Patent GB-794857-A (GB)
Title: Method and apparatus for heating glass
Inventor: LABINO DOMINICK
IPC: C03B37/09
Filed: 1956-02-18
Abstract: 794,857. Crucible for making glass filaments. L. O. F. GLASS FIBERS CO. Feb. 18, 1956, No. 5092/56. Class 82(1) [Also in Group XXXV] A crucible for melting glass for filament production is made of a fire clay material the base having a plurality of orifices through which the glass may be exuded the base having a thinness and width such that application of heat laterally to the crucible to render glass therein molten provides a substantially uniform temperature condition across the material of the base. The crucible may be made of good grade porcelain, mullite or sillimanite. When made of sillimanite the crucible walls and base may be 3/16 inch thick. Mullite being a better heat conductor may be used in greater thickness. The cruciblemay be formed by slip casting or by casting an aqueous slurry of the fireclay material in an open plaster of Paris mould. When the "green" crucible has dried sufficiently it is raised to red heat and then fired at 1400- 1500‹C. giving a hard crucible of low porosity which is then drilled to provide the orifices. As shown in Fig. 1 a body 1 of refractory material is surrounded by a supporting metal casing 3 and supports a crucible 5. The body 1 has inlet parts 7 for entry of combustible gases. The shape of the crucible may be cylindrical, cup-shaped or rectangular. The inlet ports 7 direct combustion gases tangentially at the side of the crucible at about level 17. Electrodes 13, 15 extend into crucible 5 to complete an electrical circuit for control of the molten glass level (see Group by supply of fresh glass as marbles 19 from hopper 25 through electrically operated gate 23. Orifices in concentric circular arrangement are provided in the base of the crucible for passage of glass to globules from which filaments 31 are drawn by rolls 35. The filaments pass over guide block 41 and are subjected to a hot gas blast from burner 47. Fig. 5 shows a modification of the crucible in which the base is thicker and is countersunk as at 61 to provide orifices 63 which may be provided with a metallic nipple 65. The insert is preferably of platinum or an alloy thereof. The countersunk feature permits control of temperature of the glass even if the base is not thicker than the walls. Fig. 10 shows an embodiment used for drawing fine filaments wherein an upper clay crucible 91 with a single aperture 93 in the base is positioned to receive and melt fresh glass before supply to the crucible 5<SP>1</SP>. The crucible 5<SP>1</SP> may have a countersunk base which prevents gases from the chamber round the crucible leaking to the face and there burning the filaments. Heating may be by induction instead of gas combustion in which case a band of metal (e.g. molybdenum) is placed round the inside of the crucible at molten glass level and may extend to the base of the crucible. Alternatively a hollow or solid ring may be used in place of the band. The refractory characteristics of the crucible may be enhanced by impregnation with chromic anhydride: the fired crucible after cooling being immersed in an aqueous chromic anhydride solution, dried and again fired.