From: Doug Groh (dgroh11@comcast.net)
Date: Thu Aug 22 2002 - 14:48:13 EEST
A bit off topic - lost foam sand castingBen:
First off, I wouldn't say that this was "a bit off topic".
I started my apprenticeship at Chrysler Corporation in 1967 building Patterns for lost foam sand castings. The typical use was in gray iron casting of large stamping die patterns for automotive use. I know that we used a close cell polystyrene and when the foam was cut it was always a closed cell look. It was not the foam that was used in floral displays. They usually use a open cell foam that is coarse. We could sand the foam with fine grades of sandpaper and get a very nice finish. Contact a Pattern lumber supply house. That is where we get ours. I am not sure about bronze, but the gray iron used lots of risers. It was needed to get rid of the gases that were created from melting the foam as the iron hit it. Most foundries coated the patterns with a ceramic based slurry. I am not sure of the differences in temperatures, but the iron may melt hotter than bronze. (possible difference in ability to complete the cast). It could slow it up.
I visited a more modern production type lost foam house. They actually cast the patterns in steel molds using a steam and pre-expanded styrene beads. Steam is injected into a chamber behind the cavity which has micro sized holes in it. The steam expands the beads, and then the chamber is emptied of the steam and cold water is sprayed on the back of the cavities to stop the beads from expanding. The patterns were glued together at the foundry and placed on a tree similar to investment casting. The tree was dipped into a light slurry and dried and then they were put into a large cylinder where sand was cascaded over the patterns. The whole cylinder was put under a vacuum to compress the sand around the patterns and then it was moved under the casting unit to be poured. It was a very quick process. The house I went to was doing calipers and rotors for brake systems.
Doug Groh
President
3G Services Inc.
23984 Cedar Ridge Ct.
Brownstown, MI, 48174
734-262-4280
734-284-8078 Fax
----- Original Message -----
From: Ben May
To: 'rp-ml@rapid.lpt.fi'
Sent: Thursday, August 22, 2002 6:10 AM
Subject: A bit off topic - lost foam sand casting
Greetings RP'ers
Anyone out there know anything about lost foam sand casting. Most people I've spoken too seem to assume that it's an investment casting process wheras I'm sure I've heard of it being used for sand-casting. I need to know 2 things:-
What grade of expanded polystyrene is typically used for the sacrificial patterns?
Is there a foundry (preferably in the UK) that has experience of producing large bronze components using this process?
Thanks in advance for your help
Ben May
Senior Development Manager
Pankhurst Design and Developments Ltd
85-87 Richford St
London W6 7HJ
Tel: 020 8735 1111
Fax: 020 8735 1122
benmay@pdd.co.uk
http://www.pdd.co.uk
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