Moldable Iron Powder
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From: Gerhard Hoffmann on 24 Nov 2009 05:33 On Mon, 23 Nov 2009 12:41:46 -0600, Tim Wescott <tim(a)seemywebsite.com> wrote: >The paint got me thinking -- if they can make latex paint with iron >powder in it, can I buy some sort of plastic resin with iron powder in it >and make my own custom magnetics on the cheap? > >So: does anyone know of an iron-powder/epoxy (or whatever) mix out there >that you can buy, or an iron powder material that you can mix with your >own resin to mold soft magnetic materials out of? Some years ago, we were designing bias tees for 10 GB/s laser transceivers and stumbled across those conical coils made by Piconics. A colleage of mine was so delighted that he wouldn't wait for samples and decided to build a few over the weekend. On monday he showed up with some coils that looked _ugly_ but the bias tee was flat to 20 GHz. He never told us how he did it exactly, but I think he ground some cores in a mortar and added epoxy glue. We finally found a combination of cheap 0402 devices that worked nicely, too. regards, Gerhard
From: Charlie E. on 24 Nov 2009 12:53 On Mon, 23 Nov 2009 12:49:00 -0800 (PST), whit3rd <whit3rd(a)gmail.com> wrote: >> >There's uses for magnetic paint, though; like conductive paint, it >blocks EM radiation. You could, theoretically, paint the right kind >of bullseye pattern on your house siding over the primer, and under >the finish coat, to make a kind of hologram mirror (stealthy satellite >dish >construction, the homeowner's association will never know). > Reminds me of a friend, who decided to do his own roofing so that he could make sure that the spacing of the nails would not interfere with the satellite dish in the attic. He had the truss designed specially too, to give him the room and metal free window to the south... Charlie
From: Adrian Jansen on 24 Nov 2009 16:51 Tim Wescott wrote: > On Mon, 23 Nov 2009 12:49:00 -0800, whit3rd wrote: > >> On Nov 23, 10:41 am, Tim Wescott <t...(a)seemywebsite.com> wrote: >>> A long-term back-burner project just got my attention when I found out >>> that Home Depot sells magnetic paint. >>> >>> The paint got me thinking -- if they can make latex paint with iron >>> powder in it, can I buy some sort of plastic resin with iron powder in >>> it and make my own custom magnetics on the cheap? >> Firstly, why do you think it's an iron-powder paint? Nickel, cobalt, >> hematite, are all ferromagnetic (and both hematite and some kinds of >> nickel are used in paint). > > I assumed, but yes it could be some other magnetic material. >> Secondly, if you want custom magnetics on the cheap, you can get soft >> iron wire and make toroids quite easily; no powders required. Small >> cores, untwist a coathanger. Large cores, soft iron wire from >> building-supply places is reasonably priced (five pound rolls are >> common, for the ferroconcrete trades). > > I considered that, but for the shapes I want it'd be hard to get what I > wanted without considerable hand work. > >> It isn't terribly practical to make magnetic parts from low-density >> mixes >> of slightly magnetizable particles in a plastic matrix, because the size >> of the core gets larger, then you need more wire, which has to be >> thicker, so the aperture has to be larger, then the core has to be >> larger... And, if you COULD make it work, the plastic core would age >> and change values more than a solid slab of iron or a sintered bunch of >> powder or a milled/fired ceramic. It'd also be more likely to catch >> fire or outgas toxins than the 'standard' cores. > > I distinctly said that my air gaps are huge, and furthermore that I > checked this with a FEA program that shows I don't need huge > permeabilities. I also said that specific values aren't critical. Are > you saying that of all the iron-powder-in-plastic materials that you're > personally familiar with there's none with relative permeabilities in the > mid 100's? > > If you could give me a list of the brands that you're familiar with I'll > go check specifications myself, thanks. > >> There's uses for magnetic paint, though; like conductive paint, it >> blocks EM radiation. You could, theoretically, paint the right kind of >> bullseye pattern on your house siding over the primer, and under the >> finish coat, to make a kind of hologram mirror (stealthy satellite dish >> construction, the homeowner's association will never know). >> >> Parenthetically, common hematite-based black paints aren't ALL >> ferromagnetic; >> the particle size in the pigment is critical, very small particles don't >> hold a magnetization like a large crystal of the pure material would. > > > > > If you consider that the relative permeability is pretty close to the ratio of total gap to total path through the magnetic material, where the total gap includes all the gaps between the magnetic particles, you quickly see that the overall permeability of any practical mix of magnetic particles and plastic is going to have a permeability of around 10-20 at most, rather than 100. -- Regards, Adrian Jansen adrianjansen at internode dot on dot net Note reply address is invalid, convert address above to machine form.
From: Tim Wescott on 24 Nov 2009 17:49 On Wed, 25 Nov 2009 07:51:50 +1000, Adrian Jansen wrote: > Tim Wescott wrote: >> On Mon, 23 Nov 2009 12:49:00 -0800, whit3rd wrote: >> >>> On Nov 23, 10:41 am, Tim Wescott <t...(a)seemywebsite.com> wrote: >>>> A long-term back-burner project just got my attention when I found >>>> out that Home Depot sells magnetic paint. >>>> >>>> The paint got me thinking -- if they can make latex paint with iron >>>> powder in it, can I buy some sort of plastic resin with iron powder >>>> in it and make my own custom magnetics on the cheap? >>> Firstly, why do you think it's an iron-powder paint? Nickel, cobalt, >>> hematite, are all ferromagnetic (and both hematite and some kinds of >>> nickel are used in paint). >> >> I assumed, but yes it could be some other magnetic material. >>> Secondly, if you want custom magnetics on the cheap, you can get soft >>> iron wire and make toroids quite easily; no powders required. Small >>> cores, untwist a coathanger. Large cores, soft iron wire from >>> building-supply places is reasonably priced (five pound rolls are >>> common, for the ferroconcrete trades). >> >> I considered that, but for the shapes I want it'd be hard to get what I >> wanted without considerable hand work. >> >>> It isn't terribly practical to make magnetic parts from low-density >>> mixes >>> of slightly magnetizable particles in a plastic matrix, because the >>> size of the core gets larger, then you need more wire, which has to be >>> thicker, so the aperture has to be larger, then the core has to be >>> larger... And, if you COULD make it work, the plastic core would >>> age and change values more than a solid slab of iron or a sintered >>> bunch of powder or a milled/fired ceramic. It'd also be more likely >>> to catch fire or outgas toxins than the 'standard' cores. >> >> I distinctly said that my air gaps are huge, and furthermore that I >> checked this with a FEA program that shows I don't need huge >> permeabilities. I also said that specific values aren't critical. Are >> you saying that of all the iron-powder-in-plastic materials that you're >> personally familiar with there's none with relative permeabilities in >> the mid 100's? >> >> If you could give me a list of the brands that you're familiar with >> I'll go check specifications myself, thanks. >> >>> There's uses for magnetic paint, though; like conductive paint, it >>> blocks EM radiation. You could, theoretically, paint the right kind >>> of bullseye pattern on your house siding over the primer, and under >>> the finish coat, to make a kind of hologram mirror (stealthy satellite >>> dish construction, the homeowner's association will never know). >>> >>> Parenthetically, common hematite-based black paints aren't ALL >>> ferromagnetic; >>> the particle size in the pigment is critical, very small particles >>> don't hold a magnetization like a large crystal of the pure material >>> would. >> >> >> >> >> > If you consider that the relative permeability is pretty close to the > ratio of total gap to total path through the magnetic material, where > the total gap includes all the gaps between the magnetic particles, you > quickly see that the overall permeability of any practical mix of > magnetic particles and plastic is going to have a permeability of around > 10-20 at most, rather than 100 Argh. Need to keep thinking about this, then. -- www.wescottdesign.com
From: whit3rd on 25 Nov 2009 17:09
On Nov 24, 2:49 pm, Tim Wescott <t...(a)seemywebsite.com> wrote: > On Wed, 25 Nov 2009 07:51:50 +1000, Adrian Jansen wrote: > > If you consider that the relative permeability is pretty close to the > > ratio of total gap to total path through the magnetic material, where > > the total gap includes all the gaps between the magnetic particles, you > > quickly see that the overall permeability of any practical mix of > > magnetic particles and plastic is going to have a permeability of around > > 10-20 at most, rather than 100 > > Argh. > > Need to keep thinking about this, then. Err... but packing of spheres yields packing fractions of 0.523 and up, and the 'gap' fraction would be the cube root of that, 0.803 and up. This isn't a killer effect. You should be able to get fine iron shot (used in some toner cartridges) which isn't a bad fire hazard, and mix into Bondo (auto body putty, known to be compatible with/bond to iron) and form some shapes easily enough. |