GB371451A - Improvements in or relating to watch glasses - Google Patents

Abstract

371,451. Watch glasses. BAKELITE CORPORATION, 247, Park Avenue, New York, U.S.A.-(Assignees of Lindhe, H. E. ; 4347, Ellis Avenue, Chicago, U.S.A.) Jan. 23, 1931, No. 2353. Convention date, Jan. 24, 1930. [Class 139.] A watch crystal is made from a synthetic resinoid by applying heat and pressure at the deformable temperature of the resinoid (e.g. 400‹ F.) to a thin piece of the material and cooling under pressure. The resinoid is preferably one of the condensation products of a polyhydric alcohol (e.g. glycerol) with a polybasic acid (e.g. phthalic anhydride), generally known as alkyd resinoids. Instead of these, phenol-formaldehyde resinoids may be used, particularly those to which a high-boiling plasticizing agent has been added ; or phenol-formaldehyde resinoids treated with urea, as disclosed in Specification 280,520, [Class 2 (iii), Dyes &c.]; or resinoids obtained by the reaction of urea and formaldehyde. The watch crystal is shaped and cooled under pressure and cut to size and is inserted in the bezel by a clamp 17, 18, shown'in the Figure. The crystal 15 is reheated until softening commences and is pressed by spring 19 into the bezel groove. A crystal too large may be inserted by the reverse process or the crystal may be merely sprung into the bezel. The crystal (about 1 millimetre thick) is sliced from a plate or rod; and in a modified process is shaped and cut to size in a single operation.