[Illustration: Fig. 4 -Pouring the Metal]
If, after being poured, the mold sputters and emits large volumes
of steam, it shows that the sand is too wet, and the castings in
such cases will probably be imperfect and full of holes.
A mold made in the manner previously described may be poured with
any desired metal, but a metal which is easily melted will give
the least trouble. One of the easiest metals to melt and one which
makes very attractive castings is pure tin. Tin melts at a
temperature slightly above the melting point of solder, and,
although somewhat expensive, the permanent brightness and
silver-like appearance of the castings is very desirable. A good
"white metal" may be made by mixing 75% tin, 15% lead, 5% zinc and
5% antimony. The object of adding antimony to an alloy is to
prevent shrinkage when cooling.
A very economical alloy is made by melting up all the old
type-metal, babbitt, battery zincs, white metal and other scrap
available, and adding a little antimony if the metal shrinks too
much in cooling. If a good furnace is available, aluminum can be
melted without any difficulty, although this metal melts at a
higher temperature than any of the metals previously mentioned.
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