Rotational moulding from the Egyptians to the 21st century

Rotational moulding is the perfect way of manufacturing a large range of durable plastic products for 21st century use.

But the concept is believed to date back to the Egyptians who used rotational casting processes to create ceramics. 

The first documented use of rotational moulding was in 1855 when a patent was taken out by R. Peters from Britain for a rotating mechanism producing “two centrifugal motions at right angles to each other” using beveled gearing and heat. This process was used to create metal artillery shells and hollow vessels with the rotational pull ensuring the walls were uniformly thick.

Another patent was taken out in the US in 1905 by F.A. Voelke who described a process where paraffin wax and polymer were used to create hollow wax objects.

Five years later GW Perks and GS Baker made good use of the moulding processes to produce hollow chocolate eggs. And the following decade saw a completely different product when rotomoulding was used to mould Plaster of Paris thanks to RJ Powell.

According to Noel Mansfield Ward's article "A History of Rotational Moulding" (published in the Plastiquarian - no 19 - Winter 1997), the original application of plastic use in rotational moulding was for the creation of hollow dolls' heads in the early 1950s. The mould was created from electroformed nickel-copper and filled with  PVC (polyvinyl chloride) plastisol before being placed in an E Blue box-oven.

The oven was based on a General Motors’ rear axle, powered by an external motor and heated by floor-mounted gas burners. This new process resulted in the product showing no parting line and so caught on, quickly replacing the papier-mâché method of the time. Soon many other plastic toys were being manufactured by this process, such as squeaky toys and play balls. Other products it was used for included road cones and marine buoys.

But it was a slow and cumbersome process which, in the 1960s, got more efficient thanks to the development of the Engel process. Larger machinery and a system using indirect high velocity air was introduced enabling bigger shapes to be created from low-density polyethylene. The cooling process changed from placing the mould in cold water to letting the plastic harden in the mould.

This was a major turning part for the process and, by the 1980s, manufacturers could now use a wider range of plastics including polycarbonate, polyester and nylon.  This led to new uses for the process and now rotomoulding is used by plastic manufacturers to create a wide range of industrial mouldings.

Rotational moulding is used by plastic manufacturers to produce an unlimited number of plastic items including tanks for commercial cleaners, grit bins, hospital waste bins, jerry cans, inspection chambers, storage containers, water tanks, car parts, skips and cable management products. With rotational moulding, quick setup enables small batches to avoid overstocking plastic products and it is a low waste process. 

Over the years the types of material used in rotational moulding have evolved from ceramics, to metal, wax, chocolate and plaster to a whole new family of plastics and now bioplastics and environmentally-friendly alternatives are being researched and introduced.

The majority of material currently used in rotomoulding is from the polyethylene family: cross linked polyethylene (XLPE); linear low-density polyethylene (LLDPE); low-density polyethylene (LDPE); medium-density polyethylene (MDPE); and high-density polyethylene (HDPE). Polyethylene has many uses and is classed as a type 1 plastic, which means it is an easily recyclable material and the most environmentally friendly. 

When choosing which product to use in a rotomoulding process it is important to ensure that it is durable and flexible, leakproof, easy to mould, able to withstand high temperatures without cracking and be resistant to mildew and rot. It must also have a sufficient number of antioxidant molecules to prevent degradation in its liquid state when it comes into contact with the oxygen inside the mould and must flow easily through the mould because there is no pressure in the mould to push it through.

Now it is more important than ever for plastic manufacturers and their customers to use environmentally-friendly materials to fill their moulds.

A lot of research is being undertaken to create bioplastics, or biopolymers, from natural products such as sugar cane and banana plants. These products resemble conventional polyethylene but are biodegradable to capture CO2 and assist in reducing greenhouse gases. For bioplastic production the sugar cane ethanol undergoes dehydration forming ethane which is polymerised and transformed into polyethylene.

The process of rotomoulding is already relatively environmentally-friendly as no chemicals or dangerous toxins are released during production, it takes less fuel to make products with plastic and it is virtually zero waste.

If you have an idea for a product made from eco-plastic please let us know as we are actively researching this area and would be keen to find a partner.