Dear Pearse, The main two investments I have used are Ultravest and
Satincast 20. I have stayed primarily with Ultravest since 1971.
Ultravest is the best all round investment for both spin casting and
vacuum casting available. Satincast changed their formula a few years
ago (new and improved) and it doesn't work as well for spin casting.
I stopped using it. There are several factors in getting good and
consistent results from your castings. I haven't tried any of the
newer investments. I'm happy with what I work with now. If it ain't
broke don't fix it.
Try a little thicker investment. There are two or three ratios
listed for most investments. Ultravest has the powder / water ratios
in their instructions and sheet. A little thicker mix
should be slightly stronger. Don't guess at you mix ratios. Try to go
by the instructions. Keep the investment as dry as possible. Even a
little moisture can screw up your powder / water ratios. The working
time for this should be about nine or ten minutes.
Are your sprus attached right? How will the material flow? Look
at them and pretend YOU are the material going into the cavity. What
will get in your way? Are there sharp corners that could catch any
part of you? You may try more and smaller sprus.
Sometimes a thin section of design can turn out to be a razor
blade of investment. Molten metal can tear these parts off as the
metal flows by. They then solidify in your part. Can your designs be
the problem? Are the problems in the same place all the time?
Are you spin casting or vacuum casting? With the higher
temperatures of vacuum casting your investment may not have quite the
working success of lower temperatures. Spin casting at a lower
temperature may work.
Many casters (me included) tap their flask before placing them
into the casting machine. You might try this. Loose particles of
investment can be removed many times this way. Now on the other hand
if you cast stones in place you should never tap the flask.
Make sure your investment is mixed up prior to adding water. I
commented on this a while back. I keep my investment in an air tight
cement mixer. Every week I mix it up to make sure the ingredients are
consistent. All the ingredients of investment have different weights.
As they sit, they settle and separate. Just think of a bag of cement
you put in the garage. When new it looks all the same. After a year
you open the bag and some has settled to the bottom the bag without
even touching it. From the factory on, a truck transports the
investment to it's destination. This is just like a shaker. The
ingredients start to separate right from the factory. Store you
investment in the barrels and every week flip them upside down so
gravity will start to work the other way.
Good luck & best regards,
TR the Teacher
T.R. Hawkinson, Ltd.