Ferrite Rods (or work alikes)

Yes.

Fine to just by a wood dowel and slide them on it - until you get the inductance tuned in.

--

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

Btw,

As an alternative... I can just buy a bunch of 2cm 'rod' magnets from the local craft store, heat them up to kill the magnetism, and then align them end to end until I've got what I need, right?

Just a thought.

thanks!

-phaeton

It never occurred to me to try that. I happened to have a few small Radio Shack ferrite magnets so I put one on a piece of steel wire (has a small hole through the center) and put the magnet and wire into a propane torch flame. The wire glowed orange the magnet never got hot enough to glow.

The magnet is still magnetic, but compared to one that wasn't heated, there is no doubt the heated one is much weaker. Unheated picks up my small pliers - heated barely moves it (they are both at room temperature now)

I expected it might break apart when heated but seems no worse for the heating - can't see any physical difference between the two. Heated one feels a little different but that is probably just skin oil being burnt off or carbonized - little more friction with the heated one.

You may be on to something. Next time I fire up the barbie, I'll wire a magnet to the coal basket and see what happens.

--

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

NO :) ;)

Even though you killed the magnetization, you did nothing to soften the cores (magneticaly). Only a 'soft' core would act like ferrite. They are very difficult to magnetize, and you might just as well use a piece of wood.

Sorry, no.

That kind of ferrite has a very square BH loop (called hard ferrite. It has a low permeability, even when it is demagnetized. High permeability ferrite is called magnetically soft ferrite.

R33-033-450 0.33 inch 4.5 inch $8.00 R33-037-400 0.37 inch 4.00 inch $7.00 R33-050-200 0.50 inch 2.00 inch $4.00 R33-050-300 0.50 inch 3.00 inch $4.50 R33-050-400 0.50 inch 4.00 inch $8.00 R33-050-750 0.50 inch 7.50 inch $20.00

I think you may be wrong about that.

I'm seeing something that leads me to believe it becomes soft with heating.

After all that's what is done to transformer laminations for 60 HZ cores. The steel is rolled from a slab or billet and becomes hard as it is worked. It is annealed after it is rolled to lower the hysteresis losses.

The empirical results:

I fooled with the magnet that I partially demagnetized yesterday - figuring that putting it between a pair of neodymium super magnets would re-magnetize it - after all that's what should happen if it is hard ferrite, right?

It can't be re magnetized. It is now soft.

So my first thought is that it takes some special killer magnetizer to magnetize the stuff. Then I took one of the unheated magnets and used the neodymium magnets to reverse its polarity. It doesn't stand a chance against the neodymium - reverses polarity back and forth instantly - and has the same strength as the magnets that I haven't done anything to.

Conclusion - fire makes it soft.

Permeability? I can't really say for a certainty. My only way to judge the various surplus ferrite cores I have is to use a magnet -

The demagnetized ferrite is strongly attracted to a magnet so I think the permeability is relatively high.

The hole in the magnet is really too small for a toroid core, but the next time I use the barbeque, will take one and do a proper job softening and annealing it then see if I can't get some 32 gauge wire around it and make a blocking oscillator.

Interested in hearing your comments on my experiments and conclusions.

I realize heating magnets may not be the best ferrite core material, but this guy is only working at 35 KHZ and there are steel laminations that are good at those frequencies.

--

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

To follow where this is going regarding hysteresis and the magnetic properties of hard and soft iron

Explains it really well

The fact that the heated magnet can't be re magnetized supports the idea that the hysteresis curve is a lot narrower than it was before heating.

--

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

Try Dan's Small Parts or Ocean State Electronics.

Chuck

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----

The #1 Newsgroup Service in the World! 120,000+ Newsgroups

----= East and West-Coast Server Farms - Total Privacy via Encryption =----

Could be. Ive been wrong about lots of things.

Steel (and metals, in general) have a grain structure that changes with cold working and heat history. Spinel (ferrite) is a ceramic material that changes grain structure only with sustained heating well above red heat. Just heating ferrite through its Curie temperature (where it demagnetizes, completely) doesn't change its grain structure.

Only if the magnetic field strength was high enough to push it all the way to saturation. I think that the external field from a neodymium iron magnet is not quite high enough.

You haven't re magnetized it, but you haven't proved that it can't be re magnetized with a high enough field.

Bingo.

That is a pretty good test. You originally said that the heat did not eliminate all the magnetism, but only weakened it. Does that weakened magnetism reverse when you apply the external magnet?

Perhaps. But how did they make the ferrite in a kiln, originally, without making it soft? Perhaps it was fired in a low oxygen atmosphere (or some other gas than air), and heating it in air has changed its chemical makeup. The oxygen content of ferrite has a big effect on its properties.

You need to do an inductance test of a coil with either the unheated ferrite or the heated ferrite in it, as a core.

You may be right.

I would try heating it with a propane torch on a piece of fire brick.

I have a collection of ferrite pieces. If you live in the U.S., send me your address and I will send you some to experiment with.

pruning away

Agreed, that's what I've been taught and believe.

Then I wonder how important grain structure really is? In small transformers (less than 5+ KVA) they talk about the importance of grain orientation for maximum efficiency. But with larger transformers and motors the physical strength or hardness begins to be a consideration. I guess (never worked with big transformers) if you have a lamination that is a few feet long, you'd worry about it bending before you got it secure in the core - so perhaps (I really don't know, just conjecture) the relatively high efficiency intrinsic to big, versus little, is more important.

I did work with a small - wind the transformer to spec - company some time ago. My boss (only 25 people) kept mentioning his claim to fame was not taxing the iron too much - we used some grain oriented steel with moderate cost for most stuff, and stacked the laminations at 1X1, and our clients would rave about how cool the transformers ran. I assumed, back then, that not everybody was using grain oriented steel.

It does reverse polarity - even faster or with less effort than the regular ceramic magnets do. It is the regular ceramic change polarity about 1.25" from the neodymium and get sucked in, the wimpy heated magnet changes polarity at ~2" and is still in my fingers.

Maybe partial magnetization is misleading - the heat treated one is weakly magnetic.

Yes, it does indeed reverse, and some distance out from the strong magnet, compared to the regular magnets.

Well, I don't know. One of the mysteries reserved for ferrite makers? Working iron makes it hard. Perhaps there's some process that converts iron billet or ferric oxide to powder without hammering on it? Like spraying molten metal into an inert or hydrogen atmosphere?

Then how does one make hard versus soft ferrite? Maybe hard ferrite is harder to make, and it has to be processed in a different way to make ceramic magnets.

I had been assuming they took metal particles and heat and fuse them like other sintered materials, now I'm not too sure. Why call it ceramic? does it contain clay? An "off the wall question" is leading to more questions.

So far Googling hasn't worked - too much commerce or the wrong search words.

I haven't gotten any results I trusted with high frequency cores. The place I worked had a "National Radio" (I think) impedance bridge that worked very well - my home attempts haven't been trustworthy. I do trust the 60 hertz power line tests, but not any from my audio signal generator.

Not sure the propane torch is up to the task. I may have a spider living in the works. Left it outside one night . . . now the flame looks weak. The barbeque, on the other hand, will definitely exceed

1,000 degrees in the coal basket for more than enough time. Anyhow the torch is probably OK but low on fuel so I'll use it till it dies.

I'm living very frugally (both a necessity and environmental awareness predisposition) so I work the experiments in when they don't interfere with life.

I don't believe in God - man makes the mistakes and man should be fixing them, not praying.

--

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

The composition is different and the atmosphere during firing may be different. Ferrites are generally made by mixing (and milling with a ball mill) iron oxide and other metal oxides. I am more familiar with soft ferrites. These usually contain nickel and zinc oxide (if they are the high resistivity, high frequency stuff) and spiced with cobalt, copper or other metals. This mixture is pressed and fired to react the oxides into a spinel crystal structure. Sometimes the mixture is prefired as a loose powder, to start the reaction and form granules, then milled to powder again, pressed and fired again to a higher temperature. This reduces the shrinkage that happens during the reaction.

I think this material is usually fired at least part of the heat cycle in a reduced oxygen atmosphere.

The low frequency soft ferrite is based mostly on iron oxide and manganese oxide. The process is the same, but I think this stuff is usually fired in air.

If I remember right, hard ferrite is made of iron oxide and magnesium oxide, and I haven't heard what atmosphere is needed during firing to achieve the best coercive force and remnance.

I think some info may be available through Google if you want to dig a little.

A ceramic is made almost entirely of metal oxides.

Finding the right key words helps, because I have come across some discussion of ferrite production.

This one is pretty general:

(snip)

I have one of these and get a lot of use out of it.

(snip)

Thanks for all the good info John.

--

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----

The #1 Newsgroup Service in the World! 120,000+ Newsgroups

----= East and West-Coast Server Farms - Total Privacy via Encryption =----