How does Rotational Moulding work?
1st July 2023
The hollow mould is filled with powdered plastic resin. The mould then begins to rotate bi-axially and is transferred into an oven. The mould will continue to rotate as the resin melts and coats the walls of the mould. The mould will then be cooled until the resin hardens into the desired shape.
The manufacturing process of Rotational moulding is a plastic casting technique which is used to produce large hollow, seamless, and double-walled parts. This process involves a mould on a rotating frame, a heating chamber and a cooling chamber. Rotational moulded parts are high quality and are known for their durability and strength. The Rotational moulding process has 5 stages.
Stage 1. Filling the mould – The hollow mould is filled with the powdered plastic resin
Stage 2. Rotation of the mould – The bi-axially mould starts to rotate and is transferred into the oven
Stage 3. Melting the resin – The mould continues to rotate in the oven where the resin melts and coats the walls of the mould.
Stage 4: Cooling – The mould is cooled until the resin hardens into the part designed shape.
Stage 5: Mould opening – The mould rotation is stopped and the mould is opened to release the finished part (If the part has knife edges these parts will be carved out to create openings).
Rotational moulds are produced using Aluminium as they will transfer heat efficiently which will allow the moulds to cool quicker. The tooling process and production costs for rotational moulding are less expensive than injection moulding and other plastic manufacturing methods. Rotational moulding is quick for tooling as it is low-pressured and will not require any ejection or in-mould cooling . The moulds are capable of producing single and double wall products. The average time it will take to create a new mould is between 4 to 10 weeks. This will depend what the design is, the size of the design and complexity of the design.
What products have been Injection Moulded?
There are many sectors this covers. For example, Environmental, Automotive, Toy Industry and Watercrafts.
Some products that are in these sectors are; litter bins, road cones, floats, buoys, truck mudguards, deiseal fuel tanks, kayaks, canoes, Lego and children’s playground equipment.
Advantages and Disadvantages of Rotational Moulding?
Rotational Moulding Advantages
Less Expensive Tooling - Rotational moulding uses low-pressure, therefore this process requires less expensive materials to create the moulds. Rotational moulding is also without any need of ejection or in-mold cooling which reduces the initial cost significantly
More Durability – Rotation moulded parts are stronger and more durable, especially in outdoor conditions. Therefore rotational moulding is used to manufacturer products for all weather conditions.
No Limit to Part Size – Rotational moulding capacity requirements are large compared to injection moulding machines. This reduces the cost of manufacturing large parts.
Excess Plastic can be reused – Rotational moulding’s excess plastic can be reused to create other plastic parts.
Rotational Moulding Disadvantages
Complex Designs more difficult – Rotational moulding uses low pressures to create parts, therefore the plastic is guaranteed to fill all the parts of the mould. For more complex designs injection moulding is recommended.
Slower Production Time – Rotational moulding has a slower production time due to the low pressure used, therefore parts take longer to produce.
Heavier – Rotational moulding uses more plastic than injection moulding. Therefore rotational moulded parts are heavier than injection moulded parts.
If you have an idea you would like our help with designing for manufacture, please don’t hesitate to get in contact with us. We would love to help!
For more information about the Injection Moulding Process there are a few links below :
https://global-sanitaersysteme.de/en/production/
https://www.sterlingrotationalmolding.com/mold-making/overview-of-a-rotational-mold/
https://www.bpf.co.uk/plastipedia/processes/Rotational_Moulding.aspx
If you need more information about how to design for rotational moulding please don’t hesitate to get in touch.