--Using a Wedge While Welding]
In materials that will spring to some extent without breakage, that is, in
parts that are not brittle, it may be possible to force the work out of
shape with jacks or wedges (Figure 27) in the same way that it would be
distorted by heating and expanding some portion of it as described. A
careful examination will show whether this method can be followed in such a
way as to force the edges of the break to separate. If the plan seems
feasible, the wedges may be put in place and allowed to remain while the
weld is completed. As soon as the work is finished the wedges should be
removed so that the natural contraction can take place without damage.
It should always be remembered that it is not so much the expansion of the
work when heated as it is the contraction caused by cooling that will do
the damage. A weld may be made that, to all appearances, is perfect and it
may be perfect when completed; but if provision has not been made to allow
for the contraction that is certain to follow, there will be a breakage at
some point. It is not possible to weld the simplest shapes, other than
straight bars, without considering this difficulty and making provision to
take care of it.
The exact method to employ in preheating will always call for good judgment
on the part of the workman, and he should remember that the success or
failure of his work will depend fully as much on proper preparation as on
correct handling of the weld itself.
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