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1. Line the flask with asbestos or ceramic
liner. The liner is used to provide cushion to allow uniform
expansion of the investment and also to protect the flask
during devesting The liner should be placed in the flask
so that the inside of the flask is covered within 1/2 inch
of top and bottom.
2. Place a collar made of flexible rubber
or ordinary gummed tape around the top of the flask to extend
about 2-1/2 inch above flask. A 3 inch wide collar will
be adequate.
3. Place the flask on sprue base holding mounted
wax patterns.
4. Mix the investment (water/powder ratio::
38 parts water/100 parts powder.). Add powder slowly into
water and mix at low to medium speed. Mix until the slurry
is creamy thin. It may take about 1/2 hour for the slurry
to achieve a creamy consistency.
5. Vacuum the slurry in the bowl for 6~90
seconds at full vacuum. Then fill the flask up to the collar
and repeat vacuum step. Add sufficient investment to fill
the collar about 1-1/2 above the flask.
6. Let the invested flask stand, undisturbed,
in dry warm room for 4 to 6 hours. Now pour off excess water.
let flask stand overnight when the top of the flask would
have become hard and dry. Now remove the collar, carefully
trim excess investment flat and flush to the flask level.
7. Place the flask in cold furnace and raise
the temperature slowly at a rate of about 200 degrees F
( 90 to 100 degree C )per hour to 1600 degrees F ( 870 C
). Cast the flask either centrifugally or with vacuum assist
at the desired flask temperature.
Allow the flask to cool to room temperature,
until it can be safely handled with tongs or gloves. Do
not plunge the flask into water, while it is hot. because
this action may cause cracking of the castings.
Remove investment using standard devesting
procedures.
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