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Metal Selection

The most commonly used metal for pinch-off is OFHC (Oxygen Free, High Conductivity) copper. ASTM B 133-83 (B 170-82) (CDA-101) gives the specifications, chemistry and state of ductility for pinch-off grade copper. Because the material undergoes a deformation of approximately 350% during pinch-off, it is important that the material be fully annealed, preferably in a hydrogen atmosphere.

Another commonly used material is high-purity nickel #200 (ASTM-B-161). This material offers several advantages: minimal outgassing during bake-out and pinch-off, minimal oxidation and higher temperature bakeability. As with copper, nickel tubulation must be fully annealed at pinch-off.

Good results also can be obtained with aluminum (annealed 3003 H14), pure iron, gold, platinum, silver and columbium.
The cold-welded area will be work hardened during pinch-off and micrographs will show a dense, elongated grain structure.
The size or length of the cold-welded area depends on: material type, annealing, cleanliness, wall thickness and radius of the pinch-off anvil inserts.