Steam Casting Class #2-Boring Stuff You Need To Know Before
Trying To Cast or Kind of Interesting Stuff You Might Want To Know
That Will Make Casting Easier by Don Norris
(Please respect the copyright) Before we start this whole
process, I want explain my basic understanding the mechanics of
casting metal and the physics (basic natural laws) that affect
the castings. If you like, you can call them “Don’s Principles of
Casting”. I believe will help you understand why we have to do
certain things to get consistent good castings.
Don’s First Principle of Casting-Something has to force the
metal into the mold. Well, I guess this has to be Principle #2.
Don’s First Principle of Casting should be “You Have To Have A
Mold”. In other words, you can not just pour metal into the air
and have it make something. Of course, if you were high enough,
you could pour metal in to the air and it would freeze, probably
in to small balls before it hit the ground. The air and air
pressure would actually be the mold. Or, if you could pour it in
to space, with out gravity, it might be real interesting and make
some real neat jewelry. If you pour molten metal in to water,
the water becomes the mold. You could just look for an
interesting place (safe places), pour the metal in it, or on it
and you might get an interesting casting. What ever you pour the
metal on, or in, becomes the mold. So, Don’s Principle of
Casting #1: You have to have a mold.
Don’s Principle of Casting #2: Something has to force the metal
in to the mold. In other words, metal will not jump out of
whatever you melt it in, and magically fill the mold. The only
forces that I can think of that are used for casting art metals
for jewelry and sculptures are, gravity, vacuum, centrifugal or
spinning, steam and pressure. I would like to discuss each
briefly.
Gravity is one of the oldest forces used for casting, for all
the “natural reasons”. We all know what gravity is, right. Well, I
do not. Yes, I understand that it is a law of nature, but I truly
do not think we know all there is to know about gravity and why
it acts as it does. For casting let me just say that the force of
gravity pulls metal down towards the mass of the earth just as it
pulls everything “down” towards the mass of the earth. This seems
over stated, but if you are gravity casting, it is very difficult
to make the metal run horizontally, or back up against the force
of gravity. Although when I teach sand casting, I routinely,
prove that you can make the metal flow up against the forces of
gravity, but that may be a whole other article. Types of gravity
casting are -sand, RTV, natural, water, cuttle bone, fire brick,
charcoal block and bean casting. (I plan to write an article on
each, if you would like. Please give me feed back on which one
you would like me to write first after this Steam Casting
Article. Visit my site at http://www.frii.com/~dnorris and put
your comments on my quest book.).
Vacuum is a little more difficult to understand. So, divide it
into two different types of vacuum casters. One that most small
volume jewelers and craftspeople use and one that high volume
casters use. I will be the first to admit I am not familiar with
the latter. I believe that these casters are very expensive ( in
the thousands and tens of thousand of dollars). But, I believe
that they may actually use the force of vacuum to cast the metal
and the small vacuum casters that are under $1,000.00 do not use
the force of vacuum to actually cast the metal. Now, before the
manufacturers of these machines or all you vacuum casters get
too excited, please read my explanation carefully. I believe that
in the large casting machines the mold is placed in a chamber and
an actual vacuum is created in this chamber. So a true vacuum is
created in the chamber and the mold. The molten metal is then
allowed to fill this vacuum. Thus vacuum casting. However, on the
small vacuum caster the mold sets on top of the caster. A vacuum
is not created in the mold, it is created in side the caster. I
always use the bell jar to create more vacuum. Then just as the
metal is poured in to the mold, a switch is moved so that the
vacuum creates a suction action that “sucks” the metal in to the
mold. If I am wrong about this, please let me know, but be very
specific about it. I believe that it is not the force vacuum that
actually casts the metal in to the mold, but the force of suction
that does the casting. BUT, the real force of the suction is air
pressure, not the vacuum. In other words, the small vacuum caster
builds up a vacuum (void of air and air pressure) with in the
caster and/or the bell jar. The mold is placed on top of a small
hole on top of the caster, and as the metal is poured a lever is
moved. The air pressure outside the mold tries to equalize, as it
always does (something to do with gravity again!). So the air
tries to rush into the vacuum. It has to go through the mold
(investment) as it does this. As the metal is poured into the
mold, it gets in the way of the air. The air pushes it into the
mold. Am I right or am I wrong? Any physicist or science teachers
out there? My science teacher always taught me that if it were
not for air pressure and the vacuum that we formed in our lungs,
that we could not “suck” our favorite drinks through a straw.
Special note: At high altitudes there is less air pressure, there
for less sucking action., thus making it more difficult to
“vacuum” cast at high altitudes. I live in Estes Park at about
8000 feet above sea level. A lot higher than Mile High Denver
even. This is why I say vacuum casting sucks. It sucks the metal
in to the mold. I, also, believe that gravity has a lot to do
with this kind of casting. Think about it, if it was truly the
metal trying to move in to a vacuum, we could set the caster on
it’s side and the metal would move toward the vacuum. I want to be
very careful here to make sure that everyone knows that I own two
of these small vacuum casters and would not want to be without
them. I use them for vacuuming my investment to remove bubbles.
Centrifugal or spinning creates a force that is somewhat hard to
understand, too. I know there is a natural law about this, but I
really do not understand it, either. We all know that when we
were kids we could grab our little brothers legs and spin real
quick, around and around, and he would spin out and fly around in
a circle. Then, we could let him go and crash him in to the wall.
Wasn’t it fun, I miss that! Well, that is how centrifugal and
spin casters work. They are two different kinds of casters. A
spin caster is a casting machine that is motor driven, has large
rubber molds and usually is used to cast pewter. The molds are
spun and the pewter is poured in to a center hole in the mold. As
it enters the mold, the centrifugal force pushes (or pulls, I not
really sure) the metal to the outer edge of the rubber molds and
in to the cavities. The molds are spun until the metal cools and
freezes. A centrifugal caster, or broken arm caster uses this
same force, but with a little angle. The mold is placed on an arm
that is hinged in the middle and is cocked at a 90 degree angle.
When the caster melts the metal, he releases this arm that has
been wound up and is driven by a spring, the arm begins to swing
in a circular motion. As it does, the half of the arm that has
the metal and the mold on it swings out straight. The centrifugal
action causes this. Within the first half turn, the arm is
straighten and this action throws the metal (by centrifugal
force) into the mold. The caster is left spinning for a few
minutes to allow the metal to cool and freeze solid. The actual
casting is done instantly. Centrifugal casting actually uses a
force that is stronger than gravity. It is important to really
understand this point. Remember swinging the bucket of water over
your head. The centrifugal force actually was greater than
gravity and kept the water in the bucket. Interestingly enough,
this is how the first centrifugal casting was done. In Egypt,
thousands of years ago, centrifugal casting was done just that
way. A rope was tied onto a mold, the metal was poured in to the
mold and a very dumb person swung the mold around and around his
head until the metal cooled and froze. Even more interesting is
that most platinum is cast just like that today. Oh, no, not by a
very dumb person, but by a vertical centrifugal casting machine.
Pressure casting is used in large companies for casting what I
call industrial metals. Metal like high tech alloys and metals
like magnesium. So, I will not discuss this method much. Mainly,
because I know very little about it. ( I do know that some of
these casting machines use a powdered metal and a screw to build
up the pressure as the powder is squeezed it is melted and then
released into the mold). The only reason I mention it here is
that now and again you will read or hear about a pressure caster
built with a bicycle air pump. It always sounds like a Rube
Goldberg type of machine, over engineered for what it does.
Basically, the pump is used to build up air pressure in a chamber,
the metal is melted or poured on top of the mold. The pressurized
“caster” is then placed tightly on top of the mold and the air
pressure is released. The air pressure tries to equalize again,
rushes out of the chamber, through the mold. The metal gets in
the way of this air pressure and is pushed into the mold. I am
sure it works. It is more pressure than gravity, any way. But, if
you are not a machinist the caster itself can be hard to make.
Steam pressure is fairly easy to explain and even easier to use.
It is definitely cheaper to use than any of the other methods.
Steam is created when water, or most liquids, are heated to a
temperature at which they turn in to a gas. When water turns in
to a gas, it expands. I, almost, believe that steam might be the
most powerful force in nature, after nuclear power. It is hard to
beat the force of the sun and a good old atom bomb. By the way,
the sun is just to far a way to use it’s nuclear force and even a
small nuclear bomb would probably wake the neighbors. So, I
ruled both out for casting. But STEAM, man, it is powerful. If
you doubt this, just remember, the force of some volcanoes. Those
explosions are not usually caused by some ignition of an
explosive, like dynamite or gas. I believe that most, like Mount
Saint Helena, is caused by the steam built up by the ground water
being heated by the extreme temperatures of the magma. Again, am
I right or am I wrong? Science teachers let me know? In any case,
we have all heard the terrific stories of pressure cookers
exploding, old steam engines blowing up, sinking steam ships
blowing up when the water hit the boilers. The best proof is that
a fire in a steam locomotive, created enough power, not only to
pull tons of cars full of tons of supplies and goods in to every
part of this country, it literally had the power to build this
country. So, even though, we all know what steam pressure is,
please let me explain how a steam caster uses this force to cast
metal. It is important to know that when steam is created it is a
force that is expanding in all directions, 360 degrees. It must
be controlled. Unlike all the other forces used to cast, steam
does not follow a definite direction. We must find a way to
control this force and direct it in to the mold, so that as the
metal gets in it’s way, it is forced in to the mold. For now,
just understand that we will heat water to the point that it
turns in to a gas, steam, in a small contained space. We only
give the steam one way out of this contained space and that is
through the mold. We melt the metal on top of this mold so that
the steam, in it’s attempt to escape, the pressures of the gas
expanding in this small space, pushes the metal down into the
mold.
This article is not about which method is best. There is no one
answer to that question. However, by the end of March I will have
a page on my site dedicated to helping beginners choose the
method that is best for them. It will compare costs, amount of
knowledge needed, the quantities of castings needed, the quality
needed, the kinds of metals being cast, and misc. “stuff” that
can make a difference in choosing a method. Under each method, I
will include comments about that method made by visitors to my
site, via the guest book. The kinds of metals that will be cast is
a major factor in choosing a method and more importantly how you
might use each method.
Don’s Principle of Casting #3-All metals do not cast the same.
It is important that you know the basics of metals. I taught
metals for most of my 13 years as a junior high school teacher.
Then the last three years, I taught art. I teach all my classes
as a metals teacher, not an art teacher. I believe that if you
understand metals, how they melt, bend, react to heat and oxygen
and all that boring stuff, the better silversmith and
silvercaster you will be. So next week, we will cover metals.
So, here is your assignment for this week. Get the supplies
below and lets make our equipment. Remember do not buy anything
that you may already have. If you have something similar, and
you have a question about if it will work, email me at
dnorris.mail.frii.com.
Caster
$ 1.00 1 empty tuna can (mix the tuna with mayo and eat it with
crackers while reading the rest of this steam casting info).
$ 1.00 1 six inch piece of broom handle or one inch dowel.
$ 1.00 1 roll of paper towels (you need 3 towels but you can
use the rest to clean up your tuna and crackers mess!)
$ 0.10 1 sheet metal screw #10 by 1 inch
$ 8.50 1 box of 10 guage wax sprue wire (can be ordered from
Rio Grande , 1-800-545-6566, part # 700-742
$ 2.00 1 package of childens clay or cheap sculpting wax or a
roll of aluminum foil.
$ 1.00 1 small tall narrow can of tomato paste
$ 2.00 1 small one package of Satin Cast 20 from Rio Grande #
702-099/1 or local supplier.
$ 2.00 1 wax pattern, either carve one yourself or purchase
one from a supplier.
Build the caster.
Cut a 6 inch piece off an old broom handle or any other old
round handle that you might have around the house, or buy a 1
inch dowel rod from the hardware store and cut off 6 inches of
that. This is the handle for you steam caster. Drill a small 1/8
inch hole in the center of the cut (flat) end. Be careful
drilling this hole. The use of a vise to hold the handle would be
good, but if you do not have a vise use a c-clamp to hold it down
to a table while you drill it. If you do not have a c-clamp, have
a real trusting friend (and I find that getting them drunk first
is helpful) to hold it for you. Really, it is not that
dangerous, but caution should be used so that the dowel does not
begin spinning during the drilling process. Drill or punch a hole
into the center of the empty tuna can bottom. Put the #10 by one
inch sheet metal screw through this hole so that it is sticking
out the bottom of the can. The head of the screw is in the can. I
will have photos on my web site at http://www.frii.com/~dnorris
with in the next week or so. Screw the can on to the end of the
dowel. The hole that you drilled into the handle will keep it
from splitting. Besure to tighten the screw. Tear up three paper
towels into approximately 2 inch pieces. Soak these in water and
pack them in to the can. Pack them in as tightly as possible. You
can even use another can that is slightly smaller than the tuna
can to help you pack it tightly. Just pack the paper towels in to
the tuna can, then turn it over and press it down on the smaller
can until no more water can be squeezed out. It is important that
no more water can drip out of the caster. The paper towels should
be damp now, not soaked and dripping. You now have a steam
caster! If you want to get more sophisicated than this, paint the
handle!
Until Next Week
Get the rest of the supplies, open the tomato paste can, use it
in your favorite receipe and send me the reciepe. I am offering a
$20.00 cash prize for the best receipe, with the fewest
ingredients. Just visit my web site, and post it on my web site
at http://www.frii.com/~dnorris.
Next week we will talk about spruing and investing .
Don Norris
@Donald_Norris
PO Box 2433 Estes Park, CO 80517