EP0216674A1 - Spraying device for spraying powder - Google Patents

Abstract

Re-homogenization of an air-powder mixture, before the projection of this product.

A pulverulent product projector according to the invention comprises a housing (12) crossed by a section (20) of flexible conduit driven in oscillation, for example by means of a vibrator (22) such as for example a pneumatic ball vibrator ( 23).

The vibrator can be replaced by a "Vortex".

Description

The invention relates to a method for spraying a pulverulent product and relates more particularly to the improvement of the homogeneity of the powder jet. The invention also relates to a powdered product sprayer implementing this method.

Powder spraying is used in the most diverse industrial fields such as: insecticide spraying, the dispersion of mineral or organic additives on metal or plastic parts, during their preparation, to modify their characteristics, spraying adjuvants on the surface of food products or even dispersing hot-melt paint powder on objects to be covered, before passing these objects through an oven. All these applications, and in particular the last mentioned, require a relatively homogeneous powder jet. The powder is generally taken from a reservoir where it is maintained in the fluidized state by a gas stream, in practice air, distributed to the lower part of the reservoir, through a porous bottom wall. A calibrated gas jet, sent into a Venturi device, enables the gas-pulverulent mixture to be speeded up and transported, over several meters of pipe, to an ejection device or projector, often having the general shape a "pistol", to facilitate handling. In this type of installation, inhomogeneous powder projections are sometimes observed, which can be due to several factors such as in particular the concentration of the mixture and its speed of circulation in the pipe. First of all, the flow of the mixture is only regular within a certain range of flow speeds, of the order of 7 to 15 m / s. Below a certain lower limit speed, the flow takes place in powder packets. A flow at low speed also promotes powder deposits in the horizontal parts of the pipe and the projector. Thus, when the latter is held substantially horizontally by the user, which is most of the time the case, there is often an accumulation of powder inside the housing of the projector, which promotes inhomogeneous projection or even partial obturation. .

Furthermore, it is nevertheless advantageous to maintain a relatively low flow speed in order to obtain a fairly wide and slow jet, which reduces the wear of the nozzle, avoids "blowing" the powder onto the area to be covered and allows a better electrical charge of the particles when the headlamp is of the electrostatic type. It is therefore not possible to increase the circulation speed of the mixture in the pipe without inconvenience. Finally, another cause of "defluidization" of the powder (and therefore of non-uniformity of projection) during its transfer from the reservoir to the projector, is the centrifugal force created in the curves of the pipe. This centrifugal force indeed tends to separate the transport gas and the powder so that the powder streams are concentrated in all of the curve exteriors. In particular, when the spray of powdered product is held horizontally, as mentioned above, the pipe which is connected to the rear of this sprayer draws a bend in a substantially vertical plane. The powder is concentrated at the top of this elbow, immediately behind the projector and in many cases, there is an ejection of non-homogeneous powder.

To combat all these phenomena, it has already been proposed to place a deflector on the axis of the ejection orifice. This also has the advantage of widening the powder jet, but the connecting bridges of this deflector at the end of the projector are an additional source of projection inhomogeneity. It has also been proposed to create a vortex air jet of the "Vortex" type in the vicinity of the ejection orifice. The functioning of such systems is mainly based on the creation of turbulence in the powder spray. These increase the wear of the nozzle and induce significant pressure drops which limit the powder flow and promote wear.

The invention proposes to rehomogenize the mixture immediately before its ejection (that is to say in the projector itself) according to a process which does not have the drawbacks mentioned above.

In this spirit, the invention relates to a method of spraying a pulverulent product of the type consisting in transporting said pulverulent product between a reservoir and an ejection orifice by means of a gas stream and in ejecting the mixture of said gas and said product, characterized in that it consists in circulating this mixture in a flexible duct and in agitating said circulating mixture, upstream of said ejection orifice and by oscillating a section of this flexible duct situated in the vicinity of said ejection orifice.

The invention also relates to a sprayer of powdered product connected to means for creating and circulating a mixture of a gas and said product, and comprising an ejection orifice, characterized in that it comprises a housing containing a section of flexible conduit connected to said means for creating and circulating said mixture and a means for imparting oscillations to said section.

The means for printing the oscillations on the aforementioned section may for example be a vibrator integral with the latter or an air flow device of the "Vortex" type arranged to impart an oscillating movement to said section.

• - la figure 1 représente une installation de projection de produit pulvérulent incluant un projecteur conforme à l'invention ;
• - la figure 2 illustre le fonctionnement du projecteur de la figure 1 ;
• - la figure 3 illustre un second mode de réalisation d'un projecteur de produit pulvérulent conforme à l'invention, en fonctionnement ;
• - la figure 4 est une vue de détail d'une autre variante ;
• - la figure 5 est une coupe V-V de la figure 4; et
• - la figure 6 illustre un troisième mode de réalisation d'un projecteur de produit pulvérulent conforme à l'invention.

The invention will appear more clearly in the light of the following description of several embodiments of an arrangement in accordance with its principle, given solely by way of example and made with reference to the appended drawings in which:

• - Figure 1 shows an installation for spraying powdery product including a projector according to the invention;
• - Figure 2 illustrates the operation of the projector of Figure 1;
• - Figure 3 illustrates a second embodiment of a pulverulent product projector according to the invention, in operation;
• - Figure 4 is a detail view of another variant;
• - Figure 5 is a section VV of Figure 4; and
• - Figure 6 illustrates a third embodiment of a powdered product projector according to the invention.

Referring more particularly to Figures 1 and 2, there is shown a powder spraying installation comprising a powdered product projector 11 comprising a housing 12 provided at its front part with a nozzle 13 defining an ejection orifice 14. The the housing is further extended at its lower part by a handle 15 or by means of attachment to a robot arm. A pipe 16 is connected to the rear end of the projector. It is intended to convey an air-pulverulent product mixture taken from a reservoir 17 where said pulverulent product is maintained in the fluidized state by a continuous injection of air at the lower part of the reservoir, through a porous bottom wall. 18. The sampling is carried out by means of a device 19 forming a Venturi, interposed between the pipe 16 and a conduit 19 a plunging into the tank. Compressed air is injected into the device 19 through an inlet e .

According to the invention, the housing 12 contains means for agitating the mixture, located downstream of the ejection orifice 14 and more particularly constituted here by a section 20 of flexible conduit connected to the means for creating and circulating said mixture , described above and by a means for printing oscillations to said section. In the example, the flexible pipe section 20 is simply formed by the end part of the pipe 16 which passes longitudinally through the housing 12 while being immobilized in leaktight manner at its two ends between the rear wall 21 of the housing and the nozzle 13. To obtain relatively large oscillations of the section 20, the latter is not stretched between its two anchoring points at rest (FIG. 1). The means for printing oscillations on the section 20 is here a vibrator 22 mounted floating in the housing 12 and integral with this section 20. The vibrator 22 is, according to the example, a pneumatic ball vibrator 23. It comprises an annular cage 24 surrounding the section and attached to it. The ball 23 is subject to move inside the cage. A very flexible conduit 25 connected to a source of compressed air (not shown) opens into this cage, approximately tangentially, for injecting air therein in a direction suitable for setting the ball in motion in said cage. This movement causes a circular oscillation of the section 20 of flexible conduit and of the cage itself.

Thus, if the amplitude of the vibrations is high in the section 20, the possibly more concentrated powdered nets will follow trajectories induced by the movement, substantially describing propellers whose pitch is defined by the operating conditions, in particular the speed of the mixture and the speed of rotation of the flexible pipe section. The homogeneity of the jet at the outlet will be significantly improved. If the amplitude of the vibrations is low, we will observe a resuspension of the particles and consequently, here again, a better homogeneity of the jet. The two phenomena (course deviation and resuspension) generally coexist.

According to the example, the projector further comprises a deflector 26, known per se, located in the axial extension of the ejection orifice 14 and mainly intended to burst the jet to give it a desired opening.

Figures 4 and 5 illustrate a variant of the means for printing oscillations on the section 20. The ball vibrator is here replaced by an annular cavity 28 defined in an annular body 29 fixed to the internal wall of the housing. The section 20 of flexible conduit whose diameter outside is significantly less than the internal diameter of the annular body 29, axially passes through the latter. The cavity 28 communicates by a pipe 30 with a source of compressed air, not shown. The internal side wall 31 of the body 29 is pierced with holes 32 regularly distributed circumferentially in a plane and opening in an inclined manner in the direction of the flexible duct section. This arrangement gives rise to a vortex circulation of the air leaving the cavity 28, of the Vortex type, causing a circular oscillation of the section 20 according to a mode analogous to that of the example in FIG. 1. This arrangement presents the advantage of allowing a more compact housing to be produced for a given oscillation amplitude of the flexible duct section.

It should be noted that in the case of the embodiment of FIG. 1, possibly modified in accordance with FIGS. 4 and 5, the air exiting from the ball vibrator (or from the annular cavity which has just been described) can be reused to supply another arrangement capable of defining a vortex type vortex circulation but this time defined at the front of the housing, in the vicinity of the nozzle 13, for example by a set of holes 35 regularly distributed circumferentially tangent to a cylinder and inclined by relative to the axis, that is to say practically in the form of propeller portions, to allow the air to escape towards the outside, at the rear of the nozzle, by creating a circulation eddy contributing in a known way to homogenize the powder jet. The efficiency of this arrangement is significantly improved due to the relative homogeneity of the mixture obtained by the implementation of the invention. The holes 35 can also be slightly inclined in the direction of the axis of the powder jet.

FIG. 3 represents another variant in which the similar structural elements bear the same numerical references. According to this variant, the nozzle 13 and consequently the ejection orifice 14 have a diameter larger than the external diameter of the section 20 of flexible conduit and the end 20 a of the latter is free of movement in the vicinity of the orifice 14. The means for imparting oscillations to the section 20 is here the ball vibrator described in reference to FIG. 1 but it is obvious that this vibrator can be replaced by the arrangement of FIGS. 4 and 5. The section of the nozzle 13 and of the ejection orifice 14 can be between 2 and 4 times larger than that of section 20. Operation is similar to that which has been described with reference to FIG. 1, with a jet of powdered product more open due to the movement of the free end of section 20, as illustrated in FIG. 3 It should be noted that the ejection orifice 14 does not necessarily have a circular outline. This contour can be oblong and such that at least its largest transverse dimension is greater than the diameter of the section 20, this arrangement producing a flatter jet.

In the variant of FIG. 6, the means for imparting vibrations to the section 20 has not been shown but may be, for example, a mechanical vibrator similar to that which is described in FIGS. 1 to 3 or a pneumatic system such as that described in FIGS. 4 and 5. The projector is equipped with removable and interchangeable parts facilitating the assembly and disassembly of the section 20, either to allow its replacement when it is used, or to allow it to replace a section of different diameter, depending on the order of magnitude of the flow rates desired by the user.

Thus, the projector has a removable connection tip 36, arranged in a cavity 37 of its rear wall. This end piece has externally a threaded cylindrical part 38 screwed into a corresponding threaded portion of the cavity 37. The threaded part 38 is extended by a frustoconical part 39 which is itself positioned in a frustoconical part complementary to the cavity 37. The frustoconical part 39 is extended by a cylindrical tubular end 40. A channel 41 passes through axially the end piece 36. During assembly, the flexible pipe section 20 is forced axially on the tubular end 40 until it at least partially covers the frustoconical part 39 while widening. After which, the end piece 36 is screwed into the cavity 37, the expanded wall of the section 20 ensuring the seal by being compressed between the two aforementioned frustoconical parts. The end piece 36 is also interchangeable with others, different by the diameter of the channel 41 so as to adapt to the diameter of the flexible section chosen.

In the vicinity of the ejection orifice 14, there is provided a nozzle 41 also removable and interchangeable, comprising an axial passage 42 suitable for receiving the other end of the flexible duct section 20. This nozzle comprises, externally, a threaded part and is mounted by screwing into the threaded end of the housing. It comes to bear on an internal transverse wall 44 thereof, by means of an annular seal 45 of flexible and deformable material (foam rubber for example) which, by deforming, ensures both the maintenance of the section of flexible pipe in the nozzle, the sealing of the assembly and the damping of the vibrations transmitted by said section to the housing. These vibrations are further absorbed by a block of similar flexible material 46, forming a part of the handle 15, in the vicinity of the connection of the latter to the housing 12. Of course, the connection arrangement at the rear of the housing can be combined with the assembly of Figure 3 where the end of the flexible pipe section 20 is left free. Likewise, the principle of the damping block in the handle is adaptable to the other embodiments.

Claims (12)

1. A method of spraying a pulverulent product of the type consisting in transporting (16) said pulverulent product between a reservoir (17) and an ejection orifice (14) by means of a gas stream and in ejecting the mixture of said gas and of said product, characterized in that it consists in circulating this mixture in a flexible duct and in agitating said circulating mixture (20) upstream of said ejection orifice (14) in the vicinity thereof by oscillating a section (20) of this flexible conduit located in the vicinity of said ejection orifice (14). 2. Pulverulent product projector connected to means (16, 17) for creating and circulating a mixture of a gas and said product, and comprising an ejection orifice (14), characterized in that it comprises a housing (12) enclosing a section (20) of flexible conduit connected to said means for creating and circulating said mixture and means (22, 29) for imparting oscillations to said section. 3. Projector according to claim 2, characterized in that said means for printing oscillations to said section comprises a vibrator (22) mounted floating in said housing and integral with said section (20). 4. Projector according to claim 3, characterized in that said vibrator comprises an annular cage (24), surrounding said section and fixed to it, a ball (23) movable inside this cage and means for injecting air in this cage in a direction suitable for setting said ball in motion in said cage. 5. Projector according to claim 2, characterized in that said means for printing oscillations to said section comprises an annular cavity (28) defined in an annular body (29) fixed to the internal wall of said housing and means for injecting air in this cavity, in that said section (20) passes axially through said annular body whose internal diameter is greater than that of said section (20) and in that the internal side wall (31) of said body is pierced with holes (32) opening in an inclined direction towards said section. 6. Projector according to one of claims 2 to 5, characterized in that said section (20) is immobilized at two points inside said housing, one of these points being located in the vicinity of the orifice ejection (14) above. 7. Headlight according to one of claims 2 to 5, characterized in that the aforementioned ejection port (14) has at least one dimension larger than the diameter of said section (20) and one end (20 a ) of the latter is free of movement in the vicinity of said orifice (FIG. 3). 8. Projector according to one of claims 4 or 5, characterized in that said housing has holes (35) arranged circumferentially and helically in the vicinity of said ejection orifice (14) for the evacuation of the compressed air injected into said cage or annular cavity, by creating, in a known manner, a jet of swirling air at the rear of said ejection orifice. 9. Projector according to one of claims 2 to 6, characterized in that the ejection orifice (14) above is provided with a removable nozzle (41) having a passage (42) adapted to receive one end of said section flexible conduit (20). 10. Projector according to claim 9, characterized in that said nozzle (41) bears on an internal transverse wall (44) of said housing by means of an annular seal (45) of flexible and deformable material ensuring sealing , maintaining and damping the vibrations of said section. 11. Projector according to one of claims 2 to 10 characterized in that it comprises a removable connection end piece (36), fixed to its rear wall and in that the corresponding end of said flexible duct section (20) is connected to a channel (41), defined in this end piece. 12. Projector according to one of claims 2 to 11, characterized in that it comprises a handle (15), comprising at least one part made of flexible material (46) for damping the vibrations caused by the setting in motion of said flexible pipe section (20).

Images