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Steam Casting 4 - Investing
by Don Norris
Please respect my copywrite.
Investing is the process of making a “ceramic” mold of the
waxes. Once you have done this, the waxes can be burned out,
leaving a cavity in this ceramic mold so that the metal can be
forced in to it. Remember, I am trying to teach this class with
the idea of using the least amount of equipment and at the lowest
cost.
Investment is the dry white powdered mold material that when
mixed with water, dries to make a hard “ceramic” mold. This
special investment is necessary to withstand the high temperature
of burning out the wax. Plaster of Paris can not be used for
investment. It will crack and fail during burn out.
Follow the safety instructions that will come with the
investment.
Step One: Prepare Flask For Investing. Fold the aluminum foil up
around your flask (can) to seal the bottom. (Photo 1) I use a
rubber band to hold the foil in place. (Photo 2)
Step Two: Measure The Water. Fill a can the same size as the
flask being used with water. (Photo 3) I recommend that this
water should be distilled bottled water or tap water that has
been sitting for about a week. I just use an old milk jug for
storing this water with the cap off. Pour this water into a
small mixing bowl large enough to hold at least twice the volume
of the flask. (Photo 4)
Step Three: Measure the Investment. Most investment companies
recommend that you mix investment at the ratio of one part water
and two parts investment by weight. To measure the investment
without an accurate small scale use this method. Dry the can
used to measure the water thoroughly and fill with investment,
heaping the investment over the top of the can. (Photo 5) I use
Satin Cast 20, because it is available locally. I have used R&R
Investment in the past, and many other casters have recommended
using it. I believe that you will have less bubble problems with
R&R. R&R’s phone number is 419/865-9497 or fax at 419/865-9997.
Satin Cast can be purchased in small quantities (and large) from
the Rio Grande Company at 1-800-545-6566.
Step Four: Pour the Investment Into The Water. I know this seems
too simple to be a separate step, but it is how you pour it into
the water that is very important. Pour the investment down one
side of the bowl, tipping the bowl if necessary. (Photo 6) The
reason this is important is that, if you just dump the
investment into the bowl, and the water covers the investment, it
will trap air in the investment. This will not only cause
bubbles, but also clumps in the investment (just like gravy
clumps, yak!). By pouring it down the side of the bowl the water
can seep into the investment from the bottom and force the air
out through the dry powder. You will be able to watch the air
come up. (Photo 7)
Step Five: Repeat Step 3 and Step 4. This will give you the
approximate mixture for two parts investment to one part water.
Step Six: Mix The Investment. I had a friend that would follow
the above steps and never stir the investment at all. He would
just pour it into the flasks. He would pour the investment into
the water and just wait until it was completely absorbed. It
worked great for him! I just cannot seem to be that patient!
(It’s a character flaw, I know, but one of my smaller character
flaws!) I stir the investment with a plastic spoon to insure it
is mixed well and to get a feel for the consistency. I used to do
this with my hands, it really gave me feel for the consistency,
but dried my hands terribly. It did give me a sense of being
more of an “artist,” though! Stir slowly so that you do not add
bubbles to the investment. You just want to make sure it is
mixed thoroughly.
Step Seven: Add more investment if needed. The investment should
be the constancy of heavy cream or thick pancake batter. I find
that with the great investments that are mentioned above, this is
not as important as you may think. I have had students, both
teenagers and adults, mix their investments with the constancy
of 2% milk! They still got a good cast! I have had them also
mix and pour it like molasses and still get a good cast. I have
never had a flask blow out the bottom. I guess I may have been
lucky over all these 25 plus years, but I think it is just the
improvements in the investment. If you do mix it too thick, you
are taking the chance of trapping large bubbles in and on the wax
patterns that will cast as large “balls” on the finished casting.
I add this extra investment by sprinkling it over the top and
letting it soak in, then stir gently. (Photo 8)
Note: A word or two about bubbles and debubblerizers. There is a
debate about whether you should use debubblerizers or not. I do
not recommend any one method over the other. Use debubblerizers
if you wish, and just follow their directions. You can also make
your own debubblerizers by mixing “green soap” with isopropyl
alcohol (rubbing alcohol from the drug store, not denatured
alcohol from the hardware store). Green soap can be ordered from
most large drug store chains. I have mixed it at many different
ratios and did not notice any differences in how it worked. Most
casters and debubblerizers recommend that you spray or paint on
the debubblerizer and let it dry before pouring the investment.I
like to spray it on, because I have had students break waxes
while painting it on. Again I have had students that let it
dry, and I have students that forgot to spray it on in time to
let it dry. So, they sprayed it on just before they poured. Both
got good results.
Another method that you always hear about that I have never
personally found to work, is painting investment on to the waxes
before you pour. I have never been able to get the investment to
easily “paint” on to the surface of slippery, smooth wax! It
also took too much of my time, and you risk breaking the wax or
breaking the wax off the sprue.
The new investments actually have debubblerizers contained
within them. So, I just follow the steps below, without worrying
about bubbles.
Step Eight: Pour investment into the flask. I pour the investment
down one side of the flask, while gently tapping the side of the
flask with the plastic spoon, that I used to stir the investment.
I pour down the one side for two reasons. If you pour directly
onto the wax, you could break the wax pattern or break it off the
sprue wire. I also pour down the side to eliminate the
possibility of trapping air bubbles in and on the waxes. As you
pour the investment down one side, and tap gently with the spoon,
the investment flows to the bottom of the flask and flows up and
around the waxes. As it slowly fills the flask from the bottom
it pushes the air up and out, hopefully not trapping in air
bubbles. Tapping the flask with the spoon helps “vibrate” the
investment into all the detail of the wax pattern, and gently
shakes air bubbles off the patterns. I had one student in her
eighties who swore that after the investment was poured, she
would tap the flask fairly hard three times. She just poured in
the investment, then tapped it three times, and only three times.
She told me she never had any bubbles. I have tried this and I
never got any bubbles, either. I think what happens is that any
bubbles that may be attached to the waxes are shaken off during
this process. Even though they may only move off the waxes a
fraction of and inch and are “frozen” into the investment, they
do not cast. Even if they are still just barely touching the wax
they will make a bubble that is easily cleaned off. Sometimes,
they will just “twist” off the casting with pliers.
Important Note: I pour the investment just one quarter of an
inch (1/4) over the top of the waxes. (Photo 9) I feel that this
will allow the air to escape faster out of the mold cavity. I
have also filled the flask to the top to see if it made a
difference and still got good castings. Again, these new
investments are designed so that the air flows through them
easily.
Step Nine: Let The Flask Set Up. Do not move the flask at all
after you have poured the investment. Leave it sit for about a
half hour. Most investment will get hard (set up) with in seven
to ten minutes depending on the temperature of the water used for
mixing the investment. Then I take a t-pin and scratch my
initials and a note of what is in this flask into the top of the
investment. (Photo 10)
Note: The process of the investment getting hard or “setting up”
is a chemical reaction, not a drying action. This is important
to know, because if you see the that investment has “set up” it
still contains a lot of moisture. If not allowed to dry for a
time, this moisture could turn to steam during the burn out
process. The steam could expand and break and crack the
investment, ruining the mold. This could be really bad if you
spent hours carving the wax.
Step Ten: Let the flask dry. How long should the flask dry? I
don’t know! Ask 12 casters and you will get at least 10 answers,
and all of them are probably right. Again, these new investments
are so good you can do almost anything you want to do without too
much worry about how it is going to effect the casting. To prove
this I offer the following examples. Once, I had a junior high
student invest his wax pattern, let it set up and put it into a
hot kiln (at least 1300 degrees). When I realized what he had
done, I called the entire class over and explained again why
this was just going to ruin his cast and his wax that he spent a
week carving! Less than a hour later we cast it, and he got a
good cast. There was a lot of flashing because the investment
did crack, but it did not “explode” in the kiln as we have all
heard. He cut and filed the flashing off, polished the ring, and
is probably still wearing it. Every time he looks at that ring,
he probably thinks to himself, “That Mr. Norris sure didn’t know
what he was talking about!”
I have also read that you should not wait too long to burn out
the flask. There is something about it that makes it best to
have a little moisture in the investment when beginning the burn
out. It is supposed to turn to steam, push against the wax and
help the wax pull cleanly away from the walls of the mold. I
really do not know how it can do that. The investments are so
porous anymore that air can easily pass through it. Steam always
travels the path of least resistance through the investment. I
do not believe that it can push against the wax. In any case, I
always let my flasks dry over night, but not because of any
concern for the investment. I just invest in the afternoon and
cast the next morning. For students that come to class once a
week, they invest one week and we cast the next week. We have no
problems with burn out or casting! One school year ended, and I
had several flasks left that we invested and did not cast. So,
after three months of summer, I cast them to see what was in them
and got good castings. I decided to experiment with the time a
flask could sit before casting. I invested two flasks, dated
them, and cast one about a year later and got a good cast. I
forgot about the second flask for almost two and a half years (2
1/2 years). I burned it out as usual and cast it. I got good
casting just as if I had invested it the day before.
So, I believe the drying time should be somewhere, between at
least two hours (four would be better), and two years. I will
not argue with anyone that has their perfect drying time!
If it works for them, it is perfect!
Step 11: Take The Flask Off The Sprue Base. Remove the aluminum
foil sprue base so that the investment can dry easier. (Photo 11)
We are now ready for the Burn Out.
As always I will gladly answer all questions and comments. If
you do not understand any part of this Online class please ask.
If you missed the first three sections, please vist my web site
at: http://www.frii.com/~dnorris. If you only have email
capabilities, email me and I will email you the first three
installments.
Don Norris
@Donald_Norris
PO Box 2433 Estes Park, CO 80517