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return to Plastic Information and Processes
Introduction:
Many products are made by casting rather than molding. In casting, the liquid is simply poured into the mold, rather than being forced in.
Both thermosets and thermoplastics may be cast. Commonly used materials for casting include acrylics, phenolics, polyesters and epoxies.
Plastisol Casting:
A special application of casting commonly used for the manufacture of hollow articles is plastisol casting. There are several variations; dip casting, slush casting and rotational casting. All are based on the fact that a plastisol liquid form is solidified as it comes in contact with a heated surface.
Process:
The plastic is prepared in liquid form. In some cases the resin is naturally a liquid and in others a granular solid is liquefied by heat. The liquid plastic is poured into a closed mold and air bubbles are removed. The plastic is cured at room temperature or in an oven at low heat. The cured plastic is then removed from the mold.
Dip casting:
A heated plug the size and shape of the inside of the article to be cast is dipped into a container of liquid plastisol. The mold is withdrawn at a given rate. The plastic immediately surrounding the mold adheres to it and solidifies. The slower the rate of withdrawal, the thicker will be the layer of plastic. After cure, the plastic is stripped from the mold.
Slush casting:
A liquid plastisol is poured into a heated hollow mold which is the shape of the outside of the object to be made. The plastisol in immediate contact with the walls of the mold solidifies. The longer the plastic remains in the mold, the thicker will be the layer of plastic that solidifies. The excess plastic, still in the liquid form, is poured from the mold. After the plastic is cured the mold is opened and the part is removed.
Rotational casting:
A predetermined amount of liquid plastisol is placed in a heated, closed, two-piece mold. The mold is then rotated, usually in two planes: this distributes the plastic against the walls of the mold in a thin even layer. As it comes in contact with the mold it solidifies. After the plastic is cured the mold is opened and the part removed.
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