Process and plant for the manufacture of solid castings from an

Details Process and plant for the manufacture of solid castings from an Process and plant for the manufacture of solid castings from an

1996-01-30

1997-12-30

Hoang, Tu B.

Electric heating

Microwave heating

Fluid heater

219628, H05B 680

Patent

active

057033439

DESCRIPTION:

BRIEF SUMMARY
This Application is a 371 of PCT/EP94/01275 filed on Apr. 25, 1994.
The invention relates to a process and a plant for the manufacture of solid castings from an essentially liquid reactive medium and to an oven for heating an essentially liquid medium in accordance with the respective independent patent claim.


BACKGROUND OF THE INVENTION

The manufacture of solid castings is today being used for a very wide variety of purposes. In particular, castings of the kind that include as a pan of the casting a component or some other body that has been cast inside the casting are also being produced. One area in which such a procedure is very common is the electrical engineering components field in which components or bodies are encapsulated, for example for the purpose of protection against environmental effects or for insulation.
Such processes for the manufacture of solid castings from reactive liquid media as the casting material are known, for example, from DE-A-20 28 873. In the process described therein, the casting material used is a highly reactive epoxy resin material which is distinguished especially by the fact that, when its gelation temperature is exceeded, a reaction takes place in which thermal energy is released, and the thermal energy released during the reaction ensures that the reaction, once triggered, then proceeds, as it were, by itself, and the casting material becomes solid. To produce the casting, the casting material is introduced into a casting mould of which the inner wall has been heated to a temperature that lies above the gelation temperature of the casting material. The casting material is introduced into the mould from the base. In that operation, the casting material is supplied at a temperature which lies distinctly below the gelation temperature so that the reaction does not under any circumstances commence before the casting material has been introduced into the mould.
Although the above process has proved very successful, certain improvements are still possible. For example, the duration of a cycle, that is to say the period for which the mould is occupied in order to produce a single casting, is comparatively long, since the temperature of the casting material lies distinctly below the gelation temperature when it is introduced into the mould and the casting material has to be heated at least to the gelation temperature, at which the reaction then commences. There is consequently still room for improvement as regards employing the moulds to capacity. On the other hand, however, care must also be taken that the castings do not contain any bubbles or cracks. Cracks may occur in the casting especially if either the reactivity of the casting material is markedly increased, so that the energy peak during the reaction of the epoxy resin becomes too high, or if the inner wall of the mould is heated to a temperature too far above the gelation temperature of the epoxy resin. As a consequence the thermal stresses in the casting may be too high, which may result in the formation of cracks.
An aim of the invention is therefore to reduce the duration of a cycle, that is to say the period for which the mould is occupied to produce a single casting, and at the same time to manufacture castings that are free from bubbles and cracks.


SUMMARY OF THE INVENTION

That aim is achieved in accordance with the process by substantially preheating the casting material to a temperature close to but below its gelation temperature directly before it enters the casting mould of which the inner wall has been heated to a temperature above the gelation temperature of the casting material. That measure, that is to say substantially heating the casting material to a temperature close to but below its gelation temperature directly before it enters the mould, prevents the reaction of the casting material from commencing before the material has been fed into the mould, so that it is still in a state suitable to be fed into the casting mould. Heating of the casting material in the mould therefore does not have

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