Transformer lamination heat treatment

[Vuk22]

Hi guys,
I have to heat treat mumetal transformer lamination 30x25x0,35 mm and wonder do I have to expect some dimensional variation(heat treatment at 1050°C under hydrogen atmosphere). Also, do I have to take care about placing the parts (they are mgo coated)? Is there a chance of deformation if the parts are placed randomly? Do I have to prepair some special tool to keep them tight?
I don't find any clues on this point... Thanks

 

[marcus4]

I can't help much but I can share my practical experience. I had a similar chalenge and my lams were ngt mgo coated so we used mg oxide powder to isolate the parts. The parts were placed carefully on the plate and they were not touching each other but we sanwiched them with mgo powder between. I heard that some people use special tools for packing the parts tight but I newer had experience with similar. I hope that someone more experienced can share here. I interested to hear about it to. Cheers

 

[EdStainless]

I have usually seen them treated as a uniform stack, lined up with each other.
You need to have good flat support under them so that they remain flat.

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Plymouth Tube

 

[Vuk22]

Thanks guys. So placing them on the flat surface do the job? Am I right? Sorry, my English is not so perfect so I Double check

 

[MagBen]

For relatively low tem at 1050C, if your rings are coated, you may no need to worry much about isolation. but it is still a good idea to use MgO to seperate the lams and even use the powder to pack dense and hold the postion.
Not like Fe-Co, mumetal is not supposed to have any growth or shrinkage after heat treatment. especailly for your small rings with a relatively big thickness, dimensional distortion should not be a big issue.

 

[Vuk22]

Thanks Magben. Very useful and practical advice. Yes, I was thinking what could happen if the lams are touching each other with their side edges. There is no MgO coat. So, the MgO powder will prevent lams to get stuck. Also, is it clever to put multiple layers of lamination on a trey but separate them with MgO powder?

 

[MagBen]

For naked lams, 1050C is still risky for sticking or welding if lams are packed together. Al2O3 can sometime be used. a challenge maybe the removal of powder after heat treatment.
For big sized lams, you can also try to hang your lams on some rod, using lam itself weight to keep the shape.

 

[Vuk22]

Thanks Magben. I consulted heat treatment operator about "hanging" but he has no clue how to do that. He also asked few coleagues in our area but they have no experience with transformer lamination treatment. (It's not an usuall type of service in our area). Lams has one 2,5mm hole but he is not sure if they can stick to rod or maybe deform. Can you please elaborate about rod material and how to hang the parts? Shall we hang them like skewers (horizontally)? How to ensure space between the parts hanged? All ideas are welcome