Test welds can be made and then broken, if possible, so that the
strength gained through different degrees of heat can be known before
attempting more important work.
_Welding._--When the work has reached the welding temperature after
having been replaced in the fire with the flux applied, the two parts are
quickly tapped to remove the loose scale from their surfaces. They are then
immediately laid across the top of the anvil, being placed in a diagonal
position if both pieces are straight. The lower piece is rested on the
anvil first with the scarf turned up and ready to receive the top piece in
the position desired. The second piece must be laid in exactly the position
it is to finally occupy because the two parts will stick together as soon
as they touch and they cannot well be moved after having once been allowed
to come in contact with each other. This part of the work must be done
without any unnecessary loss of time because the comparatively low heat at
which the parts weld allows them to cool below the working temperature in
a few seconds.
The greatest difficulty will be experienced in withdrawing the metal from
the fire before it becomes burned and in getting it joined before it cools
below this critical point. The beveled edges of the scarf are, of course,
the first parts to cool and the weld must be made before they reach a point
at which they will not join, or else the work will be defective in
appearance and in fact.
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