GB2054448A

GB2054448A - Production of moulded bodies with surface coatings

Info

Publication number: GB2054448A
Application number: GB8021701A
Authority: GB
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1979-07-11
Filing date: 1980-07-02
Publication date: 1981-02-18
Also published as: DE2927983B2; GB2054448B; FR2460775B1; FR2460775A1; DE2927983A1

Abstract

A moulded body 2, having a surface coating 3 and a plastics material body 2.1 having a lower melting point than that of the coating, (e.g. metal, oxide or carbide) is made by introduction of the plastics material into a mould 1 onto the heat-resistant mould face 1.1 of which the coating agent 3 has previously been applied to form a layer which can combine indirectly with the plastics body 2.1. The coating of the mould face 1.1 is effected by thermal spraying of the coating medium 3 with the mould face 1.1 at a considerably lower temperature than the temperature of the impinging coating medium, and the subsequent introduction of the plastics material into the mould 1 is effected at the earliest upon cooling of the coating medium 3 to the temperature of the plastics material 2.1. <IMAGE>

Description

SPECIFICATION Production of moulded bodies with surface coatings This invention relates to a method of producing a moulded body, having a surface coating, made from a plastics material having a lower melting point than that of the coating medium by introducing the plastics material into a mould onto the heat-resistant mould face of which the coating medium has previously been applied to form a layer which can combine directly with the basic body moulded from the plastics material.

In such a production method for moulded bodies made from hardenable plastics material, it is known, with a view to forming a particularly-intimate inseparable bond between the basic body of the moulded body and its surface coating, to use a coating medium having admixed binding agent which contains a hardenable plastics material (See, for example, German Patent No. 22 18320). In this case one is restricted to a surface coating which has a proportion of plastics material selected for the moulded body and which, consequently, is generally not as wear-resistant as a pure metal coating. For the pure metallizing of plastics material, one is still only able to apply the metal, after the moulding of the plastics body, in a separate operation.If this is to take place for metal coatings of fairly great layer thickness (of the order, for example of millimetres) for reasons of economy by thermal spraying, however, one is naturally restricted to low-melting point metals, otherwise carbonsation of the plastics material has to be reckoned with. Moreover, even in the case of plastics materials, the spraying requires preparation oftheworkpiece. Good adhesion of the surface coating can be achieved only in the case of a surface which has previously been roughened for example by sand-blasting.

The problem underlying the invention is, in the production of surface coatings in the case of moulded bodies made from plastics material having a lower melting point than that of the coating medium, to be able to use thermal spraying in an unrestricted manner, i.e. more especially without restriction from the melting temperature of the plastics material, and thus also to be able to produce surface coatings from high-melting metals, oxides, carbides and the like, and on this score to make do also without the need to involve the preliminary measure of producing an adhesive base.

In accordance with the invention, this problem is solved by providing a method of producing a moulded body, having a surface coating, made from a plastics material having a lower melting point than that of the coating medium by introducing the plastics material into a mould onto the heat-resistant mould face of which the coating medium has previously been applied to form a layer which can combine directly with the basic body moulded from the plastics material, characterised in that the coating of the mould face is effected by thermal spraying of the coating medium with the mould face at a considerably lower temperature than the temperature of the impinging coating medium and subsequent introduction of the plastics material into the mould at the earliest upon cooling of the coating medium to the temperature of the plastics material.

Accordingly, the. invention does not just involve mere recourse to a known method which by its nature is meaningfully applicable only for surface hardening, e.g. of a decorative design on a moulded body. On the contrary, the invention presupposes the recognition that the coating of a heat-resistant surface, by thermal spraying, with a coating medium using, by contrast, a considerably lower surface temperature, leads to a layer solidifying thereon which on the one hand enters into only an extremely loose bond with the surface as a result of the quenching effect resulting from the temperature difference and which on the other hand is of such roughness on its (free) surface remote from the face, depending on the choice of the grain size of the spray particles, that this rough surface is an ideal adhesion base for plastics material or for a mechanical bond to a basic body formed therefrom only upon the application of plastics material. Only with such recognition is the proposed use, in accordance with the invention, of the face, coated by thermal spraying of a coating agent (of high melting temperature as compared with the plastics material) as the prepared mould face for moulding the basic shape of a moulded body of plastics material required to be coated, able to have a meaning, in order to achieve, simply by the introduction of the plastics material into the mould (at the earliest upon cooling of the coating medium to the temperature of the plastics material) or in other words in a single moulding operation, an intimate bond of the plastics material with the coating medium.This has been able to be confirmed by tests in which, in a layer formed by thermal spraying on a cold metal mould face, at its free surface peak-to-valley heights up to 50 lim were readily able to be achieved. Decisive for this is the choice of the grain size of the spray particles, i.e.

with increasing grain size the roughness and porosity of the sprayed layer becomes greater. Relative to the possibility of bonding of this layer to the mould face, it has become apparent that, with the face having been prepared by polishing, the removal of the coated moulded body from the mould presents no difficulties of any kind.

The method in accordance with the invention has proved to be a time-saving and economical method of production for moulded bodies made from duroplastics (possibly with fibre reinforcement) and from thermoplastics having surface coatings made from all substances which are not liable to decompose.

Thus, for the surface coating not only metals, particularly high-melting point metals, for example for particular protection against wear and erosion, are unrestrictedly possible, but also for example oxides for heat-protection of the relevant moulded body or carbides, if at the same time protection against wear and heat is required. A preferred application servesforthe production of plastics bodies which are protected against lightning and/or erosion, for which purposes, as is well known, relatively large layer thicknesses of the surface coating are needed if damage to the basic plastics body of the moulded body is to be precluded with the greatest certainty.For such layer thicknesses possibly, up to millimetres, it is advisable for the spraying on to be effected as a succession of spraying-on operations, in which case it is advisable for cooling to be effected between the individual spraying phases to such an extentthatthe individual spray layers are held at their solidification temperature. This can be effected, between successive spray layers, by means of compressed air and prevents inherent tensions arising in the individual spray layers.

The invention will be described further, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a diagrammatic sectional elevation illustrating a mould being employed to carry out the method of the invention; and Figure 2 is a diagrammatic fragmentary detail, magnified about 50 times corresponding to the part circled at Z in Figure 1.

As shown in the drawing a mould 1, made from metal, is used for the production of a moulded body 2 from a plastics material, for example heathardenable plastics material, such as synthetic resin, possibly with a matrix of reinforcing material such as layers glass or carbon fibre fabric. In order to provide this moulded body 2 (or its plastics basic body 2.1) with a surface coating 3 made from a high-melting metal, for example titanium (e.g. for protection against erosion) prior to the introduction into the mould 1 of the plastics material from which the basic body 2.1 is moulded, initially the mould face 1.1 thereof is coated with the metallic coating medium 3.

This takes place on the mould face 1.1 after preparation thereof by polishing, by thermal spraying of the coating medium 3, for example by plasma spraying by means of a so-called plasma burner or spray-gun.

The mould face 1.1 which is cold upon spraying thereon of the coating agent 3 as compared with the impinging spray particles, causes quenching of the sprayed particles, which are warm, with the result that the forming layer of coating medium 3 enters into only a loose bond with the mould face 1.1. On the other hand, by using an appropriately-selected gain size for the sprayed particles, depending on the sprayed material, for instance in the range from 20 to 70 um, the result is achieved that the layer of the coating medium 3 has, at its surface remote from the mould face 1.1, a roughness with peak-to-valley values for instance between 20 and 50 Fm. This can also be influenced by appropriate control of the spray particle velocity. Thus, it is practical to work, in the closing phase of the spraying, with a considerably lower spray particle velocity than the high speed which is necessary to achieve a particularly great density (or thickness) of the surface coating 3.

Consequently the layer of the coating medium 3 on the mould face 1.1 forms a suitable bonding base for the plastics material of the basic body 2.1 which is then introduced into the mould 1 as soon as the layer of the coating medium 3 has cooled down to the temperature of the plastics material. After hardening of the plastics material (possibly under pressure in an autoclave) the moulded body 2, with the surface coating 3 clinging fast to its basic body 2.1, is removed from the mould 1. As a rule there exists such an intimate bond of the surface coating 3 that it does not loosen even in the event of distortion of the moulded body 2.

Claims

1. A method of producing a moulded body, having a surface coating, made from a plastics material having a lower melting point than that of the coating medium by introducing the plastics material into a mould onto the heat-resistant mould face of which the coating medium has previously been applied to form a layer which can combine directly with the basic body moulded from the plastics material, characterised in that the coating of the mould face is effected by thermal spraying of the coating medium with the mould face at a considerably lower temperature than the temperature of the impinging coating medium and subsequent introduction of the plastics material into the mould at the earliest upon cooling of the coating medium to the temperature of the plastics material.

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2. A method as claimed in claim 1, characterised in that the mould face is prepared for the coating by polishing.

3. A method as claimed in claim 1 or characterised in that the coating medium is applied to the mould face as a plurality of layers which are cooled or allowed to cool between the individual spraying phases.

4. A method as claimed in claim 3, characterised in that the cooling of each of the spray layers is effected by compressed air.

5. A method as claimed in any preceding claim wherein the surface coating medium is a highmelting point metal.

6. A method as claimed in any preceding claim wherein the surface coating medium is applied with a layer thickness which is adequate for protection against lightning and/or erosion.

7. A method of producing a moulded body having a surface coating substantially as herein before described with reference to and as illustrated in the accompanying drawing.

8. A moulded body, having a surface coating, produced bythe method of any preceding claim.