INVESTMENT PROBLEMS
Proper mixing of the investment powder is critical in maintaining
a quaIity cast. The only procedure to follow is the manufacturers.
Many casters add extra water to make the mix easier to stir and
vacuum. This should never be done, because it weakens the investment
walls. Pieces of the investment wall will break off and end up
causing holes in the castings. These holes will usually be oblong or
rectangular, fairly deep and clean. A similar problem occurs when
flasks are placed in a hot oven. The moisture is evaporated too
quickly which breaks down the investment wall. Always place flask in
a cool oven, not greater than 120' F. Allow 2 hours after investment
solidifies in flask before starting burnout cycle. Bubbles on the
pattern surface is air trapped when vacuuming flask. Follow
recommended vacuum time, usually 11/2 minutes after vacuum builds
(approx. 30 seconds).
Monday Morning Breakdown Blues is a condition where the
investment wall breaks, cracks or weakens due to the investment
powder drying out between Friday and Sunday night when burnout
begins. This is due to the investment wall losing too much water
before burnout occurs. Two suggested solutions are:
- Soak flask in bucket of water after initial set-up time. A
20 second soak after allowing investment to set for 1-2 hours
usually leaves enough moisture to prevent breakdown.
- Mix investment on Sunday.
This condition is usually worse when humidity is low. |
