| 摘要 |
<p>In a compression moulding process for producing audio or video record discs, the material is brought to temp. by a succession of brief high frequency induction heating impulses during which the blank disc may also be compressed to bring it to the correct size and temp. for definitive shaping and cooling while using sustained compression. Used for moulding gramophone or video discs from thermoplastic moulding materials, having a high dielectric loss tangent, such as PVC, cellulose acetate, acetal polymers, etc. Reduces heat use and losses compared with processes in which heat transfer for heating and cooling is effected by conduction involving bulky metallic components in significant repetitive temp. changes. Use of intermittent inductive heating results in a more uniform temp. distribution than continuous induction, by reducing the effects of preferential heat adsorption by any relatively warm material having thereby an enhanced dielectric loss factor.</p> |
