Because this pipe is due to the difference in the rates of contraction of interior and exterior, it may be lessened by retarding the cooling of the mass as a whole, and it may be prevented from stretching down deep by retarding the solidification of the upper part of the ingot, as, for instance, by preheating the top of the mould, or by covering the ingot with a mass of burning fuel or of molten slag. [Please select]
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To secure this widely distributed increase the various methods of preheating are adopted. [Please select]
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_--This material should be beveled in the same way that cast iron is handled, and preheating and slow cooling are equally desirable. [Please select]
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It requires only a local preheating around the point to be welded. [Please select]
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The necessity of preheating, however, depends entirely on the material, form and size of the work being handled. [Please select]
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Preheating of other adjacent parts to care for contraction is done at this time by an additional torch burner. [Please select]
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_--The actual work of welding and cutting requires preliminary preparation in the form of heat treatment for the metals, including preheating, annealing and tempering. [Please select]
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