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Hi,

I'm a plastics scientist, involved in college level education, but with some
industrial experience, too.

The application cited is pretty tough. Most 2-part resins, like epoxy, and
especially urethanes, or 1-part resins, like polyester (the embedding
material available in hobby shops) will be too "sticky" to the glass.
Urethane or polyester are likely to be the most durable, with polyester
being the more light-stable and easiest to obtain. You would probably have
to add an antiblocking (hard, slippery) substance to get the material to
slide well. Talc is usual, but that will probably lead to scratching.
Possibly of use would be to add powdered polyethylene or teflon to the resin
to create a hazy but non-stick surface that, with moderate polishing with a
fine-grit sandpaper, would probably slide pretty well without scratching
uncoated safety glass (Acrylic is probably out as a transparent surface. It
scratches very easily.) Fluorinated epoxy or urethane resins would probably
work, but these are rare, specialty resins and usually expensive.

Another approach is to dipcoat a hot magnet in powdered polyethylene, nylon
or teflon of desired formulation (that is, color and ultraviolet light
stability). The melting point of nylon and teflon would possibly cause
problems with the magnet (I'm not sure what the curie temperature of Nb
magnets are), plus are generally higher melting than is easily handled in a
safe manner. PE melts at about 120 C, safely accessible on a kitchen stove.
Finding PE powder is not hard, but not necessarily simple. You should be
able to request some sawdust from a plastics cutting shop, which should work
just fine.

Any further questions, by all means contact me.

Regards,
Tom Twardowski, Ph.D.

**********************************
Thomas Twardowski
6725 Ridge Ave #206
Philadelphia, PA 19128
267/980-1915


-----Original Message-----
From: Informal Science Education Network
[mailto:[log in to unmask]]On Behalf Of Kathy Krafft
Sent: Thursday, May 26, 2005 7:28 PM
To: [log in to unmask]
Subject: Re: embedded magnet casting


ISEN-ASTC-L is a service of the Association of Science-Technology Centers
Incorporated, a worldwide network of science museums and related
institutions.
****************************************************************************
*

I've never tried embedding magnets-- but I used one product from Polytek
to make a rubbing plate that has lasted for over 6 years.  They make all
kinds of mold and casting products;  you can choose color and many other
properties.  I cast the 2-part product I used (poly 15-3) in a baking
sheet (greased with vaseline) and then used a Dremel tool to put the
pattern in it (Aztecs counted in base 20 using symbols like finger,
flag, and feather); you can machine this as well.

You can order smaller quantities to try out.  610-559-8620.  As I
recall, they were pretty helpful on the phone.

Kathy Krafft
Director of Exhibits
Sciencenter
Ithaca, NY

PS I got this information originally by calling another museum- one of
our volunteers had seen a rubbing plate in another museum.. so the cycle
repeats itself!
William Katzman wrote:

>I was wondering what medium most people out there used for embedding
>magnets in.  Specifically, I want to have neodymium (rare earth) magnets
>pull  items around on the opposite side of a pane of tempered glass &/or
>acrylic.  So I was going to imbed the magnets in a casting of a urethane,
>epoxy or some style plastic cast that would allow its use but wouldn't
>scratch up the glass.  (You might think of the typical flow tunnel
>magnets).  So...what casting mediums have people out there used with
>success for this endeavor.  Information on where to get your favorite
>mediums would be appreciated as well.
>
>-William
>
>William Katzman			[log in to unmask]
>Director of Exhibits			(828) 322-8169 x307
>Catawba Science Center		(828) 322-1585 (fax)
>"Try not to become a man of success, but rather to become a man of value"
>-A. Einstein
>
>
>
>
>

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