Moulding Process: Centrifugal Force

The rotational molding process is a high-temperature, low-pressure plastic-forming process that uses heat and biaxial rotation (i.e., angular rotation on two axes) to produce hollow, one-piece parts. Critics of the process point to its long cycle times—only one or two cycles an hour can typically occur, as opposed to other processes such as injection molding, where parts can be made in a few seconds. The process does have distinct advantages. Manufacturing large, hollow parts such as oil tanks is much easier by rotational molding than any other method. Rotational molds are significantly cheaper than other types of mold. Very little material is wasted using this process, and excess material can often be re-used, making it a very economically and environmentally viable manufacturing process.


Rotational Molding Process
 The rotational moulding process consists of four distinct phases:
  1. Loading a measured quantity of polymer (usually in powder form) into the mold.
  2. Heating the mold in an oven while it rotates, until all the polymer has melted and adhered to the mold wall. The hollow part should be rotated through two or more axes, rotating at different speeds, in order to avoid the accumulation of polymer powder. The length of time the mold spends in the oven is critical: too long and the polymer will degrade, reducing impact strength. If the mold spends too little time in the oven, the polymer melt may be incomplete. The polymer grains will not have time to fully melt and coalesce on the mold wall, resulting in large bubbles in the polymer. This has an adverse effect on the mechanical properties of the finished product.
  3. Cooling the mold, usually by fan. This stage of the cycle can be quite lengthy. The polymer must be cooled so that it solidifies and can be handled safely by the operator. This typically takes tens of minutes. The part will shrink on cooling, coming away from the mold, and facilitating easy removal of the part. The cooling rate must be kept within a certain range. Very rapid cooling (for example, water spray) would result in cooling and shrinking at an uncontrolled rate, producing a warped part.
  4. Removal of the part.

To learn more about process of rotational moulding or to get in contact with us regarding an enquiry you can find us at our website here, or via email on

A world full of possibilities.

We can supply many different rotationally moulded or vacuum formed plastic products, A one stop shop that includes Tooling, mold-making service for the home, garden, OEM components and engineered products. Materials we commonly use include ABS and Polyethylene including LDPE, LLDPE, HDPE and cross-linked polyethylene) . We can supply on a bespoke basis, a wide variety of plastic products.

Previous & existing customer products include: Garden pond, pots & containers, Cases, for the materials handling industries, Consumer Goods, Barrels, Tanks, Containers, Cabinets, Trays and Totes boxes, Automotive components, Playground parts, Domestic furniture, Toys, Floats, Barriers, posts and barricades, Storage equipment etc.

Rotational moulding has opened up a whole new way of thinking in the plastic industry, allowing for designs that would not have been possible with conventional manufacturing methods. The materials used in the production process are environmentally friendly and fully recyclable. It is precisely the unique combination of material and method that explains the great success of rotationally moulded plastic products.

The word ‘plastic’ is from the Greek word ‘plastikos’ meaning ‘to grow’ or ‘to form’.

Rotational or rotomoulding is an extremely popular and well-used process for producing items that are usually hollow. It’s most often used for very large articles which are usually made in small quantities. Items such as children’s toys, garden furniture, storage tanks are manufactured by rotational moulding.

Rotomoulding uses polymer in a powder form which is introduced into the mould along with any additives such as pigments or finishers. The mould is closed and then spun both vertically and horizontally and moved into an oven.

As the paste starts to melt and the mould continues rotating, it’s flung to the walls of the mould by centrifugal force where it forms a skin. After a fixed period, the mould is removed from the oven and allowed to cool carefully to avoid the product shrinking or warping.


Vacuum Forming is one of the oldest and most common methods of processing plastic materials. Vacuum formed products are all around us and play a major part in our daily lives.
The process involves heating a plastic sheet until soft and then draping it over a mould. A vacuum is applied sucking the sheet into the mould. The sheet is then ejected from the mould. In its advanced form, the vacuum forming process utilizes sophisticated pneumatic, hydraulic and heat controls thus enabling higher production speeds and more detailed vacuum formed applications.

Nature of Use and Limitations

Vacuum forming offers several processing advantages over other forming processes such as injection moulding. Low forming pressures are used thus enabling comparatively low cost tooling.

Since the process uses low pressures, the moulds can be made of inexpensive materials and mould fabrication time can be reasonably short. Prototype and low quantity requirements of large parts, as well as medium size runs therefore become economical.

Unlike other thermoplastic forming processes, where powder or resin are the starting point, vacuum forming uses extruded plastic sheet. With vacuum forming a secondary process may be required to trim the formed sheet to arrive at the finished part. The trimmed waste can then be re-ground and recycled.

What Kinds Of Molds Are Used?

Vacuum forming tools used for prototyping can be made from a variety of materials. The material choice will depend on the application and will vary in cost. At Jobec UK Ltd, we use wood or resin for prototyping as much as possible because it is the least expensive. However, wood does have some limitations and cannot be used in every application.

Production tools are typically made from machined or cast aluminum which are temperature controlled and last indefinitely. In terms of cost, an aluminum tool is much more expensive than a wood prototype tool and sometimes only slightly more expensive than an production resin tool. As a rule, the more detailed or large the part, the more expensive the tool.

In Terms Of Cost, How Does Vacuum Forming Compare To Other Processes?


Tooling Costs Part Costs
Fabrication very low high
Vacuum Forming Low low/med.
Rotational Mold Low medium
Injection Mold high very low


Why Choose Jobec UK Ltd?

Jobec has been involved in the manufacture of high quality vacuum formed and rotationally formed products for over 20 years. We have, between the staff, 40 years experience in the manufacture and supply of vacuum formed and roto formed products. Our broad knowledge base and expertise allows us to supply parts in all commercially available thermoplastics to your specifications. Jobec is also proud of our environmental conscience in the fact that, when performance parameters and customer requirements allow, we work with recycled and reprocessed materials whenever possible.

Acrylonitrile Butadiene Styrene ABS
Polyester Copolymer PETG
Polystyrene PS
Polycarbonate PC
Polypropylene PP
Polyethylene (sheet and foamed sheet) PE

Typical Products Produced

Baths & Shower Trays Pallets
Ski-Boxes Boat Hulls
Machinery Guards Vehicle Door Liners
Garden ponds Tote trays
Parts of vehicle cabs Exterior Shop Signs


Let Jobec UK help form the success of your business!

If you’d like to discuss a project in more detail with us or view some of our products in our portfolio that we have created you can contact us at

Affiliate Websites:

Tanks On Demand

Rotational Moulding Website