WO1986003991A1

WO1986003991A1 - Fluid spraying device

Info

Publication number: WO1986003991A1
Application number: PCT/GB1986/000016
Authority: WO
Inventors: Roberto Francesco Cosentino; Carlo Maria Pensa
Original assignee: Pharmindev Limited; O.D.L. S.R.L.
Priority date: 1985-01-09
Filing date: 1986-01-09
Publication date: 1986-07-17
Also published as: EP0215806A1; GB8500488D0

Abstract

A fluid spraying device or atomiser of the kind in which liquid to be sprayed is delivered onto the surface of a disc (14) rotating at high speed. The disc is confined within an enclosure (10) having a gateway (30) affording an outlet path for only a limited sector or angular range of the spray (34) of fluid shed from the periphery of the disc (14). To avoid dripping from the spray outlet, edges (40, 44) of an opening defining the gateway (30) are shaped to cause excess fluid to flow or drip into the enclosure.

Description

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The present invention relates to a fluid spraying device or atomiser and, more particularly, to such a device wherein fluid to be atomised is delivered onto a rotary disc so that in use a spray of finely divided fluid is shed from a peripheral portion of the disc. Various spraying devices are well known in the art, by which particles of liquids or emulsions are atomised into minute droplets by the centrifugal force and produce a spray around a 360 degree arc . Of the available spraying systems, the finest and most homogeneous spray is obtained using rotatable disc spraying devices, but the fact that the output spray is developed around a 360° arc represents a considerable drawback.

A directional spray can be produced using nozzle systems with or without air injection, high pressure or other contrivances, but such systems invariably suffer from clogging. Also the size of particles contained in the spray, varies considerably - both very small and very large particles being mixed together. We aim to avoid or at least mitigate both of the problems referred to above and, in accordance with the invention, propose a method of producing a directional spray of liquid wherein liquid to be sprayed is delivered onto a surface of the disc rotating at high speed and is shed from around the periphery thereof in the form of a finely divided spray and comprising confining the disc within an enclosure having a gateway affording an outlet for only a predetermined sector of the spray. The remaining or unused fluid is preferably collected within the housing for recycling to the rotatable disc .

Also in accordance with the present invention,we propose a directional spraying device comprising a housing defining a chamber, a rotatable disc enclosed within the chamber, a motor for driving the disc at high speed, a feed system for delivering liquid to be sprayed onto a surface of the disc to be shed from around a peripheral portion thereof in the form of a finely divided spray, the housing having a gateway aligned with the peripheral portion of the disc in a direction normal to the axis of rotation and corresponding in angular extent to only a sector of the peripheral portion of the disc whereby the spray of liquid emerging from the housing through the gateway has a predetermined limited angular range.

The size of the rotary disc is selected or is variable according to the nature of the liquid to be atomised and of the desired output and the disc is preferably driven by a motor having a variable speed of from 0 to 60,000 rpm. To avoid a dispersion of the electrostatic charges when the spraying device is used for electrostatic deposition, the housing is best made of non conductive material. The rotatable disc is preferably dished and may be either inverted or upright, the liquid in each case being delivered onto the internal (i.e. concave) surface thereof and due to the action of centrifugal force, distributed over the lip of the dished disc to produce a finely divided spray around a 360° arc. The angular range of the spray emerging from the housing is determined by the size of the gateway which may be variable in size to permit adjustment of the spraying range .

In addition to restricting the angular range of the emergent spray to a predetermined sector of the spray generated by the disc, the shape and size of the gateway may be such as to restrict the field of spraying in other directions, to produce any desired contour.

The gateway may be defined by an outlet opening in the walls of the housing or in a baffle or the like suspended in the path of the spray to the outlet opening, or by -a combination of the two. In order to avoid dripping of excess liquid from the housing edges of an opening at least partly defining the gateway, are preferably mitred or otherwise shaped to form lips that serve to encourage excess liquid to flow or drip into the housing. Liquid may be delivered either from an external source or recycled from a sump within the housing, by a liquid feed system incorporating a pump. Alternatively, the spraying device may have a recycling duct to which suction is applied by rotation of atomising disc or by a separatre impeller. The spraying device of the present invention is particularly suited for use in the electrostatic deposition of coating materials inter_a_l_ia_ because the electro-static effect is enhanced due to the homogeneity and fineness of Lhe obtained droplets.

When used for electrostatic deposition, the spraying device of the present invention is connected to a high potential difference for charging the particles whether by ionisation, induction or contact depending upon the properties of the liquid employed: fluidity, viscosity, surface tension, conductivity, capacity of the metering device .

One important factor in obtaining a thin continuous and uniform coating film by electrostatic spray deposition, is the ratio charge/mass of the particles. From this point of view, the spraying device of the present invention is ideally suited for use in electrostatic spray deposition.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a cross—section of one embodiment of liquid atomiser according to the present invention;

Figure 2 is a part cross-sectional view on arrow A in Figure 1 ;

Figure 3 is a cross-section of another embodiment of atomiser particularly suitable for spraying hot liquids;

Figure 4 shows a detail of a modified embodiment similar to the embodiment of Figure 3; Figure 5 is a part cross-sectional view on arrow B in Figure 2;

Figure 6 is a cross-section of a third embodiment of atomiser according to the invention;

Figure 7 is a cross-section of a fourth embodiment of liquid atomiser according to the invention; and

Figure 8 is cross-section on arrow C in Figure 7. The liquid atomiser of Figure 1 comprises a square housing 10 on which is mounted a variable speed motor 11 which is normally a pneumatic motor, the output shaft 12 of which extends downwardly into a chamber defined within the housing 10 and has mounted fo.r rotation therewith an inverted dished disc 14 arranged within a splash guard in the form of a cylindrical skirt 16.

Although shown square in Figures 1 and 2 this shape is not essential. It may be polygonal, circular or even irregular in shape. Liquid is pumped from a reservoir 20 having a level control 21, along an inlet pipe 22 communicating with transverse passages 24 in a discharge head 26, from which liquid is delivered onto the underside surface of the disc 14 rotating at high speed. Due to the action of centrifugal force, liquid spreads over the disc and is shed in a finely divided spray from all around the peripheral edge of the disc in a plane generally normal to the axis of rotation of the disc.

On one side of the housing 10 is a gateway 30 including an outlet slot 32 through which a portion of the finely divided spray 34 issued from the housing. As will be seen from Figure 2, the gateway 30 is arranged symmetrically with respect to the direction of rotation, about a diametral line through the disc 14, the sector or angular range of the spray 34 emerging from the housing 10 being detercined by the length of the slot 32. The remainder of the spray 34 collides with the interior of the housing and drains into a sump 36 at the bottom of the housing 10, the sump 36 being connected by a pipe 38 to return unused liquid to the reservoir 20.

It will be understood that the direction of the spray can be adjusted by adjusting the position of the housing and that the angular extent or field of the spray depends upon the length of the outlet slot 32 which, if desired, may also be made adjustable.

In order to prevent liquid dripping from the outlet slot 32 the peripheral edge 40 thereof is mitred as shown so that the slot converges in the spraying direction to a lip 42 on the downstream side. Along the inner edge of the slot 32 liquid incidient thereon will simply drain down into the sump 36 but along the top edge liquid would flow to the lip 42 from which drips would fall outside the housing To avoid this, that edge may be mitred in the opposite direction but in the illustrated embodiment the gateway 30 includes a mitred member 44which is disposed adjacent the upper edge of the opening so forming a V-shaped channel 46 between the downstream lip and an upstream lip 48 on the mitred member. Any drops thus fall into the chamber and drain into the sump 36. The embodiments of Figures 3 - 5 are similar to the embodiment of Figure 1 in that they include an inverted dished disc 14 but in these embodiments liquid is drawn upwardly from the sump 36 along a suction tube 50 from which it is delivered onto the underside of the disc. In the embodiment of Figure 3 which is designed for liquids to be sprayed hot, liquid is drawn upwardly along helical grooves 54formed in an extension 52 of the motor shaft 12 rotating within the tube 50. In Figure 4 a separate impeller 56 connected for rotation with the motor shaft 12, is provided and serves also to cool down the liquid to be sprayed.

In other respects the embodiments of Figures 3 to 5 are similar to the embodiment of Figures 1 and 2 except that the gateway 30 includes an additional mitred member 58 provided along the inside lower edge of the outlet opening 32 so defining with the mitred edge of the opening an open ended V-shaped channel 60 between the upstream 62 and downstream lips 64, along which liquid can drain into the chamber . The embodiment of Figure 6 differs from the above described embodiment, in that the dished disc 14 is upright, so that liquid delivered onto the disc moves radially outwardly and upwardly to the peripheral edge, to be shed therefrom in a finely divided spray. Figures 7 and 8 show an embodiment of atomiser for producing a directional spray 70 inclined below the horizontal and is suitable for applications in which, a product to be sprayed is moved past the atomiser on a conveyor. The top 72 of the housing 10 on which the motor 11 is mounted, is inclied such that the motor shaft 12 and the disc 14 rotate about an axis that is inclined to the vertical producing a spray radiating from the axis in an inclined plane.

The gateway 30 in this embodiment, is provided by a baffle plate 74 secured to the housing wall by a pillar 76 and suspended between the disc 14 and an outlet slot 78 in the housing wall. The edges of a slot 80 in the baffle plate 74 are mitred so that the slot diverges to form a lip 82 at the downstream side of the baffle plate. It is the length of the slot 80 in the baffle plate 74 and not the outlet opening 78 that determines the field of. spray 70 emerging from the housing and the baffle plate shields to a considerable extent the housing wall in the region around the outlet opening. For this reason, most of the excess liquid drops from the baffle plate directly into the sump, however, and dripping from the outlet opening is largely eliminated. If needed, however, a lip such as shown in Figure 1 or Figure 2 may be provided around the outlet opening.

In any of the embodiments described but as shown only in Figures 7 and 8, the housing may have an inner chamber 84enclosing the rotating disc 14 and an outer chamber 86 around the inner chamber providing a heating jacket for heating the liquid to be sprayed. This is necessary when spraying certain viscous fluids. Heat may be supplied in any convenient manner known to those skilled in the art. Preferably, the jacket is filled with oil an_d heate_d by an electric heating element

Claims

1. A method of producing a directional spray of liquid wherein liquid to be sprayed is delivered onto a surface of the disc rotating at high speed and is shed from around • the periphery thereof in the form of a finely divided spray and comprising confining the disc within an enclosure having ,- a gateway affording an outlet for only a predetermined sector of the spray .

2. A method according to claim 1 and comprising causing the outlet spray to pass through an opening at least partly defining the gateway and having edges that are mitred or

10 otherwise shaped to cause excess liquid to flow or drip into the enclosure, thereby avoiding the. excess liquid dripping outside the enclosure.

3. A directional spraying device comprising a housing defining a chamber, a rotatable disc enclosed within the

15 chamber, a motor for driving the disc at high speed, a feed systerr. for delivering liquid to be sprayed onto a surface of the disc to be shed from around a peripheral portion thereof in the form of a finely divided spray, the housing having a gateway aligned with the peripheral portion of

20 the disc in a direction normal to the axis of rotation and corresponding in angular extent to only a sector of the peripheral portion of the disc whereby the spray of liquid emerging from the housing through the gateway has ^' a predetermined limited angular range.

25

4. A device according to claim 3 wherein the housing is polygonal in cross-section and wherein the gateway comprises an opening in one wall of the housing and is arranged symmetrically with respect to the direction of rotation, about a diametral line through the disc.

5. A device according to claim 3 or claim 4, and comprising a sump arranged such that liquid sprayed against the walls of the chamber drains into the sump, the liquid feed system incorporating a pump for recycling liquid from the sump.

6. A device according to any one of claims 3 to 5 wherein the disc is mounted for rotation about a vertical axis or an axis inclined to the vertical, the gateway comprising an opening in a vertical wall of the housing.

7. A device according to any one of claims 3 to 6 wherein at least a part of the gateway converges in the spraying direction to a lip at the downstream side.

8. A device according to any of claims 3 to 7 wherein the gateway comprises a first portion that is divergent from a lip at the upstream side and a second portion that is convergent to a lip at the downstream side.

9. A device according to claim 8 wherein the second portion of the gateway comprises an opening in the wall of the housing and the first portion is defined by a mitred member disposed adjacent the interior housing wall along at least an upper peripheral edge of the opening and preferably also along the lower peripheral edge thereof so as to define between the two lower lips an open ended drainage channel.

10. A device according to any one of claims 3 to 7 wherein the gateway comprises an opening in baffle plate disposed between the peripheral portion of the disc and an outlet opening in a wall of the housing the opening having a shape and size selected so to produce a desired field of spray.

11. A device according to claim 7 wherein the opening in the baffle plate converges in the spraying direction to a lip at the downstream side thereof.

12. A device according to any one of claims 3 to 11 wherein the disc is dished, the liquid feed system being adapted to deliver liquid onto the concave surface thereof.

13. A device according to any one of claims 3 to 12 in which means are provided to heat the liquid to be sprayed, the heating means preferably comprising a heatin_g jacket around at least part of the chamber.