The methods specified are selectively suitable for use with the following range of materials: rigid and semirigid thermoplastics moulding, extrusion and cast materials, including compounds filled and reinforced by e.g. short fibres, small rods, plates or granules but excluding textile fibres in addition to unfilled types, rigid and semirigid thermosetting moulding and cast naterials, including filled and reinforced compounds but excluding textile fibres as reinforcement, and thermotropic liquid crystal polymers.