Hello all,


I'm looking to start building.  I need to make an interesting shape to guide magnetic flux around, but I am going to have a diametrically magnetized ring magnet spinning inside part of the shape.  I want to reduce any magnetic damping by eddy currents, so I want to stay away from pure steel.  I have looked at ferrite and laminated stuff, but can't find any company or method to make the simple shape I want.  Does anyone have any experience with building custom shapes that have minimal losses for a magnet spinning near the metal?

Magnetite powder + Polyester resin= any shape , fair permeability compared to plain steel
or
Magnetite powder + nickel oxide powder + polyester resin = Best properties
ratio must be so that just enough polyester resin added to hold the powder mix together and enough to make it strong too
good luck
Nickel oxide powder:
http://www.ebay.com/itm/Black-Nickel-Oxide-Powder-500g-Free-P-P-/151237457743?pt=UK_BOI_Medical_Lab_Equipment_Lab_Supplies_ET&hash=item233674774f
or Cobalt nickel alloy powder
http://www.ebay.com/itm/CoNi-Cobalt-Nickel-Alloy-Spray-Arc-Welding-Powder-By-the-Lbs-/261323764921
and magnetite powder, basic need
http://www.ebay.com/itm/MAGNETITE-500g-Magnetic-non-conductive-COIL-CORE-POWDER-Fe3O4-Ferric-Oxide-/261141008974?pt=LH_DefaultDomain_3&hash=item3ccd37924e

polyester resin (remember not all resins are good for this, this one is great and cheapest per kg
http://www.ebay.co.uk/itm/Polyester-Resin-1kg-Lloyds-Approved-GRP-repairs-/370429558755?pt=LH_DefaultDomain_3&hash=item563f527fe3

Thanks for the tips!  Is there any tutorials on how to mix them/ratios?  I'm needing a high permeability/low hysteresis weird shape.  Would you just make a mold, and pour the epoxy/powder mix in and let it harden?  I've never done anything like this before.  How would it compare to a bunch of steel plates cut to shape and pressed together?

Thanks so much for the help, it's very helpful.

what kind of shape would you like to make?  plain pure iron if annealed with pure hydrogen has second greatest permeability with 200000 ,
metglas has 1000000
you might as well just tell to a local metalcraftsman to cut the required shapes for you from pure iron , since pure iron, (not carbon steel,permeability of only 100)
 99.95% iron has a permeability of 5000 untreated.
i dont know the actual permeability of magnetite powder, but i think its way lower than 5000.
but i made powder cores before and they are excellent,   you need to experiment with the ratios, and you make a mold and just pour it in the mold and wait for it to cure and take them out, you can make lots of identical cores if you make a mold which can be dissasembled with a couple of screws.  wear gloves and goggles!

cutting out pure iron sheets and pressing them together is far greatest by the waay..

you are welcome and looking at the diagram its a great research field. great idea.  if you do choose to make the powder techique then i would suggest you use only iron powder and no nickel in it since you want it for low alternations,    addition of nickel is good in high frequency cores.

another interresting thing to add from me,  when i experimented with iron powder i realized that i could align the particles of iron with a magnet then when the resin cured iit stayed like that.  just something to think about.

Surf board resin is very thin compared to most. It also has excellent wetting abillity. So it should be an easy mix. Like Luc says, if you want a core that is even close to what can be bought, the mix should end up like a thick putty, very dense with magnetic material. Not so thick that there is possibility of lots of air pockets.

Another idea that might work well is very thin CA (superglue) from a local hobby shop. This is on my list of things to try, as I have recovered some nice fine iron powder from a bead blaster cabinet at work using a magnet, and have the thin CA on hand.  Ill try to do a small sample to see if it works well or not. I need to do the test anyway before I waste the powder that I have. The density of the iron should prevent the CA from heating up too much and curdling/boiling as in some situations CA can do. The very thin ca has excellent wetting also. So just fill your mold with the magnetic material and apply the CA. It should seep into every nook and cranny. It just might be the new way to go.  About 10 bucks for 2oz at your local hobby shop. A bit more for ZAP brand.  Ebay also, just add shipping.

Mags

Hey Mags

one guy had a great idea at the EF topic I posted above. Use paraffin wax for experimental molds. When you heat it it's very thin and penetrates, once cold it should be had enough for experiments. When done and you want to make a change, just heat and re-mold.

Luc

Hey Luc

It would be interesting to see if something like that holds together.  Sort of like pie crust dough, too much flour and it might not hold together well. But would be interesting to try. 

Mags

I think it's worth a try... if it crumbles just re-heat and add a little more wax but I would try it in a small scale first to see the results.

Luc

I agree, always test before wasting too much material and time going to far before you know for sure it will work. Thats why I will test the CA before making a core I intend to actually work with.

Mags

Excellent posts guys. I'm going to use the information from above and order some supplies based on your experience, you guys have saved me a lot of money. it'll be interesting to see how well I can do at it.


I'll keep you updated on any molding I do. It would be great if someone offered a service on here to just send a design and have a custom shape made. I will have fun testing though!

No problem Blain

If using resins, you need to mix the 2 parts first, then add the magnetic material. Otherwise, the 2 parts mixed after infusing the resin with the magnetic powder, will be hard to thoroughly mix and may not cure in some areas.  If using the surf board resin, do a couple tests with the resin itself by adding various levels of hardener(MEKP) to see what your time frame is for curing. Then you will know your approximate working time, and additional time with material infused.  if it takes till tomorrow to cure, then thats what it takes.  Get some plastic mixing cups, stirring sticks and a box of cloves. And MEKP, that stuff is very bad for you. Do not get it on your hands or any body parts. Use the rubber gloves when handling the MEKP particularly. Keep its container in one of the plastic cups when not in use. It seeps from the cap threads where a little excess resides after use and will run down the bottle, onto the table, on your hands when handling, etc.

The thin CA superglue will cure pretty fast Im sure..  But seems to be a possibly quick alternative to resin.  Just got done doing a real carbon fiber covering on a front spoiler at work. Used the CA to hold the carbon fiber cloth in place, like around sharp corners and small radius bends, then apply the surf board resin, about 5 layers. One on top of another without sanding in between layers is fine as the surf resin has no wax like other resins do and have to sand between layers. I was mixing it hot, meaning it cured enough to sand in 30min.  Before sanding, if needed, wipe the surface with a cloth and acetone. It takes a thin sticky layer off the surface and sanding is like butta.     With the magnetic material, sanding will be much harder. If you have to sand anything, like sharp edges/corners afterwards. Usually when in the mold, those surfaces are not sticky, only surfaces exposed will be, like when I was brushing it on the spoiler, the top surface needs the acetone wipe, or the sand paper loads up with the sticky stuff.

lol went to far on that, but ya never know how far a project can go, and its nice to have info first.

Mags