EP0364311A1 - Pneumatic spraying device for liquids having a flat spraying nozzle - Google Patents

Abstract

According to the invention, the spraying nozzle (16) which comprises ejection channels (40, 41) for shaping the jet, arranged to give the jet a flat fan shape, is shaped such that all the shaping air-ejection channels, to the exclusion of any other air-ejection channel, communicate with a same compressed-air distribution circuit (14, 20, 49). The other air-ejection channels can be supplied by a different compressed-air source. <IMAGE>

Description

The invention relates to a pneumatic liquid spraying device in particular for applying paint or varnish; its main purpose is to improve the spraying conditions and to facilitate the shaping of the spray of liquid sprayed.

A device is known for spraying liquid using compressed air both to transform the liquid into a bundle of fine particles and to give this bundle a desired shape, more particularly a relatively flat fan shape having a cross section d thickness as constant as possible.

Such a device is for example described in US Patent No. 2,646,314. This known device comprises a spray nozzle at the center of which are arranged a liquid ejection channel and a drive air ejection channel , annular and coaxial with said liquid ejection channel. In addition, said nozzle has other air ejection channels which, by virtue of their respective main functions, will be called spray air ejection channels and beam conformation air ejection channels. Said spraying air ejection channels are arranged symmetrically on either side of the axis of the liquid ejection channel and in this embodiment, converge towards a point on this axis (which will be called by convenience "spray point") located downstream of the liquid ejection orifice, to disperse the jet of liquid in fine droplets. Furthermore, conformation air ejection channels are also arranged symmetrically on either side of this axis and converge in pairs towards it, downstream of the spray point, that is to say to a location where the liquid jet is already sprayed. To do this, these channels are formed in horns projecting from the front surface of the nozzle on which the channel opens. liquid ejection. These horns are symmetrical with respect to the axis of the channel. The action of the "shaping air" is therefore to flatten the beam of sprayed liquid to give it the desired shape of a fan.

When it is desired to open the fan formed by the jet of liquid to the maximum, it is necessary to increase the action of the air jets of conformation from the horns. When this action becomes very important, these air jets tend to hollow out the fan in its central part, or even to cut it into two parts. An impact of the spray of liquid spray on a surface perpendicular to the spray axis thus takes the form of a full eight. To reduce this tendency, two other groups of conformation air ejection channels, opening onto the front face of the nozzle, are provided. They produce jets of additional air directed substantially parallel to the axis of ejection of the liquid. These additional air jets intercept the air jets from the horns, widen them and "spread" their action on the jet of sprayed liquid. In addition, these additional air jets tend to fill the barometric depression created at the base of the horns by the Venturi effect caused by the shaping air from said horns. The additional air jets therefore make it possible to reduce the parasitic deposit of liquid on the front face of the nozzle. They therefore also have a protective role preventing the nozzle from being soiled by the sprayed liquid.

To simplify the structure of the nozzle, all the channels opening onto the front face originate in the same pressurized air supply chamber, adjacent to and surrounding the central liquid ejection channel, while the channels used in the horns originate in an independent chamber, coaxial with the previous one and generally supplied under a different air pressure. In most cases, the two chambers are supplied by the same source of compressed air, the chamber connected to the horns being supplied by a conduit bypass with adjustable pressure drop. In other known devices, the two chambers are supplied by two independent and adjustable compressed air sources. In all of these known arrangements, the air supplied to these two chambers is acted on to adjust the width of the fan jet and the fineness of the spray. However, the actions of all these air jets interfere, which makes adjustments difficult, long and tedious.

The invention results from a more in-depth study of the specific roles of the different air jets acting on the beam; it consists in redistributing the air supply of the various air ejection channels mentioned above.

In this spirit, the invention therefore relates to a pneumatic spraying device for liquid with flat spray jet, comprising:
- a spray nozzle at the center of which is arranged a liquid ejection channel,
- at least one drive air ejection channel,
- beam-shaping air ejection channels, comprising first channels located in two parallel horns projecting from the sides of a front surface of the nozzle on which said liquid ejection channel opens, said horns being arranged symmetrically with respect to the axis of this channel and said first channels being substantially located in a plane passing through said axis and second channels located in said plane and oriented substantially parallel to said axis symmetrically with respect thereto, the orifices of these channels opening onto said front surface, and
- spray air ejection channels, characterized in that all of said conformation air ejection channels communicate with the same first compressed air distribution circuit while said air ejection channel d drive and said spray air ejection channels communicate with the same second compressed air distribution circuit.

Thanks to such an air distribution, the air jets additional shaping always have a "force" adapted to that of the shaping air jets from the horns, the ratio between the air flows of these two types of shaping jet being fixed by construction. This avoids gu'au low spray air pressures, the shaping jets from the horns hollow or cut the fan in the middle. Furthermore, at high spray air pressures, it is better able to adjust the "vigor" of the shaping air jets making it possible to give the fan a transverse thickness as constant as possible. Finally, the parasitic deposits of liquid at the base of the horns are further reduced because the barometric depression, due to the Venturi effect, caused by the jets coming from the horns, is better filled than in the past, whatever the conditions spraying, since the "vigor" of the jets of additional shaping air increases with that of the jets of shaping air from the horns causing this depression.

• - la figure 1 est une vue générale en perspective de la partie extrême du dispositif conforme à l'invention et plus particulièrement de la buse de pulvérisation;
• - la figure 2 représente partiellement le dispositif de l'invention, vu suivant une coupe longitudinale II-II dans un plan P représenté à la figure 1; et
• - la figure 3 est une coupe partielle III-III de la figure 1 dans un plan médian PM du faisceau en éventail.

The invention will be better understood and other advantages thereof will appear more clearly in the light of the following description of an embodiment of a device in accordance with its principle, given solely by way of example and made with reference to the accompanying drawings in which:

• - Figure 1 is a general perspective view of the end part of the device according to the invention and more particularly of the spray nozzle;
• - Figure 2 partially shows the device of the invention, seen in a longitudinal section II-II in a plane P shown in Figure 1; and
• - Figure 3 is a partial section III-III of Figure 1 in a median plane PM of the fan beam.

The liquid spraying device 11 comprises a body 12 of which an approximately cylindrical part has been shown and in which are defined a certain number of conduits capable of being placed in communication with a liquid inlet 13 (in particular paint or varnish), a first air inlet 14 connected to a first source of compressed air S₁₄ and a second compressed air inlet 15 connected to a second source of compressed air S₁₅. The two compressed air sources are here adjustable independently of each other. A spray nozzle 16 is fixed to one end of the body 12, by means of a threaded sleeve 17. The liquid inlet 13 is here represented by a conduit which opens into a chamber 13 a ; this duct is connected to a source of pressurized liquid, not shown. The compressed air inlets 14 and 15, also represented by conduits, open into respective chambers 14 a , 15 a . The body 11 houses an air control needle 18 slidably mounted along an axis x′x. It should be noted that the three chambers 13 a , 14 a , 15 a are aligned along this axis which is also the axis of ejection of the liquid. The needle 18 has two frustoconical bearing surfaces 14 a , 15 b controlling the communication of the chambers 14 a , 15 a with air distribution ducts 20, 21, respectively, extending in the body 12. A control needle of paint 22 is also mounted along the axis x′x. It moves partly in the needle 18 and partly in the body 12. It controls the communication of the chamber 13 a with a paint distribution duct 25 defined axially (always along the axis x′x) in a insert 26. The latter is inserted axially between one end of the body 12 and the spray nozzle 16; it is screwed into a threaded part of said body. At the end of the insert 26, in the extension of the conduit 25, is placed a liquid spray nozzle 28 terminated by a liquid ejection channel 30 which projects through the spray nozzle, in the center of it. The axis of this channel 30 is of course, the axis x′x. The spray nozzle comprises two horns 35, symmetrical with respect to the axis x′x, parallel and admitting the plane P for the median plane. The horns 35 protrude on the sides of a front face 36, substantially circular, of the spray nozzle 16. The liquid ejection duct opens through an orifice 30 to the center of this end face. Air ejection channels are provided in the spray nozzle. According to an arrangement known per se, a distinction is made between the following channels:
- A drive ejection channel 38, of annular section and arranged coaxially and parallel to the liquid ejection channel 30. It is defined between the liquid spray nozzle 28 and an axial hole in the spray nozzle 16. it therefore opens through an annular orifice 38 has on the end face 36. of course, this single annular duct could be replaced by several parallel to channel 30 and channels distributed regularly on a cylindrical surface.
- Spray air ejection channels 39, mainly characterized in that, opening onto the front face 36 through orifices 36 a , they are oblique with respect to the axis x′x. In the example, the ejection axes of these channels converge at A on the axis x′x, downstream of the orifice 30 a , relative to the direction of ejection of the liquid. As a variant, the arrangement may be such that only certain channels 39 converge towards the axis, the others being oriented on either side of this axis.
- First air ejection channels of conformation of the beam 40, formed in the horns, oblique to the axis x′x and arranged in pairs (s); they are located in a plane P, containing the axis x′x and the orifices 40 a of these channels open onto the opposite faces of the horns 35; the axes of these channels converge two by two on the x′x axis at points B1, B2 ... staggered along this axis, downstream from point A.
- Second air ejection channels of conformation of the beam 41 located here in the plane P, oriented substantially parallel to the axis x′x (or very slightly inclined with respect to it) and whose orifices 41 a open onto said front face between the axis and each horn 35, respectively. Additional air jets from of these channels participate in the conformation of the beam since they slightly "crush" the air jets coming from the orifices 40 a , which limits the risks of having a beam dug or cut in the vicinity of the plane P. In addition, as indicated above, these additional air jets prevent sprayed liquid splashes from settling at the base of the horns 35.

The plane PM containing the axis x′x and perpendicular to the plane P is defined as being the desired median plane of the fan beam 45 of sprayed liquid.

A first annular chamber 49 is defined between the nozzle 16, the insert 26, the body 12 and the sleeve 17, by the assembly of these different parts. The conduit 20 opens into the chamber 49. Thus, upstream of the spray nozzle 16 is defined a first compressed air distribution circuit comprising the chamber 49, the conduit 20, the chamber 14 a , the conduit 14 .. This first air distribution circuit is thus supplied by the source of compressed air S₁₄. Similarly, a second annular chamber 50, of generally conical shape, is defined between the spray nozzle 16 on the one hand and the liquid spray nozzle 28 and the insert 26, on the other hand. This chamber 50 therefore internally extends the drive air ejection channel 38 up to the conduits 57 formed in the insert 26 and opening into an annular chamber 58. The conduit 21 also opens into this annular chamber 58. Thus , upstream of the spray nozzle and more particularly of the channel 38, a second compressed air distribution circuit is defined, comprising the chamber 50, the conduits 57, the annular chamber 58, the conduit 21, the chamber 15 a , the duct 15 ... This second air distribution circuit is therefore supplied by the source of compressed air S₁₅.

According to the invention, all the air ejection channels of conformation of the bundle 40, 41, with the exception of any other aforementioned air ejection channel, communicate with said first compressed air distribution circuit. More in particular, said first channels 40 located in the horns communicate with the annular chamber 49 via conduits 48 also extending in said horns approximately parallel to the axis x′x, while said second channels 41 are connected to the same chamber 49 by oblique conduits 52 extending in the central part of the nozzle 16.

In addition, the drive air ejection channel 38 and the spray air ejection channels 39 communicate with said second compressed air distribution circuit. More specifically, the spray air ejection channels 39 communicate with the second annular chamber 50 by conduits or cavities 55 (FIG. 3).

With the device which has just been described, the width of the jet of sprayed liquid can be adjusted over a larger area. It is also possible to use a beam conformation air pressure which may be higher than that of the atomizing air without risk of deformation of the jet and without parasitic deposition on the atomizing nozzle. The structure which has just been described does not require precise machining of the channels 52 and cavities 55.

In addition, it should be noted that this kind of air distribution can be easily adapted to already existing pneumatic sprayers, including a sprayer provided with an adjustable bypass supplying the shaping air from the air supply. spraying, since the modifications essentially concern and can be limited to the structure of the spraying nozzle. For the user, there is no major difference in operation (no new learning) but greater ease of adjustment, within wider limits.

Of course, the embodiment which has just been described is only one example of embodiment among others. The same air distribution can be obtained in a different way, for example using intermediate separating rings between the different air inlets.

The invention makes it possible to avoid too high a flow rate of the additional air coming from said second conformation air ejection channels. This results in a reduction in air consumption and therefore a reduction in the polluting fog around the fan jet. In the case of an electrostatic application, a more effective electrostatic enveloping effect is also observed.

Claims (3)

1- Device for pneumatic spraying of liquid with flat spray jet, comprising:
- a spray nozzle at the center of which is arranged a liquid ejection channel (30),
- at least one drive air ejection channel (38),
- beam-shaping air ejection channels (40, 41), comprising first channels (40) located in two parallel horns (35) projecting on the sides of a front surface (36) of the nozzle on which opens said liquid ejection channel (30), said horns being arranged symmetrically with respect to the axis (x′x) of this channel and said first channels being substantially located in a plane (P) passing through said axis and second channels (41) located in said plane and oriented substantially parallel to said axis symmetrically with respect thereto, the orifices of these channels opening onto said front surface (36), and
- spray air ejection channels (39), characterized in that all of said shaping air ejection channels (40, 41) communicate with the same first compressed air distribution circuit (14, 20, 41) while said drive air ejection channel and said spray air ejection channels (39) communicate with the same second compressed air distribution circuit (15, 21, 58, 57, 50). 2- spray device according to claim 1, characterized in that it comprises a first annular chamber (49) forming part of said first air distribution circuit and into which open out
- conduits (48) extending in said horns and establishing the connection with said first channels, and
- oblique conduits (52) extending in the central part of said nozzle and establishing the connection with said second channels. 3- Spray device according to one of the preceding claims, wherein said drive air ejection channel is internally extended by a second annular chamber (50) forming part of said second compressed air distribution circuit, characterized in that conduits or cavities (55) extend between this chamber and said spray air ejection channels (39).

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