The two different types of patterns used in investment casting are called expendable and permanent. Expendable patters are made of wax, are joint less, and yield a casting with a higher degree of accuracy than the permanent pattern method. The permanent pattern method uses a pattern that is made of wood, steel, or some other type of solid material. Using the permanent pattern method is usually cheaper than the expendable pattern method. One disadvantage of the permanent pattern method is that the molds must be assembled in separate parts, which makes it less accurate than the expendable pattern method.

The first step of the ceramic shell investment process is to dip or invest the cluster pattern into a liquid slurry or refractory slip made of graded suspensions of refractory grains in suitable media with binders. After this the cluster pattern is coated with a dry sand (stucco) on top of the liquid coating. It is important that this first coat is left to dry thoroughly before adding additional coats. Once the first coat is properly dried, supplementary coats of liquid and dry material are added to the cluster pattern until a sufficient shell is created (up to 5 mm). After the shell is built up to the desired thickness the entire investment must be left to air for 20-150 minutes. As soon as the investment is dried it is ready to be de-waxed. The conventional method for de-waxing an investment is to heat up the investment to slightly above the melting point of the wax. As the wax melts it drains out of the investment and is collected and reused. Approximately ninety percent of the wax is collected and reused from each investment. Once the majority of the wax is melted out of the investment, the shell still needs to be heated a while longer until the wax coating inside of the investment burns away. Another method used for de-waxing an investment is called flash de-waxing. In flash de-waxing the investment is placed into a furnace where the temperature is around 1000 degrees. By doing this the wax is melted out of the investment and the ceramic shelled is fired all in one step. If the conventional method of de-waxing is used the shell must be fired in a furnace after the wax is melted out of the shell. Firing the shell cures the ceramic coating of the investment and also makes the coating stronger. Flash de-waxing is nice because it eliminates a step otherwise found in the conventional de-waxing method and is much faster than conventional de-waxing. This whole

Hitchcock, Howard.

Some common words found in the essay are:
Celsius Wax, Processes Investment, investment casting, pattern method, ceramic shell, Casting Institute, Investment Casting, wax melted, permanent pattern, permanent pattern method, Beeley PR, Hitchcock Howard, wax melted investment, expendable pattern, flash de-waxing, cluster pattern, melted investment, de-waxing investment, expendable pattern method, gating feeding system, Altos California, investment casting institute,
Approximate Word count = 1288
Approximate Pages = 5 (250 words per page double spaced)