Re: [rp-ml] Invision Water Absorbtion

Date: Tue Jan 04 2005 - 14:16:18 EET

One potential problem is that the water absorbed is released as steam when
using an investment casting process.
The part absorbs water as a part of the investment process, and then releases
it when burned out. If the water is released as steam because of a rapid
transition to high temperature, we have what can be called "popcorn". It is
highly doubtful that this popcorn is what the designer had in mind when creating
the design.
A more likely outcome is that the part being investment cast will not come
out as "popcorn", but rather a part with surface defects.

A solution that should work for investment casting is to dip the part into
mineral oil ( or equivalent) to seal the part from absorbing water during the
investment process. Then there will be no water to escape as steam during the
burnout phase. This process has been reported to produce far superior
investment castings from Invision masters.

Another version of the above process is to remove the support wax from the
Invision part with BioAct VSO warmed to about 55 degrees C. The residual VSO
file on the part provides a seal to minimize water absorbtion.

Either of the two processes should be done soon after the part is fabricated,
so that water is not absorbed within a high humidity environment.


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