SOME CERAMIC MANUFACTURING DEVELOPMENTS 257 



in obtaining a suitable supply since manufacture of parts of this general 

 class was largely a side line incident to the production of artificial 

 gems. Development of a technique for molding these lenses was 

 therefore undertaken. The method adopted consists of forming the 

 lenses from glass rod softened by heating in gas flames. The forming 

 is performed by using steel dies in a small punch press on the front of 

 which are mounted the gas fixtures. 



Since the colored glass rod used in lens manufacture was obtainable 

 at that time only from European sources, with the advent of the World 

 War it was decided to undertake manufacture of the rod. This 

 development required a careful consideration of the characteristics 

 desired in lenses for use in switchboard lamp caps. These lenses 

 must have sufficient light dispersion characteristics to make the lens 

 visible at any angle from which it may be viewed in service. The 

 degree of opacity must also be such as to make either weak light 

 signals visible or to prevent glare with strong light signals. In view 

 of the cost relation between lamp cap lenses and switchboard lamps, 

 variations in the light diffusion and light transmission of lenses must 

 be kept at a minimum since the degree of such variations frequently 

 determines the useful life of the lamps. In addition the lenses must 

 be able to withstand repeated impact shocks from plug tips and the 

 relatively rapid heating in the operation of forming the lenses by 

 punching. 



In view of the characteristics desired, glasses having approximately 

 twenty to thirty per cent lead oxide were investigated. Small gas- 

 fired crucible furnaces were used in the preliminary work for batch 

 melting and an impact machine was devised to simulate blows received 

 in service in order that theoretical life tests could be made on the glasses 

 developed. Comparative tests were also made on the light trans- 

 mission qualities of the various glasses developed. 



Originally, light dispersion in lamp cap lenses was obtained with 

 sandblasted lenses of clear glasses. The first work therefore consisted 

 of the development of suitable clear glasses of the desired colors. 

 Silica, sodium oxide, and lead oxide combinations were investigated 

 and approximate limits for these constituents were established to 

 cover glasses of suitable viscosity, durability, and clarity. Final 

 compositions were then evolved by progressive small changes in the 

 amounts of the various constituents used. Since the color and working 

 characteristics of the glasses were influenced by the rates and amounts 

 of heating, the furnace conditions, and other variations encountered 

 in melting and working the glasses, these progressive changes involved 

 considerable time to evaluate properly the results of'any composition 



