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Induction hardening of bearing journals

Induction hardening of bearing journals

(OP)
Hello!

I'm having an issue with the induction hardening of a bearing journal - on certain parts 2 distinct thin tracks of 'spatter' are visible on the journal. It looks as if the coil has contacted the journal there or come so close that the current has 'arced'and burnt the journal material. The vast majority of the surface is good, hardened correctly and unburnt.

In our analysis we have noticed that certain parts in the soft condition have light scratches on the journal (handling damage) in the area where the hardening problem occurs.

I believe that the two are related. Does this make sense? Do scratches or surface defects act as 'current intensifiers' to cause this kind of very localised overheating / burning? Is there someone with more experience of induction hardening out there who can help!?

Many thanks in advance for any help, advice or clues!

Mark

RE: Induction hardening of bearing journals

The major variables in performing an induction hardening operation are power settings and time spent within the hardening coils.

Assuming your part is rotating as it is drawn through the coils a likely reason for "spatter" formation would be if the part is offset to one side such that it is closer to one side of the coil than the other.  This will cause more heat on the side closest to the coil which will cause a spiral pattern to form.

If arcing has occured caused by contact with the induction coils as you mention then the copper coils will be damaged as well as the bearing.  Induction coils are usually hollow and water cooled so will deteriorate faster than the part being hardened.   

I have never heard of scratches acting as current intensifiers during induction hardening.

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