What method is used to form hollow plastic parts by employing air pressure?

Blow moulding is the method used to form hollow plastic parts by employing air pressure. This process involves inflating a heated plastic tube, or parison, within a mould using air pressure. The air pushes the softened plastic against the walls of the mould, allowing it to take on the desired shape. As the air continues to inflate the parison, it fills the cavities of the mould, resulting in hollow structures such as bottles and containers.

The key to blow moulding lies in the controlled use of air pressure to expand the plastic, ensuring even thickness and a precise form. This technique is particularly effective for creating lightweight, durable parts that require uniform wall thickness.

In contrast, the other methods mentioned, such as injection moulding, compression moulding, and rotational moulding, do not involve the inflation of a parison using air pressure to create hollow shapes. Injection moulding involves injecting melted plastic into a mould to take shape, while compression moulding uses heat and pressure to shape pliable materials. Rotational moulding involves heating plastic in a rotating mould, which allows the material to coat the inside surface but does not specifically rely on air pressure to form hollow products.