Al A. wrote:
DoN. Nichols wrote:


I would advise not doing it.

The laminations are designed to be electrically separate to
minimize eddy currents. There is an insulator coating between
laminations, and your cleaning would remove this. It also keeps the
magnetic fields oriented along the laminations, not across them.

I'm not sure what process is used to generate the insulating
layer, but at least the rust will not conduct electricity like the
cleaned laminations would.

Good Luck,
DoN.



The insulating coating on transformer and motor laminations is
generally a thin oxide layer that is put onto the steel, with some sort
of a steam process. It is a finish not entirely unlike some types of gun
blueing. Usually the transformer is varnished after the laminated core
is assembled onto the coils. They are immersed into a varnish tank, and
often the tank is closed and a vacuum drawn in the tank to help draw any
trapped air out from the windings and the laminations.

You don't want eddy currents in the core, and you want to minimize any
gaps in the magnetic circuit to minimize core losses and idle currents.
Coating the individual laminations with varnish will introduce lots of
gaps in the core, which is not good. that is why they are steam
finished, it forms a very thin insulating layer.

Don is correct. You would probably be best off to leave them alone,
stack your core and varnish.

A number of years ago, I stacked hundreds and hundreds of these things
by hand. Used to work for a custom transformer house.

Hope that helps.

Al A.

Alright, it looks like the consensus is that I should leave them alone.
I thought they were varnished to prevent eddy currents, but now you
mention it there is a noticeable green layer on the plates. I assume
that this is the oxide layer formed by the steam. I had to dismantle the
core to rewind, so that isn't wasted effort. The reason for cleaning off
the rust was to make reassembly a bit cleaner. The rust is thin and
dusty and gets everywhere. Perhaps I should just wipe them with a rag
soaked in white spirit as I reassemble?

Thanks for the suggestions.

Chris