WELDING OPERATIONS I - OD1651 - LESSON 1/TASK 1
steel weld metal, the carbon picked up from the cast iron by the
weld metal, and the hardness of the weld metal caused by rapid
cooling must be considered.
Steel shrinks more than cast iron
when cooled from a molten to a solid state and, when a steel
electrode is used, this uneven shrinkage will cause strains at
the joint after welding.
When a large quantity of filler metal
is applied to the joint, the cast iron may crack just back of the
line of fusion unless preventive steps are taken.
To overcome
these difficulties, the prepared joint should be welded by
depositing the weld in short string beads, 3/4 to 1/4 inch long,
made intermittently and, in some cases, by the step-back or skip-
welding procedure. To avoid hard spots, the arc should be struck
in the V and not on the surface of the base metal.
Each short
length of weld metal applied to the joint should be lightly
peened, while hot, with a small ballpeen hammer and allowed to
cool before additional weld metal is applied. The peening action
forges the metal and relieves metal strain during cooling.
(b) The electrodes used should be 1/8 inch in diameter so as to
prevent generating excessive welding heat. The welding should be
done with reverse polarity.
Weaving of the electrode should be
held to a minimum.
Each metal deposit should be thoroughly
cleaned before additional metal is deposited.
(c) Cast iron electrodes are used where subsequent machining of
the welded joint is required.
Stainless steel electrodes are
used when machining of the weld is not required.
The procedure
for making welds with these electrodes is the same as that
outlined for welding with mild-steel electrodes. Stainless steel
electrodes provide excellent fusion between the filler and base
metals; however, great care must be taken not to overheat the
base metal.
Overheating the base metal will cause cracking of
the base metal alongside the weld metal.
The reason for this
cracking of the base metal is that stainless steel expands and
contracts approximately 50 percent more than mild steel in equal
changes of temperature.
7.
Electric Arc Welding of Nonferrous Metals
a. General. Most of the nonferrous metals used in Army ground
equipment can be successfully electric arc welded provided the
proper procedures are
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