FLEXIBLE REPEATER MANUFACTURE 119 



by being conducted at a high rate from the copper parts to the water 

 in the cooling jackets used to contain the heat in a very narrow band. 



Circulating cooling water within a jacket prevented heat from being 

 conducted down the copper container tube to the preceding seals or to 

 the repeater unit. This water-cooled jacket was positioned only | inch 

 below the inductor, and the water was in intimate contact with the con- 

 tainer tube, which is sealed off at both ends with rubber "0" rings. In 

 addition, for the glass seal braze, the glass inside the seal cavity was kept 

 covered with water during the heat cycle. The water was fed in and si- 

 phoned out to a constant level which was kept under observation by 

 the operator and the inspector to make sure that the glass was covered 

 at all times. The rubber seal was also water jacketed on the inside of 

 the seal to prevent deleterious effects of the heat on the rubber insulation 

 around the central conductor. The inner cover braze was cjuenched before 

 the 10-second maximum interval had expired to insure that the heat did 

 not penetrate to the polyisobutylene at a sufficient rate to deteriorate 

 it or the rubber inside. 



Distribution of the heat around the container tube at the braze area 

 was controlled by locating the work in the inductor so that the color 

 came up essentially evenly all the waj^ around and at the proper level to 

 bring a fillet up to the top of the braze joint within the allowable time 

 limit. The time limit was determined by experiment so that none of the 

 previously assembled parts were damaged by the heat. This determina- 

 tion of the proper heat pattern and the prevention of overheating re- 

 quired the development of considerable skill on the part of the operator. 

 The variables encountered made it essential to rely on an operator to 

 control the heat rather than to utilize the timer with which the induction 

 heating equipment is normally controlled. 



The area to be heated for brazing was protected from oxidation by 

 enclosing it in a separable transparent plastic box and flooding the in- 

 terior with a gas consisting of 15 per cent hydrogen and 85 per cent nitro- 

 gen. This atmosphere is somewhat reducing and not explosive. The 

 brazing surfaces of the parts were chemically cleaned immediately before 

 assembly and extreme care was exercised to keep them clean until brazed. 



The container tube was shrunk to the respective glass, rubber, core 

 tube, and cover seals using hydraulic pressure so that the surfaces to be 

 brazed and the brazing alloy were in intimate contact within the brazing 

 area. If the parts were clean and kept from oxidizing by the protective 

 atmosphere, the alloy would flow upward by capillar}- action and form 

 a fillet around the top of the seal, impervious to any leak. 



The braze in each case was then leak tested with a helium mass-spec- 



