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Investment compound


#1

I have been casting up some small items with thin, delicate walls No
matter which way I sprue them I am having problems with small
particles of the investment breaking away during the pour I am using
a rather standard investment and am looking for suggestions on
another investment compound I might try Thanks in advance

Pearse


#2

Pearse, The ratio of water to investment is critical in most cases.
If you are not measuring the water and investment you could be
having weak investment. I found that even though I use an electric
mixer for about 1.5 minutes to mix my investment I still have small
clumps of partially mixed investment. I now pour the investment
into the flask through a kitchen strainer. Those small clumps of
investment are weak and can cause trouble. The force of the flow of
the metal can cause very thin pieces of investment to break away.
Try to sprue where the metal will not hit a thin section of
investment. I believe a burn out at too high of a temperature will
cause the investment to start to break down. the breakdown probably
occurs in the thinner sections of the investment first. My guess is
that the flasks adjacent to the heating coils see a hotter
temperature that the ones near the front door. I am sure everyone
has their favorite investment. I use Ransom and Randolph. There is
an investment that has some type of fibers in it. I think it is
used for bronze casting. I tried it once. It was almost impossible
to remove the investment from the casting and the surface seemed to
be very slightly grainy. It was very strong. I am sure the generous
casters on the list will have some great suggestions.

Good Luck
Lee.


#3

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.

  1. 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.

  2. 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.

  3. 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?

  4. 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.

  5. 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.

  6. 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,

Todd Hawkinson
TR the Teacher
T.R. Hawkinson, Ltd.