FLEXIBLE REPEATER MANUFACTURE 117 



square inch hydraulic pressure, and the glass seal was then high-fre- 

 quency brazed to the copper sheath. 



To keep the ocean bottom pressure off the glass seals and also to ter- 

 minate the cable insulation, a rubber seal is brazed in to the copper con- 

 tainer tube adjacent to each glass seal. This rubber seal consists of rub- 

 ber bonded to brass, which has been brazed to the copper portion of the 

 seal. The rubber terminates in polyethylene through five steps of com- 

 pounds containing successively less rubber and more polyethylene. The 

 polyethylene can be readily bonded by molding to the polyethylene in- 

 sulation of the cable. The central conductor passes through a central 

 brass tube in the rubber seal, which is also bonded to the rubber. 



To protect the rubber seals from the deleterious effects of salt water 

 immersion for long periods of time, a copper core tube is brazed over 

 each rubber seal. The core tube is arranged to equalize the pressure in- 

 side and out when submerged at ocean bottom pressure. This is accom- 

 plished with a bulge of neoprene filled with polyisobutylene, on the far 

 end of the core tube, which transmits the pressure to the inside of the 

 core tube seal. 



To make doubly sure that no salt water reaches the rubber seal, a 

 copper cover is brazed into the container outside the core tube connector 

 on each end. This cover is also brazed to the core tube connector. The 

 interstice between each of the above four seals is filled with polyiso- 

 butylene, which is viscous and inert and has very good insulating 

 qualities. 



Each end of the repeater closure (Fig. 3) contains five successive brazed 

 joints. Any one of these ten brazes, if not perfect, could cause the loss 

 of the repeater closure and jeopardize the entire repeater. All of these 

 brazes were made with the repeater in a vertical position to insure an 

 even distribution of the brazing alloy fillet around the joint. 



An upending device was provided at the pit brazing location to raise 

 the repeater on its carrier to a vertical position with either end up and 

 move it into position for brazing. The repeaters were brought into the 

 brazing area on an overhead monorail and an electric hoist. The shorter 

 repeater assemblies, before core tube and cable stub assembly, were up- 

 ended by hand and brazed from a raised platform. 



It was necessary to make all of these brazes by high-frequency induc- 

 tion heating, since the heat must be intense, contained within a very 

 narrow band, evenly distributed, and the area protected from oxidation 

 by a somewhat reducing atmosphere. The heat must be very intense 

 since the time interval for the shortest braze was 10 seconds maximum 

 and the longest was 30 seconds. A large part of the heat was dissipated 



