Localized demagnetization of Rotor Journal without removing from Casing?? 1

[faisalakhan]

Dear Experts;
I have seen and experienced that for demagnetization of Steam turbine or Compressor Rotor journal areas, complete rotor need to be removed from Casing (Turbine / Compressor) and best practice is to hang it, using overhead crane, to avoid its contact with ground.
Is is also possible to do localized demagnetization of rotor sensitive parts (Journals / Thrust disc etc) if rotor is not removed from casing and we have only inspected the bearings?
I would like to know the suggestion / guidance from all experts in the field and any care if this is possible without any Reliability issue.

best regards,

 

[waross]

You can try a "C" core and very low frequency AC and reducing voltage. That may demagnetize the area between the ends of the "C"s.
Roll your own with a cutaway of an old transformer core. Beware of saturation if you energize the coil when it is not in contact with the journals.
Generally any way that you are able to induce magnetism in the magnetized area with an electromagnet may be demagnetized with a very low frequency AC and a gradually dropping voltage.
Don't assume that it works. Check for residual magnetism after treatment.
The challenge is to induce the electromagnetism in the area of the problem residual magnetism.

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Ohm's law
Not just a good idea;
It's the LAW!

 

[faisalakhan]

Thanks Waross for your reply.
I also have fear that we may induce further magnetism in the zone and nearby areas. Do you have experience of using C core with low frequency AC for localized degaussing?

Best regards,
Faisal

 

[waross]

Sorry, no.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!