Work when hot is larger than it will be after cooling. This must be remembered when fitting parts or trouble will result. A two-foot bar of steel will be 1/4 inch longer when red hot than when cold.
The temperatures of iron correspond to the following colors:
Dullest red seen in the dark... 878°
Dullest red seen in daylight... 887°
Dull red....................... 1100°
Full red....................... 1370°
Light red...................... 1550°
Orange......................... 1650°
Light orange................... 1725°
Yellow......................... 1825°
Light yellow................... 1950°
Bending Pipes and Tubes.--It is difficult to make bends or curves in pipes and tubing without leaving a noticeable bulge at some point of the work. Seamless steel tubing may be handled without very great danger of this trouble if care is used, but iron pipe, having a seam running lengthwise, must be given special attention to avoid opening the seam.
Bends may be made without kinking if the tube or pipe is brought to a full red heat all the way around its circumference and at the place where the bend is desired. Hold the cool portion solidly in a vise and, by taking hold of the free end, bend very slowly and with a steady pull. The pipe must be kept at full red heat with the flames from one or more torches and must not be hammered to produce the bend. If a sufficient purchase cannot be secured on the free end by the hand, insert a piece of rod or a smaller pipe into the opening.
While making the bend, should small bulges appear, they may be hammered back into shape before proceeding with the work.
Tubing or pipes may be bent while being held between two flat metal surfaces while at a bright red heat. The metal plates at each side of the work prevent bulging.
Another method by which tubing may be bent consists of filling completely with tightly packed sand and fitting a solid cap or plug at each end.
Thin brass tubing may be filled with melted resin and may be bent after the resin cools. To remove the resin it is necessary to heat the tube, allowing it to run out.
Large jobs of bending should be handled in special pipe bending machines in which the work is forced through formed rolls which prevent its bulging.