Sealed beam lamp of borosilicate glass with a sealing glass of zinc silicoborate and a mill addition of cordierite

Claim 1

A sealed beam lamp comprising a filament mounted in a fixed relationship in a reflector member, the reflector member being hermetically sealed to a glass lens member by a layer of sealing material intermediate opposed sealing surfaces on the lens and reflector members, the lens and reflector members being molded from a borosilicate glass having a coefficient of thermal expansion in the range of 30 to 40×10 -7 /°C., and the layer of sealing material being a fused mixture having an effective coefficient of thermal expansion not greater than that of the borosilicate glass, the mixture being composed of a sealing glass and a mill addition, the sealing glass having a softening point below 700° C., a coefficient of thermal expansion greater than that of the borosilicate glass parts, and containing, as part of its composition, an infra-red absorbing oxide selected from copper oxide, iron oxide, and mixtures thereof, and the mill addition, as compared to the sealing glass, having a substantially higher softening point and a lower coefficient of thermal expansion, said sealing glass being a zinc silicoborate composed essentially of 60-70% ZnO, 10-16% SiO 2 , and 19-25% B 2 O 3 plus the infra-red absorbing oxide, and said mill addition being a glass having the approximate composition of the mineral cordierite.