- May 20, 2021
LOL at #5Preheat has four purposes in ferrous welding.
One is to reduce thermal stresses both during and after the weld caused by variation of temperature in the workpiece.
Two is to increase ductility so that some of the stress can relieve itself...in-process thermal stress-relief
Three is to cook off contaminants
Four is to slow the cooling of the weld and HAZ. Flame-hardening works by heating the surface rapidly so the undelying metal is still cool. When the heating is removed the hot surface is quenched and hardened by the heat being rapidly conducted away to the underlying cold metal. Just what you do not want, usually, in a weld
Fifth is to roast the weldor by radiant heat, so you are not shy to charge a lot of money for the job.
When you're wrapped up head to toe in heavy leather surrounded by weld curtains on a humid, 100 degree day, you don't feel bad about what you charge.
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