wrote in message
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On Jan 10, 9:27 am, "Maxwell" #$$9#@%%%.^^^ wrote:

How can you mold or sculpt invest foam articles with a simple hobby
process,
and then get something as detailed as air cooled fins on a foam or wax
investment to withstand even the most careful ramming process for green
sand, oil sand or air set casting?
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Dear Maxwell,

While there are some pretty sturdy plastic-like waxes that can
withstand ramming-up in a core box, most of the methods using lost wax
begin by DIPPING the wax model in a slurry of high-temperature CLAY,
after all of the sprues, vents gates and supports have been attached
manually. After the clay dries it is BAKED, first at a fairly low
temperature ( ie 200F ), during which it is rotated several times to
get rid of the casting wax, and finally at a higher temperatures, such
as 500F for about two hours. The resulting product is then stiff
enough to withstand ramming.

There are variations to this theme. Some call for several dipping &
baking episodes using different recipes of clay. Dentists are the
best source of information on this procedure. The main down-side is
the HIGH COST of the refractory clay dips.

-Bob

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I'm well aware of the variations in the investment casting process, but you
hand already limited the discussion to a sand casting, and for economic
reasons I would have to agree. But there is no way to use a wax investment
in a sand casting. Subsequent melting of the wax will contaminate the sand
mold, regardless of green sand, oil sand or air set.

Considering the use of foam, first we have to mold or sculpt a foam cylinder
head in full detail for each head we have to produce. Then adequately pack
sand between the fins of a foam pattern, when the fins are as detailed as
this project would require. Doesn't sound possible, much less practical to
me.