Which process forms large, simple hollow shapes by rotating a mould with heated material?

• A. Rotational moulding
• B. Compression moulding
• C. Injection moulding
• D. Vacuum forming

Answer: (A)

Rotational moulding forms large hollow shapes by coating the inside of a heated mould as it slowly rotates. Plastic material, usually in powder form, is placed inside the mould; as the mould spins, the powder melts and adheres to the interior walls, building up a uniform wall thickness. The rotation continues during heating to ensure even coverage, then during cooling so the part retains symmetry. When cooled, the hollow product is ejected. This method is ideal for big, simple hollow items like tanks and drums because it uses low pressure and relatively simple moulds, and can produce large single pieces. Other processes rely on high-pressure injection or sheet forming and are better suited to solid or thinner, more complex parts and smaller sizes, making them less suitable for very large hollow shapes.