Welding Cast Iron

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B-16	OPERATION	B-16
4. The bead should be put on with a weaving motion,		When breaking
and it should be 1/2-3/4” (12.7-19.0mm) wide. Do
not let the arc blow over the edge, as that will dull		the weld stays on
the edge. (See drawing below.)		one piece

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Work Table	Strike Arc
Work Table	Here	Sharp Edge
Brick	Here


Plow Share		1/2-3/4" width
Plow Share		(12-20mm)
		(12-20mm)
Positioning of Share	Weaving Motion

To overcome this, the welding operator has two choic- es:

1.Preheat the entire casting to 500-1200°F (260- 649°C) 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.

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5.Use the back-stepping method. Begin to weld 3” (76mm) from the heel of the share and weld to the heel. The second weld will begin 6” (152mm) from the heel, the third weld 9” (229mm) from the heel, etc.

B	A	C	D	E First weld from A to B; then
	3"				from C to A; then from D to C;
					from C to A; then from D to C;
					then from E to D; and so on.
(75mm)					then from E to D; and so on.
(75mm)				BACKSTEPPING
				BACKSTEPPING

Backstepping greatly reduces the chances for cracking of the share, and it also greatly reduces warping.

NOTE: The entire process is rather fast. Many begin- ners go much too slowly when hardfacing plowshares, running the risk of burning through the thin metal.

When welding on a piece of cold cast iron, the tremen- dous 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. (See drawing below.)

2.Weld 1/2” (12.7mm) at a time, and do not weld at that spot again until the weld is cool.

This way, no large amount of heat is put into the mass.

Most inexperienced welders will probably use the sec- ond method, because they have no way of preheating large castings. Smaller castings can easily (and should) be preheated before welding. A forge, stove, fire, or the Arc Torch are all excellent means of pre- heating.

When using the 1/2” (12.7mm) at a time method, it is recommended to start 1/2” (12.7mm) away from the previous bead and weld into the previous bead. This is called backstepping.

After welding Cast Iron, protect the casting against fast cooling. Put it in a container of warm, dry sand or lime.

If sand or lime is not available, cover it with sheet metal or any other non-flammable material that will diminish drafts and retain heat.

Cast Iron Plate Preparation

hot

coldcold

White brittle cast iron

Wherever practical, the joint to be welded should be “veed” out by grinding or filing to give complete pene- tration as shown in figures (a), (b) and (c) below. This is especially important on thick castings where maxi- mum strength is required.

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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. (See drawing).

Lincoln Electric SVM197-A service manual Welding Cast Iron, Cast Iron Plate Preparation

OPERATION

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