Lincoln Electric IM348 AC-225-GLM - Manual (Page 15)

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5. Use the back-stepping method. Begin to weld 3" from
the heel of the share and weld to the heel. The second
weld will begin 6" from the heel, the third weld 9" from
the heel, etc.
Backstepping greatly reduces the chances for cracking of
the share, and it also greatly reduces possible warpage.
NOTE: The entire process is rather fast. Many beginners
go much to slow when hardfacing plow shares, running the
risk of burning through the thin metal.
Hardfacing of Idler and Roller (Metal to Metal Wear)
A very common application of hardfacing for metal to
metal wear is the hardfacing of idlers and rollers and the
rails that ride on these rollers and idlers.
The reason for hardfacing these parts is primarily mone-
tary. A few dollars worth of electrode will completely build
up a roller or idler, and the hard surface will outlast sever-
al times the normal life or such rollers and idlers.
If the following procedure is followed, it is not even neces-
sary to remove the grease bearing while welding. This will
save a lot of time:
1. The roller (or idler) is inserted on a piece of pipe that is
resting on two sawbucks. This enables the operator to
turn it while welding.
2. Use Jet-LH ® BU-90 electrodes, 5/32" at 175 amps or
3/16" at 200 amps.
3. Weld across the wearing surface. Do not weld around.
4. Keep the roller (or idler) cool by quenching with water,
and by stopping the welding periodically. This will pre-
vent shrinking of the roller (or idler) on the grease bear-
ing.
5. Build-up to dimension. The weld metal deposited by
BU-90 electrode is often so smooth that machining or
grinding is not necessary.
NOTE: The quenching of the roller (or idler) has another
purpose: It increases the hardness — and thus the service
life — of the deposit.
The hardfacing of the rails is a lot easier:
1. Place the rails with the side that rides on the rollers and
idlers upwards.
2. Use Jet-LH BU-90 electrodes. Same ampere setting as
on the idlers and rollers.
3. Build-up to size.
4. Do not quench. This will make the deposit slightly soft-
er than the deposit on the idlers and rollers. That means
that the wear will primarily be on the rails, which are a
lot easier and less time-consuming and cheaper to build-
up.
NOTE: The same electrode — BU-90 — will give the
operator two desired hardnesses, just by a difference in
cooling rate, making it possible to put the hardest deposit
on the most expensive parts.
NOTE: The outside of the rails (the side that comes in con-
tact with the ground) should be surfaced with Abrasoweld,
since this side has Metal to Ground wear.
Welding Cast Iron
When welding on a piece of cold cast iron, the tremendous
heat from the arc will be absorbed and distributed rapidly
into the cold mass. This heating and sudden cooling creates
WHITE, BRITTLE cast iron in the fusion zone.
This is the reason why welds in cast iron break. Actually,
one piece of the broken cast iron has the entire weld on it,
and the other piece has no weld on it.
In order to overcome this, the welding operator has two
choices:
1. He can preheat the entire casting to 500-1200°F. If the
cast iron is hot before welding, there will be no sudden
chilling which creates brittle white cast iron. The entire
casting will cool slowly.
2. He can weld 1/2" at a time, and not weld at that spot
again until the weld is completely cool to the touch.
In this way no large amount of heat is put into the mass.
Most inexperienced welders will probably use the second
method, because they have no way of preheating large cast-
ings. Smaller castings can easily (and should) be preheated
before welding. A forge, stove, a fire, or the Arc Torch are
all excellent means of preheating.
When using the 1/2" at a time method, it is recommended
to start 1/2" away from the previous bead and weld into the
previous bead (backstepping).