Abstract: An extruder according to the invention comprises at least two annular conical feed gaps (9) one within the other, formed between a rotatable rotor (1) and a stator (4, 5). At lest some of the material to be extruded is subjected in the different feed gaps (9) of the extruder alternately to a higher pressure and then to a lower pressure. The rotor (1) or stator (4, 5) between the feed gaps (9) can then be balanced such that the pressure effect provides a hydrodynamic bearing, whereby, when the extruder is used, even at worst a very small force is exerted on the other bearings of the rotor (1) or stator (4, 5). By the method of the invention, a product can also be produced which contains cross-linked and at least partly oriented polyethylene.

Abstract: A method for renovation of pipelines, comprising introduction of lining layers into the existing pipeline, the lining layers corresponding in length to the length of the pipeline to be renovated. The lining layers consist of fusible polymers and are presurized and fused together by the introduction of a heat source into the inside of the innermost lining layer.

Abstract: A continuous process and apparatus for producing oriented plastic tube comprising the steps of extrusion, temperature conditioning, diametrical expansion and cooling, characterized by the step of inducing axial draw of the tube between first and second haul-off means located upstream of the expansion step.

Abstract: The invention relates to a method for manufacturing a pipe fitting, said method comprising manufacturing a preform (1) of plastic, and forming an additional layer (3) on top of it. According to the invention, the additional layer (3) is formed by winding a film on the preform until the desired total wall thickness is reached, and the film is wound using at the same time pretensioning in a desired direction. The invention further relates to a pipe fitting manufactured by this method.

Abstract: A service riser 10 comprises a steel jacket 11 around a polyethylene pipe 12 which terminates in the riser at a transition zone 20. The transition zone 20 comprises a retainer sleeve 30 inserted in the end of the pipe 12 and sealed thereto by an O-ring 38. The retainer sleeve 30 extends out of the pipe 12 and is provided with grooves 46 separated by lands 48 on which an elastomeric sealing band 52 is received. The tube 11 is swaged down forming a swage groove 56 around the retainer sleeve 30 compressing the gasket 52 to a large extent over the lands 48 and a lesser extent over the grooves 46, the ideal compression for the gasket 52 being arranged somewhere between such degrees of compression. By this means the ideal degree of compression at some regions of the gasket 52, forming an annulus around the retainer sleeve 30, is guaranteed, despite tolerances in the dimensions of the tube 11 (especially) as well as the band 52 and sleeve 30.

Abstract: The present invention relates to an apparatus for producing pipes of a moldable material, preferably plastic, comprising an extruder, a cylindrical mold comprising chill molds (4, 5), a mandrel (8) inside the extruder and a kernel (9) as an extension of the mandrel. The mandrel is attached at its front end to the extruder. The mandrel (8) and the kernel (9) can be kept concentric with the extruder and the mold if the mandrel and the kernel are joined to each other in such a manner that the angle between their center lines is adjustable.

Abstract: An extrusion material is extruded through a tool and a fluoropolymer is between the extrusion material and a surface of the tool for reducing friction between the extrusion material and the surface of the tool. The surface of the tool is of a material with thermal conductivity greater than 30 W/mK.

Abstract: The invention relates to a co-extruded multilayer plastic pipe comprising an inner pipe and an outer pipe and between them a middle layer of a softer material than the inner pipe. The invention also relates to a method of producing a co-extruded multilayer pipe in a multilayer extruder, and an apparatus for producing the co-extruded multilayer pipe.

Abstract: A method of expanding a tube of plastics material in which a longitudinally travelling tube is progressively diametrically expanded in internal fluid pressure in an expansion zone between an upstream plug and an expandable downstream plug. Expansion of the tube is controlled in response to parameters which directly or indirectly indicate variation in the relative velocity at which material is delivered to and removed from the expansion zone, such as detecting upstream velocity, early expansion diameter, axial force on a sizing device or the tube diameter just before the expansion zone.

Abstract: A method for joining a first tubular member to a second tubular member. The method provides a stretchable and compressible welding ring having a flexible inner ring, a resistance coil wound around the inner ring and at least one layer of plastic coating the resistance coil. The method includes the step of arranging the first and second tubular members in overlapping relation with an end of the first tubular member inserted into an end of the second tubular member and with the welding ring encircling the first tubular member and compressed between the first and second tubular members. The method also includes the step of applying electric energy to the resistance coil to melt the at least one layer of plastic so that, upon cooling, the respective ends of the first and second tubular members are welded to the welding ring.

Abstract: The present invention relates to a branch pipe connection including a locking ring and a sleeve that are arranged against one another and can be tightened in their axial direction. The connection further includes a support flange. The locking ring is of such a flexible material that the locking ring can be placed inside a pipe or the like through a hole made for the branch pipe from outside the pipe or the like, although the smallest outer diameter of the flange of the locking ring is larger than the largest diameter of the hole.

Abstract: The invention relates to a pipe joint for joining pipes with a bent pipe or branch (1) comprising a body (2) having an inner diameter less than the exterior diameter of the pipe (4) to be joined, and sleeve portions (3a, 3b) having an inner diameter substantially equal to the exterior diameter of the pipe (4) to be joined. Thus a step is formed between the body (2) and the sleeve portions (3a, 3b). The sleeve portion (3a, 3b) is eccentrically disposed relative to the body (2) in such a way that at the outer edge of the pipe joint the height of the step between the body (2) and the sleeve portion (3a, 3b) is substantially equal to the wall thickness (e) of the pipe (4) to be joined, and at the inner edge of the pipe joint the height of the step is less than 0.5 times the wall thickness (e) of the pipe (4) to be joined.

Abstract: A method for producing a homogeneous material with an extruder is provided. The extruder has at least two annular conical feed gaps situated between a rotatable rotor and a stator so that the material to be extruded is supplied between the rotor and the stator. Between the delivery point of the material to be extruded and the nozzle of the extruder in the direction of travel of the material the at least one rotor or stator of the extruder is provided with openings passing therethrough so that at least some of the material to be extruded is made to flow through the openings from one annular conical feed gap to another annular conical feed gap. The invention also relates to an extruder and to a multilayer plastic pipe.

Abstract: The present invention relates to a branch pipe connection for connecting a branch pipe to a lightly constructed underground sewage and drainage pipe. The connection includes a locking ring and a sleeve that are arranged against one another and can be tightened in their axial direction. The connection further includes a support flange. The locking ring has a slit by means of which the locking ring can be placed inside the underground sewage and drainage pipe through a hole made for the branch pipe from outside the underground sewage and drainage pipe. The pipe connection also comprises a sealing that is arranged to extend from the inner surface of the underground sewage and drainage pipe as far as the sleeve. A compact, dismountable connection for improving the ring stiffness of the underground sewage and drainage pipe is produced in this way.

Abstract: A method of forming a two-layer plastic pipe (4;8) to be laid in the ground for conducting material therethrough forms a core pipe (2) consisting essentially of a first plastic material and forms a detachable outer hose (3;7) of a second plastic material around said core pipe (2) by a suitable coating method, including in said second plastic material an amount of additives effective to protect said core pipe with said outer hose from stresses and loads of laying said core pipe and outer hose and usage thereof in ground.

Abstract: The invention relates to a method for relining an underground branch conduit (10) of an underground main conduit (11) by a relining pipe (14) in the form of a radially stiff double-walled pipe with a corrugated outer wall (14A) and a smooth elastic inner wall (14B) being inserted by use of a traction rope (22), a draw shoe (20) and a pressure plate (25). A stop element (27) is provided on the traction rope (22), which can be pressed against the draw shoe by the motion of the traction rope in relation to the draw shoe.

Abstract: The present invention relates to a method and a mould for forming an expansion, such as a socket, in a plastic pipe, and a plastic pipe. According to the method, the heated end of the pipe is placed in an external mould (2) and pressed against the mould surface (6) to form a socket. Two grooves (8, 9) can be formed in the socket by a simple method, using a mould ring (12) which is separate from the other parts (3, 4) of the mould and by means of which the grooves of the socket are formed. The ring is simultaneously locked into the socket (7), thereby functioning as a reinforcement ring.

Abstract: The invention relates to a method and an apparatus for forming ribs with sideward projections in a plastic pipe. The projections are formed by means of elongated rolls (10) each moving around the pipe and rotating about its central axis, the rolls being in an inclined position and at an oblique angle with respect to the central axis of the pipe.

Abstract: The invention relates to a material wherein the main constituent is PVC for manufacturing pipes to be used for relining underground pipelines by the pipe in a folded condition being drawn into the pipeline and being engaged with the inside surface of the pipeline by temperature increase. By the addition of polymer thermoplastic elastomers which can be mixed with PVC the material has a glass transition temperature ranging from 45.degree. to 75.degree. C. and a ratio (Emod, T=20.degree. C.)/(Emod, T=75.degree. C.)>20. The invention also relates to a method for restoring underground pipes by relining such pipes with a pipe which has been folded after the extrusion.