Tungsten inert gas welding copper to stainless steel - to form vacuum tight joints suitable for helium cryostats

摘要

Process for heterogeneous welding between a copper part and a stainless steel part, uses an electric arc in inert gas. The novelty is the use of a sandwich formed by clamping a Cu plate between two stainless steel plates, the edges of the three plates being on the same level and the arc being directed onto the edge of the sandwich. The thickness of the Cu plate is pref. twice that of each of the steel plates and the edges of the plates should be sharp and without chamfer. For butt welding two tubes, both are pref. provided with a flange, and a stainless steel washer placed next to the flange on the Cu tube to form a sandwich, the tubes being rotated during welding. Process is used e.g. in helium cryostats where the welds have survived numerous thermal cycles between 4 degrees K and 620 degrees K., maintaining a vacuum of 10-9 torr with no leakage of He.