Abstract: The invention relates to a sandwich tube comprising an inner and an outer fiber reinforced layer of thermosetting resin and an intermediate layer therebetween consisting of inorganic filler material coated with thermosetting resin and obtained by spraying a finely divided resin into a case of loosely laid inorganic filler material. A non woven is present between the intermediate layer and the outer fiber reinforced layer.

Abstract: A pipe having an annular ring of a foam plastic material on its outer surface and a covering layer of thermoplastic material on the outer surface of the foam plastic ring. An opening between two free ends of foam plastic layer ring lying opposite each other of adjoining pipes is closed by a connecting layer which cooperates sealingly with the covering layers. A ring of rigid material is positioned under the covering layer at the point where the connecting layer is clamped onto the covering layer.

Abstract: Plastic socket of fibre reinforced thermosetting material comprising an inner push edge, a first recess at each end for positioning sealing means, which are held by means of a retaining ring which is accommodated in a second recess. The inner wall between the first recess and the push edge tapers outwardly.

Abstract: A foam plastic layer is sprayed onto a metal pipe, whereafter a tape of polyethylene at the extrusion temperature is helically wound around the foam layer.

Abstract: The invention relates to a method for providing a thermoplastic pipe with an inner groove, by subjecting a heat plasticized pipe to the action of some rotatably supported deforming rollers which are expanded and rotated by means of a mandril. A relative rotating motion between said deforming rollers and the pipe is maintained until the pipe is no longer permanently deformable and the relatieve rotating motion is maintained to strengthen the walls of said groove.

Abstract: A device for manufacturing a plastic tube with transverse or helical grooves consisting of an extruder, two movable halves of die with an inner ribbed profile and being capable of forming a hollow mould, said halves of die each provided with circular elongations for heating the region between the opening of the extruder and the beginning of the mould, an inflatable member in the tube for conforming the tube to the profile of the mould. The inflatable member comprises a movable cylinder having two expandable end discs, an inlet and an outlet for compressed medium being situated between the two end discs, the valve closing said outlet being loaded by a spring such that only pressure medium will escape after the end discs have formed a closed space with the inner side of the tube.

Abstract: A device for directing strips of thermoplastic material which is provided with a first roller and first movable needles or photo electric cells, for correcting the position of the strip in a longitudinal direction in which the first roller and the first needles or cells are driven at the same rate, and second movable needles or photocells and a second roller for correcting the position of the foil in a transverse direction with, the second movable needles or cells and second roller being driven at the same rate.