Newsgroups: rec.guns
From:
Ed.Harris@p0.f417.n109.z1.fidonet.org (Ed Harris)
Subject: Re: Quality Parts AR-15
Keywords: casting
Date: Mon, 18 Jun 90 19:20:38 GMT
In article <1990May29.172051.233@ism.isc.com>
rats@ihuxz.att.com (D. Woo) writes:
>According to a mechanical engineer whom examined the receivers, he said
>that the EA receivers were sandcasted. I am not certain if anyone would
>want to trust their life on an Aluminum sandcasted receivers...
I think you might be confusing sand casting with investment casting.
The sand casting process not been used in the firearms industry except
for making non-stressed parts like barrel bands and buttplates on
blackpowder guns. The investment casting process used for precision
high-strength parts is done by making an injection moulded wax form of
the part to be cast. These parts are then gated together to form a
"tree" which may be grouped to contain maybe 30-40 rifle receivers or
60-80 rifle bolts, or several hundred small parts. The "tree" is then
dipped in a slurry of silica and water, alternating with layers of
granular silica and more of the silica "mud" until the "vestment" is
strong enough to withstand normal handling in the foundry. After air
curing the forms are fired in a kiln, which burns out the wax, hence
the name "lost wax" often used to describve the process. In casting the
parts the forms are heated in a has furnace and then filled with molten
steel, aluminum, titanium, or what have you. Small parts are usually
done in a centrifugal caster which spins the trees to ensure good
fillout, whereas large pieces are poured similarly to casting a BIG
bullet, except that aluminum and most stainless steels are cast in a
controlled atmosphere, usually argon, or nitrogen, to avoid oxidation
and to control shinkage porosity. When I was at Ruger the high-strength
parts, such as rifle receivers and bolts or revolver frames were all
X-ray quality and ultrasonically tested. They are in fact stronger than
forged parts made by traditional stock removal machining methods.
--
Ed Harris at The Black Cat's Shack (Fidonet 1:109/401)
Internet:
Ed.Harris@p0.f417.n109.z1.fidonet.org
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