GB1006929A - Improvements relating to glass-to-metal seals - Google Patents

Abstract

<PICT:1006929/C1/1> <PICT:1006929/C1/2> A "glass to metal" seal includes a massive (defined) inner member, e.g. rod or tube and a massive outer member encircling the inner member and possessing a higher coefficient of expansion than that of the glass forming the hermetic seal between the two members and located substantially wholly within the axial length of the outer member, wherein the electrical creep path between the two members is increased by extending the glass forming the seal to cover an outwardly flared internal surface of the outer member. In Fig. 2 the outer annular member 2 is sealed from the coaxial inner member 1 by means of glass 3 having an extended coating 4 over the inner surface of member 2. It is stated that by this means tenstile stress in regions 4 and 5 is mainly avoided. Where the glass seal is exposed to sub-atmospheric pressure it is preferable to shape the side of the seal having no adjoining extension with an annular concavity 7, which may be formed by a removable graphite mould 8. Fig. 3 shows an outer annular member shaped with tapered inner surfaces 9, 10. The sealing glass has extended portion 4 which is maintained in compression by shoulders 11. The radial thickness of the outer member and in some cases the inner member is greater in the seal area. The metal members may be of mild steel and the glass, the composition disclosed in Specification 582,353. At the seal area the inner member may be made of the alloy described in Specification 642,668 with coefficient of expansion matching the glass seal and the outer member of low carbon steel. The metal members may be enamelled before sealing and the seal, (for concavities up to 30 degrees from the flat) may be made using flat faced graphite moulds.