On Sat, 24 Jun 2006 02:49:17 GMT, "Ian Iveson"
wrote:

Jerry said

I have a R-40 core and bobbin on my desk. The core was wound on a
rectangular mandrel. The first and last layers have been spot welded.

The core has been vacuum impregnated with a thin epoxy. It is very
well done. The core is rock solid.

The lamination strip width on the first and last turn is .195" in
width. The width of the center turn is .812".

The available winding area for one bobbin is only 1.542" x .125" which
isn't much concidering the size of the core.

This lamination is very similar in size to UI75 lamination as shown in
Tempel Steel Corp. book. www.Tempel.com

Economics dictated that we utilize the UI lamination design because
of the difference in the core cost and overall labor cost.

...We utilized
high speed bobbin winders and automated lamination stackers.

The
stray flux emanation was lower in the R-Core but the UI was
acceptable.

I think that I made this comparison in the very late 1970s for a
medical instrument.


Much thanks, Jerry.

Yes it is wrapped round a mandrel...that's the only way to use a single
continuous strip as far as I can see.

The key for me in your description is what I couldn't see from the pictures: the
adhesive filler.

If you wind strip round a mandrel, then no matter what the shape of the mandrel,
the winding will eventually end up round. I dimly remember there is even a law
devoted to this phenomenon. The less plastic the strip, the harder it is to
maintain the shape of the mandrel. GOSS is hard and elastic, hardly plastic at
all, and winding a shape with straight sides is impossible even for a few turns.

Even if you clamped the core and tack welded the ends of the strip, then when
you took it off the mandrel it would spring into an oval shape, with some
awkward wriggling round the welds.

That's why I suggested that the final process must be clamping, and bonding the
strip along its whole length. This could be done either by impregnation, or by
using coated strip, with the former being much easier if the results are good
enough.

I wonder if a notched mandrel is used? Otherwise it must be difficult to get
successive layers of wider strip to sit true on thinner ones. If so, then two
half-mandrels are required (or possibly four quarters), perhaps held apart so
that the straight sections of core are left free for the tack welding. Once
wound, the mandrels could be moved together to free the core, which would spring
into whatever shape it fancies.

Finally, I suggest, it is impregnated and then pressed to hold it in shape until
the adhesive filler goes off.

Is the cross-section round, BTW? It doesn't look round in the pictures.

cheers, Ian


Well Ian, I measured the R40 core and found that the diameter of the
core is 2.75". The dimensions are .873" x .830" and give me an area
value of 94.8% of that of a perfect circle, so I would say that you
could consider it to be circular in nature.

Consider that the very long strip of core material has to have a width
of .195" which progresses to .812" when at half length then the with
progressively narrows back to .195" on the last layer. That is some
piece of computer operated equipment that does that. I would like
to see their equipment.

If we assume the thickness of the material to be .006" GOSS, there
would be about 138 layer. The strip of steel would be 1013" long.

For those who might fight with my lack of exact math, It is hard
to get precise dimensions because of the bobin wound coil.

Jerry