From: firstname.lastname@example.org (ERich10983)
Subject: Re: HELP....HSS tool bits (Sapphire)
Date: 2 Aug 1998 11:26:10 GMT
>>For an interesting experiment, because I would like to know, I'll GIVE
>>you a piece of sapphire rod to try. e-mail me for an address and send me
>>a SASE. We grow the stuff, and have lots of it in the scrap buckets.
>That's interesting - how do you grow sapphires? And what do you do with
>them when you have them? Do you have a page with details?
I've covered this before, but for new people...
Sapphire (or ruby) is basically aluminum oxide. When is melted at about
4000F/2200C, it becomes a liquid. When cooled, it is single crystal sapphire.
That isn't much use to anyone, so our process is a little different. We melt
the sapphire in a moly crucible using induction heating. The crucible contains
a cappilary die with the top the shape of the crystal we want. It might be a
.002" fiber, a rod, a 1" diameter tube, or a sheet as wide as 12". The
thickness is whatever the width of the die is.
We then dip a seed crystal of the proper crystalline orientation into the melt
and slowly withdraw it, allowing the crystal to grow onto the seed. As the
crystal is pulled, it will assume the shape of the top of the die. At these
temperatures, we have to use a non-oxidizing atmosphere of argon. Insulation
and temperature control is quite important. We try for +/- 1 degree. The pull
rate for a 4 inch wide sheet would be about 4 inches an hour, and that rate has
to be very smooth. Servo motors with gear boxes and a long lead screw is
necessary. We usually grow these up to 8 feet long and then diamond cut or
scribe to near finished length.
Most common uses are for supermarket scanner windows. Sapphire is second only
to diamond in hardness, so you can drag 50 pound sacks of kitty litter across
it for years and never scratch it. Other uses are in semiconductor processing
because of sapphires resistance to chemical attack by just about anything. It
also is used because of zero particle generation for the new, larger wafers
that use smaller parts.
Thats a quick explanation. We have some good info on our web page
I have given away samples to RCM readers for the cost of a stamped self
addressed envelope (SASE). Just send me a possible use you might have, and
I'll send along a couple of sheets or other parts. 3 or 4 ounces of postage on
a padded envelope is the right amount. I do this with the full support and
knowledge of the company. They aren't set up to handle small sample requests,
usually requiring drawings, specs, etc. I can just walk over to the scrap
buckets and take what I want, no loss to anyone. And no complaints from the
customer about sample defects 8>)
I'll keep this up unless I get overwhelmed. Wasn't a problem last time.
33 Powers St
Mont Vernon, NH