It is sometimes necessary to straighten a casting which has become warped or twisted. Cast iron may be twisted or bent to quite an extent if worked cautiously. The bending may generally be done at about the ordinary hardening heat of tool steel and should be done by a steadily applied pressure, not by blows. There is more danger of breaking the work by working it at too high a heat than by working at too low. As an example of how iron may be twisted, a bar of gray cast iron 1 inch square and a foot long may be twisted through about 90 degrees before it will break. Pipe Bending. A piece of pipe when bent always has a tendency to collapse, and, if this collapsing can be prevented by keeping the sides of the pipe from spreading, a pipe may be successfully bent into almost any shape. One way of doing this would be to bend the pipe between two flat plates as shown in Fig. 146, the plates being the same distance apart as the outside diameter of the pipe. In bending large pipe, the sides are sometimes prevented from bulging by working in with a flatter. Where a single piece is to be bent, it may be done by heating the pipe and inserting one end in one of the holes in a swage block as shown in Fig. 147, the pipe being then bent by bearing down on the free end. As soon as a slight bend is made it is generally necessary to lay the pipe flat on the anvil and work down the bulge with a flatter. Where many pieces are to be bent, a grooved jig such as shown in Fig. 148 is sometimes used. The jig is of such a shape that the pipe is completely surrounded where it is being bent, thus not having any opportunity to collapse or bulge. Pipe is sometimes filled full of sand for bending. This helps to some extent. Care must be taken to see that the pipe is full and that the ends are solidly plugged. For bending thin copper tubing, it may be filled with melted rosin. This gives very satisfactory results for this character of work. After bending, the rosin is removed by simply heating the pipe. Duplicate Work. Where several pieces are to be exactly alike in a shop that is not equipped for special work, it is sometimes practical to use a jig for performing the operations. For simple bending the jig may consist of a set of cast-iron blocks. Fig. 149 illustrates a simple bend with the block used for doing the work. The work is done as shown at B. The piece to be bent is placed, as shown by the dotted lines, with the bending block on top. The bending is done by one or two strokes of the steam hammer. For convenience in handling, the bending blocks are sometimes held by a spring handle as shown in Fig. 150. The blocks in this case are for bending the hooks shown at A. The handle is simply a piece of 1/2 inch round iron with the ends screwed into the cast-iron blocks and held firmly by the lock nuts shown. This makes a cheap arrangement for a variety of work, as the same handles may be used on various sets of blocks. Where a great number of pieces are to be made, these blocks or bending dies may be made of such a shape that they can be keyed on the steam hammer in place of the regular flat dies.
Fig. 146. Method of Bending Pipe.
Fig. 147. Bending Pipe on Swage Block.
Fig. 148. Bending Pipe in Grooved Jig.
Fig. 149. Block for Simple Bend.
Fig. 150. Spring-Handled Bonding Jig.