Anyone bought small quantities of custom ferrite cores?
I'm looking for a couple of special shapes, but made from common material like 3C90 or whatever (it's not very critical).
Size will be fairly large-- several cubic inches of material.
Any idea of sources and ballpark NRE costs?
AFAIK ferrite is hard to manufacture (which is why _my_ question was about iron powder!)
Could they be cut from flat plates? Plates are obtainable, and I'll bet that they're cutable by laser or water jet or some such.
-- www.wescottdesign.com
Yes, now that I read it, your application has some similarities. Large air gap too.
Water jet uses abrasive that is basically ferrite AFAIUI (garnet) so I don't know how well it would cut. Maybe my shapes could be cut from flat plates and stacked up/epoxied together. Maybe. Who sells these ferrite plates of which you speak?
IIRC, ferrite cores are made by sintering powdered ferrites. I don't think they machine them any further. So its probably a matter of having a mold constructed and specifying the exact mix of powder to acheive the required magnetic properties.
I wonder if one can obtain the powders, make a ceramic mold and borrow a small pottery kiln to roll your own.
-- Paul Hovnanian mailto:Paul@Hovnanian.com ------------------------------------------------------------------ Parity on, dudes!
Planar EI configurations offer plates with large surface areas that would translate into significant cross-sections, when stacked. The last ones I bought were polished on both surfaces ~ flat.
EPCOS, Hitachi, NEC/Tokin, TDK and FDK market ferrite polymer composite materials. This was initially in sheet form, but it is supposedly suited to injection molding.
The FDK and NEC materials are low temperature and lossy, the EPCOS is high temperature (200C) and useful in resonant power circuits, though permeability is low. The TDK markets composite material mainly for magnetic apps.
Tooling for an injection mould can be pretty steep, unless amortized over large production volumes.
RL
Dangit! I _distinctly_ remember seeing this in the Fair-Rite catalog, and now it isn't there!
-- www.wescottdesign.com
In a past life, I was lab engineer at a Philips ferrites factory.
You need to find a supplier for the highly specialised ferrite powder composition you want. Mostly the making of that is a propietary process. I doubt any ferrite manufacturer would sell a small quantity.
Then you need a high pressure press capable of about 500 Kg/sq cm and tool-steel dies to do the powder pressing. Life of a steel die is around
500-2000 cycles. Production dies are spark eroded from tungsten carbide, expensive.Firing needs a temp around 1400 celsius, and a controlled atmosphere, air in first part of cycle, tapering on a strictly controlled curve to pure nitrogen during cooling after peak temp. This is way beyond what you can do in a typical pottery kiln.
Cutting shapes from block blanks would be possible using diamond grinding wheels and drills. Ok for very small qty, but still expensive for the tooling.
Water cutting was not around when I did this, but maybe with silicon carbide or diamond grit, it might be possible.
-- Regards, Adrian Jansen adrianjansen at internode dot on dot net Note reply address is invalid, convert address above to machine form.
I want someone to make ferrite Lego.
-- www.wescottdesign.com
About 7000 PSI.
500 cycles is plenty.
Yup.
Thanks for the detailed info, Adrian. Very useful.
Do you remember about how much the ferrite changes in size after firing?
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Typical shrinkage on firing is 20-22%. IE you make the die 20% bigger than the final size you want. We used to test each batch of powder for a number called the "Dry Press Density" which was around 2.7 gm/cc when pressed at 500 Kg/sq cm. Final fired density has to be close to 4.8 gm/cc. You can easily calculate the linear shrinkage from the density ratio.
The fun part starts when you press a long shape, like the leg of a U core. Then friction between the die wall and the powder changes the density along the leg. So the bottom and top get denser, the middle less dense, leading to a leg tapered outwards at each end, and of course the bottom of the U ends up denser than the legs, also leading to odd distortions. You have to size a die to take account of all this.
-- Regards, Adrian Jansen adrianjansen at internode dot on dot net Note reply address is invalid, convert address above to machine form.
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