Induction melting permits the use of either graphite or ceramic crucibles.

In the case of graphite, great care must be taken to avoid graphite inclusions in the melt. Graphite quality is extremely important and a new crucible should be pre-washed with alcohol to remove graphite powder residual from the manufacturing process.

The new crucible should then be coated internally with a wash of lead-free boric acid dissolved in water - using a brush. The crucible rim should also be coated. Make sure that the film thus applied is thin, otherwise borax inclusions within the castings will result.

It is desirable to use a crucible matched to the melt size. As a general rule, a crucible should be at least half full. Less than this, and the following adverse consequences will result:

A - Since the crucible acquires heat by induction from the coil and trans

fers this by conduction to the metal, the top half will tend to overheat.

B - Inefficient heat transfer from crucible to metal results in a slow melt.

C - When the metal reaches liquidus, the mass of the crucible will be at a higher temperature, resulting in distortions to the metallurgical properties of the casting. Ideally, the colour of light emitted by the heated crucible should be similar to that emitted by the metal.