812 Agricultural Mechanics and Technology Systems
Copyright Goodheart-Willcox Co., Inc.
heat input. Welding a joint using intermittent short beads, rather than welding
the entire joint with a single bead, is another method of controlling distortion.
The order and placement of intermittent welds can also affect distortion
in a weld joint. The welding of a joint should usually begin at the center
and progress toward each free end. If attached at one end, begin welding
at the point of attachment and proceed toward the loose end. Use only the
minimum number of passes required to complete a weld. Overwelding
introduces excess heat to the metal and creates unnecessary points of stress.
The following common procedures are used to minimize distortion:
• Preheat parts before welding. Preheating counteracts movement from
distortion by creating a larger area of expansion and contraction than
just the weld joint.
• Use clamps, jigs, or other fi xtures to hold parts solidly in place while
welding and cooling, thereby minimizing distortion.
• Position parts to be welded slightly out of the desired position. The
distortion is planned to result in contraction that moves the pieces into
fi nal position.
Welding Cast Iron
Cast iron contains much more carbon and silicon than steel, making it
less ductile and more challenging to weld. However, successful cast iron
repair welds are possible and can lead to extreme savings on investments
in equipment. Several different types of cast iron are commonly used in the
construction of equipment. Each type reacts a little differently when welded.
An important factor for success in welding cast iron is the age and condition
of the casting.
Before welding cast iron, use cleaning solvents to clean the surface to be
welded and the area surrounding it. Make sure the surface is free of defects
and surface contaminants. Used parts are likely to be dirty and impregnated
with oil or grease. Contaminants missed by solvents and other cleaners can
often be burned out with an oxidizing oxyacetylene fl ame, followed by wire
brushing or grinding. New cast parts may be contaminated with foreign
material left from the casting process. This foreign material must be removed
prior to welding.
To prepare a crack for welding, fi rst drill a hole at each end of the crack
to prevent it from spreading. Then, grind the crack out to the bottom. Be sure
to remove any residue left by the grinder.
In most cases, preheating is required when cast iron is welded.
Preheating reduces the heat input requirements and relieves internal stresses.
Using a cast-iron fi ller metal requires a much higher preheat because the
fi ller metal has low ductility and is susceptible to cracking. An alternative to
preheating is to use a nickel-based electrode, which produces a welded bead
that yields during cooling and absorbs stresses that could cause cracking in
or near the weld.
Often a heat treatment needs to be applied to welded cast iron parts
after welding. This can be done with a multi-fl ame heating attachment on