"William Wixon" wrote in message
...

"Tim Wescott" wrote in message
...
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.

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?

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).

Thanks.

--
www.wescottdesign.com


in the 80's i did some casting using polyester resin. i was hired to make
reproductions of the ornaments on the cast iron buildings in soho, new
york city. i was kinda making it up as i went so i have no idea of the
longevity of the stuff i made. i mixed iron powder into the resin before
adding the hardener. the finished castings *actually DID look* like cast
iron, i was amazed. they even rusted. thing is the iron powder is heavy
and would settle to the bottom of the casting if you had a long curing
time. i mean, not all of it, but it generally tended to start settling to
the bottom, even in the mixing bucket, and even with heavy doses of
"thixotropic powder" etc. but it was cool. and they did look like cast
iron. i never thought to touch a magnet to them, i'd bet they were
magnetic. i got the iron powder from some sort of scientific materials
supply house, but i bet you could probably find a place that sells it much
cheaper. i'm sure there must be lots of information out there about
adding metal powders to resin castings. in my case, you're not supposed
to use polyester resin to do castings, it heats up and i think i've heard
it can even catch fire. i fudged it so i opened the molds when the resin
was cured enough to hold it's shape but before they got too hot. i worked
in fiberglass mat/fibers before closing the mold (polyester is brittle and
would snap like ice if you don't have some sort of reinforcing material in
it.)

If you buy casting resin, rather than laminating resin, you can cast thick
sections without it getting too hot. You also can reduce the accelerator
("catalyst") to keep it cooler but that's risky business, because, if you go
below the tolerable threshhold, the resin won't cure hard at all.

Casting resin is widely available from resin suppliers. It's usually much
clearer than laminating resin.

Iron powder has been used to fill epoxy for making short-run forming dies.
There have been entire books published about using filled epoxies
(aluminum-filled, mostly, but also stone aggregate and iron) for dies and
similar applications, but I haven't read one since around 1980, so I don't
know what's current.

--
Ed Huntress


when i was in college ('78~'82) there was a guy there who was making
larger than life size castings (of human figures) in polyester that had
(lots) of bronze powder mixed in. i think they called it "cultured
bronze". looked, more or less, like bronze. no idea there again of the
longevity.
i'd think there'd be no problem mixing in iron powder. (but then again i
don't really know you're trying to do, i'd imagine if you were trying to
cast lucite ALL the iron would settle to the bottom before it cured.)
good luck. let's see some pics. ("cores", huh?)

b.w.

"Tim Wescott" wrote in message
...
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.

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?

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).

Thanks.

--
www.wescottdesign.com


in the 80's i did some casting using polyester resin. i was hired to make
reproductions of the ornaments on the cast iron buildings in soho, new york
city. i was kinda making it up as i went so i have no idea of the longevity
of the stuff i made. i mixed iron powder into the resin before adding the
hardener. the finished castings *actually DID look* like cast iron, i was
amazed. they even rusted. thing is the iron powder is heavy and would
settle to the bottom of the casting if you had a long curing time. i mean,
not all of it, but it generally tended to start settling to the bottom, even
in the mixing bucket, and even with heavy doses of "thixotropic powder" etc.
but it was cool. and they did look like cast iron. i never thought to touch
a magnet to them, i'd bet they were magnetic. i got the iron powder from
some sort of scientific materials supply house, but i bet you could probably
find a place that sells it much cheaper. i'm sure there must be lots of
information out there about adding metal powders to resin castings. in my
case, you're not supposed to use polyester resin to do castings, it heats up
and i think i've heard it can even catch fire. i fudged it so i opened the
molds when the resin was cured enough to hold it's shape but before they got
too hot. i worked in fiberglass mat/fibers before closing the mold
(polyester is brittle and would snap like ice if you don't have some sort of
reinforcing material in it.)
when i was in college ('78~'82) there was a guy there who was making larger
than life size castings (of human figures) in polyester that had (lots) of
bronze powder mixed in. i think they called it "cultured bronze". looked,
more or less, like bronze. no idea there again of the longevity.
i'd think there'd be no problem mixing in iron powder. (but then again i
don't really know you're trying to do, i'd imagine if you were trying to
cast lucite ALL the iron would settle to the bottom before it cured.)
good luck. let's see some pics. ("cores", huh?)

b.w.