Lincoln Electric LTW2 manual Hardfacing of Idler and Roller Metal to Metal Wear, Welding Cast Iron

8 LEARNING TO STICK WELD 8

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 monetary. A few dollars worth of electrode will com- pletely build up a roller or idler, and the hard surface will outlast several times the normal life or such rollers and idlers.

If the following procedure is followed, it is not even necessary to remove the grease bearing while weld- ing. 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 Wearshield™ BU electrodes, 5/32" (4.0mm) at 175 amps or 3/16" (4.8mm) 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 prevent shrinking of the roller (or idler) on the grease bearing.

5.Build-up to dimension. The weld metal deposited by Wearshield™ BU 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 Wearshield™ BU electrodes, 5/32" (4.0mm) at 175 amps or 3/16" (4.8mm) at 200 amps.

3.Build-up to size.

4.Do not quench. This will make the deposit slightly softer 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-consum- ing and cheaper to build-up.

NOTE: The same electrode — Wearshield™ BU — 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 contact with the ground) should be surfaced with Wearshield™ ABR, 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. (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.

2.He can weld 1/2" (12.5mm) 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 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, a fire, or the Arc Torch are all excellent means of pre- heating.

When using the 1/2" (12.5mm) at a time method, it is recommended to start 1/2" (12.5mm) away from the previous bead and weld into the previous bead (back- stepping).