Cast Iron Welding; Expansion And Contraction - Craftsman 113.201392 Owner's Manual

DISTORTION TRENDS
WHEN COOLING
BUTT W£L_
Figure 23
_T IST mLBH_ T_ yRt9 _. ET_
Figure 20
Figure 24
Figure 21
To simulate actual conditions tack-weld a piece with an
irregular edge to another piece leaving numerous gaps
along the iolnt. Use the _vhlpp[ng motion and deposit a
fairly heavy bead, slowing down the rate of travel where
the gaps are widest to budd up a weld of umform size
throughout Its length. If the gaps are rather wide, fil_ them
first, clean off the slag and lay _n a fillet weld the entire
length of the joint (fig 20)
When you can lay slngle.pass butts and hllet welds you will
be able to make an overhead weld of any size, as it is
simply a matter of fusing a number of straight beads to-
gether, one on top the other (fig. 21).
Weld appearance can be improved by grinding with a
properly guarded abrasive wheel mounted on the end of
a flexible shaft.
EXPANSION AND CONTRACTION
Metals expand when heatedi contract when cooled In arc
welding, the deposited metal and edges being joined are
molten and the metal surrounding the weld is heated suf-
fiaently to cause expansion. When the deposited metal
so|id_fies, it becomes a part of the plates; but, being unre-
stricted in its expansion in the molten state, it tends to
contract more than the heated surrounding metal If the
surrounding metal is free to move (not clamped or tacked)
It cannot resist these forces and bends (fig 22)
The weld also contracts in width, as well as _n length,
tending to pull the plates together, resulting in locked-up
stresses(fig. 23). This is not too serious when weldlng mild
steel up to 1/2-inch thick, as the ductJhtyand elongation of
the metal will permit it to deform shghtly to compensate
for these forces, and prevent cracking On sheet metal and
light structural members, long continuous welds may cause
conslderabb bending and result in a badly distorted weld-
ment. Fortunately most of this can be avoided by studying
the effects of expansion and contrachon, as related to the
job before welding and working out a procedure to follow
For example: first assemble the job with tack welds, and
_nstall temporary braces tack-welded to support parts that
might bend. The braces can be removed after the lob is
completed. Lay the beads GO the stresseswill counteract
or nbutralize one another, by running a short pass first on
one side then on the other, etc. Often the neutralizing weld
is at the other end of the job. Do not concentrate too many
welds m one place but space them to distribute the heat
and stresses throughout the enhre structure Use intermittent
welds whenever pass.hie, ff continuous welds are necessary
to make a water-tlght compartment, use the back-step
method as shown in figure 24, fusing each bead together
at the end.
CAST iRON WELDING
Previous experience in handhng the arc, plus good ludg-
rnent regarding expansion and contraction, wdl enable
you to weld grc_y cast Iron successfully m a short t_me.
Two types of electrodes are used, namely: non-mach_nabEe
for use in cases where the weld does not have ta be
machined, and machinable which deposits a file-soft weld
that can be drilled or machined to close tolerances Non-
rnachJnabJe rods are used for most repair iobs such as
cracked motor blocks, water jackets, pump and gear hous-
ings, etc. I{ the weld must be made across a machined
surface that need not be refinished to a close tolerance,
the face of the weld may be ground flush wtth an abrasive
wheel.
As cast iron is ve,"y brittle, care must be taken to control
expansion and contraction, and thus avoid cracking of the
weld or the casting Because of tow tensde strength and
lack of ductility it cannot bend, stretch or d_stort itseJf ta
conform to the contraction of the weld metal. In same cases
_t may be necessary to pre-heat the entire casting before
weJd_ng. However, as most cast _ran welding lobs can be
clone without pre-heatmg, this method will be considered
first
The part must be free of rust, grease, paint or dirt, cleaned
by w_re brushing, grinding or washing with solvent The
crack should be beveled for penetration. If the parts are
broken apart completely, they may be ground on an abrasive
wheel to a single or double bevel, depending upon the
thickness of parts and whether or not the ioint can be
we_ded from bath sides. Do not bevel to a sharp edge along
the entire crack. Instead, allow approximately 1/16-,nch
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