Rotational
Moulding
Understanding
the
Process and the Markets
The
Indian rotomoulding industry is on the threshold of entering a new
era, into demanding sectors like automotive, infrastructure, material
handling, defense, recreation, furniture etc.
Introduction
Rotational moulding which is also known as rotocasting
or rotomoulding, is a low pressure, high temperature manufacturing
method for producing hollow, one piece plastic part. As with most
manufacturing methods for plastic parts, rotational moulding evolved
from other technologies. The basic principle of forming a coating
on the inside surface of a rotating mould dates back for many centuries,
but the process did not gain recognition as a moulding method for
plastics until 1940s. The first commercial application used vinyl
plastisols to coat the inside surface of a hollow metal mould. This
process using PVC is still widely used. Typical products included
play balls and toy dolls. With the introduction of appropriate powder
polyethylene grades in 1950s, the rotational moulding process expanded
more quickly. Now-adays, polyethylene accounts for over 90% of the
total tonnage of plastics used in the rotational moulding worldwide.
This is mainly because the powder flow, melt flow and thermal stability
of this material are ideally suitable for the process. In the current
scenario, rotational moulding is a very competitive alternate to blow
moulding, thermoforming and injection moulding for manufacturing hollow
plastic products. It offers designers, the opportunity to achieve
the economic production of stress–free articles, with uniform
thickness and potentially complex shapes. Table 1 shows comparison
between commonly used plastic processes.
Advantages of Rotational Moulding
There are many advantages associated with the
rotational moulding process. Firstly, moulds are relatively cheaper
and simpler. This is because rotomoulding is a low pressure process
and therefore, it is not necessary to manufacture the moulds from
expensive metal alloys, as in injection moulding process. Wall thickness
of parts produced from rotomoulding is more uniform in comparison
to products from other processes and it is possible to alter the wall
thickness of the part without altering the mould. It is also possible
to produce double-wall mouldings. It is also possible to mould different
types of parts at the same time. Parts manufactured by rotational
molding are hollow, seamless and virtually stress-free. The main advantages
of rotomoulding are:
*A hollow part can be made in one piece
with no weld lines or joints
....contd.
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