Large Ferrite Rings

Thread Starter

DC_Kid

Joined Feb 25, 2008
924
Posting in Rf forum only because ferrite rings are used quite a bit in various applications where Rf is involved.

I am looking for a US supplier/seller for a ferrite D ring that looks like this one. It's gonna be fairly large, diameter of ferrite 3/4 to 1", and 4-5" across.
If I can't buy it as cots then I will investigate making it myself. It could be a solid D and I can cut out the opening.
 

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MisterBill2

Joined Jan 23, 2018
11,900
A description of the application will do a whole lot to make the readers understand just what variety of material you need.
Include the frequency intended and the power level.
 

MrSalts

Joined Apr 2, 2020
1,762
Posting in Rf forum only because ferrite rings are used quite a bit in various applications where Rf is involved.

I am looking for a US supplier/seller for a ferrite D ring that looks like this one. It's gonna be fairly large, diameter of ferrite 3/4 to 1", and 4-5" across.
If I can't buy it as cots then I will investigate making it myself. It could be a solid D and I can cut out the opening.
Do you specifically need ferrite or any type of inductor core material (muMetsl, iron powder core, ...).
Also, ferrites are ceramics. They are not extruded as cylinders and bent into a D-ring. They are typically powders with a small amount of binder material filled into die and pressed into a green part then put in a kiln and fired. That said, a square/rdctangular cross section would be much easier to form and a less expensive die and less likely to crack in the kiln - there is no good way to evenly apply pressure to a circular cross section (especially one that is 3/4" diameter).
Note: you may have seen cylinder shaped ferrite but those are pressed along the logical axis of a simple cylinder - a D-ring has completely different symmetry.
 

DickCappels

Joined Aug 21, 2008
8,710
Ferroxcube makes some fairly large rings.

A long time ago a friend who was a Feroxcube representative told me that I could go into their office and Dudley would open the storeroom up to me and I could help myself. I managed to get several large rings which came in very handy because I was designing some inductors for a client. I still have some today.
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
924
100Hz to 10kHz , in an odd transformer. The amps in wire could be 10-200A.

In making my own, coated Carbonyl in a polyurethane epoxy in 70/30 volume ratio, would be my choice. I would make a shape using PVC, cap the ends, and then create a vacuum/pressure port, and a fill port in the middle of radius of the D. I would fill it, apply a vacuum to get the air out of the epoxy, then apply +PSI while it cures.

I have also seen powders mixed in with fire cement, packed into a mold, cooked around 200F for a few hours, carefully remove from mold, then cook 500F for 4-5hrs.
 
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MisterBill2

Joined Jan 23, 2018
11,900
Is this supposed to be some sort of current transformer? Or is the large cross section because it will be handling power? There are transformer cores that are two halves with mating lapped surfaces so that they can be assembled inside wound bobbins. Similar to those flyback transformer cores, but different. Is the purpose of the gap to have an intense flux field pass through something? A circular core with a slot cut could possibly be made from a high power choke core.
 

MrSalts

Joined Apr 2, 2020
1,762
100Hz to 10kHz , in an odd transformer. The amps in wire could be 10-200A.

In making my own, coated Carbonyl in a polyurethane epoxy in 70/30 volume ratio, would be my choice. I would make a shape using PVC, cap the ends, and then create a vacuum/pressure port, and a fill port in the middle of radius of the D. I would fill it, apply a vacuum to get the air out of the epoxy, then apply +PSI while it cures.

I have also seen powders mixed in with fire cement, packed into a mold, cooked around 200F for a few hours, carefully remove from mold, then cook 500F for 4-5hrs.
Carbonyl iron is the right material but you'll need much higher volume% iron than your formulation. You'll also have to insulate/passivate it before you form it - otherwise you'll get lots of Eddie current losses and heating.
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
924
@MisterBill2 The open part of the D will be a transformer secondary. I could use just a basic round ring, but I need the cross-section to be circle and not a rectangle.

@MrSalts how do you mean "insulate". You mean wrap the core with paper or plastic before wrapping a coil? The insulated Carbonyl powders do reduce eddy and core ohms. The online vids for the mix showed that using this method, and 80/20 was no better than 70/30. Probably a limitation of that DIY method.
 

MrSalts

Joined Apr 2, 2020
1,762
@MisterBill2 The open part of the D will be a transformer secondary. I could use just a basic round ring, but I need the cross-section to be circle and not a rectangle.

@MrSalts how do you mean "insulate". You mean wrap the core with paper or plastic before wrapping a coil? The insulated Carbonyl powders do reduce eddy and core ohms. The online vids for the mix showed that using this method, and 80/20 was no better than 70/30. Probably a limitation of that DIY method.
Commercially, the hard or the hydrogen-reduced iron powered is reacted on its surface in a nano-meter thick layer to insure there is no electrical conductivity between particles. Insulating more than 10s of nanometers thicknesss will significantly reduce the amount of magnetic iron in your formulation.

I have no doubt that an 80/20 ratio is no better than a 70/30 mix in the test capabilities you have available. If the permeability and saturation current you achieve with a 70/30 or even 80/20 mix meets your needs, you should continue with that. I really doubt anything in the range of 20A will be part of your result with such a low iron content. High quality iron powder cores will be more than 95 and up to 98% iron powder. With that, you should understand the difficulty of pressing forms with circular cross-section. At low iron content, you should be able to form the urethan binder like clay and let it cure but those low levels of iron content are suitable for a novelty diy demonstration but not a 20A choke or transformer.
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
924
Just for clarity, 70/30 mix by volume, 70% powder. Urethane epoxies like to hold air when mixed, so was thinking to apply a good vacuum (low micron vacuum) to allow the air to come out, and then let it cure 24hr with 2-3ATM. I can add PSI using air, or argon, or 100% O, or CO2. I don't want to push a gas into the urethane, etc.
 

MrSalts

Joined Apr 2, 2020
1,762
Just for clarity, 70/30 mix by volume, 70% powder. Urethane epoxies like to hold air when mixed, so was thinking to apply a good vacuum (low micron vacuum) to allow the air to come out, and then let it cure 24hr with 2-3ATM. I can add PSI using air, or argon, or 100% O, or CO2. I don't want to push a gas into the urethane, etc.
Typically, vacuum is applied in the press tool before several tons of pressure is applied.
 
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MisterBill2

Joined Jan 23, 2018
11,900
@MisterBill2 The open part of the D will be a transformer secondary. I could use just a basic round ring, but I need the cross-section to be circle and not a rectangle.

@MrSalts how do you mean "insulate". You mean wrap the core with paper or plastic before wrapping a coil? The insulated Carbonyl powders do reduce eddy and core ohms. The online vids for the mix showed that using this method, and 80/20 was no better than 70/30. Probably a limitation of that DIY method.
It is not at all clear to me what you mean by "The open part of the D will be a transformer secondary." An air gap in a core is where one would place a magnetic flux sensor. If your intention is to have another segment with a winding on it, there are easier methods available,I think.
And we still have no idea as to what this is actually supposed to do.
 

MrSalts

Joined Apr 2, 2020
1,762
And we still have no idea as to what this is actually supposed to do.
"actually supposed to do" is an optimistic phrase. Maybe we can ask what it will "actually" do and what it is "supposed" to do as different questions. I don't think the answers will be the same once tested.
 
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