GB543172A - Improvements in methods of and apparatus for drawing glass tubing - Google Patents

Abstract

543,172. Making glass tubing. BRITISH THOMSON-HOUSTON CO., Ltd. (Ferguson, J.). Jan. 31, 1941, No. 1322. [Class 56] A method of making glass tubing consists in blowing glass vertically downwards from a tube-shaping orifice in a furnace, supporting the weight of the tubing so formed in order that it may move downwards at a predetermined speed, and passing an electric current between the flowing glass and the walls of the orifice to minimize the cooling of the skin of the glass. A furnace 11, Fig. 1, is provided with a discharge opening 15 having its lower end in contact with an orifice block 19. This block comprises an outer cylindrical shell 21, Fig. 2, and an inner cylindrical co-axial shell 22 connected at their upper ends by ribs 26 in which passages 27, 28 are formed. The molten glass flows past the ribs and through the space 23 between the shells, and air is admitted to the bore of the tubing through the passages 27, 28 and the chamber 24 within the shell 22. The block is of electrically-conductive heatresisting material, such as graphite, and electricity is passed between a terminal attached to the block and an electrode in the furnace. The heating-effect of the current prevents surface chilling of the flowing glass and provides a means by which the rate of flow of the glass through the block can be controlled. The flowing stream of glass forms into a tube which attains the required dimensions at the point 35 where the glass has set. The setting of the glass may be hastened by surrounding it with a cylindrical chamber 36 provided with nozzles 37 from which air jets are directed in to the glass. The downwardlymoving tube is supported, and its rate of movement is regulated by a conveyer composed of two endless chains 52 passing around sprockets 51 carried by pairs of parallel links 45. The chains are pressed into contact with the tube by gravity, the pressure being adjusted by a spring 56. The chains are driven in unison with one another by an electric motor at a pre-determined speed such that they frictionally support the weight of the tubing while permitting it to move downwards at the correct speed for drawing; Beneath the conveyer is a cutting-device composed of two cutter arms 71 carried by screws 69 mounted in a cylindrical casing 68. This casing is rotated periodically in alternate directions by the drive of the conveyer chains, the direction of rotation being reversed by clutches operated by electromagnets. The screws 69 are rotated by a stationary gear 76 so that the cutter is alternately moved upwards and downwards. The gearing is so arranged that the cutters move downwards in contact with, and at the same speed as, the tubing. During this movement, the cutters score or sever the tube. When the rotation of the casing 68 is reversed, the cutters are moved out of contact with the glass and move upwards again to the upper end of the casing. Specification 319,361, [Class 56], is referred to.