System
description
[email protected] | www.romanoff.com
2019-10-16
4
–22
4.16
Investment process
Investment process means, that powder is mixed for a certain time with water in a special
ratio into slurry and filled into a flask.
This stirring can be done in an open bowl with a spatula. However, air is also introduced =
bubble formation in the investment material = bubbles on the surface of the wax plastic
parts after embedding. The mixing of the investment material with the water should there-
fore be carried out under vacuum.
If investment material is stirred and then filled into the flask, air bubbles are also expected
on the parts, even if the filled flask is then placed in a vacuum: is likewise not very suc-
cessful. There is also a vibrator of little help.
Mixing under vacuum helps to avoid air bubbles.
Filling under vibration helps to avoid air bubbles.
When both operations happen in one machine: Optimal.
Please note:
As already explained: the mixing ratio investment material and water is very pre-
cisely defined. If the final, still liquid embedding compound is left under vacuum for
a long time, the bulk water is removed i.e. this mixing ratio will change! The reason
for this is that water under vacuum has a boiling point at room temperature. As-
cending bubbles in the liquid investment material are not blowing with air bubbles:
They are bubbles of water vapor! Therefore important: Release vacuum immedi-
ately after filling.
The liquid investment material requires a certain time to set (approx. 1 hour). The
beginning of the setting phase (the surface becomes dull) starts much earlier. Dur-
ing the complete setting phase, the flask should rest in a quiet and vibration-free
place. In the case of the "manual" method ( venting under filling
into the flask + evacuating the flask + vibration), the setting phase has long begun
until the flask finally has its rest.
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.
Figure 18: Indu Mix for MC16
