GB2041243A - Electrostatic powdering method and apparatus - Google Patents

Abstract

Method of electrostatically powdering a part (2) to obtain a colour grading on at least one surface thereof. A first layer of powder is applied to a face (A1) to be treated, and then a subsequent layer is applied in a non-directed manner to the opposite face (A2). Application to enamelling objects by electrostatic powdering. <IMAGE>

Description

SPECIFICATION Electrostatic powdering method and apparatus The present invention relates to an electrostatic powdering method and apparatus for creating a colour grading over one or more surfaces of a part.

Apparatus for electrostatically projecting a powder generally comprises a projection system, a source of material to be projected, and a source of electrical high tension for charging the particles to be projected.

The aim of the invention is to make use of the capability of particles to get round behind an obstacle. This capability is due to the characteristics of the powders used and to several phenomena including, interalia, the turbulence of air jets when they meet an obstacle whether they are charged with particles or not, and the attraction of charged particles to an earthed part.

The present invention provides a method of electrostatic powdering for obtaining a colour grading over the surface of a part by means of electrostatic projection of powder, the method including at least a first application of powder onto a first face of the part and a second application of powder in a nondirected manner onto a face of the part opposite to the first face.

In a first mode of performing the invention, the first application of powder is performed with powder of a base colour to give a background tint, while the second application to the opposite face is performed with a powder of a second colour to give a flambe effect.

In the case of parts which have interior angles, e.g.

a cover, the second application of powder is made in a directed manner towards the interior angles of the part.

Two modes of performing the invention are described by way of example with reference to the accompanying drawings in which: - Figure 1 shows one type of part to be treated on one face; - Figure 2 shows schematically the method of obtaining a colour grading on one face; - Figure 3 show schematically apparatus for performing the method in accordance with figure 2; - Figure 4 shows a type of part to be treated on two faces; - Figure 5 shows schematically the method of obtaining a colour grading on both faces; and - Figure 6 shows schematically apparatus for performing the method in accordance with figure 5.

With reference to figure 1, a part to be treated is constituted by a flat part 1 having holes 2 and on which it is desired to obtain a colour grading from the edges 3 and around the holes 2 in zones 4 on the face Al of the part. The principal used in achieving this variation in tint, as shown schematically in figure 2, consisting in first applying a layer of base colour to the face Al in the direction indicated by the arrow F1. The base colour provides the background tint of the part. The second, or flambe effect colour is then applied by projecting powder in a non-directed manner to the face A2 in the general direction indicated by the arrow F2.The jet carrying the coating particles of the second colour will be subject to tur bulence on meeting the part, which will encourage the deposit of the second powder along the direction indicated by arrows F3 on the face Al around the edges of the part and around the holes 2.

The result of these manipulations is a part having a background tint in accordance with the base colour, and a colour grading such thatthe colour merges progressively towards the flambe colour the nearer one approaches the edges and the openings.

The variation in colour is slow and no clear demarcation line can be distinguished between the two coatings.

Figure 3 shows schematically apparatus for electrostatic powdering to provide the desired colour grading on types of part where only one face is to be treated.

The apparatus comprises two electrostatic powdering cages A and B, parts 1 being introduced via an opening 5 in the upper portion of each cage. The cage A applies the base layer on face Al on the part 1 which is moved vertically while facing the projection system. The part 1 is then removed from the cage A and turned about an axis R. After being turned about, the part 1 is subjected to the same powdering operation but in cage B which contains the flambe powder. Heat treatment applied to the part transforms the two powder layers into an enamel coating which has the feature of colour grading on its face Al such that the tint tends towards the flambe colour the closer one approaches the egdes of the part.

Small cages can be used such as those constituting the subject matter of the Applicants' French patent application n" 7833 945 filed 1 st December 1978.

With reference to figure 4, the part to be treated is constituted by a flat part 6 having a rim 7, e.g. a cover, on which it is desired to obtain a colour grading on both faces Al and A2.

In some applications it is difficult to obtain adequate thickness of powdering in interior corners, such as 8, of a part to be enamelled. To overcome this difficulty a second layer of powder has in the past been specifically directed into the corners. Such an extra powdering operation is in itself a manufacturing drawback except in a case, such as that of the present invention, where an extra powdering operation is required for other purposes (e.g. colour grading). Under such circumstances the extra powdering operation can be arranged to provide both functions (corner filling and flambe colouring) in a single, combined operation.

The operations are outlined in figure 5: they consist in applying a first deposit on the faces Al and A2 in the direction of arrows F1 and F2 but in a nondirected manner using the base powder. The second deposit is made in a directed manner into the corners 8 along the arrow F5. The jet carrying the particles of the second colour coating is subject to turbulence which encourages its being deposited on the edges of both faces along arrows F6 and F7.

Figure 6 shows schematically apparatus for electrostatic powdering enabling the desired colour grading to be obtained on parts where both faces are to be treated. The apparatus comprises two electrostatic powdering cages C and D, the parts 6 being introduced therein via slots 9 by a continuously moving conveyor.

The cage C deposits the base layer on both faces of the part.

The cage D has two fixed pistols projecting a directed jet into the upper and lower corners of the part. Two moving pistols move along an inclined path and project the colouring material into the corners of the vertical edges. The cage D contains the flame' powder.

Cages such as those which constitute the subject matter of the Applicants' British Patent application nO 7939 105 filed 12th November, 1979, may be used.

The result of these operations, after the part has been fired, is a coating whose background tint matches the base colour, and having a colour grading such that the colour tends towards the flame' colour the closer one approaches to the edges of the part.

An advantage of the invention is to facilitate obtaining colour gradings while using industrial powdering cages.

It is applicable when the particles used have the capability of getting round behind an obstacle.

Claims (10)

1. A method of electrostatic powdering for obtaining a colour grading overthe surface of a part by means of electrostatic projection of powder, the method including at least a first application of pow der onto a first face of the part and a second application of powder in a non-directed manner onto a face of the part opposite to the first face.

2. A method according to claim 1, wherein both the first and second applications of powder are applied to opposite faces of the part in a nondirected manner, and including a third application of powder directed into interior angles present adjacent at least one of said faces of the part.

3. A method according to claim 2, wherein the third application of powder constitutes a layer for reinforcing the powdering in areas which are difficult to treat.

4. A method according to claim 1,2 or 3, wherein the initial application or applications are performed using a base colour powder which determines a background tint of the part and wherein the last application is performed using a powder of a second colour to obtain the said colour grading or flambe effect.

5. A method of electrostatic powdering for obtaining a colour grading overthe surface of a part by means of electrostatic projection of powder, substantially as herein described with reference to the accompanying drawings.

6. Powdering apparatus for performing the method according to claim 1 or claim 4 as appendant on claim 1, the apparatus comprising two cages: a first cage for applying a first layer on one face of the part; and a second cage for applying the flame effect powder in a non-directed manner on the opposite face, the part being turned about before being inserted into the second cage.

7. Apparatus according to claim 6, wherein the cages are of the type whereby the part is inserted from above.

8. Powdering apparatus for performing the method according to claims 2,3 or claim 4, as appendant on claim 2 or 3, the apparatus comprising two cages: a first cage for applying one layer onto two opposite faces of the part; and a second cage for applying the flambe effect powder into the interior angles of the part.

9. Apparatus according to claim 8, wherein the cages are of the type whereby the part is introduced via a slot by a continuously moving conveyor.

10. Apparatus according to claim 8, wherein the second cage includes two fixed pistols for covering the angles of the upper and lower edges of the part, and two moving pistols for covering the angles on the vertical edges, and moving along an inclined part.