In other cases it is only desired to soften
the metal sufficiently that it may be handled easily. In some cases both of
these things must be accomplished, as after a piece has been forged and
must be machined. No matter what the object, the procedure is the same.
The steel to be annealed must first be heated to a dull red. This heating
should be done slowly so that all parts of the piece have time to reach the
same temperature at very nearly the same time. The piece may be heated in
the forge, but a much better way is to heat in an oven or furnace of some
type where the work is protected against air currents, either hot or cold,
and is also protected against the direct action of the fire.
[Illustration: Figure 4.--A Gaspipe Annealing Oven]
Probably the simplest of all ovens for small tools is made by placing a
piece of ordinary gas pipe in the fire (Figure 4), and heating until the
inside of the pipe is bright red. Parts placed in this pipe, after one end
has been closed, may be brought to the desired heat without danger of
cooling draughts or chemical change from the action of the fire. More
elaborate ovens may be bought which use gas, fuel oils or coal to produce
the heat and in which the work may be placed on trays so that the fire will
not strike directly on the steel being treated.
If the work is not very important, it may be withdrawn from the fire or
oven, after heating to the desired point, and allowed to cool in the air
until all traces of red have disappeared when held in a dark place.
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