Pressure Casting

Pressure casting is rapidly being implemented in the production of different components. The need for shorter casting times, reduced costs, and improved physical properties of the cast has contributed to its development. However the level of science and fundamental knowledge is still quite limited. Most of the factories run a pressure casting machine at the suggested pressures and cycle times specified by the supplier of the equipment. Little variation is usually done in either the cycle time, ramping rate, and pressure levels.

Basically, pressure casting refers to the application of pressure to the slip to increase the casting rate. Originally, plaster molds were used for this purpose, but because of its lack of strength and limitation of the applied pressures, porous plastic molds are used now. Development of these molds allowed the pressure to be increased tenfold. Blanchard (Ref 28) reported results for different bodies for a 6 mm thick compact. He observed a decrease in time from 45 to 15 min by increasing the pressure from 0.025 to 0.4 MPa for a porcelain formulation.

There are two types of pressure casting systems: medium pressure (0.3 to 0.4 MPa) and high pressure (up to 4 MPa). Pressure casting is currently being used in different applications such as in sanitaryware in the case of medium-pressure systems and dinnerware in the case of high-pressure systems.

There are several advantages of pressure casting over slip casting. Complex shapes become easier to cast with applied pressure because the quality of the greenware is improved and the fluctuations reduced. The filtration rate of plaster molds used for slip casting is slow, thus requiring a large number of molds and available space. The casting cycle using pressure casting is shorter, reducing labor costs and improving productivity.

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