Recently I have started working on casting investments and would
appreciate getting some feed back from you veterans for the following
questions. Thanks in advance.
Kayce
Why Silica and refined silica (Cristobalite) are used as the
major ingredients in any casting investment formulation?. Other than
the high temperature tolerance and porosity, I cannot think of any
other rationale for the inclusion of silica in the investments.
Could anybody help me in my quest in finding on
investments- websites, books, research papers, conferences, trade
shows, journals, societies, associations, internet newsgroups on
investments (other than this one).
Kayce Chidambaram Ph.D. Principal R&D Chemical Engineer The Bell Group
7500 Bluewater Road NW Albuquerque NM 87113 Tel: (505) 839-3523 Fax:
(505) 839-3525 Email: @Kayce_Chidambaram
try the artmetal site, also check out lindsaybks.com for antique
approaches. The hobby casters and art bronze founders often
experiment with alternative investments, for cost reasons. Glass
casters (art/crafts ones) know a lot about odd investments and
mixtures. It remember hearing of an investment substitute for metal
casting that was (roughly) 1/3 portland cement, 1/3 loam, 1/3 plaster
of paris. Never tried it. Dental industry folks too probably tried all
kinds of investmenst in the 1890’s through the 1920’s. Perhaps check
old patents?
When I was writing my book on safety for jewelers (carried by rio
grande-The Jewelry Workshop Safety Report) we contacted a number of
investment companies and I looked for substitutes for cristobolite
without success.
I would be very interested in what you find out.
best
Charles
Charles Lewton-Brain
Box 1624, Ste M, Calgary, Alberta, T2P 2L7, Canada
----When I was living in Northern Montana, I observed how the bronze
casting foundries worked their craft. The investment they used seamed
to be nothing more than -casting plaster and 200 mesh. silicon sand…
I believe it was 5 to 1… I tried this casting my gold, mixed opinion,
until I added powdered graphite…This worked extremely well,
especially when recasting different colors metals and stones in place.
Do enjoy----Next?
Gypsum plaster based investments for lost wax casting utilize the
plaster only as a binder . The silica acts as a refractory and the
fused silica form or cristobalite is used to control expansion effects
during the burn out and casting. Other materials are included to
modify the hydration "setting " time, reduce the possibility of
bubbles on the model surface etc. Porosity can be controlled by the
water added over that required for hydration. Various types of the
base Gypsum plasters are produced largely by the process in which the
original gypsum rock is dehydrated to produce the plaster. Books by
F.H. Norton on ceramics and refractories with different focus points
may give some assistance. Go to USG ( US Gypsum). They produce many
different grades of Gypsum plasters for various purposes and can
provide Doesn’t Rio Grande now own an investment
supplier?? There isn’t any magic in the principles. Literature
searches shouldn’t be tedious . A piece of cake for a Ph.D. Chemist -
engineer?
Jesse ChE ( very long ago and this is not my field)
‘Glass Casting and Moldmaking’ by Boyce Lundstrom has a lot of
formula’s and reasoning on refractories for investments. also other
refractories, zirconia and olivine sand. ‘From Clay to Bronze’ by Tuck
Langland gives tha sculptural peoples point of view As far as I can see
the quartz is the to expand when the plaster shrinks when it gets hot
, and is cheap bulk .I read somewhere (artmetal forum) that if you put
a sample of investment plaster with 10 times the normal amount of
water in a test tube and centrifuge it you will be able to clearly
see the various proportions of plaster and grades of sand, never tried
it though. In England we have two suppliers , Specialist Refractory
Supplies who are cheap but dont do more than two or three types of
investment, and Hoben International who do about eight different types
of investment all of which they say are excellent . I find this a bit
confusing and am doing some comparisons . The Santa Fe Symposium 1999
has a couple of articles on plasters and reckons that the formulations
are much the same apart from the last 1% which is the interesting bit
(debubbleiser, foam reducer , adjusting the setting time). There seem
to be so many variables , I would never want to make up my own
formulation but I would like to know what to ask for ie increased
porosity , better surface finish, increased strenght for really large
moulds .
Emerging as from a fog, a memory comes from long ago. Your reality
may differ. It goes something like this,—the expansion (or
contraction) of the investment as the crystobolite changes to quarts,
(the other crystaline form of silica)(at some high temperature like
1000 F) tends to counter the shrinkage that normally occurs when
casting metal. In fact, I believe that the compensation was almost
perfect for some dental alloys. Dentists like this because it is good
to have your teeth fit well.
Looking forward:
Alan Shinn
Experience the
beginnings of microscopy.
Make your own replica
of one of Antony van Leeuwenhoek’s microscopes.
visit http://www.sirius.com/~alshinn/
