Metglas core problem

[jimbofitz]

The Metglas cores we are using in our transformer assemblies are flaking (delaminating and breaking off) due to handling while we build the transformer. I would like to coat the surface of them to prevent this from happening. I have a sample of Dolph AC-46 air dry varnish on the way to try out. Has anyone has similar problems with these cores and solved this problem? I can't use our typical varnish system because these cores are sensitive to temperatures above 150 deg C. Another issue is the buildup of this coating is going to be limited as the mechanical design is pretty tight already.

All comments and suggestions are appreciated.

Thanks,
Jim

 

[Skogsgurra]

Yes! But our problem is that the flakes get into the skin like glass-fiber and irritates immensely. We use gloves to avoid the irritation. We do not have so much loss of material that it impairs function.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[jimbofitz]

I agree, that stuff is very irritating to our guys on the floor... those little cuts don't like to stop bleeding.

It's a problem after we band the unit together when the whole assembly is encapsulated. If the flakes end up in the wrong place they are causing corona failures. I am not having an issue with core loss due to flaking.

One lesson I've learned is to stay away from this stuff unless you know what you are getting yourself into!!

Regards,
Jim

 

[Skogsgurra]

Our problem was similar. We use "metal glass" cores for common-mode filters in drive systems. Having those flakes coming loose was OK - if you didn't have lots of cooling air moving at high speeds in the drives.

We used two C-cores to put around the motor cable and that worked very well until we got "unexplainable" errors in the drive. When we found those flakes in the electronics, so the errors were not so "unexplainable" any more.

We now use toroids that have been encapsulated in plastic containers. No more flakes, no bleeding hands.

The only problem is that we now have to disconnect the cables when we want to put a common-mode filter on the drive. So we have to wait for the right moment and it also takes a few hours to do it when there are four parallel 185 mm2 cables connected. But we find it worth that extra effort to avoid the problems.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...