Developments
in
Rotomoulding Technology
There
has been a tremendous development in technology resulting in state-of-the-art
rotomoulding machines, which challenge product designers and guarantee
deliverables.
There
has been a tremendous development in technology resulting in state-of-the-art
rotomoulding machines, which challenge product designers and guarantee
deliverables. In various forms, rotomoulding has now been known for
almost a century. There have been tremendous technology developments
over the decades. The technology of rotomoulding is done on different
types of machines, which directly relate to the technology. The evolution
of the process and technology is presented here.
Evolution
The Beginning Crude methods were deployed to manually
manufacture cylindrical and spherical products e.g. balls etc. The
technology has made great advances; the developments - close to the
chronological order of the actual developments are expressed below.
Rock-n-Roll Machines
The beginning was followed by better methods of rotomoulding
in the following decades, and the rock-n-roll method of rotomoulding
was evolved, which eliminated the need of manual work. This was and
still is a very effective method of rotomoulding and it can mould
cylindrical and sphericallike objects. The process is somewhat slow,
but it has its advantages. The rock-n-roll machine rotates the mould
continuously in one axis and rocks the mould in the other axis. The
system is very simple and low in cost, but has its limitations, in
the type of parts it can rotomould. The open flame creates tremendous
pollution, and may not be considered appropriate in most developed
countries. It normally rotomoulds cylindrical or spherical type of
parts, and with minor adjustments cylindrical tanks, where one has
to be very careful about the bottom, especially in the centre. Infact,
one has to generally maintain a higher wall thickness and weight to
meet the requirements of having the minimum wall thickness and deposits
in the bottom of the mould. The corners tend to be too thick, which
take-up unnecessary higher quantity of resin. It is difficult to rotomould
square or other such articles. But this is an ideal technology for
product like kayaks and canoes. This cannot produce double walled
products. This process has further developed considerably and is still
in use almost all over the world, though the numbers are depleting.
The closed oven version of rock-n-roll machines is more prevalent
now. This has a hot air recirculation system in a closed oven, which
rocks in one and axis and rolls in the other axis. This is gaining
popularity in some areas, but is a far slower system demanding more
manpower.
Directly Fired Machines
This is common in low cost rock-n-roll machines - open or closed
type. The process involves direct heating of moulds, and exposes plastic
resins to unusually high temperatures in moulds causing stress, poor
control, poor heating at vertical surfaces at ends, and has severe
limitations on the type of parts that can be rotomoulded. It is however
very simple to operate, repair and build. This was improved by closed
oven version, which did improve the heating and saved heat losses
with better results from its predecessors but never-the-less remained
a very directly fired system.
....contd.
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