GB448746A - Improvements in and relating to glass-to-metal seals - Google Patents

Abstract

448,746. Uniting metal to vitreous material by heat. BRITISH THOMSONHOUSTON CO., Ltd., Crown House, Aldwych, London. Sept. 16, 1935, No. 25676. Convention date, Sept. 15, 1934. [Class 39 (ii)] A hermetic seal for a leading-in or supporting conductor of an electrode of an electric discharge device having a metal envelope comprises a mass of glass or like vitreous material completely filling the space between the conductor and the periphery, encircling the conductor and spaced therefrom, of an aperture in the envelope or of a hollow metal member itself secured to the envelope. In one form, a leading-in conductor 15, Fig. 3, is sealed within a metal eyelet 32 by a mass of glass 33, the lower end of the eyelet being formed with an outwardly directed flange whereby it is attached to the exterior or interior of the metal wall 3 of a discharge vessel. To increase the leakage path between the conductor 15 and eyelet 32 the portion of the glass within the vessel is formed with a mushroom head obtained by passing the conductor 15 through a glass cylinder 33 of such length and diameter that, when placed within the eyelet 32 and heated, the upper portion of the glass flows over the edge of the eyelet. Preferably, the glass 33, eyelet 32, and conductor 15 are composed of materials which have substantially the same thermal expansion characteristic over the entire temperature range between 0‹ C. and the softening temperature of glass, as described in Specification 449,807, [Group II]. In another form, the conductor 15, Fig. 6, glass tube 39, and eyelet 42 are sealed together by mounting their lower portions in a rotary metal block and directing a gas jet upon the upper edge of the eyelet so that the parts are fused together, after which a glass cap 43 with a central aperture is placed upon the upper end of the seal and a gas jet 41 directed upon it while the whole is rotated ; the glass parts are fused together and the seal produced has extended leakage paths at its upper and lower ends. Figs. 11 and 12 show the formation of a seal from a piece of glass tubing 51 of considerably larger diameter than the conductor 15, these members being rotated while the lower part of the tubing is heated to form a thick globule of glass. This globule is placed upon the end of the eyelet which is then surrounded by a high-frequency coil 52 to fuse the glass so that it enters the eyelet. In a further modification, the eyelet is dispensed with, and the conductor 15, Fig. 18, is secured directly in a flanged aperture in the part 3 of a metal wall by a mass of glass formed by heating the central part of a glass tube 54 by gas jets 41 while the assembled parts of the seal are on a rotating jig. The heated glass moves radially inwardly upon the wire and bulges outwardly to close the aperture in the metal wall, a metal block 57 being provided to regulate the distance through which the glass member is lowered. Specification 449,125, [Group XL], also is referred to.