Manufacture of Polyvinylchloride Products

When moulding PVC into products for usage, a few processes are carried out.

• For plastic moulding, molten plastic is injected at high pressure into a mold, which is the inverse of the product's shape.
• For rotation moudling, the moulding process carried out in four steps, especially suitable for hollow parts, parts with low residual stress and thick walled parts. Parts with negative undercuts can be made as well. The required amount of plastic material is poured into the mould which is then closed. While rotating around two axes the mould is first heated to the melting-point of the plastic and then cooled again.
• For blow moulding, which is a method used for hollow parts of all sizes, a tube of molten plastics is extruded into an open mould. The mould closes and thereby the bottom of the part welds. Hot air is blown into the tube and it is blown up until it fills out the mould cavity.

An example of a product of polyvinylchloride: a children's doll.

Introduction to manufacturing process of a children's doll: Two major plastic forming processes are used. The heads and limbs are made by rotational molding, producing hollow, seamless products of all sizes and shapes with uniform wall thickness. Blow molding is sometimes used to make the torso if cost is an issue since it is a faster, more economical method.

The processes involved in the manufacture of a children's doll are as follows:

1. During rotational molding, the mold cavities are first filled with a predetermined amount of the compound, in liquid form. Each metal mold consists of multiple cavities and the quantity depends on the size of doll.
2. After the molds are closed, they are placed in a heated oven and rotated biaxially. During the heating cycle, the resin melts, fuses, and then densifies into the shape of the mold cavity.
3. Next, the molds are slowly cooled inside a chamber using air and water. Once cooled, the molds are removed from the chamber, opened, and the finished part is removed
4. Finally, during blow molding, a hollow tube called a parison is first formed out of molten plastic by extrusion through a tubular reservoir.
5. This tube is then placed between two halves of a steel mold and forced to assume the shape of the mold cavity by use of air pressure. The air pressure, ranging from 80-120 psi, is introduced through the inside of the tube, forcing the plastic against the surface of the mold.
6. With a few trimmings and decorations, the doll is produced (in bulks).

Glossary/Summary
Blow molding: a technique for making hollow objects, such as bottles, by injecting air under pressure into a molten mass of glass or plastic and shaping the object within a mold.
Rotational molding: a method for molding hollow plastic objects by placing finely divided particles in a hollow mold that is rotated about two axes, exposing it to heat and then to cold.