US3063642A - Rotating heads for electrostatic atomizing and spraying apparatus - Google Patents

Description

Nov. 13, 1962 AND SPRAYING APPA RATUS Filed March 21, 1960 12a 12 Q h 'w I HIGH L POTENTIAL SOURCE Fig.4"

y W41... fi fl nited fitates The present invention relates to improvements in rotating electrostatic heads for electrostatic atomizing and spraying apparatus, which comprise in particular a sharp edge for electric leakage and combine electrical atomizing with atomization by centrifugal force. As is known, such heads may be employed in stationary, movable or portable apparatus for coating objects, according to an electrostatic process, with fine particles of materials such as paints.

Among the factors which influence the technical properties and the appearance of the object which is coated according to this method, one factor is of prime importance. This is the regular and uniform feeding of paint, which is still in the liquid state in the electrostatic head, towards the spraying edge.

In order that the paint may progress regularly and be regularly atomized and sprayed, it is necessary to ensure a progressive feeding of the paint towards the atomizing edge without sudden variation of direction and without reflections from the walls of the head.

Such sudden variations of direction can only add unnecessary resistances of varying degree which have an adverse effect on the regular flow of paint.

Reflections from the walls of the head must be carefully avoided, becausethey may create eddies in the circulation of the paint and these eddies may cause obstructions, particularly in the case when very heavy paints are utilised, such as red lead, oil paints or zinc oxide paints, etc. Eddies which are produced with such paints may create zones where there is no circulation and Where a sedimentation of the paint will be produced, which will impede or may even block the flow of paint towards the atomizing edge.

The invention has for its object to provide improvements in electrostatic heads by means of which a regular and progressive supply of paint towards the atomizing edge is ensured.

In order that the invention may be more fully understood, some embodiments thereof will now be described by way of non-limiting examples, and with reference to the accompanying drawings in which:

FIGURE 1 shows a front view of one embodiment of an improved electrostatic head according to the invention.

FIGURE 2 is a longitudinal section along XOY of FIG- URE 1.

FIGURES 3 and 4 are sections, which are similar to that of FIGURE 2, of modified embodiments.

Referring to FIGURES 1 and 2, it can be seen that the head 1, which preferably has a cylindrical shape, comprises a central part or hub 2, at the centre of which is a housing 2 by means of which the head 1 can be attached to a member (not shown) which imparts to it its rotary movement about its axis.

In accordance with the invention, the external surface of the hub comprises several successive surfaces, flaring progressively relative to the direction of feeding of the paint, in order to terminate in wide apertures through which said paint flows towards the atomizing edge.

In FIGURE 2 only two such surfaces 2a, 2b are shown externally of the hub and in FIGURE 1 only four such 3,063,642 Patented Nov. 13, 1962 apertures are shown, but it is obvious that the numbers indicated are in no Way intended to be limiting.

Preferably, these apertures 3, 4, 5, 6 are inwardly curved, in the arc of a circle about the axis of rotation O of the head. For the same purpose these apertures have a relatively small radial width in the upstream portion and flare towards the downstream portion in the direction of flow of the paint. In this manner, circulation towards the atomizing edge is facilitated through the effect of centrifugal force.

The upstream inlet of these apertures is in communication with the paint feed channel 7 which, owing to the shape of the external surface of the hub 2, offers a minimum of resistance to the flow of paint and moreover ensures a regular feeding of the paint. No eddies due to reflections of the paint can be created at any point of this circulation path and thus the above mentioned drawbacks are avoided.

Such a head, which may be made of metal or of a high resistivity material, has given excellent results during tests. In one particular embodiment, the head is constituted by a high resistivity material comprising parts by weight of a thermosetting resin of the ethoxyline or epoxid type and 3 parts of lamp-black, but the invention is obviously not limited to this example which is given simply by way of illustration. This is also true of the geometrical shape of the apertures 3 to 6.

- In the embodiment of FIGURE 3 the head comprises a substantially hollow cylindrical external part 11 which is fixed to the hub 12, whose external surface also comprises several successive surfaces 12a, 12b, flaring progressively relative to the direction of paint feed. The driving shaft for rotating the head is shown at 13.

In this embodiment the paint is fed through a nozzle 14 which is directed in such a manner that the paint jet leaving the nozzle makes a very obtuse angle with one of the external surfaces of the hub 12. arrives very obliquely on these walls and this prevents any reflection of the paint jet on any wall of the head. Therefore, the liquid advances regularly towards the apertures 15 provided between the hub and the external part 11 of the head and thereafter towards the atomizing edge.

In the case when the paint is fed through a nozzle such as 14, in order to prevent a back-fiow of this paint along the nozzle 14, this nozzle is advantageously pro vided with an ejector 16, which cooperates in directing the jet of liquid very obliquely on to the external flared surface of the hub 2 and which moreover prevents a moistening of the paint inflow pipe and consequently avoids a back-flow of the paint.

In FIGURE 3, the inlet nozzle 14 is shown substantially parallel to the longitudinal axis of the head, but ohviously, it could also be slightly inclined relative to this axis. The important condition to be fulfilled is that the paint is fed very obliquely on to the external wall of the hub 12, without being subjected to a sudden variation of direction and without reflection on any wall of the head.

FIGURE 4 shows a modification, similar to that of FIGURE 3, which is particularly suitable for heads intended to supply a large output of paint. The external part 17 of the head, instead of being cylindrical like the part 11 of FIGURE 3, has a slightly truncated cone shape. This shape combined with the external surface of the previously described hub 12, enables a film of liquid to be obtained which is thinner than in cylindrical heads and avoids any accumulation of paint inside the head. Obviously, it is also possible to provide an ejector 16 as in the previous embodiment.

I claim:

1. A rotary head for electrostatic atomizing and spraying of a fluid and combining electrical atomizing with Therefore, the liquid apeaeea atomization by centrifugal force, comprising a body portion having an edge for electric leakage, a hub within said body portion and surrounded by apertures, said hub comprising plural successive external surfaces which progressively flare outwardly towards said body portion at increasing angles with respect to the axis of rotation of the head and which are all inclined at an obtuse angle with respect to said axis of rotation, means for directing the fluid to be sprayed on to that one of those external surfaces adjacent the axis of rotation of the head in a direction substantially parallel to the axis of rotation of said head, at least one external surface of the hub serving as a centrifugal gradient to feed said fluid progressively and without sudden variations in direction towards the apertures through which it passes to the atomizing edge, and said apertures being arcuately curved and circularly disposed about the axis of rotation of the head and having a relatively small radial width in the upstream portion and flaring towards the downstream portion in the direction of flow of the fluid.

2. A rotary head for electrostatic atomizing and spraying of a fluid and combining electrical atomizing with atomization by centrifugal force, comprising a body portion having an edge for electric leakage, a hub within said body portion and surrounded by apertures, said hub comprising plural successive external surfaces which progressive'ly flare outwardly towards said body portion at increasing angles with respect to the axis of rotation of the head and which are all inclined at an obtuse angle with respect to said axis of rotation, a fluid inlet nozzle for directing the fluid to be sprayed on to that one of those external surfaces adjacent the axis of rotation of the head in a direction substantially parallel to the axis of rotation of said head, at least one external surface of the hub serving as a centrifugal gradient to feed said fluid progressively and without sudden variations in direction towards the apertures through which it passes to the atomizing edge, and an ejector provided at the end of the fluid inlet nozzle, said ejector including means in order to avoid said hub portion comprising at least two external surface a back-flow of the fluid on the outersurface of the nozzle. 40

parts inclined at diiferent and progressively increasing angles with respect to the axis of said head but which are all inclined at an obtuse angle with respect to said axis and which thus progressively flare outwardly towards said apertures.

4. In apparatus for electrostatic atomizing and spraying and combining electrical atomizing with atomization by centrifugal force for coating objects with fine particles of a material such as paint, a rotary generally cylindrical head member having an edge for electrical leakage, a hub within said head member comprising several successive external surfaces which progressively flare outwardly relative to the direction of feed of the paint jet, said jet being directed on to that one of those surfaces adjacent the axis of rotation of the head at a substantially obtuse angle, at least one surface of the hub serving to feed this paint regularly towards apertures which finally feed it to the atomizing edge, whereby any sudden variation of direction of the paint and any reflection of the paint on any wall of the head is substantially avoided and said apertures being arcuately curved and circularly disposed about the axis of rotation of the head and having a relatively small radial width in the upstream portion and flaring towards the downstream portion in the direction of flow of the paint.

References Cited in the file of this patent UNITED STATES PATENTS 2,926,106 Gauthier Feb. 23, 1960 FOREIGN PATENTS 1,110,350 France Oct. 12, 1955

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