| 摘要 |
Phenolic resin-impregnated fibrous material is cured by passing therethrough a low-frequency alternating current by means of electrodes in contact with the material. The current is initially small but builds up rapidly and then falls to a small value on completion of the cure and may be interrupted at any time to give the desired degree of cure. Current flow may be promoted by preheating the material, e.g. to a temperature in the range 80 DEG to 140 DEG C., the preheating increasing the initial current and reducing the time required for curing. A small part only of the material may be preheated, this part then passing current and causing adjacent parts to be heated and to pass current and so on. By this means the maximum current required is reduced. The invention may be applied to the curing of one or more stacked layers of impregnated fibrous material, e.g. asbestos, or to the continuous production of sheets of impregnated fibrous material by double belt machines or to the production of rods and tubes by extrusion (see Groups V and VIII). |
