GB918143A - Improvements in or relating to the formation of flanges on glass tubes - Google Patents

Abstract

918,143. Sealing glass. M-O VALVE CO. Ltd. July 18, 1961 [July 18, 1960], No. 25058/60. Class 56. In a method of forming a flange on a glass tube an annular disc is coaxially supported with the tube and the adjoining region heated to soften the glass whilst the disc and tube are rotated about their common axis to cause the glass of the tube to be pressed into sealing contact with the disc by centrifugal force. The glass tube 9 is supported at its lower end in the recess 10 of the adjustable support 4 with its upper end projecting through and closely fitting the hole 11 at the centre of the annular graphite disc 1. The annular glass disc 2 providing the flange is fitted over the upper end of the tube 9 and rests on the graphite disc 1, located by closely fitting upstanding wall at the top of holder 2. An electric motor M drives the holders through gears 8 at the same speed. The holder 2 is preheated to 450- 500‹ C. and a gas burner 13 is arranged to direct a narrow needle flame at the region of the seal most heat being applied to the tube, whilst the holders are rotated at 1500 r.p.m. The centrifugal force generated by rotation causes the softened glass of the tube to seal to the inner edge of the annular disc. The seal area is then annealed and cooled. The flange and tube may form part of the apparatus for an electronic travelling wave tube. When a glass flange is required it is of the same composition as the tube. A composition is given in weight percentages: 65.4 SiO 2 , 15.8 B 2 O 3 , 5.7 Al 2 O 3 , 1.9 ZnO, 2.5 BaO, 0.9 CaO, 4.3 Na 2 O, 3.0 K 2 O, 0.3 F, 0.2 Sb 2 O 3 .