1. About Rotational Moulding: Rotational moulding, known also as rotomolding or rotocasting, is
a process for manufacturing hollow plastic products. For certain
types of liquid vinyls, the term slush molding is also used.
Rotational molding has particular advantages in terms of relatively
low levels of residual stresses and inexpensive molds. Rotational
molding also has few competitors for the production of large (>
2 m3) hollow objects in one piece. Rotational molding is best known
for the manufacture of tanks but it can also be used to make
complex medical products, toys, leisure craft, and highly aesthetic
The process begins with specially developed and uniquely applied
resins. They can include plastisols, polyethylene, polycarbonate,
acetate butyrate, polyamide, elastomers, polyurethane,
polypropylene, ethylene vinyl acetate and fluorocarbons. Some of
the most advanced work is being done with cross-linked polyethylene
and even nylon.
The principle of rotational molding of plastics is simple.
Basically the process consists of introducing a known amount of
plastic in powder, granular, or viscous liquid form into a hollow,
shell-like mold.The mold is rotated and/ or rocked about two
principal axes at relatively low speeds as it is heated so that the
plastic enclosed in the mold adheres to, and forms a monolithic
layer against, the mold surface. The mold rotation continues during
the cooling phase so that the plastic retains its desired shape as
it solidifies. When the plastic is sufficiently rigid, the cooling
and mold rotation is stopped to allow the removal of the plastic
product from the mold. At this stage, the cyclic process may be
repeated. The basic steps of (a) mold charging, (b) mold heating,
(c) mold cooling, and (d) part ejection are shown in Figure below.