The glass to metal seal is a problem of practical importance, concerning which many investigations have been reported. In the previous paper, we studied the stresses which come from the differerence of expansion between glass and metal, as to the case of soft glass to Dumet seal.
In this paper, the auther further proceeded to the cylindrical seals with tungsten, molybdenum and fernico inside, each of which shows equal expansion in radial and axial directions, showing that no particular considerations are necessary in the stress calculations of Hull and Burger as in the case of dumet seal.
The outcome of photo-elastic experiments indicates that tungsten sealed in borosilicate glass introduces tensile stresses in tangential and axial directions while molybdenum and fernico result in tension in radial direction.
When the photo-elastic pattern proved to be tonsile as in the former, it is necessary to raise the ratio of diameter (glass vs. metal
b/
a) or to cool with as slow rate as possible after sealing lest tangential and axial cracks should happen:
On the other hand when it is compression, the reduction of
b/
a or the moderate rapid cooling is rather desirable for the prevention of oxide film from being broken by radial tension.
We determined experimentally the moderate rate of cooling as well as the breaking stress of oxide film in the fatter case.
It is of great interest to pressume the stress relaxation by viscus flow of glass during annealing, as to which some experiments were carried out in the tungsten seal.
Several fernico alloys were tested as the adequate metals sealed in soft glass, and the results suggested that Fe 47, Ni 30, Co 23 alloy could be used with success as the sealing metal in the button stem of receiving tubes in the place of dumet which has been fairely difficult to be sealed when the diameter is larger than 1mm.
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