Have the laws of Physics changed recently?

When I was a lad at school, we were taught that iron cores in AC
applications were lossy and so were made from laminations that were
insulated from one another by a coating on the iron. Indeed transfomers
held together with bolts had fibre washers under the heads. If these
washers were left out things got quite hot. Similar precautions were
seen on some motors too.
However in the last year or so, servicing various AC items I've seen
both transformers and motors with a neat welded line joining all the
laminations together as well as uninsulated bolts. Yesterday, and AEG
washer motor had 4 such welds evenly spaced around the stack of
laminations
Can anyone explain a) why this is done and b) why it does not cause
excessve loss and hence overheating
TIA
Bob
Reply to
Bob Minchin
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Seems to depend on the grade of lamination and the type of circuit you are using the lams for.
We make up a lot of trannies in our workshop, we wind up to 3kVA, any larger and we get them made at a specialist up North.
The grades of Lam we use vary, as does the material. Basic stuff is 800/50 grade then 600/50, 400/50 and then you're into grain orientated lams which are thinner and for high performance stuff.
We use either heat-treated lams which are annealed in a special process without air IIRC, or we used insulated lams with a varnish coating.
We always use fibre washers under the screws etc etc,
Motors in particular have had the welded lams for some years, and most automated transformer lines have welding facilities as you cannot get a machine to interleave the E's and I's as we would normally do by hand on the bench. The larger transformers are usually made from strip steel and clamped rather than the E I lams that we use on the smaller stuff, most being made by Linton & Hirst who also do the lams for welding.
I can't immediately answer the question, Bob, but I will ask our design guy during the week, assuming we haven't had a definitive reply before then.
Peter
-- Peter & Rita Forbes snipped-for-privacy@easynet.co.uk Engine pages for preservation info:
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Reply to
Peter A Forbes
Bob,
I think it's a cheaper way of securing the laminations to stop them vibrating; as you say varnish is best but must take a long time to dry. As long as there aren't welds on the inside /and/ outside of the core, the uneven gaps between laminations don't form a true shorted winding... they might even stamp lams from pre-varnished sheet to reduce the likelyhood. But I can't imagine a fat multinational like AEG putting energy-saving over profit ;)
Guy
Reply to
Guy Griffin
Also (my spies tell me) in a motor, the field is rotating so welds in several places will cause less of a problem, provided as guy says they are all on the outside & there is good insulation between the lams elsewhere.
Cheers
Tim (Repair man has just arrived to fix AEG washing machine )
Tim Leech Dutton Dry-Dock
Traditional & Modern canal craft repairs
Reply to
timleech
Thanks to Tim and others who have responded on this question. Since becoming aware of welded laminations I seem to be seeing them more and more. I guess the advantages in manufacture of not having to have assembly jigs to compress the stack when finally assembling motors/trannies are high.
Regards
Bob
Reply to
Bob Minchin

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