Abstract: The invention provides a method and apparatus for injection moulding a plastics article having thin and thick wall sections (14; 15). A quantity of molten plastics material (19) is introduced sufficient to fill the mould cavity, followed by a further quantity of molten plastics material sufficient to pack at least the portion or portions of the mould cavity in which the thin wall section or sections (14) are formed. Pressurized fluid is introduced through the or each fluid injection member to penetrate the plastics material whereby a fluid-filled void (20) is formed within the plastics material adjacent to the inner end of the fluid injecting member, and fluid pressure is maintained within the or each void so that the void expands in response to the shrinkage of the immediately surrounding plastics material, during cooling, until the plastics material is self-supporting.

Abstract: The production of an injection moulding of plastics material that includes introducing a supply of plastics material through one or more openings in a mould space, and introducing by way of at least one gas supply passage, a pressurized gas through a separate opening in the mould space into the plastics material within the mould space whereby the gas creates a gas containing cavity in the plastics material. An opening and closing of the gas supply passage is controlled by a valve which is opened by the pressurized gas with the valve featuring a valve port at the outlet end of the gas passage, and a movable valve member extending longitudinally of the gas passage for opening and closing the valve port. The valve member at least when in its extended or valve port open position, protrudes into the mould space and penetrates the plastics material to assist the gas in entering the plastics material.