GB602126A - Improvements in or relating to the production of optical lenses and other devices having an optically accurate finish - Google Patents

Abstract

602,126. Moulding lenses &c. from plastic materials. JOHNSON, J., and COMBINED OPTICAL INDUSTRIES, Ltd. Oct. 12, 1945, No. 26747. [Class 87(ii)] An article having an optically accurate finish is moulded by laying a preformed blank 12 of thermoplastic material on a metallic die 13, applying a high-frequency electric current to an upper metallic die 14 to heat the blank and, when the blank reaches moulding temperature, switching the current off and raising a press platen 20 to apply the moulding pressure to the blank. The blank is cooled during moulding by the dies which are relatively cold due to their high thermal capacity and the fact that very little heat is generated in them by the high frequency current. The dies may be positively cooled by making them hollow and passing water through them or by supporting them in hollow sockets which receive cooling water, in which case the dies are electrically insulated from the sockets by a good conductor of heat such as mica. The cooling arrangement described in Specification 572,748 may be used. The upper die 14 is screwed into a metallic socket 15 which is rigidly secured to the upper platen 17 of the press. A block 16 of insulating material is positioned between the socket and the platen. The lower die 13 is slidably mounted in a surround 18. A helical spring 21 is situated beneath the die to restrain the downward movement of the die and to facilitate removal of the moulded article by raising the die when the platen 20 is lowered. The lower platen is earthed. One or both of the dies may be mounted in surrounds of insulating material such as glass or porcelain. The blank may be prepared by mechanical operations as described in Specification 556,743. The general arrangement of the moulding press may be that illustrated in Specification 556,743 or Specification 572,748. Specification 585,580 also is referred to.