On Mon, 19 Jun 2006 23:33:58 +0100, Pooh Bear
wrote:

There is so much wrong with Ian's post below that after considering it I'm not going
to even attempt to reply !

Cast and pressed cores my arse !

Graham


Ian Iveson wrote:

Graham wrote

They seem to be common when cast or pressed cores are used,

Eh ? Please give an example of a cast or pressed core !

Search for "amorphous core".

There are two ways of making amorphous cores. One is to cast a glassy strip and
wind it, and the other is to press a powder very hard. Generally it seems the
first is used for larger cores, presumably because of the problems of pressing
big things. I am assuming amorphous is a poor electrical conductor...?

As it happens, it looks like amorphous R-cores are most commonly made using cast
strip. I guess this is because the problems of winding small bobbins in-situ?

Searching under "amorphous core" or "r-core" gave very different results from
last time I tried. Seems like suddenly *everyone* has jumped on the bandwagon.

Anyway, pressed R-cores aren't as common as I thought, although pressed
amorphous toroids are. Cast amorphous strip-wound is increasingly common. I
would like to know how they clamp the straight sections to stop the laminations
springing out or buzzing.

The guys that make the cores and accesories have it sorted for sure. You need
to buy
a special winding machine too.

Of course, otherwise it would be labour-intensive. As it happens it is
complicated-and-expensive-machine-time-intensive. Quite possibly such machines
require more minding, I'll grant you that. I just wanted to dispel the notion
that they are all hand made, and that a shuttle is required. That would not be a
viable proposition.

The (relatively) simple method is to wind the wire on to a split bobbin in-situ
(as with an R-core), and then wind it off the bobbin onto the core. Clever eh?

As for the idea that R-cores are a recent "invention", I just don't see
it...pretty obvious idea don't you think? I assume that practical realisation
has been the sticking point. Perhaps the existing technology for strip-winding
toroidal cores could be adapted at relatively low cost.

cheers, Ian
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.

Jerry