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.