--- In STMFC@..., cj riley <cjriley42@...> wrote:

Correct me if I am wrong, since my days of college industrial work

are way in

the past, but I seem to remember bagged powdered additives in the

sand to help

the cavity to hold its shape.

CJ Riley

CJ - The sand was special; it was almost an art in itself selecting
the appropriate sand for casting work. Not just any sand will
work.

Some of the additives to the sand in earlier days included sawdust
and oatmeal(!) to give the molded sand cohesiveness during the short
time between ramming it in the pattern and pouring of the hot
metal. Most formulations were proprietary and may or may not have
been founded on good science - more on "art". Proper moisture
content of the sand was of primary importance.

Some of the more modern additives to the sand include furan
compounds (furanal or furfural aldehyde) that form a glue-like
cohesion between sand particles. These compounds burn completely
away when the hot metal is poured so that the sand can be reused. A
sand mold made with furan resin binders can be stored for a lot
longer time than a conventional mold because moisture content is not
an issue. However, since these came into wide use in the 1970's,
they are out of the germaine time period.

If the sand gets too dry, it will disintegrate back into a formless
pile of sand! The purpose of the additives is to give it the body
to hold the shape of the pattern until the metal is poured. Then,
ideally, the additives (and the moisture) all dry up or are
destroyed by the hot metal so the sand can be used over and over.

Tony T. is the resident metallurgist here - he can address this more
completely. Freight car content: Almost all cast iron parts on
steam era freight cars were sand cast! A.T. Kott