Instruction manual

OPERATING_MANUAL_MC20V.DOC 18.03.11 KS Seite 28
3.17. Mixing instructions for flasks in Investing process
Investment process means, that powder is mixed for a certain time with water in a
special ratio into a slurry and filled into a flask.
It is generally possible to do it by hand in an open rubber bowl. But during this
process you will mix in air which creates bubbles afterwards in the investment and on
top of the castings as well. Vacuum is required!
After mixing by hand you can put the investment slurry into a vacuum for a short
while to suck out air bubbles. After then fill slurry into a flask and place the filled flask
into vacuum again, if possible on a vibrator.
But this is a not really good way to make a proper investment:
To mix air into slurry and suck it out after by vacuum is making no sense:
prevent investment slurry against mixing in air = do whole mixing process
under vacuum.
Ratio of water/powder is given in instruction manual. Whenever slurry comes
under vacuum, the boiling point of water comes down from 100°C to room
temperature! Water steam comes out (you can see the bubbles in the slurry)
and the ratio of the water: powder mixture changes.
Mixing slurry, a working time is given for mixing and filling of flask. After then
slurry has to get a rest to become solid without moving or vibration in a quiet
place. If processing time takes too long, slurry already starts becoming solid
during this phase. This will cause problems.
The target is to mix slurry under vacuum, to fill slurry under vacuum into the flask
under vibration and to release vacuum as soon slurry is in the flask. This is only
possible in a system called investment mixing apparatus.
After filling the flask: give slurry 1 hour time to become totally solid. No moving of the
flask, place in on a quiet place without vibration.
Afterwards: remove rubber base.
Investment mixer for MC20V