Torque Power, Live Steam Models, Hyattstown, Box 144-D, R. F.
D., Ijamsville, Maryland 21 754
Hi There Young Engineers:
Most of you out there probably wear some type of ring. Maybe it
is a high school ring, military ring or a wedding band. Have you
ever wondered how it was made? Well, they were cast by a method
known as investment molding. Most jewelry, whether it be costume or
the finest gold and silver, is made by this method. Fine
silverware, metal bridges for false teeth and parts for small
machines are also made by this method.
Investment molding basically amounts to the making of a wax
pattern to which a wax riser is attached. The wax pattern is then
suspended by a string in an open cardboard container (Fig. 1).
Plaster is then mixed to a pouring consistency and poured in around
the wax pattern. The riser must be slightly above the level of the
plaster. The mold is then allowed to set up and the cardboard
container is peeled away. The mold is then allowed to air dry,
which may take a few days. The mold is then placed over the open
end of a tin can, the riser is facing down into the can so that the
wax can run out when melted. The whole setup is then placed in an
oven and the temperature is gradually raised to the point where the
wax will melt and run out into the can. The can of wax melted from
the mold is then removed and the mold set up right in the oven. Now
the temperature in the oven should be raised slowly to its maximum,
this will vaporize any remaining wax in the mold. It is important
that all wax in the mold be removed otherwise the mold may explode
when the metal is poured in.
In industrial practice the wax pattern is not hand carved.
Instead, a mold is made in which the wax patterns are cast. The
patterns are then attached to a wax tree. As many as a hundred
castings may be made in one mold. The metal is generally under
pressure when it is put in the mold. This is so the metal can fill
all the cavities in the mold as quickly as possible and it makes
for better castings. When making your own castings be sure to make
the risers as large as possible, the larger you make the riser the
more pressure there will be at the bottom of the mold.
You may wonder how to attach the wax riser to the pattern. All
you do is weld the two together by heating them at their point of
contact with a soldering gun or iron. You may sometimes have to use
two or more risers depending on the size of the casting.
If you do not have the equipment to make working models, you can
make non-working display models like the ones you often see
advertised in the Album. This is especially good for the young
beginner in model building. You can get some experience in molding
work and at the same time have the satisfaction of building a nice
looking model. One of the nice things about this type of molding is
that you can get all the detail in the casting that you can carve
in the pattern. Another thing is that you don’t have to make
cores as they are a part of the mold itself. Cored spaces are
carved in the wax pattern and the plaster fills them in when the
mold is made. When you do make a mold, it is a good idea to shake
the pattern in the plaster before it sets. This is to help any air
bubbles come to the surface. The rest is up to you to learn through
experience.
Now, the third type of molding process, that of using permanent
metal molds, is very limited as to what you can do. What this
amounts to is the same thing as molding bullets or sinkers. The
molding part is easy. It’s the making of the mold that is
hard.
I have two metal molds in which I cast aluminum parts for my
Father’s guitars. One of the molds is made in two sections that
come apart and the other is made in three sections. This type of
mold is not for a beginner to try. An example of something you can
make with it would be the grout or tread for the drive wheels on a
model traction engine. This type of molding is only practical where
you have a large number of one part to make such as in the above
example. To make this part you would make the mold out of two
pieces of soft steel hinged together (Fig. 2). You would then mill
or cut out with a Dremel tool the shape of a wheel grout or tread
into one of the steel plates. When this is finished the two halves
should be clamped together. Then drill a hole on the center line of
the two halves. The hold should be in line with the mold cavity and
come to within one eighth inch of it. Now, file out the remaining
portion leading into the mold cavity. You should put some handles
on it so you can open and close it. It is also a help if you can
fix it so that it can be clamped in a vise. You should preheat the
mold with a torch before casting. If you don’t, the first few
castings you make will not come out right. Now again, the rest is
up to you to learn through experience.
In one of the previous issues, I was very pleased to read the
article, In Encouragement of the Young, by Mr. H. L. Fox. We need
more people like Mr. Fox, who realizes the value of the young to
the Hobby and the Hobby’s value to the young.
Well, This is all for right now.
