Clean, fresh investment, water and investment at room temperature, de-ionized
or distilled water or water that has been sitting overnight. Follow the
proportions suggested by the investment manufacturer.
Usually 40cc of water to 100 grams of investment is good. Use a dust filter
mask and gloves. Time yourself.
Remember: 'Well begun is half done'
1. If investing by eye rather than
using measurements then fill flask between 2/3 and 3/4 full of water,
and pour it into the mixing bowl.
2. Sift the investment gently but fairly
rapidly onto the water's surface and mix well with a spatula, smoothing
out any lumps. Note the time. The investment procedure should be finished
about nine to nine and a half minutes after beginning to mix.
3. As soon as the investment is smooth
swirl the bowl in your hands so that the investment continually moves
and any bubbles are removed. Don't whip in more bubbles. If desired use
a vibrator on the investment to encourage bubbles to leave.
4. At about the five minute mark vacuum
the investment for 1-2 minutes or until the investment boils for a moment
or two. Too much boiling may damage the investment.
5. While the investment in the bowl
is vacuuming pour debubblizer over the wax in the flask and then pour
it back into the bottle again, draining the flask well. While it is not
supposed to be necessary to use it with vacuum investing I have found
debubblizer is of some help in aiding trapped bubbles to slide off the
6. Remove the investment from the vacuum
bell and swirl it, then pour it into the tilted flask and rotate the flask
while pouring to encourage bubbles to leave. Swirl the flask gently. This
is when you realize why one puts tape around the top of the flask.
7. Assuming there are no air bubbles
present in the wax vacuum the flask well. When finished this should put
one at about the nine minute mark from starting. Remove the flask from
the vacuum bell and if the investment is not yet reasonably hard gently
swirl it until it thickens. This will discourage water tracking. When
the investment seems thick and sluggish let it be. Glossing off should
occur at about thirteen and a half minutes after beginning to invest.
If it does not occur by fifteen minutes after starting then either the
investment proportions were too watery or the investment has absorbed
water from the air, is no longer fresh and therefore the ratio of water
to investment was wrong. This can lead to water tracking and investment
8. After the investment is hardened
slightly (about 30 minutes from starting) remove the rubber sprue base
with a slight twisting motion and clean off any excess investment from
the outside of the flask. A small flask may be burned out immediately,
a medium sized one should rest for a little while and a large one may
dry overnight without damage. If one wishes to cast later one can store
the flask in a sealed plastic bag until required for casting (I would
suggest under a week).
A sample burnout schedule for a medium to
small flask (oF)
|| 3:00-Cast when ready.
Note that the larger a flask the longer and more gentle the burnout should
be. The flask should sit at the high temperature for some time. When the
investment looks white you are ready to cast. Dark investment will work
but the results may not be good. When melting metal: Oxygen is your
enemy Do all you can to limit oxygen access at high temperatures to your
metal. Preheat the crucible intensely and use a slightly gassy flame.
Roll your metal out as thin as it will get and roll it up into coils for
melting. Keep the melt covered by the gassy flame at all times and consider
adding a chunk of charcoal to the crucible to consume oxygen. Cast into
an appropriate flask temperature. The shorter the melting time the less
oxygen can be absorbed by the metal. Do not add to much oxygen to the
flame to shorten melting time.