How are ‘Rotomoulded’ water tanks made?

Rotomoulding or rotational moulding  is a low pressure, high temperature plastic forming process that uses heat and biaxial rotation (i.e., angular rotation on two axes) to produce hollow, single-piece parts.

Rotational moulding equipment at the JoJo Tanks factory.

Disadvantages are long production cycles —only one or two cycles per hour can typically occur, compared to other processes like injection molding, where parts can be formed in a few seconds.  Rotomoulding does have great advantages. Manufacturing big, hollow parts such as water tanks is much easier by rotational molding than any other method. Rotational moulds are significantly cheaper than other types of mould.

Very little plastic material is wasted using rotomoulding for water tanks, and excess material can often be re-used, making it a very economically and environmentally viable manufacturing process.

The rotational molding process consists of 4 basic steps:

1. Placing a measured quantity of polymer (usually in powder or pelleted form) into the mould cavity.
2. Heating the mould in an oven while it rotates, until all the polymer has melted and adhered to the mould 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 mould spends in the oven is critical: too long and the polymer will degrade, reducing impact strength. If the mould 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 mould wall, resulting in large bubbles in the polymer. This has an adverse effect on the mechanical properties and quality of the finished product.
3. Cooling the mould, usually by blowing cold air from a fan. This stage of the process can take some time. The polymer must be cooled so that it solidifies and can be handled safely by the operators. This typically takes tens of minutes. The part will shrink on cooling, coming away from the mould, 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 product.
4. Removal of the product, such as a water tank, from the mould cavity.

Source: Wikipedia

JoJo Tanks South Africa uses a specialist type of rotomoulding process, perfected and refined over more than 30 years of manufacturing high quality, durable water tanks and other polyethylene products suited for harsh African conditions.  JoJo water tanks are one-piece moulded products and do not have the seams that potentially split on inferior brands of water tanks. See A Visual Tour of a JoJo Tanks factory in South Africa.

Click on the links below to view the wide range of JoJo water tanks, JoJo chemical tanks, JoJo septic tanks, JoJo tank stands and other high quality JoJo Tanks products.

JoJo Tanks South Africa offer a wide range of products such as plastic water tanks and chemical tanks to suit every household, business or agricultural need, including silo tanks and silo tank stands as well as other high quality JoJo Tanks products.  See JoJo Tanks’ VERTICAL TANKS, HORIZONTAL TANKS (transporter tanks), STEEL TANK STANDS and OTHER JOJO PRODUCTS and see JoJo Tanks’ NEW 6000 LITRE UNDERGROUND TANKS. Also see our FAQ and WATER TANK PRICES.