Glass-to-Metal Seals

JSGT 1945 V29 T048-T076

Photoelastic measurements have been made on standard sandwich seals over a wide temperature range by means of the stress-optical bench. Between room temperature and the annealing range for a seal the stress varied considerably and usually changed its sign. The stress at any temperature could be altered considerably by a change in the thermal treatment of the seal. Change of stress with temperature depended mainly on differential free contraction between glass and metal, but in the annealing range of the glass the stress was modified by viscous flow. Where the metal had a low yield point (e.g.copper), the stress in the glass was much lower than that anticipated from differential free contraction. Axial stresses (p₀) were determined for bead seals at room temperature using the method of A. W. Hull & E. E. Burger; and the theoretical relationship between p_zand the ratio of the radii of the glass and metal components was verified by measurement. Hence the determination of axial stresses in seals could be used for rapid routine checks on the thermal expansion properties of glasses. It was also concluded that the permissible value of the stresses in bead seals at room temperature depends on their actual design and application, and in some cases can safely be considerably in excess of 1 kg/mm²tension.

G. D. Redston & J. E. Stanworth