FLASK TEMPERATURE
Proper flask temperature is important to control porosity levels.
When flask temperature is too high, porosity levels due to
design/shrinkage problems are increased. When dealing with shrinkage
porosity lower flask temperature in 50 degree F stages. Proper flask
temperature should be the lowest possible, as long as complete solid
filling of cast parts takes place. The lower the temperature the
smoother the cast surface. The proper temperature will vary with
flask size, weight of parts, type and karat of metal and type of
casting machine (vacuum or centrifugal). When flasks are too hot,
hot tearing may take place. Gases may also be released when flasks
are too hot due to the calcium sulphate in the investment powder.
When sulphate reactions occur, a yellow color is noticeable on the
investment wall at the main tree feeder and (or) an odor of sulphur
(rotten eggs) may occur. When this reaction takes place, gas
porosity will take place. The metal quality and reusability of the
remaining metal will be greatly reduced due to heavy oxide buildup,
created by gas reaction.
NOTES: It is recommended to keep similar size and weight pieces
on the same tree, thus avoiding different solidification rates. When
different weight parts are on the same tree, place heaviest parts
nearest parts nearest the base, which allows the heavier parts to
fill last when metal is slightly cooler. It is very important to
keep metal as clean and fresh as possible to avoid oxide buildup
when using cooler flask temperatures. Heavily oxidized metal and
cool flask temperatures add up to oxide inclusions in the cast
parts. |
