An old method of bending very large diameter pipes without dies by heating a narrow section of the pipe and then putting as deep a bend as possible in it without causing the material to buckle or split.
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A complete guide to the principles of the 4-Step set-up for tube-bending tools
This is a printable handbook showing how to implement in four standardized steps the “forward mandrel” set-up for rotary-draw tube-bending machines and establish process control over the so-called black art. The procedure is based upon the guiding principle that the tools make the bend and takes advantage of the inserted design of modern mandrel tooling.