Moldable Iron Powder
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From: whit3rd on 23 Nov 2009 15:49 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). 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). 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. 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.
From: Martin Brown on 23 Nov 2009 16:06 Tim Wescott wrote: > A long-term back-burner project just got my attention when I found out > that Home Depot sells magnetic paint. > > The project is a levitating globe thingie, designed as a control systems > trainer that lets the student program the control rules in C and see how > different control strategies lead to different sorts of system > performance. How about a ping-pong ball into a chemical silvering mirror solution and then electroplate iron onto it in a simple ferrous plating bath? > > 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? Yes. Although the raw material when dry requires a bit of careful handling preferably in an inert atmosphere. Finely divided iron powder intended for magnetic crack detection is usually supplied as a suspension mixed in kerosene. In the air as a dust it can be pyrophoric. It is fun to paint some on a magnetic card strip you no longer need. > > 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? > > I'm looking to build some cores, and maybe have some made at a low volume > if the prototypes work. I do _not_ need super high permeability -- the > air gap in this is so big that according to the FEA program I'm using > there's not much difference between core material with a relative > permeability in the hundreds vs. iron (with relative permeability in the > thousands). You might be better off with finely ground magnetite. That is easier to handle and doesn't go woof. This stuff is in vogue these days for fancy magnetoresponsive goops in various esoteric devices. You can make it do some of the T2 type flow then rigid things with a bit of effort - except it is dirty black gunge and gets everywhere instead of a nice mirror finish like in the movie... and a bit fanciful in some articles by the proponents of the technology. eg http://science.howstuffworks.com/liquid-body-armor2.htm Someone like Alfa or an NDT specialist supplier will sell you the stuff but whether you will think the price is reasonable is harder to answer. Regards, Martin Brown
From: Tim Wescott on 23 Nov 2009 17:18 On Mon, 23 Nov 2009 14:52:16 -0500, jeff wrote: > Hi Tim, > There are a lot of iron filled epoxies out there. Two names that come to > mind immediately are Moglice and Devcon. I recall Dave Trumper at MIT > had a nice mag-lev demo that used a photocell as feedback. Thanks Jeff. That gave me the keywords I needed. Goodness but it's expensive stuff, at least from McMaster. Gotta think about this again, maybe. -- www.wescottdesign.com
From: Tim Wescott on 23 Nov 2009 17:32 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. -- www.wescottdesign.com
From: Jerry Avins on 23 Nov 2009 17:47
Tim Wescott wrote: > On Mon, 23 Nov 2009 13:55:37 -0500, PeterD wrote: > >> On Mon, 23 Nov 2009 12:41:46 -0600, Tim Wescott <tim(a)seemywebsite.com> >> wrote: >> >>> A long-term back-burner project just got my attention when I found out >>> that Home Depot sells magnetic paint. >>> >>> >> Interesting! What is it called, and is there a web reference? > > Searching on "magnetic paint" on the Home Depot or Rust-Oleum sites > should get you there. It's either soft iron, or it needs a strong field to polarize it. How is it used? (IIRC, the permeability of ceramic magnets id low, so they support large gaps too.) Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ |