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SOLUTIONS: Cast Iron

monitored by means of temperature indicator crayons or by an electronic thermometer. It is important that the temperature does not exceed 600°C, as this may result in structural changes in the base material, which may drastically reduce its strength.

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Opposed to cold welding, hot welding can proceed continuously. The finished welded part must then be allowed the slowest possible cooling down to room temperature. Burying the piece in kieselguhr, sand or cinders will help to give it a slow cooling rate. The reason why slow cooling is important is that if the rate of cooling is high, the carbon will have no time to segregate as graphite in the crystal border areas. We will instead have the carbon bound to the iron in the form of iron carbide. This structural state will be very similar to that of white cast iron; hard and brittle.

Smaller parts, free to expand, may be hot welded. NB: Allow to cool off slowly!

Cold welding

Large, complicated parts should be cold welded.

Amperage setting

When cold welding cast iron a low ampere setting should be used. Thereby deep fusion between the filler material and the base material is avoided. It should be remembered that deep fusion will dig up and bring into the weld pool more graphite than need be. This graphite will give rise to iron carbide, with resulting hard zones when the weld cools off. Deep fusion will also put lots of unwanted heat into the base material with increased risk of cracking.

In order to avoid digging into the base material, and to reduce the heat input, one can also point the electrode 10° in the direction of travel. This will cause the molten pool to blow forward and act as a cushion.

If the necessary equipment for preheating or for achieving the required slow cooling rate is not available, the alternative is "cold" arc welding. The method is so called because of the low heat input to the base material when correctly executed.

On board cold arc welding is by far the most commonly used method, and large cast iron parts, or parts which are difficult or time-consuming to dismantle should be cold welded.

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Do not overdo low amperage setting. The molten pool must be clear of slag, and easy to control. If the deposit has a high bead contour, the setting is too