I have finished the third installment of the Steam Casting
"Class", I have not had time to edit it and the photos should be
on my web site very soon. I am so late in getting it done I have
decided to just get it sent unedited. Hope your more interested
in content than good Enlish. The next installment will not be
this long!
If you have any questions, or a better way to do any thing,
please let us all know.
Steam Casting 3 - Spruing
What is spruing? It is the process of putting your wax pattern
on to a wax wire, and attaching the wax wire to a sprue base of
some kind. The purpose of this process is to hold the wax pattern
up in the air so that when a flask is placed over it and
investment is poured into the flask, the wax pattern is covered
by the investment.
Wait, wait, wait a minute! What is a wax pattern? What is a
sprue base? What is a flask? What is investment? What the heck am
I talking about as if everyone knows what these terms and
processes are. Sorry! lets go over the terms necessary for all to
understand this “Class” on steam casting.
Lost Wax Casting: The process of using a wax pattern of
something that you want to cast in metal, by making a "ceramic"
mold of it, putting this mold in an oven, and burning out the wax
pattern. Therefore, it is lost! This leaves a cavity in the mold
so that metal can be cast into it.
Wax Pattern: The object to be cast. A copy of anything made of
wax or any other material that can burn, that is used to cast.
Sprue base: the bottom of a mold that holds the waxes so that
they stand up in the flask (can) as the investment (mold material
is poured over them). In commercial casting this is usually a
rubber sprue base. (Photo 1)
Sprue button: The center part of a sprue base that forms a
"funnel" for the metal to enter the mold. Wax patterns are
attached to this button. (Photo 2)
Sprue wires: (Photo 3) When preparing the mold these are wax
wires that hold the wax patterns up from the sprue bases. After
burn out, they make the path in the mold for the metal to fill
the cavity left by the wax pattern.
Flask: a can or steel tube that is placed over the patterns and
investment is poured into it to form the mold. (Photo 4)
Investment: A powered material that is mixed with water and
then poured into the flask over the wax patterns to form a mold
that will withstand the heat and casting procedures. I use Satin
Cast 20, because it easy to find.
Crucible: anything that is used to hold metal while it is being
melted.
Getting the mold ready and spruing is very important in any kind
of casting, but is the most important step in steam casting. If it
is not done correctly, then you probably will not have much
success. So, please follow these steps completely and very
closely. Nothing is more frustrating than to take time to mold,
burn out, and cast something only to get an unrecognizable piece
of junk. If you have spent hours carving the item, it is even
more devastating.
First, we need a wax pattern. It can be purchased from a wax
pattern company through mail order. (Photo 5) If you search for
wax patterns several dealers will come up. Or, you can make
something. A quick easy method to make a freeform pendant is to
carefully melt some wax, any kind will do, even some crayons or
old candle will do. Melt it in an old spoon and pour it in to
some cold water, it will make some interesting patterns. (Photo 6
and 7) Vary the temperature of the water for different results,
swirl the water before pouring in the wax for even different
patterns. After choosing a portion or carving off the unwanted
parts, melt a hole with a heated wire (a paper clip will do)
where you can insert a jump ring after casting for putting it on
a chain. (Photo 8)
Spruing the wax pattern: You may want to make a “nudgit”. This is
a soldering tool/ wax tool that you might want to try. It is
patent pending, or at least I am thinking about it, but go ahead
a make as many as you like. Take a small wooden dowel about 1/4
inch in diameter, put a rubber thing on one end, put a “T” pin
(call a quilting pin now and found in the craft section of
Walmart) through this rubber end, cut off the sharp point and
you have a great wax tool. If you like, you can sharpen it and use
it as an pencil! (Photo 9)
Sprue the wax pattern by taking a half inch piece of the 8 gauge
round wax wire and melting it on to the wax pattern. Attach it to
the wax pattern in a place that is easy to clean. Some thought
has to be given to positioning the wax pattern so that it will
cast. To do this just think of the metal flowing though the wax
wire and into the wax pattern in only one direction away from the
sprue button. (Photo10) Take your nudgit, heat it over the
candle and carefully melt one end of the round sprue wire and
attach it to the wax pattern. (Photo11) To make sure that it does
not come off when pouring the investment over it, I have a
special way to attach it. After the wax pattern has been
initially attached, heat your nudgit, and melt a little of the
sprue wire and a little of the wax pattern on just one side of
the sprue wire, not all the way around it, only on one side. If
you go all the way around, the pattern will likely just drop off.
Let it cool completely, then do the other side of the sprue
wire. Then let this cool completely. Note: you can purchase a
sticky wax callrd treeing wax that can also be used for this.
Making the sprue button.
There are two things that will make the difference between a
good cast and no cast at all. The size of the sprue button and the
torch that you use to melt the metal. The sprue button is
probably the most important, because it, also, becomes the
crucible. If it is not large enough, it will not hold all the
metal to be melted. If it is too deep, you can not keep all the
metal melted at the bottom of the sprue button, even though a
larger torch can solve some of this problem. (Photo12)
Step One: Make a sprue base. Cut off a large piece of aluminum
foil and fold it several times to get it down to a 4" to 4"
square and at least 4 thickness’. This is your sprue base.
Step Two: Make a sprue button. Take a little clay and make it in
to a ball. Stick it on to the middle to the sprue base and begin
to smash and smooth it out, so that it makes a mound. . (Photo13)
Step Three: Cover the top of this clay mound with some wax
melted from the sprue with a candle. (Photo14) We do this because
it will make it easier to attach the sprue wires to the sprue
button. Here are the problems that makes this step so important.
Remember some kind of force is needed to push the metal into the
cavity of the mold. Problem #1: In this case it is steam and we
have to control it. Problem #2: If the molten metal begins to
flow down the sprue wires, before we apply the steam, the surface
area of the sprue wires will cool it, and the metal will freeze
in place in the sprue wire. Once this has happened it is, I think,
impossible to get it melted again (unless it is pewter), because
the entire flask would have to be heated to the melting point of
the metal being used.
Problem number 1: Controling the steam and it’s pressure. SAFETY
HAZARD: If moisture is allowed to drip into molten metal, it
will create an explosion and molten metal will be sprayed in
every direction. The reason for this is quite simple: the water
hits the molten metal and flows into and under the surface of the
metal. It instantly turns to steam and expands. As it does this,
it blows the blow the molten metal in all direction with terrific
force. Molten metal can be poured in to a lot of water with out
this happening. But if you pour molten metal in to a small amount
of water or on a moist surface, it will explode. I might as well
tell you about this experience that I had.
Warning this is a true story, but is not completely necessary to
read for steam casting. As a college student, I had a job at night
to pour lead pigs in a water cooled mold. These pigs were used
for a Linotype Machine. The mold was safe because the water ran
through it kind of like coolant in an engine. I was told never to
have anything to drink in this casting room. So I did not. It was
a room about the size of a small bedroom. (10x10). One night I
wanted to test this theory of explosion! So I took a coke with me
to work with some ice in it. I had a plan! I poured four pigs of
lead, about 100 pounds. I ran to the door, grabbed one small cube
of ice, threw it on to the lead, slammed the door and waited to
hear an “explosion”! I heard a little hissing, but no explosion.
I was disappointed, until I opened the door. Almost no lead
remained in any of the four pigs. The mold was almost empty. BUT,
every square inch of that room was covered with shinny splatters
of lead. It was beautiful. Then it occurred to me that I was going
to get fired, and it would probably even effect my grades if they
found out. It was two in the morning and I started scraping! At
six in the morning, I got it all cleaned up. If I had stayed in
that room, I think it would have killed me. Instead, I got a 25c
raise for being the first student to clean that room in 20 years!
It’s the story of my life. I am the luckiest, dumbest guy you’ll
ever meet!
Moral of the story. You can not let water drip into the metal
that you melt in the top of you flask, that is now called the
crucible. If it does, it is going to splatter everywhere, and
you will probably not get a raise from your significant other for
burning holes in you, your clothes and any other keepsakes in the
room. I will talk about this more when talking about the caster.
By the way, I was casting pewter into a RTV rubber mold in my
garage when I spilled some on the cement floor. It started
running along the floor and started to bubble. Remembering my
lead pouring, I backed away quickly. Sure enough, the moisture in
the floor finally turned to steam and blew a golf ball size of
cement and some of the pewter into the air!
We need to talk about it here, because we need to control the
steam, and the size and shape of the sprue button (now the
crucible) will do it for us. If the moist part of the caster
touches the molten metal first, it will create steam mixed with
the metal, and it will try to explode in all directions. We want
the steam to force the metal in one direction: down and into the
mold. This is relatively easy to do.
Solving problem #1.
Make the spure button deep enough to hold all the metal, after
it has been melted, so that the metal is below the top of the
flask and the investment. This way when the caster is pressed on
to the flask, only the top of the investment hits the moist
material in the caster. This does two things: 1, it seals the
chamber where the metal is melted so the steam can not escape and
2, it creates steam in the air pocket above the molten metal.
This steam does not have any where to go, but through the mold
and it pushes the molten metal down in to the mold as it does.
Thus, casting the piece. Therefore, we need the sprue button deep
enough to allow about a 1/4 of an inch above the metal after it
is melted. However , if it is too deep, it will be nearly
impossible to get all the metal melted because the investment
will constantly cool it.
So make the shape of the sprue button as this drawing .
(Photo15) Notice that there is also a 1/4 inch of investment all
the way around the edge of the flask. (Photo16) This is the
portion of the investment that touches the moist part of the
caster and creates the steam. (not the metal!)
Solving problem number 2. Because the metal is melted on top of
the flask, with the sprue button acting as the crucible, we have
to devise a way to keep the molten metal from entering the mold
too soon. Then, as we melt the metal, it does not prematurely
run down in to the sprue wire and “freeze”. This is due to the
surface temperature of the investment cooling the metal. When this
happens, the metal will block the sprues and prevent any further
casting. To prevent this, we will use something called “surface
tension”. As with most of what I do and teach with metal, I try
to use the laws of nature and physics to help me. Surface tension
is a great one to use. An example of surface tension is a drop of
water sitting on a pile of dirt as a perfect drop, without
getting absorbed in to the dirt. Then you touch it and it quickly
disappears and mixes with the dirt. Or, I think, it is like the
drop of oil on top of the water and will not mix. Then you add
soap, it acts as a surface tension reliever and the oil mixes
with the water?
Anyway, if the metal is melted on top of large holes made by the
sprue wires, it may flow into them too soon and freeze. If we make
small holes, by using small sprue wires, the metal will sit on
top of these holes and surface tension will keep the metal from
flowing down in to the sprues to early. Then, when we apply the
steam pressure it forces the metal down through the sprue wires
and into the mold. Problem solved., I hope.
Attaching the wax pattern to the sprue base. It is now time to
attach the wax pattern to a sprue button., but before that, we
need to prepare it to create the surface tension that we need.
Step #1 Split the 8 gauge wire into two forks on opposite ends
of the wax pattern. (Photo17) this is the quickest way to do
this that I have found. You could twist four 14 or 18 gauge wires
together to form a “quad pod” and then attach it to the end of
the sprue wire if you like. It takes more time and patience. I
have, also, been informed about using a small 1/4 inch piece of
sheet wax for this purpose. I will investigate this at a later
time and let you know. The is in the October, 1998
issue of Rock and Gem. It sounded like a good article. Step #2
Attach the split ends to the sprue base carefully. If you do not
do this carefully, you will end up with large holes leading to
the sprue wires. I found that by heating my nudgit and gently
melting the wax on the sprue button, (Photo18) then quickly
putting the sprue wires into the melted wax works the best (Photo
19) . You can not go back and remelt this area. It will only lead
to making a mess and enlarging the sprue wire openings. Once
this is successfully accomplished, you are finished spruing!
We are now ready to “invest”. Investing will be covered next
week. Put away your sprued wax pattern in a safe cool place until
then.
Don Norris
@Donald_Norris
PO Box 2433 Estes Park, CO 80517