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To simulate actual conditions
tack-weld
a piece with on
irregular
edge to another
piece leaving
numerous gaps
along
the ioint. 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 ioint (fig: 20),
Whei_ y0u can:10y single-pass butts and fillet welds you will
be6bleto,
make anioverhead
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_heOted; cOntraCt:when coo_ed. In;arc
:anti: edggs being
oined: are
molten and: the metal ::sUrroundirfg: ithe weld is }_eaie(JlsufL
flc entt_/ to cause eX :ansion _Whe:_ ::the :de 0sted
meta
: ......
p ....
: ..........
....
P....
solidifies; it becomes €¢parf all the: plates; but, :being Unr_
stricted in its eXpansi0n in:the
molten::state, it I tends: t0
c0ntract_m0re
thanlthel
heated SurroOn_Jing_metal_ lf 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 in length,
tending
to pull the plates together,
resulting in locked-up
stresses (fig. 23). This is not too serious when welding mitd
steet up to 1!2-inch 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, lor_g continuous welds may cause
considerable
bending and result in o 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 job with tack welds, and
install temporary braces tack-welded
to supporl parts that
m_ght bend. The braces can be removed after the job is
completed.
Lay the beads so the stresses witl counteract
or n_utralize one another, by running a short pass first o_
one side then on the other, etc. Often the neutralizing
weld
is at the other end of the iob. Do not concentrate too many
welds in one place but space them to distribute the heat
and stresses throughout 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
at the: end.
CAST:
iRON
WIELDING
Previous experience in handling
the arc, plus good judg-
ment regarding expansion
and contraction,
will enable
you to weld gray
cast iron successfully in o short time.
Two types of electrodes are used, namely: r_on-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 to close tolerances. Non-
machinable
rods are used for most repair
jobs such as
cracked motor blocks, water iackets, pump and gear hous-
ings, etc. If 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 with an abrasive
wheel.
As cast iron is very
brittte,
care
must
be taken
to controt
expansion
and contraction,
and thus c_void cracking
of the
weld or the casting. Because of low tensile strength and
Jack of ductility it canno_ 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 jobs can be
done without pre-heating,
this method wilt be considered
first.
The part must be free of rust, grease, paint or dirt; cleaned
by wire brushing, grinding
or washing
with solvent. The
crack shouid be beveIed for penetration.
Jf 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 joint can be
welded from both sides. Do not bevel to a sharp edge along
the entire crack. Instead, allow
approximately
1i16_inch
!-14
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