What Is Rotational Moulding?
Rotational moulding (or Roto moulding as those in the industry know it), is a relatively simple process used to manufacture plastic parts that are traditionally too large to manufacture by other conventional means.
Although the process is relatively simple, there is a lot of science behind what makes this process a viable means to convert plastic into items for everyday use.
Essentially this conversion process takes ground/powdered polymer that is put into a “mould” or a “tool” and is slowly heated to the melting point of the polymer. During this process, the polymer is not only heated up, but it is also being “rotated” or turned around within the mould/tool so that as the polymer is reaching it melting point, it will “lay up” and adhere to the wall of the mould/tool creating the shape.
Figure 1: Rotational Moulding Process
As stated, this process is typically used for the manufacture of large and typically hollow parts like a water tank or similar agricultural parts like troughs, feeder boxes and similar items. However roto moulding is also used for smaller, more intricate parts for applications such as furniture, leisure craft (kayaks and small boats) and even OEM automotive applications.
A key benefit for roto moulding is the relatively low cost of the processing equipment compared to other traditional plastic conversion processes. Some equipment can be very basic, and yet still achieve the necessary outputs for the desire applications (open flame “rock and roll” type set ups are common). However some roto moulding processing equipment can also be very expensive by the use of very large ovens or oil heated tooling that demand a high level of skill and knowledge to operate successfully.
There are many roto moulding resins, however the majority of applications use LLDPE type Polyethylene as it is very well suited to the process and can give a broad range of performance. Think of this, a water tank that is exposed to the full sun for over 20 years in the middle of the Australian outback, this tank would see a huge variety of conditions, from full sun and +40°C temps to near freezing conditions.
The last thing that the owner would want is for the tank to not perform and fail, so the science behind making this plastic work is quite serious and has been developed over many years of development. It is definitely a case of knowing what to use when choosing the right polymer for the job.
