Cold Drawing : Hollows - Pennsylvania Cold Drawn

Cold drawing involves pulling steel tubes over an inside die (called a mandrel) and, at the same time, through an outside die. This process results in extremely close ID, OD and wall thickness tolerances. Cold drawing also improves the surface condition of the tube, and can be used to create interior or exterior shapes, such as square or hexagons.

The Process:
Steel tubes are heat treated to improve workability, and then "pickled," cleaning them in an acid bath. Once cooled, the tube is "pointed," squeezing one end smaller to fit the jaws on the cold draw machine.
The internal die, called a mandrel, is inserted and then the jaws begin to pull the hollow tube over the mandrel and through an outside die. An area of reduction of 20-35% is normal for cold finishing.
After cold drawing, the tube is annealed to relieve internal stresses and straightened. The tubes are then cut to length, cleaned in an acid bath, dipped in a rust inhibitor and bundled for shipment.

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