GB515692A - Improvements in the moulding of thermo-plastic mouldable materials - Google Patents

Abstract

515,692. Moulding glass. COMBINED OPTICAL INDUSTRIES, Ltd., and WILLIAMS, W. E. June 3, 1938, No. 16749. [Class 56] [Also in Group V] In moulding glass by pressing between dies I, 2 having jackets 13 for heating and cooling fluid, the dies and jackets are so constructed and arranged that the isothermals in the dies, during setting of the material, have curvatures coincident with, or are disposed parallel or convex to, the moulding surfaces of the dies whereby the material sets simultaneously and evenly throughout, or begins to set from the centre outwards. Optical defects or warping due to internal strains on setting are thus avoided. In one form, the interior surfaces of the heating jackets and of the dies in contact therewith are shaped similarly to the moulding surfaces. In other forms the jackets have plane faces. For moulding flat discs, the dies are provided with external guard rings, such as 14, 15, of material, such as steel, having the same conductivity as the dies so that the cooling of the plastic material is substantially uniform. The gap 16, between the rings is made as small as possible and may be further protected by an auxiliary ring. An insulating sleeve 17 of asbestos paper may be provided. For moulding a lens 18, as shown, the dies 1, 2 are of uniform thickness and conducting bodies 19, 20 are disposed between the dies and jackets 13. The bodies 19, 20 and guard rings 14, 15 are formed of material such as copper or a copper-silicon alloy having a' higher conductivity than the steel dies. The upper ring 14 may be provided with a steel annulus 14a. For convex lenses, in order to extract more heat from the centre of the lens, the bodies 19, 20 may be convex towards the lens, so that the isothermals'are similarly convex. In addition, for a very thick lens, the guard rings are made shorter and in the gap is provided a copper sleeve so as to retain heat at the periphery of the lens during cooling. The copper, sleeve may be heated electrically and encased in asbestos paper. Specifications 416,398 and 475,035, [both in Group XX], are referred to.