Packing transformer core plates.

[ELS122]

what is the most efficient/fastest way to build an EI core around a bobbin? and how is it done in automated manufacture?
and can anyone link some documentation on the comparison of core types (C core vs EI core for example)?

and a random question, was the paper insulation on old transformers yellow from the beginning? I know paper yellows over time but I've never seen even a picture of an old transformer with white wrapping.

[jonpaul]

laminations are stacked with a laminating machine

possible prototype short run by hand

laminations are supplied with insulation on surface

contact the laminations steel manufacturers for specs and proceedures

After assembly, lam stack is held by screws, bracket or varnish impregnated

jon

[mag_therm]

When search "kraft transformer insulation" > images will show lots of photos of transformers with new insulation before impregnation.

In the old days of hand stacking, the lams were often not individually stacked opposite handed.
They did it "3 in hand" etc to save time. It was a tedious job.
So if you look at an old transformer near the ends of the E, you will see the number of lams across the gap.
That increased I mag a bit compared to piece by piece stacking in machine.

In the larger transformers, there were two sets of lam packs (of different dimensions)  laid alternately to distribute the gaps.
Of course, in a gapped core, like a DC choke, the lams are all in same orientation.

[ELS122]

When search "kraft transformer insulation" > images will show lots of photos of transformers with new insulation before impregnation.

In the old days of hand stacking, the lams were often not individually stacked opposite handed.
They did it "3 in hand" etc to save time. It was a tedious job.
So if you look at an old transformer near the ends of the E, you will see the number of lams across the gap.
That increased I mag a bit compared to piece by piece stacking in machine.

In the larger transformers, there were two sets of lam packs (of different dimensions)  laid alternately to distribute the gaps.
Of course, in a gapped core, like a DC choke, the lams are all in same orientation.

why not cut the middle leg shorter in an EI core transformer for the gap?

the old transformers I've taken apart, none have had any adhesive to hold the core together, they just have been packed tight, and have a case for the mounting which surrounds the core

[jonpaul]

gapped center lamps available on special order, cutting is not practical
simple paper gaps are fine for 99% od use
any mains transformer will be noisy if not varnished

Jon

[ELS122]

any mains transformer will be noisy if not varnished

Jon

well I disagree to that a lot.
while I have some old transformers that buzz so loud that I've put them in the parts bin, at the same time the quietest transformers I have are rusted unvarnished ones.
I've seen other transformers having paint on them, but weirdly only on the front and back, not on the side faces where the side of the core sheets is seen... the laminations themselves arent painted on both sides.