The Strength of Glass-to-Metal Seals

JSGT_1939_V23_T308_T328

The results communicated relate to bead seals of a particular glass on cylindrical wire of a metal which contracts more than the glass when cooled. It is found that the strength increases continually for increasing bead diameter on a given 1;1 size of wire. For b/a (bead diameter/wire diameter) = 3, the strength is only 50% of that with b/a = 9. For constant b/a (= 9), the strength has a maximum for a certain angle of contact of glass and metal of about 40°. For this angle the strength is about 20% greater than for angles of 0° or 90°. It is shown that, as a consequence of these results, the maximum permissible stress measured at the centre of a seal must depend on the shape and size of the seal. In favourable cases this maximum may be considerably greater than the limit of 1 kg/mm­² laid down by A. W. Hull and E. E. Burger. Confirmatory experiments are described which show that the results may be applied to practical cases, and application to a particular case is discussed.

C. J. Milner, M.A., Ph.D., A.Inst.P.