[0001] 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.
[0002] 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.
[0003] Fig.1 is a diagrammatic fragmentary cross-section of a known nozzle/needle combination.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] "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.
[0020] Fig. 2 of the accompanying drawings is a fragmentary diagrammatic sketch of a prior
art airbrush air and paint (needle) control means.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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. 3
a, 3
b and 3
c. 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. 4
a, 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. 4
a could be provided in one half of such a coupling.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] Shaft leakage of paint from the pump 33 can be returned
via the return pipe 37 to the reservoir 35.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
6
a to 6
h.
[0034] In Fig. 6
a, the nozzle 12 is shown as having three distinct regions of external taper. A first
region 12
a permits internally a relatively large passage for paint terminating in a steep internal
shoulder 13
a. The second region 12
b 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 12
c 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 12
d 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.
[0035] Fig. 6
b illustrates a nozzle tip similar to that shown in Fig. 6
a. 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.
[0036] Figs.6
c, 6
d and 6
e 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.6
c), to provide a terminal land on the nozzle tip (Figs.6
d and 6
e) or to provide a stepped taper on the needle tip (Fig.6
e).
[0037] The nozzle/needle combination shown in Fig. 6
f 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.
[0038] Figs.6
g and 6
h 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.
[0039] 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. 7
a) 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.
[0040] 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. 7
b) 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.
[0041] 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.
[0042] 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.
[0043] 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. 10
a, 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] Another feature which may be utilised in an airbrush is shown diagrammatically in
Figs. 14 and 14
a. 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.
[0050] As shown in Figs. 14 and 14
a, 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.
[0051] 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).
[0052] 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.
[0053] 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.
[0054] It will be appreciated that the links 75, 76 operate only in tension and could therefore
be replaced by cords, wires or the like.
[0055] Figs. 14
b and 14
c 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.
[0056] 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.
[0057] 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.
[0058] 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 14
a. 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.
[0059] In accordance with a desirable further feature of an airbrush as described herein,
control of the air supply to the nozzle can be enhanced.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. 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.
9. 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.
10. 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.
11. 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.
12. 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.
13. 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.
14. 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
1. Appareil pulvérisateur, en particulier pulvérisateur à gaz, comprenant une buse (12)
en plastique avec une tubulure (40) de distribution de milieu, ladite tubulure ayant
un orifice de sortie de taille réduite a son extrémité avant, un pointeau (10) situé
dans la tubulure (40) et disposé, a l'emploi, pour coopérer avec l'orifice de sortie
en vue de formerun joint d'étanchéité, caractérisé en ce que la buse (12) est fabriquée
en un plastique pouvant être étiré par le pointeau (10), que le pointeau (10) est
effilé et qu'il a une première position dans laquelle il forme un joint étanche avec
l'orifice de sortie de la buse mais peut se déplacer pour passer à une deuxième position,
ou position d'arrêt, au-delà de sa première position d'étanchéité, dans laquelle l'orifice
de sortie de la buse est dilaté, le matériau de la buse ayant suffisamment de mémoire
résiliente pour revenir à sa forme non étirée quand le pointeau est rétracté, à l'emploi,
pour distribuer le milieu, de sa deuxième position pour reprendre la direction de
sa première position et aller au-delà de celle-ci.
2. Appareil selon la revendication 1 caractérisé en ce que la buse (12) est moulée par
injection à partir d'un plastique également résistant aux milieux à distribuer.
3. Appareil selon la revendication 1 ou 2 caractérisé en ce que la conicité du pointeau
(10), à sa zone d'engagement d'étanchéité avec l'orifice de sortie de la buse, dans
la première position du pointeau, est de l'ordre de 0 à 6 degrés.
4. Appareil selon toute revendication précédente caractérisé en ce que la tubulure (40)
de la buse (12) s'effile intérieurement jusqu'à l'orifice de sortie de taille réduite,
la conicité étant inférieure à 8 degrés.
5. Appareil selon toute revendication précédente caractérisé en ce que la tubulure (40,
53, 52) de la buse (12) s'étend axialement sur toute la longeur de la buse, le pointeau
(10) étant disposé axialement à l'intérieur.
6. Appareil selon toute revendication précédente caractérisé en ce que le pointeau (10)
est de longeur effectivement proportionnée à celle de la buse (12) et peut être préassemblé
avec cell-ci de manière à constituer une unité susceptible d'être introduite coaxialement
dans un orifice de sortie de gaz (44) de pulvérisateur à gaz.
7. Appareil selon la revendication 6 caractérisé en ce que la buse (12) possède ses propres
joints d'étanchéité (43, 47) intégrés pour constituer une étanchéité, à l'emploi,
entre les tubulures de milieux et d'air dans l'appareil pulvérisateur.
8. Appareil selon les revendications 5 ou 7 caractérisé en ce que la buse (12) comporte
des rainures (15) dans sa surface extérieure afin de coopérer, à l'emploi, avec les
surfaces internes de l'appareil pulvérisateur pour définer les tubulures d'air.
9. Appareil selon les revendications 7 et 8 caractérisé en ce que le joints d'étanchéité
(43, 47) comprennent un moyen de coopération, à l'emploi, avec les surfaces internes
de l'appareil pulvérisateur, pour pallier la différence de pression entre les tubulures
d'air et la tubulure de milieux afin d'empêcher l'air de s'introduire dans les milieux.
10. Appareil selon la revendication 6 ou toute revendication en dépendant caractérisé
en ce que la buse (12) comporte une partie au moins de sa surface externe de forme
non circulaire disposée, à l'emploi, pour s'apparier à une partie de forme correspondante
des surfaces interne du pulvérisateur de manière à empêcher toute rotation de la buse
(12) lors de son introduction dans ledit appareil pulvérisateur.
11. Appareil selon la revendication 6 ou toute revendication en dépendant caractérisé
en ce que le pointeau (10) comporte un moyen (57, 58) de centrage permettant de le
centrer dans la buse (12), ledit moyen de centrage étant agencé de manière à exercer
une force infime ou nulle sur le pointeau (10), transversalement par rapport à son
axe, dans l'extrémité de la buse.
12. Appareil selon la revendication 6 ou toute revendication en dépendant caractérisé
en ce qu'il existe un système à ressort (54, 66) dans la buse (12) afin d'amener le
pointeau (10) à s'écarter de sa position d'étanchéité.
13. Appareil selon la revendication 12 caractérisé en ce que le système a ressort (54;
66; 69) est précomprimé afin de fournir une force initiale élevée, et ultérieurement
de préférence sur toute la gamme de fonctionnement du ressort, une force à peu près
constante pour faire en sorte que le pointeau (10) puisse être déplacé, d'emblée et
sans heurts, vers sa position de retrait.
14. Appareil selon la revendication 6 ou toute revendication en dépendant et selon la
revendication 12 caractérisé en ce que l'appareil pulvérisateur comporte un plongeur
(60) rétractable qui coopère avec le pointeau (10), le plongeur (60) étant chargé
par à ressort vers une position d'arrêt dans laquelle le pointeau (10) est amené,
de ce fait, à former un engagement d'étanchéité avec la buse (12), aux termes duquel,
quand le plongeur (60) se retire, le pointeau (10) se retire, dans la buse, sous l'action
de son propre ressort.
1. Sprühapparat, inbesondere ein Gasdrucksprühapparat, bestehend aus einer Düse (12)
aus einem Kunststoffmaterial mit einem Durchlauf (40) für zu dosierendes Medium, wobei
der Durchlauf an seinem vorderen Ende einen Auslaß von kleinerer Größe aufweist, einer
im Durchlauf (40) befindlichen und bei Gebrauch zum Zusammenwirken mit dem Auslaß
zur Bildung einer Dichtung angeordeneten Nadel (10), dadurch gekennzeichnet, daß die
Düse (12) aus einem durch die Nadel (10) dehnbaren Kunststoffmaterial hergestellt
ist, die Nadel (10) zugespitzt ist und eine erste Stellung hat, in welcher sie eine
Dichtung mit dem Düsenauslaß bildet, aber zu einer zweiten Ruhestellung jenseits der
eine Dichtung bildenden ersten Stellung beweglich ist, in welcher der Düsenauslaß
ausgedehnt wird, wobei das Düsenmaterial genugend elastisches Erinnerungsvermögen
hat, um in seine ungedehnte Form zurückzukehren, während die Nadel bei Gebrauch zur
Dosierung von Medium von der zweiten Position in Richtung auf die erste Position und
darüber hinaus eingezogen wird.
2. Ein Apparat gemäß Anspruch 1, dadurch gekennzeichnet, daß die Düse (12) aus einem
auch gegen die zu dosierenden Medien resistenten Kunststoffmaterial spritzgegossen
ist.
3. Ein Apparat gemäß Anspruch 1 oder 2, dadurch gekennzeichnet, daß die Konizität der
Nadel (10) im Bereich ihres eine Dichtung bildenden Eingriffs mit dem Düsenauslaß
in der ersten Stellung der Nadel im Bereich von 0 bis 6 Grad liegt.
4. Ein Apparat gemäß einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß
der Durchlauf (40) der Düse (12) innen zum kleineren Auslaß hin spitz zuläuft, wobei
die Konizität weniger als 8 Grad beträgt.
5. Ein Apparat gemäß einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß
der Durchlauf (40, 53, 52) der Düse (12) axial über die gesamte Länge der Düse verläuft,
wobei die Nadel (10) axial darin angeordnet ist.
6. Ein Apparat gemäß einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß
die Nadel (10) im wesentlichen eine mit der Düse (12) gleiche Länge hat und damit
als eine Einheit zur koaxialen Einführung in einen Gasauslaß (44) eines Gasdrucksprühapparates
vormontierbar ist.
7. Ein Apparat gemäß Anspruch 6, dadurch gekennzeichnet, daß die Düse (12) ihre eigenen
integralen Dichtungen (43, 47) zum Abdichten, bei Gebrauch, zwischen den Medien und
den Luftpassagen im Sprühapparat aufweist.
8. Ein Apparat gemäß Anspruch 5 oder 7, dadurch gekennzeichnet, daß die Düse (12) in
ihrer Außenfläche bei Gebrauch zur Abgrenzung von Luftpassagen mit den Innenflächen
des Sprühapparates zusammernwirkende Nuten (15) aufweist.
9. Ein Apparat gemäß Anspruch 7 oder 8, dadurch gekennzeichnet, daß die Dichtungen (43,
47) bei Gebrauch mit den Innenflächen des Sprühapparates zur Vermeidung des Druckunterschiedes
zwischen den Luftpassagen und dem Mediendurchlauf zusammenwirkende Mittel (49) einschließen,
und dem Entweichen von Luft in die Medien vorzubeugen.
10. Ein Apparat gemäß Anspruch 6 oder einem davon abhängigen Anspruch, dadurch gekennzeichnet,
daß die Düse (12) bei Gebrauch mindestens einen Teil ihrer nicht kreisförmigen Außenfläche
zur Anpassung an einen entsprechend geformten Teil der Innenfläche des Sprühapparates
angeordnet hat, um Rotation der Düse (12) bei deren Einführung in einen solchen Sprühapparat
zu verhindern.
11. Ein Apparat gemäß Anspruch 6 oder einem davon abhängigen Anspruch, dadurch gekennzeichnet,
daß die Nadel (10) Mittel (57, 58) für ihre Zentrierung innerhalb der Düse (12) hat,
wobei solche Zentriermittel fur die Ausübung einer geringen oder keiner Kraft auf
die Nadel (10) quer zu ihrer Achse in der Düsenspitze angeordnet sind.
12. Ein Apparat gemäß Anspruch 6 oder einem davon abhängigen Anspruch, dadurch gekennzeichnet,
daß in der Düse (12) Federmittel (54, 66, 69) zur Wegdrängung der Nadel (10) von ihrer
Abdichtstellung vorgesehen sind.
13. Ein Apparat gemäß Anspruch 12, dadurch gekennzeichnet, daß die Federmittel (54, 66,
69) zur Erzeugung einer hohen anfänglichen, und vorzugweise anschließend im wesentlichen
konstanten Kraft über den Wirkungsbereich der Feder vorgespannt sind, um zu gewährleisten,
daß die Nadel (10) einfach und leicht in Richtung auf ihre eingezogene Stellung hin
beweglich ist.
14. Ein Apparat gemäß Anspruch 6 oder einem davon abhängigen Anspruch und Anspruch 12,
dadurch gekennzeichnet, daß der Sprühapparat einen einziehbaren Kolben (60) hat, der
mit der Nadel (10) zusammenwirkt, wobei der Kolben (60) in Richtung auf eine Ruhestellung
gefedert ist, in welcher die Nadel (10) dadurch in einen eine Dichtung bildenden Eingriff
mit der Düse (10) gedrängt wird, wobei sich die Nadel (10) in der Düse (12) bei Einziehen
des Kolbens (60) unter der Einwirking ihrer eigenen feder einzieht.