Cast Iron Welding; Expansion And Contraction - Craftsman 113.201892 Owner's Manual

Figure 20
Figure 21
To simulate actual conditions tack-weld a piece with an
irregular edge to another piece leaving numerous gaps
along the joint. Use the whipping motion and deposit a
fairly heavy bead, slowing down the rate of travel where
the gaps are widest to build up a weld of uniform size
throughout its length. If the gaps are rather wide, fill them
first, clean off the slag and lay in a fillet weld the entire
length of the joint (fig. 20_).
When you can lay single-pass butts and fiffet welds you will
be abie to make anoverhead 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 or= the end of
a flexible shah.
EXPANSION AND _ CONTRACTION
METAL BENDS
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F;gure 24
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 in length,
tending to pull the plates together, resu)ting in locked.up
stresses(fig. 23). This is not too serious when welding mitd
steel up to l/2-_nch thick, as the ductility and elongation of
the metal will permit it to deform slightly to compensate
for these forces, and prevent cracking. On sheet metal and
light structural members, long continuous welds may cause
considerable bending and result in a badly distorted weld-
ment. Fortunately most of this can be avoided by studying
the effects of expansion and contraction, as related to the
job before welding and working out a procedure to follow.
For example: first assemble the iob with tack welds, and
install temporary braces tack-welded to support parts that
might bend. The braces canbe removed after the iob is
completed. Lay the beads so the stresseswill counteract
or n_utralize 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 in one ptace but space them to distribute the heat
and stressesthroughout the entire structure. Use intermittent
welds whenever possible, if continuous welds are necessary
to make a water-tight compartment, use the back-step
method as shown in figure 24, fusing each bead together
atthe end.
CAST IRON WELDING
Previous experience in handling the arc, plus good judg-
ment regarding expansion and contraction, witl enable
you: to weld gray cast iron successfully in a short time.
Two types of electrodes are used, namely: non-machinable
for use in cases where the weld does not have to be
machined, and machinable which deposits a file-soft weld
that can be drilled or machined t01 rclose tolerances. Non-
machinable rods are Used for mast repair jobs such as
cracked motor blocks, water jackets, pump and gear hous-
ings, etc_ tf the weld must be made across a machined
surface that need not be refinlsbed to a close tolerance,
the face of the weld may be ground flush w_thon abrasive
wheel.
As cast iron is very brittle, care must be taken to control
expansion and contraction, and thus avoid cracking Of the
weld or the casting. Because of tow tensile strength and
lack of ductility it cannot bend, stretch or distort itself to
conform to the contraction of the weld metal In some cases
it may be necessary to pre-heat the entire casting before
welding. However, as most cast iron welding iobs can be
done without pre-heating, this method will be considered
first.
The part must be free of rust, grease, paint or dirt; cteaned
by wire brushing, grinding or washing with sotvent. The
crack should be beveled for penetration. If the parts are
broken apart compteteb!,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 joint can be
welded from both sides. Do not bevel to a sharp edge along
the entire crack. Instead, allow approximately 1/16-inch