Torque Power hive Steam Models Hyattstown, Box 144-D R. F. D., Ijamsville, Maryland 21 754
Hi There Young Engineers:
In the last article I did not get to the subject of coring which is something of an art in itself. Cores are used to hollow out a portion of a casting such as a cylinder bore, the steam chest, and steam ports. I do not recommend that you try to core the steam ports as they are too fragile with which to work. It is much easier to drill or mill the ports.
The core box is a mold in which the core is made. It is simply two blocks of wood pinned together so that they can be easily taken apart (Fig. 1). If you are making a cylindrical core you would drill a hole the diameter of the core print at the point where the two blocks join together. Now the core print makes a space for the core to rest in and it extends beyond the casting itself. In making this type of a core the core box is the same length as the core is to be. And, the core should be just long enough to fit between the core prints. You should coat the core box with linseed oil and let it soak in.
Now, how to mix the core material. This is not the way the foundries do it, but it does work. Mix 2/3 green molding sand with 1/3 non-rising flour and add water in the same way you would to temper molding sand. Be sure to mix the sand and flour thoroughly before adding the water. Before you fill the core box you should dust it well with parting dust or flour.
You should have a stiff piece of sheet metal on which to make the core. Place the core box on the piece of sheet metal and pack the core material in it. It should be packed very firmly. Now, take a tool and tap the core box until the core becomes loose. Remove the core box, leaving the core standing on the piece of sheet metal. Place it in an oven and bake it until it is dark in color.
A cylinder core has two points of support, but, some cores do not. These are self-supporting cores which mean that 2/3 of the core rests in a single core print (Fig. 2). Such as, in the case of the steam chest core which is shaped like a block. If the steam chest is to be cored ' deep, the core should be made 1' in depth. The extra 1' would be the portion which rests in the core print.
Now, if you have a core which must be made an odd shape, you can carve one out of a solid piece of core material. Make a core box to form a piece of stock material and then file it to shape using a rasp. The rasp won't be much good after using it, but, it will do the job. Well, this finishes the subject of sand molding.
By now you should have some ideas to what it is all about. You will learn more by trying it than anything else. In the next article I will go into investment molding which you may find easier than sand casting.
Well, that will have to be all for right now. See you at the steam shows!