Device for coating objects with pulverized or granular particles or flakes or fibres

Abstract

An arrangement for coating objects by depositing small metal particles on a collecting element includes an insulating support for the particles, a first electrode on one side of the support, a counter-electrode on the other side of the support having spaces therethrough, and an arrangement for creating a first alternating current electrostatic field between the counter-electrode for moving the particles off of the support and a second arrangement for creating an electric field between the collecting element and the electrode on the opposite side of the counter-electrode from the support to cause the particles to move to the collecting element, the counter-electrode and the collecting element being charged with different potentials.

Description

The present invention relates to an apparatus for coating objects with pulverized or granular particles or flakes or fibres, in which the particles used for coating are sprayed or hurled by means of an electrostatic field on a collecting element which is the object to be coated. The invention also relates to a device for performing this method.

The process according to the invention is characterized in that the coating material is brought in a fine dispersion uppon a support preferably of insulating material, on the side thereof facing the collecting element so that it is spread in an even or almost even layer loosely on the latter further that the coating material lying on the support is shaken free of the support, e.g. by electrical means, preferably by means of an alternating field, or by mechanical means such that it becomes immersed into an electrostatic field between the support and the collecting element, further that the loosened particles of coating material are accelerated by the electrostatic field until they reach the collecting element, and further that the particles of coating material hurled off the support are made to adhere to the collecting element by allotting or associating to the latter a potential which differs from the potential of one of the electrodes of the electrostatic field, after which the coating material may be intimately bonded with the collecting element by baking or by means of adhesive.

The new device is distinguished by the fact that perfect coating of the desired collecting element may now be achieved in the most simple manner, e.g. even in mass production and that an adequate intensity for any number of applications of the new method is obtained, and, moreover, the adhesion of the particles to the collecting element may be achieved in the most simple manner. Above all, however, with the device according to the invention, a layer of even thickness on the collecting element may be obtained because only charged particles are "shot out," with the consequence that these particles are orientated to one another and dispersed evenly over the surface.

A further advantage of the device according to the invention consists in that expenditure on apparatus is low, thus, e.g. change of colour of the coating material may be carried out faster and more easily and no conventional recovery system is necessary. A device according to the invention to execute the new method is characterized in that on the side of the insulating support facing away from the collecting element an electrode is provided and between the insulating material and the collecting element there is at least one counter electrode which may be in the form of a lattice or grid or may consist of single wires and may possibly be insulated, and that either the collecting element itself is an electrode or an electrode is placed before or behind it.

In the drawings there are shown several examples and embodiments of the invention. There show:

FIGS. 1 and 2 two different embodiments of the new device for performing the method according to the invention diagrammatically and in side view,

FIG. 3 a detail of further modification of the invention again in diagrammatical representation,

FIGS. 4, 5 and 6 various embodiments of the device according to the invention in a merely schematical representation in side view and

FIGS. 7, 8 and 9 further modifications of the invention in a cross sectional side view and in detail.

The first embodiment of the device according to the invention shown in FIG. 1 comprises as its most important features an insulating support 1, which, e.g. may be a plate, a hollow body of synthetic material, or may be in the form of a tape or of a conveyor belt, or which, e.g., in certain applications may be a sieve or plate of permeable material, e.g. synthetic foam or ceramic, a collecting element 2 which is the body or support to be coated and faces the insulating support 1 and electrode 3 on the side of the insulating support 1 facing away from the collecting element 2, a counter electrode 4 between the insulating support and the collecting element, and a further electrode 5 on the side of the collecting element facing away from the insulating support. The electrodes 3 and 5 are grounded or connected to earth, the counter electrode between the insulating support and the collecting element is connected to a potential of the desired level. The counter electrode is in the form of a lattice or grid, it may also be in the form of single wires, e.g. laid in loop form, or in the form of stretched wires, which may, e.g. surround one another concentrically. In any case it must be permeable, i.e., it must permit passage of the particles 6 in powder or granular form which are lying on the side of the insulating support 1 facing the collecting element 2. First, the coating material 6 is finely dispersed onto a support 1 lying opposite or facing the collecting element -- in the embodiment according to FIG. 1 it is a sheet of insulating material -- in such a manner that it lies on this in a uniform, or almost even or uniform, loose layer. After this step, the coating material on the insulating support is vibrated or shaken loose of this support. An electrostatic pulsating field is generated between the insulating support and the collecting element and the shaking or vibrating movement is executed in such a manner that the coating material becomes immersed in the electrostatic field. The loosened coating material is then accelerated by the electromagnetic field and hurled and sprayed against the collecting element. The single steps could possibly be carried out in series, like in a mass production, e.g. by making pass consecutive plate-like insulating supports or a conveyor belt acting as the insulating support first through a station where the coating material is brought thereupon or applied thereonto and then by subjecting it to the effect of the electrostatic field at a subsequent station. In the arrangement shown in FIG. 1, the shaking or vibrating loose of the coating material is carried out by electrical means. The particles sprayed or hurled onto the collecting element 2 as indicated by the arrows 14 are held on the collecting element in that the latter is assigned a potential which differs from the potential of one of the electrodes of the electrostatic field, e.g. an electrode 5 which is grounded or connected to earth may be provided at the side of the collecting element facing away from the counter electrode 4, whereas the counter electrode 4 is connected to the respective potential. Finally, the coating, if it consists of pulverized or granular particles of synthetic material will be bonded to the collecting element by stoving, baking or burning in. In other cases, when the coating material consists, for example, of sand, the side of the collecting element facing the insulating support may be coated with adhesive in order to improve and strengthen adhesion. The adhesive effect may eventually also be increased by "shooting" the particles on a sheet or synthetic material which has been made soft and sticky on the side facing the insulating support. To achieve this end, the collecting element may be warmed or heated. Finally, there are also applications, e.g. when the coating material is of polyvinylchloride, in which the coating applied forms a single cohesive layer after baking, so that this layer may be stripped off or detached from the collecting element.

In the arrangement shown in FIG. 2, between the insulating support 15 to which one electrode 17 is assigned on the side facing away from the collecting element, and the collecting element 16 there is provided on the one hand a counter electrode 18 and, on the other hand an auxiliary electrode 19 associated or connected with a high d.c. voltage or potential, e.g. again consisting of single stretched wires or in the form of a lattice or grid. The counter electrode is insulated. It may consist, for example, of wires surrounded by a layer of insulating material, e.g. synthetic material, it may, of course remain uninsulated, however. The auxiliary electrode and the counter electrode may have the same potential, in which case they may e.g. be connected to one another by insulated connecting electrodes, but they may also have different potentials. In the arrangement shown in FIG. 2, the collecting element 16 is itself the electrode.

Of course, the electrodes 3 or 5 of the arrangement shown in FIG. 1, and 17 and 16 of the arrangement shown in FIG. 2 may be connected to a sole potential, and the counter electrodes 4 (FIG. 1) or 18 and eventually 19 (FIG. 2) may be grounded or connected to earth. Of course, all the counter electrodes between the insulating support and the collecting element -- two or more such electrodes may be provided -- may be connected to the same potential. It may also be that some of the counter electrodes are of a different potential. It is also possible e.g., to ground the electrode associated to the collecting element, to connect the electrode between the insulating support and the collecting element to a d.c. voltage, and to connect the electrode on the side of the insulating support facing away from the collecting element to an a.c. voltage. When there are several counter electrodes, the counter electrode nearest to the insulating support and the electrode facing the collecting element may be grounded, whereas the electrode facing away from the insulating support may be connected e.g. to a d.c. voltage of up to 30 KV and more (e.g. 100 KV) and the electrode associated to the insulating support may be connected to an a.c. voltage of e.g. 6 - 16 KV.

For the even distribution of the pulverized or granular particles on the layer of insulating material, a sheet or layer 20 of open-pored synthetic foam material is provided above the insulating support 22 which is held in a frame 21 or mounted on some other form of support and which moves to and fro in the manner of the shaking or vibrating movement of the machine frame in a direction indicated by the arrow 23 which is parallel or almost parallel or eventually also as indicated by the arrow 24 obliquely or at an angle to the surface of the support 22 carrying the particles 25 of the coating material. This plate 20 of synthetic foamed material is connected to, e.g. an electric drive motor not shown here, which imparts the vibrations when the plate is operated, but may, however, be arrested during the remnant time. Instead of foamed material, another material, e.g. ceramic material or the like may be used. This device may also serve for cleaning contaminated or pollated coating material.

The device for performing the method according to the invention shown in FIG. 4 has an insulating support 31 of synthetic material which has the form e.g. of a pot- or basin- or bowl-like container open at the end facing the object to be coated and closed at the other end by a closing wall, for example, a bottom wall. This container 31 is thus open in the direction facing the object to be coated 32 and closed at the other end by the bottom wall 33. It also has side walls 34 so arranged as to permit immersion of the object to be coated more or less deeply into the pot. The electrode 35 is mounted on the side of the bottom wall facing away from the object to be coated, and on the other side of the bottom wall there is at least one counter electrode 36.

The rims 35a of the electrode 35 and 36a of the counter electrode 36 are turned upward slightly so that they face the lowest part 34a of the side walls of the container and cover this part towards the outside or the inside. In this way any desired orientation of the particles of the coating material may be obtained. Furthermore, it is thus possible to prevent the powder (coating material) from being deposited on the rims and from drifting towards the centre with round or circular containers.

With the arrangement shown in FIG. 5, the insulating layers 38, 39 are of synthetic material and are stairshaped or stepped. However, these layers may also be given the form of an "L" or similar shape, whereby it is essential that there are at least two surfaces running transversely or approximatively rectangularly to one another, of which the one surface -- in the drawing of the embodiment, respectively the surfaces 38a and 39a -- serves as receiving portion to receive the coating material which is fed in as indicated by the arrow 40. The insulating support extends conveniently along the entire length of the object to be coated. It may, however, correspond to only a section of this length so that some provision will have to be made for the movement of the insulating layer and the collecting element in relation to one another in longitudinal direction, e.g. in that the object to be coated is moved past the insulating layer. On one side of the receiving portion which receives the coating material, there is an electrode 41 or 42, and on the other side there is the counter electrode 43 or 44, whereby the rims 41a, 42a, 43a, 44a of the electrode and the counter electrode are turned upward on the side facing away from the object to be coated 40c such that they cover the lowermost edge of the rear surface 38b or 39b (as viewed from the object). This again has the object of permitting the orientation of the movement of the powder particles. On the side facing the object to be coated, the rims of the electrode and the counter electrode are shorter than the surface 38a of the insulating support between them so as to stand back by the amount 40d. The coating material falling on the receiving surface as indicated by the arrow 40, is first thrown up as indicated by the arrow 40a and shaken or vibrated loose from the surface and then as a consequence of the above-described arrangement of the electrode and counter electrode, it is sprayed and hurled as indicated by the arrows 40b in the direction of the object to be coated 40c. Several stepped or stair-shaped, L-shaped or similarly shaped insulating supports may be arranged over one another or facing one another and may be parallel or at an angle, e.g. in zig-zag configuration, to one another.

The device may be provided with means for generating an air cushion, which in the case of extremely great distances serves to aid the movement of the particles of coating material in direction towards the surface to be coated. An improvement in the same direction may be obtained if, in accordance with an embodiment of the invention not described further here, a feed container is provided at some greater distance or at a greater height above the insulating support, whereby the coating material is conveyed to the receiving surface e.g. by free fall.

The flow of coating material in the direction of the surface to be coated may be further intensified in that the ends of the wires of the grid-like counter electrodes pointing towards the object to be coated, are free on the side facing the said object and protrude by a specified amount beyond the rest of the counter electrode. In this manner, the particles of the coating material will be hurled with greatest intensity and concentration on the surface to be coated. As shown in FIG. 6, the insulation support may also be given the shape of a shallow bowl basin 45, whose side walls 45a, 46a slope slightly upwards and outwards, its outer edges may, but do not have to, be bent downwards as shown by 45b, 46b. The coating material falls from above as indicated by the arrow 47 onto the bowl or basin, but may also be supplied from below, e.g. via a house 48 or a pipe. In this case a sloping surface 49 may be provided beneath the insulating support to catch falling coating material which then flows as indicated by the arrow 50 in the towards direction of the collecting surface or outlet opening 51. An arrangement of this type is suitable for coating the inner surface of hollow bodies 52.

FIG. 7 shows a modification of the invention in which the insulating support 65 may be given the form of an elongated body which may be curved as shown in the drawing or prismatic or cylindrical, with an opening which may be either circular or rectangular. The coating material is fed in at the end 66 and emerges at the other end. The side walls of the body 65 are covered on the outer side by the electrode 67 and on the inner side by the counter electrode 68, either partially or entirely, whereby they conveniently leave uncovered the extreme end of the insulating support in the area of the outlet opening. In this way a short circuit between counter electrode and electrode becomes impossible. In the modification shown in FIG. 8, the outlet opening 80 of the insulating layer has an L-shaped section. In the modification shown in FIG. 9, the outlet opening 81 of the insulating layer has a T-shaped section.

An arrangement is also possible in which, for example, an insulating support runs obliquely or at an angle to the direction of feed, forming an angle with it which may be 5.degree. or 10.degree.. Instead of the layer itself running at an angle in this manner, a sloping catching surface may be provided beneath the insulating support which serves to remove coating material in excess. Such catching surface may cons-ist of several sections at an angle to one another, which form a kind of funnel which may be either symmetrical or non-symmetrical and which is characterized in that -- as for a collecting surface in one piece -- the sections lead to a lowest point associated to an outlet for the recovery of coating material in excess which leads to a removing channel or cavity or tunnel from which the material may be re-cycled by conventional means, e.g. pneumatically, with a worm or the like. Behind the outlet opening there may be conveniently provided a filter, serving to clean the fallen material, which may consist of a layer of openpored foamy plastic or sponge rubber or the like and which may be vibrated together with the collecting surface or surfaces.

The coating material may be fed manually or mechanically from above, from below or from the side. In one embodiment not shown in the drawing, the coating material is fed via a feed channel which may be vibrated by means of so-called vibrators or the like, said channel being mounted above the insulating support and attached at one end to a collecting funnel. This channel has numerous slits or holes which may be evenly or uniformly distributed along its entire length. Due to the vibration, the coating material coming from the feed funnel drifts slowly through the channel, which e.g., may be sloping, and can drop down on the layer of insulating material.

Claims

What we claim is:

1. A device for coating objects with small particles on a collecting element which comprises an insulating support means for such particles, means to agitate particles on the support, a first electrode member on one side of said support means, a counter-electrode member on the other side of the support means from said first electrode member, said counter-electrode member having spaces therethrough, said agitating means comprising means to create a first alternating current electrostatic field between the first electrode member and the counter-electrode member to displace particles from said support means, and means to create a second electrostatic field between the counter-electrode member and a collecting element on the opposite side of the counter-electrode member from the support means, said last means comprising means to charge said counter-electrode member and said collecting element with different potentials, whereby to deposit particles from said support means on such collecting element.

2. In a device as claimed in claim 1, said second field creating means comprising a second electrode member on the other side of the counter-electrode member from the first electrode member.

3. In a device as claimed in claim 1, one of said members being grounded.

4. The device as claimed in claim 1, the insulating support means having the form of a basin-like body open at the end facing the collecting element and closed at the other end and the first electrode member being located at the side of the bottom wall facing away from the collecting element to be coated, and at least one said counter-electrode member being located at the side of the wall facing the collecting element to be coated, the rims of the electrode member and the counter-electrode member being turned slightly upwards, the wall of the basin-like body extending further upward than the rims of the electrode member and the counter-electrode member.

5. The device as claimed in claim 1, in which the insulating support means comprises a layer of insulating material and has at least two transverse surfaces at different levels from each other, of which one serves to hold the coating material, and the insulating support means extending along the entire length of the collecting member on one side of the insulating support means, the rims of the electrode member and the counter-electrode member on the side facing away from the collecting element being turned upward so that they cover the lower edge of the rear surface as viewed from the collecting element.

6. The device as claimed in claim 5, in which the insulating support means comprises several stepped stair-shaped insulating supports over one another in which the surface which hold the coating material, when viewed along the length of the collecting element slope to such an extent that viewed, along the length of the supporting means, the beginning of one is on the same plane or at the same height as the end of the following one.

7. The device as claimed in claim 6, in which there is provided a feed container associated with the insulating support means arranged at a greater height above it, from which the coating material is fed onto the surface holding it by free fall.

8. The device as claimed in claim 1, in that the insulating support means has the form of a shallow bowl with sides sloping slightly upwards and outwards, and means for feeding the coating material is fed into it.

9. The device as claimed in claim 8, wherein the insulating support means has a wall running at a slight angle to the direction of feed, said wall comprising several sections at an angle to one another in such a manner that the sections of the surface to a lowermost point where there is an outlet for the recovery of coating material in excess and leading to a removing channel from which the material may be recycled.

10. The device as claimed in claim 1, in which the insulating support means has the shape of an elongated prismatic body at one end of which the coating material is fed and whose opening serves to expel the coating material, the side wall of the body being at least partially covered in the outside by the first electrode member and on the inside by the counter-electrode member, said members leaving the extreme end of the insulating support means uncovered in the area of the outlet opening.