Abstract: Moldings of cross-linked thermoplastic polymers are obtained by the method comprising: melting a cross-linkable thermoplastic polymer admixed with a cross-linking agent by applying a temperature and a pressure insufficient to cause a cross-linking reaction; passing the thus-melted molding material through a first orifice thereby to raise its temperature by a shearing action to an extent that will start a cross-linking reaction; passing the thus-treated melted molding material through a second orifice thereby further to raise its temperature to an extent that will effect a rapid cross-linking reaction of the molding material; and then introducing the thus-treated molding material into a pre-forming die to advance the cross-linking reaction of the molding material and then cooling the molding material by means of a liquid under an elevated pressure.