GB372848A - A method of drawing tubing particularly applicable to silica glass - Google Patents

Abstract

372,848. Making silica tubing. QUARTZ ET SILICE, 8, Rue d'Anjou, Paris. Feb. 23, 1931, No. 5617. Convention date, March 28, 1930. [Class 56.] A method of drawing tubing from material which has been rendered plastic by heat or by other physical agency, particularly fused silica, consists in providing a container or crucible with a die for shaping the tubing, a mandrel so arranged that it can be moved longitudinally through the material in the crucible and become centred in relation to the die, and means .for locking the mandrel in the desired position within the crucible. The crucible 1 is lagged with heat-resisting material la and is heated bv any suitable means. Its lower end is constricted and is fitted with a ring 24, and a member 26 with an axial passage fits into the ring. The mandrel consists of a carbon tube 14 which is provided at its lower end with a collar 21 and a conical point 22. The collar 21 co-operates with the ring 24 to shape the tubing as it is drawn: The mandrel 14 is attached to the lower end of a tube 12 which has an enlargement 11 having a spherical lower end that seats in a spherical cavity in a member 8. The tube 12 also carries a weight 16 and, at its upper end, a pointer 15. Screws 30 enable the tube 12 to be locked in any desired position which can be indicated by the pointer 15 and an index pointer 20. The material to be drawn may be in the form of a tubular ingot or a solid block. In the first case, the ingot is placed in the furnace, the mandrel is passed through the hole in the ingot until it reaches the position shown, and the crucible is heated until the material melts. If the material is in the form of a solid block, the mandrel is lifted and the point 21 is allowed to rest on the block. As the material is softened by the heat, the weight 16 forces the mandrel through the material until the part 22 becomes centred in the aperture in the member 26. In both cases, after continued heating, the member 8 is screwed upwards until it is in contact with the member 11 and supports the mandrel within the crucible, and the mandrel is then locked in position by the screws 30. The member 26 is then removed, and the molten material flows downwards and is drawn out into a tube by suitable apparatus, such as that described in Specification 270,692, [Class 56, Glass]. Air passes through the hollow mandrel into the interior of the crucible by . way of a hole 31, and the draught thus caused prevents the interior of the drawn tube from being soiled by condensed vapours.