It will usually be found, however, that the metal has
cooled below the point at which it can be worked to advantage. It should
then be replaced in the fire and brought back to a forging heat.
[Illustration: Figure 52.--Upsetting and Scarfing the End of a Rod]
While shaping the work at this forging heat every part that has been at a
red heat should be hammered with uniformly light and even blows as it
cools. This restores the grain and strength of the iron or steel to a great
extent and makes the unavoidable weakness as small as possible.
_Forms of Welds._--The simplest of all welds is that called a "lap
weld." This is made between the ends of two pieces of equal size and
similar form by scarfing them as described and then laying one on top of
the other while they are hammered together.
A butt weld (Figure 52) is made between the ends of two pieces of shaft or
other bar shapes by upsetting the ends so that they have a considerable
flare and shaping the face of the end so that it is slightly higher in the
center than around the edges, this being done to make the centers come
together first. The pieces are heated and pushed into contact, after which
the hammering is done as with any other weld.
[Illustration: Figure 53.--Scarfing for a T Weld]
A form similar to the butt weld in some ways is used for joining the end of
a bar to a flat surface and is called a jump weld. The bar is shaped in the
same way as for a butt weld.
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