| May/June 1982

Split Patterns

Figure 1

RFD 2, Box 470, Knightstown, Indiana 46148

Casting has been popular for many years. It provides uniform grain structure superior in strength to a similar part machined from the same type of metal. Production procedures for casting are normally quicker and cheaper due to lack of machining time and little material waste.

Metal casting is a process whereby liquid metal is poured into a mold. The metal cools and solidifies in the mold, taking on its shape. The metal discussed hereafter in relation to casting will be aluminum. It works best because of its low (1218°) melting temperature. However, the casting process is very much the same for other metals.

The first step is to make the pattern. An original part makes a good pattern or patterns may be made from wood, aluminum and even styrofoam. However, styrofoam patterns may be used only once, for they are destroyed when the molten metal contacts them. The wood or aluminum pattern may be reused. There are a number of different types of patterns-the one-piece or solid being the simplest. One-piece patterns are used for parts having simple shapes or when only a few castings are desired. Split patterns are used for parts of greater complexity, or those which cannot conveniently be molded from a one-piece pattern, a split pattern is made in two parts (Figure 1).

After the pattern is made, it is necessary to give it a light dusting with a parting compound. This will let the pattern be easily removed from the sand without sticking.

A pattern must also have draft which enables it to be lifted from the mold without breaking the mold (Figure 2).