Hi Annette and all, I had been following this and was only going to
add a little but since installing the new version of eudora, and it
really messed up my email programs, I have not been able to look up
the previous messages. I’m sure most of you have said most of the
things I am going to say here but I thought I should mention a few and
add my two cents!
I’ll start with the investing and work towards the casting.
When investing it is important to use the exact ratios as stated by
the investment manufacturer. Too little water and too much will cause
many problems you don’t want. The investment while being mixed goes
through a mechanical and chemical change. So it needs to be wet enough
for these changes to take place but not too wet. The reason there are
a couple of suggested ratios for investment is so you can find the
proper one for your conditions. That is the first consideration the
second is the finish on your cast pieces. the more water you use the
rougher your surfaces. the less water the smoother the surface of your
castings. The more water the less strength the investment will have
because the water is 'pushing the investment particles away from each
other. You lose the mechanical bond. Too little water and now you lose
the chemical and mechanical bond.
Unless you build a room that is sealed and the environmental
conditions are completely controlled you will have variations in your
investment mixes from day to day and season to season. Humidity and
temperature changes all the time so it will affect your mixing. There
is a lot of trial and error that goes on in this until you have cast
enough to instinctively know what is needed and when. In our shop we
had gas heat and swamp coolers for cooling. We went from the heaters
removing almost all moisture in the air to having very high humidity
during the summer! This has many effects not only on the investing but
other steps in the whole process as well.
The majority of moisture should be removed at the lower temps. Again
if the times are not long enough the moisture will not be eliminated.
The lower temps are for melting the wax out and eliminating moisture.
As the oven temp is raised the purpose is to bring the flask slowly up
to total burnout temp. and to burn the wax and eliminate moisture.
Your top temp. is to completely burnout the wax (organics).
If the lower temps are rushed the wax will not melt out completely
and the moisture will not be eliminated. When the moisture is heated
it will expand and evaporate. If the moisture is still in the flask it
will expand and break up the investment. If the wax has not been
completely melted out it will tend to penetrate into the investment
creating a barrier for the moisture and preventing the moisture from
leaving the flask. There will be a small amount of wax that penetrates
into the investment no matter what you do. Steam dewaxing reduces this
One practice we used was to invest using exactly the recommended
ratios for the investment. Then set them to harden for about 30
minutes. We used a steam dewaxer to eliminate the wax. After steam
dewaxing the flasks were set out to dry for about an hour. Then placed
in the oven. the first temp. on the program was 150 degrees F. and it
was held for 1-1/2 hours. then the temp was brought up to 300 degrees
F. and we set it to take 30 minutes to bring it up to this temp. Then
it was held for another 1-1/2 hours. And so on. The first couple of
temps., times and ramps are critical as are the last couple. The
temps. times and ramps in the middle are important but not as much.
They are mainly for burning the wax and bringing the flask up to temp.
Again you don’t want to rush these as this could also cause problems.
We used flasks ranging in size from 2" diameter up to 6" diameter.
All in the same ovens and all with the same burnout program. The only
time we had casting problems was if someone mixed the investment wrong
or sprued a piece too close to the edge of the flask or at the
beginning of a season. The ovens were electric and we were switching
to gas kilns for a better burnout. The gas kiln will allow a faster
burnout because it can remove the wax and moisture so much faster and
it gets more oxygen into the cavity so combustion of the wax takes
place more completely and faster. However a gas kiln is not for
You are right in that you need to get all the moisture out of the
flasks during burnout. But the moisture should be out by the time the
flasks are ready to cast. The rule of thumb is to hold the high temp.
- usually 1300 to 1350 degrees F - for one hour for every inch of
diameter on the flask. Then to get the entire flask to casting temp
you will need to do this again. The casting temp. is usually 1000 to
1150 degrees F. These numbers are not exact because there are too many
variables that can change them. We were casting sterling and 14 KY
gold. For stone in place casting the temps were much lower and the
times were much longer.
So for the rule a four inch diameter flask needs a ‘soak’ time of 4
hours. A 2 inch diameter flask needs a 2 hour soak. The length of the
flask isn’t important.
The reason for the soak time is the entire flask will not get to the
oven temp if this minimum time is not reached. So even though your
oven is at a temp it doesn’t mean your flask is. And even if the
outside of the flask is at temp the inside may not be if the oven has
not been held at the specified temp according to the rule.
From this you can see that there should not be any moisture left in
the flask if they are soaked for the proper times and temps.
So if you are using something and sticking it in the door to see if
there is moisture condensing on it the burnout has been way too fast
and you may have problems that can be easily eliminated by extending
the length of the burnout.
One thing I didn’t see anybody say in the postings and I may have
missed, was when taking the flask out of the oven be sure it is taken
out the way it is in there. For instance: if you have the flasks in
with the spur opening facing down pull the flask out with the spur
opening facing down then tip the flask very slightly and blow across
the surface where the spur opening is. Do not blow into the opening!
What you are doing is getting rid of any loose material on the
investment so it won’t fall into the opening when it is turned over.
Some people will brush the surface to get the loose material off but
it still will need to be blown off.
Also when turning the flask over watch the opening closely. If you
see anything fall into the opening turn it upside down again. If it
doesn’t come out your out of luck. There isn’t much you can do about
One thing I want to mention here is the fact that investment is very
hazardous to your health. Please make sure you have very good
ventilation and when mixing investment and handling the flasks
whenever possible wear a respirator even if your have plenty of
ventilation. When getting a respirator make sure you get one that fits
properly If you don’t know the proper procedure for test fitting I can
help with that or as much as I hate to say it call OSHA. Also take a
breathing test to see if you can work with a respirator. Do not use
one unless you take a breathing test. Heavy smokers won’t pass a
breathing test! So if you can’t pass the breathing test don’t invest.
Hire someone who can wear a respirator do the investing. Your life and
health are worth the cost of these safety items.
By the way the investment you see is not what is harmful! Anything
you can see if you breath it in you can breath it back out. The
harmful stuff is what you cannot see. These particles are not
respirable (you can’t breath them back out). When you get these in
your lungs they stay there forever. They are very sharp and stay that
way. When they land on your lung tissue they will cut it and as you
breath they cut again and again. What ends up happening is that your
lungs don’t heal where these particles keep continuously cut them. So
when you have enough build up of these particles in your lungs the
lungs build up some scar tissue and are at the same time being cut up
repeatedly. This reduces your ability to get oxygen into your blood.
Eventually you will die from this. So let me say this again. Your life
and health are worth the cost of these safety items.
There is more I could write about burnouts, investing and casting But
if unless this has raised any questions I’ll stop here.
The hardest part of casting is experience. You can’t buy it unless
you hire someone with it and you can’t get your own without doing the
work. Which means a lot of trial and error sometimes and a whole lot
Good luck with your casting and remember if at any time you need
anything let me know. Were not here to just sell equipment and
repairs. I’ll answer any questions anyone might have even if it means
sending you to buy from someone else. Honesty is better than making an