Abstract: This invention relates to a method and an apparatus for the production of ribbed pipes. According to the method a plastic material is fed through an extruder into a pipe molding space (12) defined by an extrusion sleeve (4), a mandrel (9) and chill molds (1, 2) moving in the direction of the central axis of the mandrel. When the pressure of the molding space (12) deviates from a desired value, a gap is formed between the chill molds (1,2), and plastic material is squeezed into the gap, or grooves (13) of the chill molds are filled up incompletely. In order to restore the pressure to the proper value, the pressure of the material contained in the molding space is directly measured by means of a pressure sensor (14) which adjusts the speed of the extruder or the chill molds.

Abstract: A method and apparatus for producing a pipe transports first and second sets of chill moulds respectively along first and second endless paths, the chill moulds of each set being so transported one after another, and the endless paths being positioned such that junction faces of the respective chill moulds of the respective sets are positioned against each other in a pipe moulding zone of the endless paths. So positioning the respective chill moulds of the respective sets also defines outer surfaces thereof that are opposite the junction faces and outer surfaces that extend along edges of the junction faces at least generally in the direction of the transporting of the chill moulds.

Abstract: Method in extruding a double-walled plastic tube by using plastic materials of different colors for the inner layer and the outer layer, a portion of the material for the inner layer being diverted to form a longitudinal strip of the outer layer on the outside surface of the tube. The invention also relates to an extrusion tool for working the method, wherein an element (21) is provided inside the tool to divert material from a passage (19) for material for the inner layer to a passage (16) for material for the outer layer.

Abstract: A method of forming a hole in a plastic pipe feeds a plastic layer for the plastic pipe from a nozzle about a mandrel into chill moulds being displaced along an elongated mould cavity about the mandrel formed by the chill moulds. All of the plastic layer is pressed into the chill moulds with a pressure medium between the mandrel and all of an inner surface of the plastic layer for forming the plastic pipe therefrom. Only portions of the plastic layer of the plastic pipe are then subjected to a local pressure difference exceeding the breaking limit of the plastic layer between the inner surface and an opposite, outer surface of the plastic layer at least in part from a flowing medium for forming a hole in the plastic layer of the plastic pipe, the flowing medium being one of a gas and a liquid and flowing from the mandrel at a pressure higher than that of the pressure medium pressing the plastic layer of the plastic pipe.

Abstract: This invention relates to an apparatus and a method for the production of outwardly ribbed, plastic pipes. The apparatus includes a core around which a plasticized material is pressed from a nozzle. A kernel having an essentially constant diameter is positioned at the terminal end of the core for a smooth inner face of the pipe. The outer face of the pipe is ribbed by grooves of axially displaceable chill moulds. The end zone of the kernel is provided for the cooling of the inner face of the pipe. In known apparatuses the grooves of the chill moulds are often filled incompletely and the inner face of the pipe becomes uneven on account of air bubbles, for instance. These disadvantages are avoided by heating an initial zone of the kernel for heating the inner face of the pipe and by shaping the surface of the initial zone to slightly expand conicallly in the production direction.

Abstract: The invention relates to a method and an apparatus for the extrusion of plastic pipes. Today, plastic pipes are provided with a sleeve in such a manner that the end of the pipe is heated, whereafter the end is expanded by means of a mandrel or a pressure medium. This step requires a separate sleeve machine, and it also takes plenty of time and consumes thermal energy. According to the invention a sleeve (22) is formed in connection with the extrusion of a pipe in an apparatus in which a mandrel (8) is surrounded by chill moulds (1, 2) moving in the axial direction of the apparatus. The sleeve is formed by providing some of the chill moulds with a recess (16) the shape of which corresponds to that of the sleeve (22) and by pressing a plasticized plastic hose (11) extruded through a nozzle (10) against the walls of the recess in the area thereof by means of pressure air.

Abstract: Method in extruding a double-walled plastic tube by using plastic materials of different colors for the inner layer and the outer layer, a portion of the material for the inner layer being diverted to form a longitudinal strip of the outer layer on the outside surface of the tube. The invention also relates to an extrusion tool for working the method, wherein an element (21) is provided inside the tool to divert material from a passage (19) for material for the inner layer to a passage (16) for material for the outer layer.

Abstract: This invention relates to a method and an apparatus for the production of ribbed pipes. The apparatus comprises a core which together with an extrusion sleeve forms a nozzle through which a plastic material is fed into a moulding space defined between a conically-enlarging mandrel and chill moulds moveable with respect to the mandrel. The volume of a moulding space defined between a plane at an end face of the extrusion sleeve, a surface of the mandrel, and a cylindrical plane projection from the surface of a kernel on the mandrel equals the combined volume of the grooves positioned at the mandrel at the mandrel at each particular moment. The method feeds a volume of the plastic material per unit time equal to volume of the pipe wall and ribs produced in that unit time.

Abstract: This invention relates to a plastic pipe. The wall thickness of this kind of pipes is very small and, consequently, the impact strength is poor. The impact strength of pipes made of polyvinyl chloride can be improved by adding an admixture to the raw material, which, however, increases costs. According to the invention the impact strength can be improved by a ring-shaped elevation formed at the foot of the ribs on both sides thereof, which elevation joins the side wall of the rib over a sharp transitional juncture.