GB633118A - Improvements in or relating to methods of, and apparatus for, manufacturing synthetic jewels - Google Patents

Abstract

633,118. Gems. GENERAL ELECTRIC CO., Ltd., and DAUNCEY, L. A. July 14, 1947, No. 18673. [Class 43] [Also in Group XXXV] A synthetic gem boule or rod, e.g. of corundum or spinel, is formed by progressive crystallization of molten constituent material on a surface, means being provided to move the surface away from the heat source automatically in accordance with the growth of the boule or rod. Synthetic corundum is made from alumina powder which is carried from a vibrated hopper 6 by a flow of oxygen to an oxyhydrogen burner 3 in a furnace chamber comprising a hollow cylinder 2 of glass or other transparent material. Molten alumina accumulates on the top of a ceramic rod 11, which projects into the furnace chamber and is movable downwardly by a rack and pinion drive from an electric motor 16 controlled by a photo-electric cell on which is focused an image of the molten material. The ceramic rod 11 moves slowly out of the furnace, the molten alumina progressively crystallizing to form a boule or rod. The ceramic rod 11 should move a little too quickly, so that the incandescent material moves out of focus and the photo-electrical cell stops the motor by relay means 22, the rod 1 remaining stationary until the molten alumina has built up sufficiently to switch on the motor again. If the rod moved too slowly the luminous mass would rise out of focus and would continue to do so since the motor would not then become energized. Since the voltage to operate the relay 22 is greater than that required to hold it, small reductions in the intensity of light falling on the cell would not affect the relay when operating. The circuit is therefore periodically interrupted long enough to release the relay so that it will re-operate only if the voltage is sufficient. The same result may be achieved by periodically interrupting the light path. As an alternative to starting and stopping the motor, the photo-electric cell output may control the speed of the motor which will run continuously. Various diameters of rod or boule may be grown by varying the normal position of the top of the molten material with respect to the burner, this being effected by adjusting the focus of the optical system accordingly.