Handbook-Expansion & Contraction

3 rapidly, with a torch. Not too much seems to happen. The cold part of the metal restricts any general expansion, so that the forces tend merely to ”upset”, or thicken the edges, at the spots most strongly heated. However, when the piece is allowed to cool, the slit closes at its open end, and one end may even slide past the other, as indicated in B. The forces of contraction, rather than eliminating the ”upsetting” that took place during the heating, have shortened both sides of the slit, and the metal in the uncut end of the sheet has had sufficient elasticity to allow it to act as a hinge. The point we’d like to make is this: that what happens during the cooling period is seldom the reverse of what happens during the expansion period. Fig. 11-2. Because of what may be termed the ”hinge effect”, heating and cooling will tend to close the gap between parts unless some method is provided to prevent that from happening. Fig. 11-1. When the edge of a piece of sheet steel is heated, expansion will cause the hot edge to warp or wave. (The effect shown here is much exaggerated). After cooling, however, the heated edge is likely to be a bit shorter than it was originally.