Rotational Moulding: The Process
What is Rotational Moulding?
Rotational moulding, known also as rotomuolding or rotocasting, is a process for manufacturing hollow plastic products. Although there is competition from blow moulding, thermoforming, and injection moulding for the manufacture of such products, rotational moulding has particular advantages in terms of relatively low levels of residual stresses, inexpensive moulds and economic viability for short runs. Rotational moulding is best known for the manufacture of tanks but it can also be used to make other innovative plastic products such as complex medical products, toys, leisure craft, and highly aesthetic point-of-sale products. Check out Gyro's range of plastic moulded products.
How does rotational moulding work?
The rotational moulding process is unique among moulding methods for plastics in that the plastic at room temperature is placed in a mould at approximately room temperature and the whole assembly is heated up to the melting temperature for the plastic. Both the mould and the plastic are then cooled back to room temperature.
The speeds of rotation are slow, and the powder undergoes a regular tumbling and mixing action. Effectively the powder lies in the bottom of the mold and different points on the surface of the mould tool come down into the powder pool.When the mould tool rotates in the oven, its metal wall becomes hot, and the powder begins to melt and becomes tacky. The powder sticks to the mould wall and to itself, thus building up the walls of the plastic part against the side of the mould tool.
Advantages of Rotational Moulding:
The main attractions of rotational moulding are:
- A hollow part can be made in one piece with no weld lines or joints
- The end product made by rotational moulding is essentially stress-free
- The moulds/tooling are relatively inexpensive in comparison to other forms of plastic moulding
- The lead time for the manufacture of a mould is relatively short in comparison to other forms of plastic moulding
- Short production runs can be economically viable.
- There is no material wastage in that the full charge of material is normally consumed in making the part
- It is possible to make multilayer products
- Different types of products can be moulded together on the one machine. Read more about Gyro's moulding capabilities.
- Inserts are relatively easy to mould in
- High quality graphics can be moulded in
Rotational Moulding contributes greatly to environmental sustainability both through its use of intrinsically recyclable raw materials and low energy costs compared to other materials and manufacturing methods.
Some of the sustainable advantages of rotationally moulded product are:
- Whole life cost savings - their durability means energy cost for manufacturing are incurred once over a long life span
- Reduced freight costs due to their lightweight and portability
- Reduced maintenance costs
- LDPE, the primary raw material used in rotational moulding, can be readily recycled and used again.
Check out this quick video showing how a company, Eco Birdy, recycles plastic kids toys which have seen better days, into new kids furniture using rotational moulding:
Or this video which shows how Post Industrial plastics are recycled: