a method of and apparatus for separating off waste material from a moulded article in the production of hollow articles of thermoplastics material by a blowing process in a multi - part mould involves pinching together regions of a partly - made article during closure of the mould parts around it and once a satisfactory weld seam has been created at the pinch regions then increasing the closure speed of the mould parts . control of the mould closure speed may be effected by open loop control or by automatic control , and may be made dependent on time and / or on displacement of the mould parts . the increased final closure speed can with advantage be equal to the mould closure speed at which the mould parts are moved up to the beginning of the pinching process .