Hot Top Forging Ingots: Over Imposed vs Semi Inserted
What a hot top does, how over imposed and semi inserted hot tops differ, and how it affects ingot yield and soundness.
What is a hot top?
A hot top is a refractory-lined feeder sitting on top of the mould. It insulates the head of the ingot so that steel stays liquid there longer than in the body, which feeds the shrinkage as the ingot solidifies.
Hot top in steel ingot casting: why it matters
Without a hot top, the shrinkage cavity (pipe) would run deep into the usable body. A hot top confines the pipe to the head, which is cropped off, so the remaining body is sound.
Over imposed vs semi inserted
In an over imposed hot top the feeder sits fully on top of the mould. In a semi inserted type, it sits partly inside the mould neck. Semi inserted types give a slightly lighter total ingot and are specified for certain sizes. Both appear in Kesari Alloys' ingot size chart.
Effect on yield
The head is cut off before or during forging. A good hot top design reduces how much steel is lost, which improves forging yield.
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