GB898830A - Improvements in vulcanisation - Google Patents

Abstract

<PICT:0898830/IV (a)/1> <PICT:0898830/IV (a)/2> Rubber-like materials (i.e. natural or synthetic rubber) are vulcanized by preheating to a temperature approximating to but not exceeding a "limit temperature" (defined as the temperature which cannot be exceeded, even for an instant, without the unvulcanized condition being replaced substantially instantaneously by a vulcanized condition) and charging the preheated material into a mould heated to a temperature appreciably above the "limit temperature" so as to bring the temperature of the material rapidly above the "limit temperature" throughout its mass. The preheating temperature should be such as to provide a "scorch time" longer than the time required for charging the mould and the mould temperature limited to that which the material can endure without deterioration. The result of the application of this method is claimed to be the reduction of vulcanization times which previously were reckoned in periods of minutes to periods which can be reckoned in seconds. A suitable mould is shown in Fig. 1 comprising two parts 1, 2 insulated on the outside by lagging 9, 10 and containing electric heating resistances 3, 4, 5, 6. Alternatively, the mould shown in Fig. 4 may be used, the two parts 20, 21 being of insulating material embedded in a metal reinforcing body and provided with internal metal casings 22, 23 heated by an electric resistance 24. With this mould, the preheated material can be introduced into the mould cavity before the casings 22, 23 are heated which is of particular importance if large moulds are to be filled without the risk of scorching. Other moulds (not shown) have only one metal casing covering all or part of the cavity surface of one of the mould parts. Alternatively, a continuous method of moulding in which the material is preheated before being fed on to a rotary moulding device or during the first part of its progress on the device, or a batch method of moulding, may be used.