Steam Casting #5 - Burn Out by Don Norris
Please respect my copywrite protection.
Photos can be found on my web site at
http://www.frii.com/~dnorris. Just go to my site, then to “Class
Photos”, then to “Steam Casting #5 - Burn Out”.
Before we discuss burn out I need to backtrack a little and
cover a couple of things that I left out earlier. I apologize
for these omissions. Remember that I am writing this Online
Class for everyone, but especially for those who are beginning
and have no equipment or supplies. I am teaching it for everyone
to use the least amount of equipment and supplies. This is
especially true when it comes to building a kiln.
Deciding How Much Silver You Will Need: In most kinds of casting
it is important to know how much metal you need to cast with.
The easiest way I have found to do this is to weigh the wax
pattern and sprue, and multiply its weight by 11 (some say 13).
Therefore, if a wax weighs 1/2 a gram, then the silver would
weigh about 5.5 (5 1/2) grams. This creates some problems for
beginners. Most waxes weigh less than a gram, and if you are
multiplying by 11 you need to be fairly accurate in weighing.
So, you need to be able to weigh in tenths of a gram. Most
scales that you can buy at a discount, hardware, or department
store are not that accurate. In fact most gram scales are not
that accurate. Example: if you weigh a wax pattern on a cheap
scale that only weighs in grams, you have to guess if a wax
weighs one half, one, one and half, or two grams. The amount of
metal could be 5.5 grams (about 1/5 of an ounce), 11 grams (about
1/3 ounce), 17 grams (over 1/2 ounce), or 22 grams. It becomes
just a guess.
Of course if you have a good triple beam, electronic or balance
scale there is no problem.
If you do not have a good scale this is one solution.
One solution always suggested is to fill a glass or other
container with water to the brim. Put your wax and sprue wire in
the water. The water is supposed to leak over the edge of the
glass. Then take out the wax, and this leaves space in the
glass. The next step would be to fill with the metal until the
water is at the brim again. Sounds really easy! Problem is
though, when I first started to teach steam casting, I tried this
method. I did not get good results. We tried the method with
the same wax six times. Then we weighed the silver with my
triple beam gram scale and got 6 different amounts of silver.
Again, this method turned out to be not very accurate, but maybe
good enough for steam casting. I find that I can “guess” at how
much I need just as good as this method. Try and see if it works
for you.
Once you have the amount of metal needed for your wax pattern, I
always recommend that you then add a least another ten percent
(10%) for extra metal for the sprue button.
All of the above is why I forgot to mention it before. If you
will follow my instructions for this class, this all will be
taken care of as we go. You will learn that one of the most
important aspects of steam casting is the kind of torch that you
will use to melt the metal. I am teaching this Online Class for
those who do not have any torch, and I recommended that they
purchase the $10.00 torch from the hardware store. This torch
limits what you can cast. With this torch I recommend that you
only cast one or two rings at a time.
Therefore, if you make the sprue base the size and shape I
demonstrated in spruing, the question of how much metal will take
care of itself.
I recommend that you do not go out and buy a scale just yet.
Let this Steam Casting process make you enough money first.
More about spruing!
In my attempt to keep this class as simple and as cheap to do as
possible, I forgot to include some other about
spruing. The method that I discussed and pictured will work
fine.
I also use and recommend the following for spruing for steam
casting.
The question of the size of the sprue is very important! I have
tested 10, 12, 14, 16, and 20 gauge sprues to see which gave the
best results. The 10 and 12 gauge wires were just too large,
and the silver entered the wires and froze. The 14 and 16 gauge
worked well most of the time, but if the flask was accidentally
jarred or moved in anyway during the melting process, it resulted
in no cast. The 18 gauge seemed to work fine, but is frustrating
to work with. I think it worked the best out of all I tried.
The 18 gauge worked better with pewter too. The 20 gauge was
just too small to work with and did not let the metal cast fast
enough. I usually use 16 or 18 gauge wax wire. I take two
lengths about 1 inch long (Photo 1). I fold them in half, making
four wires (Photo 2) and twist them together at the fold (Photo
3). This makes what I call a “quad pod” (Photo 4). I cut these
four 18 gauge wires off to about 1/4 inch (Photo 5). Then I
attach them to the sprue base as described earlier. I cut off
the twisted end at about 1/8 inch (Photo 6). These four 18
gauge wires are about the size of an 8 gauge sprue wire when
combined. This end is attached to the wax pattern. Remember, I
am trying to teach this for people who have no experience,
equipment or supplies. This is why I think when casting for the
first time you should just use the 8 gauge sprue wire and split
it in half. It is easy to do and works for most small castings.
Another note about spruing. At one point I made a mold of the
“quad pod” above. Then I could just make as many as I wanted. I
have lost that mold, but may make another one. If I do I will
make them available on my web site.
Burn Out
If you have a kiln, great, because almost any kiln can work for
casting. Even a ceramic kiln used for pottery and ceramics will
work fine. If you do not, then we will make one. A lot of fun
and jokes have been leveled at the idea of making a kiln out of a
flower pot and a hot plate, but it does work. I have had many,
many students use it with great success. I do not believe that
the “burn out” process is very important when it comes to
casting.
Over twenty five years ago, I started casting and read all the
books and instructions. I followed all the instructions about
burning out at 300 degrees for the first hour, then turned up the
kiln for the next hour, and then some more for the next hour, and
so on and so on. Every book I read had a different time table.
Every article I read had a different opinion according to what
book the author had read. Every caster I asked had their own
method. In short I began using “my method” with great success.
There were two factors in developing my method. One: I taught
junior high, and those kids taught me that you could do almost
anything during the burn out process without affecting the
casting. Two: I began to cast small Mountain Alder “Pine” Cones.
I was selling a lot of these cones in solid sterling silver and
had to develop a method of casting them so that I got 100 percent
of them to cast. I began to cast ten flasks per day, 2 1/2
inches in diameter by 3 /12 inch high. I would sprue 20 to 30
“pine cones” in each flask. So I averaged about 200 “pine cones”
per day and I wanted to end up with all 200. I wanted to hit 100
percent! I found that the burn out in this case was the most
critical.
My method became simple. I found that burning out the “pine
cones” at the highest temperature possible was the most important
aspect of reaching the 100 percent mark. I was burning out at
well over the 1300 degrees that almost every one recommends.
Then it happened, the pyrometer on my kiln burned out because of
these high temperatures. It was followed a few days later by the
control switch. Because it was a $450.00 kiln, and I wanted to
keep using it, I simply wired the kiln directly to the power
cord. So, the plug became my on and off switch. My method
became quite simple: 1. I loaded the kiln with 10 flasks and
plugged it in. 2. Two hours later when the kiln was glowing a
nice bright red, I cast. I am still using that kiln and I am
still using that method. I know this will upset a lot of
casters, but I have found that when I cast the flask as hot as
possible, glowing a nice dull red, I always get good castings
with no porosity, no excessive fire scale, and nothing but good
castings. This is not a vacuum or centrifugal casting class, so
I will not cover the reasons why, but I have found that the most
of what I have read about burn out just does not agree with my
experiences over the past 25 years. If you are a caster, and
your method is working for you, keep using it! I personally do
not believe one method is better than the other, because I found
that it just does not matter. I will cover this more in future
online classes about Vacuum and Centrifugal casting.
For you beginners starting to Steam Cast, I just want you to
ignore anything that you have read about expensive kilns, steam
wax removal systems, digital controls, lengthy burn out
procedures, and exact casting temperatures. This simple method
will disprove all of them. However, for more proof that all of
the above does not really matter, let me just say that I have had
junior high students do everything wrong according to the experts
and still get good casts. One student put his flask into a kiln
at over 1300 degrees, probably closer to 1500 degrees, because we
were casting insects and “pine cones.” Even though the flask was
poured and set for less than 10 minutes before he put it into
the red hot kiln, we cast it at the end of class, and he got a
good casting. It had a lot of small “flashing” from the
investment cracking due to the wet investment and the high heat,
but he cleaned up the ring, polished it, and is probably still
wearing it. One day I had a student cast a cold flask, that had
been burnt out the day before, and got a good cast. My point is
that the kiln we make will work just fine. It looks a little
laughable, but it works!
Make a Kiln. Step One: Cover the pot. Buy a six inch clay flower
pot, wrap the out side with aluminum foil (Photo 7), put it over
a heat source and you have a kiln! Wrap the pot with several
layers of the foil. Some pots will crack because of the heat,
and the foil will keep the pot held together. Do not put the
foil inside the pot. The “kiln” gets so hot that it will just
melt the aluminum.
Step Two: Make a handle for the pot. Cut a thick wire coat
hanger apart and bend it into a handle. Bend it in half (Photo
8), and then in half again (Photo 9). About three inches from
the loose ends, bend them at a 90 degree angle (Photo 10), then
bend them back again to the center (Photo 11). Bend them down
straight again (Photo 12). Put the loose ends through the pot,
put the handle tight, and bend the loose end at 90 degrees again
inside the pot (Photo 13). Spread the handle a little and you are
all set (Photo 14).
Step Three: Make the heat source. The flower pot is the easy
part, the heat source can be the difficult part. For years, I
and everyone that I knew of was taught to use an old electric hot
plate, or an old popcorn popper that was taken apart to expose
the coils. The problem is that the word “old” is the important
part (Photo 15). They have the old spiral coiled elements that
heat up to a glowing red (Photo 16). The new hot plates have
those modern elements like you find on top of the stove (Photo
17). These flat coils heat up, but rarely glow as red as the old
elements. They probably replaced the old coiled elements due to
safety factors. The new hot plates just do not do the job. I
believe it is because they do not radiate enough heat. They are
designed to heat by contact with a pan, to conduct heat, not to
radiate heat. The old coils were designed to radiate the heat to
the pan. The pans never touched the coils. They were held above
the coils by the ceramic part of the hot plate. This radiating
heat is what we need to burn out the wax from our flasks. The
problem is that the old hot plates are hard to find. I used to
go to flea markets and garage sales and buy them for $1.00 or
$2.00. Now it is hard to find them at any price. If you can
find one, use it. Many years ago, over 20, I put a pyrometer
down into the hole of the flower pot, just before I cast, after
about two hours of burn out. It read a little over 1300 degrees.
I was surprised! I did not believe that it could reach that
high of a temperature! It is high enough to burn out and cast
with for sure.
In place of the hot plate, I have found that a small propane
camp stove purchased at a Target or Walmart works great as
well(Photo 18). It does use a lot of propane, but is still a lot
cheaper than a kiln. I really like it because I always wanted to
teach steam casting at a “tail gater’s” rock show, where everyone
camps and there is no electricity a hot plate (Photo 19) can not
be used. Steam casting is perfect for these shows. These camp
stoves come with bases so use them. I also use the larger, fatter
propane bottles to make them more stable. You could make even
sturdier stands, but I have never had a problem with knocking
over a kiln. When you do this, please use all safety practices
necessary not to burn up your house and yourself. I will cover
all of these in the “Casting” part of this Online class, or you
can check them out in the Online Bean Casting Class.
You will need to put a wire mesh screen over the camp stove to
hold the flask and the flower pot (Photo 20). You can buy a
small square of steel screen at the hardware store. Even a small
mesh steel hardware cloth will do. I stress steel, because the
heat generated will melt aluminum.
You now have a kiln that will burn out one or two flasks at a
time. It seems to get just as hot as the electric hot plate, and
it is a radiating heat. I have used this kiln for about 20 casts
with great results. No problems with burn out have occurred.
Note: I had one student that used his kitchen stove with the
vent fan turned on. I cannot recommend it, but I thought it was
funny. He said it worked fine for one or two rings in a flask
and for two flask at a time! I also always wanted to try
charcoal in a grill to burn out the flasks. Some day I will try
it.
If you do, let me know how it worked.
Step Four: Begin burn out. Take the kiln outside and somewhere
safe, so that no children, pets or really stupid adults can play
with it or knock it over. I believe it should be on a table. A
card table covered with scrap plywood or particle board is great
(Photo 21). If it is snowing or raining you can not cast
outside. If it is really cold out, you will not get a good burn
out. If it is cold out place the kiln outside for the about 1/2
hour. It will burn the wax out and smoke a lot during the first
1/2 hour and then stop smoking. You could then bring it inside
your shop or garage. I do not recommend your kitchen or living
room, but I have had many students that covered their kitchen
table with plywood, did the initial burn out on the porch, and
then brought in the kiln.
Place the flask, crucible side down, on top the screen and put
the pot over it. Light the camp stove or plug in the hot plate.
The kiln will heat up and begin to burn out the wax in about 2
minutes. It will begin to smoke, then the wax can actually drip
down and catch fire and burn. This worried me at first. I did
not know what that could do if it hit the coils in the hot plate
or the flames on the camp stove. I even tried to catch this wax
in small jar lids. However, I found that it just did not make
any difference. All the flames are contained within the pot and
it has never hurt the coils or the camp stove. I just put the
flask on and let em’ burn, baby. (Photo 22)
After about a half hour, it will stop smoking and the bulk of
the wax will be eliminated. However, the flask is not hot enough
to cast. I recommend that you do not cast for a good hour or so.
This extra time allows even the wax that might be trapped in the
flask to burn away. I compare this process with a self cleaning
oven. It just gets so hot that every thing burns up, turns to
ash, then to gasses, and finally disappears. The entire flask,
including the center, has to reach a high temperature to
accomplish this burn out.
It is also necessary for the flask to be as hot as possible for
steam casting so that the surfaces of the investment do not cool
and freeze the metal before it enters the mold. The hotter the
flask is, the easier and faster it will be to melt the metal in
the “crucible” formed by the sprue button.
Caution: the kiln and the wire handle are hot enough to burn
you!
After two hours of burn out, it is ready to cast, which will be
covered
in Steam Casting #6 - Casting
Don Norris
@Donald_Norris
PO Box 2433 Estes Park, CO 80517