimed in claim 1 or 2 characterised in that the taper of the needle (10), at its region of sealing engagement with the nozzle outlet, in the first position of the needle, is in the range of 0 to 6 degrees.
An apparatus as claimed in any preceding claim characterised in that the passage (40) of the nozzle (12) tapers internally to the reduced outlet, the taper being less than 8 degrees.
An apparatus as claimed in any preceding claim characterised in that the passage (40,53,52) of the nozzle (12) extends axially of the full length of the nozzle, the needle (10) being arranged axially therein.
An apparatus as claimed in any preceding claim characterised in that the needle (10) is of substantially commensurate length as the nozzle (12) and is preassemblable therewith as a unit for insertion coaxially in a gas outlet (44) of an gas-operated spraying apparatus.
An apparatus as claimed in claim 6 characterised in that the nozzle (12) has its own integral seals (43,47) for sealing, in use, between media and air passages in the spraying apparatus.
An apparatus as claimed in claim 6 or 7 characterised in that the nozzle (12) has grooves (45) in the external surface thereof for cooperating, in use, with internal surfaces of the spraying apparatus to define air passages.
An apparatus as claimed in claims 7 and 8 characterised in that the seals (43,47) include means (49) cooperating, in use, with the internal surfaces of the spraying apparatus, for obviating the pressure difference between the air passages and media passage for preventing air leaking into the media.
An apparatus as claimed 6 or any claim dependant thereon characterised in that the nozzle (12) has at least a part of its external surface of non-circular shape arranged, in use, to mate with a correspondingly shaped part of the internal surfaces of the spraying apparatus to prevent rotation of the nozzle (12) on insertion thereof into such spraying apparatus.
An apparatus as claimed in claim 6 or any claim dependant thereon characterised in that the needle (10) has means (57,58) for centring it within the nozzle (12), such centring means being arranged to exert little or no force upon the needle (10), transverse to its axis, in the nozzle tip.
An apparatus as claimed in claim 6 or any claim dependant thereon characterised in that spring means (54,66,69) are provided in the nozzle (12) for urging the needle (10) away from its sealing position.
An apparatus as claimed in claim 12 characterised in that the spring means (54;66;69) are pre-compressed to provide a high initial, and preferably subsequently, over the operating range of the spring, a substantially constant force to ensure that the needle (10) will readily and smoothly be movable towards its retracted position.
An apparatus as claimed in claim 6 or any claim dependant thereon and claim 12 characterised in that the spraying apparatus has a retractable plunger (60) which cooperates with the needle (10), the plunger (60) being spring-loaded towards a rest position in which the needle (10) is urged thereby into sealing engagement with the nozzle (12), whereby, as the plunger (60) is retracted, the needle (10) retracts, in the nozzle (12), under the action of its own spring