Torque Power Live Steam Models Hyattstown, Box 144-D R. F. D., Ijamsville, Maryland 21 754
Hi There Young Engineers:
This article will be the first of several technical articles on subjects related to the steam engine hobby. This one is on foundry work. I am going to try and gear this article on foundry work so that any young person interested in the building of model steam engines can easily make his own castings. I will first give a little history on foundry work.
Foundry work goes back to the Old Testament times when in the day of Moses the children of Israel cast the Golden Calf. As to when the first casting was ever poured, it is not known. The basic means of foundry work has changed very little in all the time the art has been known. There has always been two ways of melting metal.
One is a cupola in which the fuel (coke) and metal (iron or bronze) are mixed together. The cupola is an iron or brick structure in which the fuel and metal are placed after a starter fire has begun. Near the bottom of the cupola are vents where air is forced in by a blower. At the bottom there is a hole to drain the metal out. This hole is kept plugged up by mud jammed into the hole along with a rod. When the rod is pulled out the metal will flow out. To reseal the hole while the metal is flowing, mud, again, is placed on the end of a rod and quickly jammed into the hole. The heat of the metal quickly dries out the mud plug. The metal being mixed with the fuel is melted as the fuel burns and runs to the bottom of the cupola. The liquid metal at the bottom, in time, floats any unburnt fuel and ash up to its surface, leaving a pool of molten metal which is drained into the molds. The level of the molten metal must not rise above the air vents. A good foundry man keeps careful account of just how much metal is placed in the furnace so that it will not overflow. This type of furnace is probably the oldest type known, first being made of brick and then iron lined with fireclay.
The second is a clay pot called a crucible in which the metal is placed. The crucible is then placed in a hole in the ground which is lined with brick. The fuel (coke or coal) is burned around the crucible. Air is forced through a pipe to the bottom of the brick-lined hole in order to burn the fuel. The crucible is picked up by a pair of tongs and the molten metal is poured into the molds.
This is okay for small amounts of metal, but after the crucible gets so big, its weight, when full, becomes too great for two men to lift safely. In the past, large amounts of metal were poured this way and often men were seriously injured or burned to death when a crucible was dropped. Today, this type of furnace has been redesigned to make it safer. For one thing the crucible itself is no longer made of clay but is made of compressed graphite. This crucible is soft, not brittle like the clay crucible, and actually becomes stronger when hot. The furnace has been changed to an above ground type made of steel and lined with firebrick. It is made so that the furnace can be tipped over and the metal can be poured without removing the crucible. This furnace uses a graphite crucible with an extended lip so that the metal can run out over the edge of the furnace when pouring. This type of furnace is fired by fuel oil or natural gas.
I have had many letters from people wanting to know how to make castings. Some want to make iron castings and others want to make brass castings. Each person wants to make castings for a particular size engine.
It is fairly easy for a person to make small castings for engines no bigger than ?' bore using aluminum. Aluminum castings of this size cost very little to make.
If you want to pour brass, then it is going to cost more to make the casting. One of the problems with brass is that, unless you have the best equipment and conditions to pour it, you will have a hard time getting a good casting. One of the most heartbreaking things is to pour a brass casting and find that it is full of gas holes or has shrunk due to improper gating.
As for iron, forget about it. Let your local foundry make your iron castings. It can be melted in a crucible, like brass and aluminum, but is dangerous to work with. Unless you know something about setting up molds and keeping the moisture content in the sand just right, you could have a mold explode in your face while pouring the iron into it. This is because of the high temperature of the melted iron being poured into a wet mold. The steam will blow the metal right out of the mold and often blow the mold apart. I had a letter from a man who wanted to make iron castings for a size steam tractor. To make the castings you would have to buy a cupola which costs $5,000 for a small one, and this does not include the materials which it takes to operate it.
The best material for a beginner to work with is aluminum which you can find in your junk yard. For a hard, long wearing aluminum, melt down old auto pistons. There is very little difference in the alloys used by the different manufacturers of auto pistons. This type of aluminum is the hardest known aluminum since it has a high silicon content. If over-heated, it will become even harder. I have had some so hard that it took the edge off of a tool bit, the same as running cast iron too fast in a lathe will take the edge off of a tool bit. Try not to over-heat it as it is normally very hard. Over-heating will sometimes cause gas in the metal, especially with aluminum. To get rid of gas in aluminum, before you pour it sprinkle some baking soda on the surface of the molten aluminum and stir it with a rod.
When making cylinders out of this aluminum, you can have the cylinder with an auto brake cylinder honer just as you would an iron cylinder. For a casting that should be soft use auto transmission housings or any kind of scrap aluminum.
It is very easy to melt aluminum if you have a forge. Then all you need is an iron pot like a plumber's iron lead pot. Get one as large as you can. Of course, this depends on how large a casting you are going to pour. You should make a handle for it. In time the pot will burn up but you will get a lot of use out of it before that happens. You should also have a standard lead ladle so you can dip small amounts of metal out of the big pot to pour little castings.
If you don't have a forge you can make one out of brick. The inside diameter should be about 15' and at least 5' deep. You will find that soft coal is the best to use as it turns to coke in time while burning. Go to your local junk yard and find some sort of blower you can rig up to use. Be sure to have a way to control the flow of air. Further information on setting up molds and making patterns will be in the next issue. In time, I will give information on what you must have to pour brass. Well, that's all for right now.