Patent EA-000540-B1 (EA)
Title: A method and apparatus for manufacturing an extruded plastic product, and a plastic product
Inventor: JARVENKYLA JYRI
IPC: B29C48/94
Filed: 1997-03-19
Abstract: 1. A method for manufacturing extrudable products, wherein the material to be extruded is fed in a powder, pellet or granulate form, by using one or more supply means (6), into a processing cavity consisting of the volumes of the grooves (7) in the rotor (1), of the grooves (8) in the stator (2, 3) and of the clearance between them, characterized in that the cross-sectional area of said cavity decreases at least partially continuously along the axis of the extruder, and by the relative rotational movement of the stator (2, 3) and the rotor (1) said material is forced to proceed along an x-axis, whereby the frictional heat caused by the shear melts a part of the material forming a bed consisting of mainly unmelted particles and some melt around them, enabling the formation of a processing cavity that is completely filled at a certain cross-section at a distance from the end of the apparatus, and hence a rise in the pressure to a level higher than needed for pushing the material through a die later on along the x-axis. 2. A method according to Claim 1, characterized in that the volume of the processing cavity is decreased along the x-axis at least until the shear zone ends typically at about the middle of the total length of the rotor (1), preferably within 1/3 to 2/3 of the screw length. 3. A method according to Claim 2, characterized in that the volume of the processing cavity after the shear zone is kept constant or increased. 4. A method according to any one of the preceding Claims, characterized in that the material consisting of melt and possible unmelted particles is homogenized and mixed in the section after the shear zone, but the geometry of the grooves is made such that the shear rate is lower than in the shear zone. 5. A method according to Claim 4, characterized in that the pressure of the material after the shear zone is not substantially increased. 6. A method according to any one of the preceding Claims, characterized in that the flow rate of the material along the groove (7) is varied by forcing the material through a ring groove (7') to enter in a new set of helical grooves. 7. A method according to any one of the preceding Claims, characterized in that the material to be extruded is processed to such a small extent that the material flow comprises, at the output end of the extruder before a possible means for heating the material, partly unmelted particles that are interconnected mainly at the surface during the continuous sintering taking place in the method. 8. A method according to any one of the preceding Claims, characterized by cooling a rotor (1) and/or a stator (2, 3) in the feed section in such a way that a heat flux arriving from the output end of the apparatus does not melt the material too early. 9. A method according to any one of the preceding Claims, characterized in that the temperature of the material inside the heating means (12) is raised higher than the temperature of the material inside the extruder. 10. A method according to Claim 9, characterized in that the temperature of the heating means (12) and the residence time of the material in the area of influence of the heating means (12) are adjusted such that the output material flow is for the most part homogenized. 11. A method according to any one of the preceding Claims, characterized in that in the middle of the product (11) there is a mandrel (10) at the end of which there is a torsion bar (14), the mandrel (10) being centered by bending it in place by means of the torsion bar (14), which rests on the inner surface of the product (11) which has already set. 12. An apparatus for manufacturing an extruded plastic product, the apparatus comprising at least one rotor (1) and at least one stator (2, 3), and a feed gap (4) between them, grooves (7) being provided on the other side of the feed gap (4) for pressing the material to be extruded out of the apparatus when the rotor (1) is rotated, the cross-section of the groove (7) being substantially unchanging, and a countergroove (8) being provided on the other side of the feed gap (4) at least over a distance of the gap exceeding the gap, the thread of the countergroove being opposite in direction to the groove (7) provided on the other side of the feed gap (4), characterized in that after the feed section there is a shear zone, the countergroove (8) being positioned substantially along the entire length of the shear zone and that the cross-sectional area of the processing cavity, consisting of the volumes of the grooves (7) in the rotor (1), of the grooves (8) in the stator (2, 3) and of the clearance between them, decreases at least partially continuously along the axis of the extruder. 13. An apparatus according to Claim 12, characterized in that the rotor (1) and the stator (2, 3) are cylindrical, and that the cross-section of the countergroove (8) decreases substantially evenly to the end of the shear zone. 14. An apparatus according to Claim 12 or 13, characterized in that the width of the countergroove (8) is smaller than the width of the flights (7a) between the grooves (7) provided on the other side of the feed gap (4). 15. An apparatus according to any one of Claims 12 to 14, characterized in that the width of the countergroove (8) is about 30 to 50% smaller than the width of the groove (7) provided on the other side of the feed gap (4). 16. An apparatus according to any one of Claims 12 to 15, characterized in that the gradient of the countergroove (8) is about 1 to 90 degree , preferably half of the gradient of the groove (7) on the other side of the feed gap (4), most preferably 3 to 10 degree . 17. An apparatus according to any one of Claims 12 or 14 to 16, characterized in that the feed gap (4) is conical at least at a section of its length in such a way that the diameter of the feed gap (4) at the end of the supply direction of material is greater than its diameter closer to the output end of the material, and that the ratio of the diameter of the wider part of the cone to the diameter of the narrower part approximately equals the ratio of the density of the solid mass of the material to be extruded to the bulk density of the mass. 18. An apparatus according to Claim 17, characterized in that material can be supplied to the feed gap (4) with several supply means (6) that are located differently in the axial direction and/or the circumferential direction of the apparatus. 19. An apparatus according to Claim 17 or 18, characterized in that the ratio of the width of the groove (7) to the depth, thereof is between 2 and 7. 20. An apparatus according to any one of Claims 12 to 19, characterized in that the grooves (7) have a substantially semicircular cross-section. 21. An apparatus according to any one of Claims 12 to 19, characterized in that the grooves (7) have a substantially triangular cross-section. 22. An apparatus according to Claim 21, characterized in that at least some of the flights (7a) of the grooves (7) are made sloping in such a way that the clearance between the rotor (1) and the stator (2, 3) is greater at the front edge of the flight (7a) than at the rear edge of the flight (7a). 23. An apparatus according to any one of Claims 12 to 22, characterized in that outside the rotor (1) there is an outer stator (2) and inside there is an inner stator (3), and that material is supplied with the same supply means (6) both to the exterior and the interior of the rotor (1), the rotor (1) comprising feed gaps (13) with bevels (13a) that are adapted to supply material to the exterior of the rotor (1) through every other feed gap (13) and to the interior of the rotor through ever other gap. 24. An apparatus according to any one of Claims 12 to 23, characterized in that material is supplied to the feed gap (4) with a supply means (6) that is a force feed screw. 25. An apparatus according to any one of Claims 12 to 24, characterized in that the rotor (1) and the stator (2, 3) are coated with a very wear-resistant coating agent, and the material they are made of has better thermal conductivity than tool steel. 26. An apparatus according to any one of Claims 12 to 25, characterized in that after the shear zone the grooves (7) in the rotor (1) and the grooves (8) in the stator (2, 3) are same-handed. 27. A plastic product containing matrix plastic to which 1 to 30% of barrier plastic has been added in such a way that a laminar structure is formed, characterized in that the barrier plastic is positioned in the product (11) by rotational flow in an extruder groove in such a way that it forms a laminar structure of a shape of a flattened roll. 28. A plastic product according to Claim 27, characterized in that the matrix plastic is polyethylene and the barrier plastic is polyamide weldable with polyethylene. 29. A plastic product according to Claim 27, characterized in that the matrix plastic is polyethylene and the barrier plastic is polypropylene. 30. A plastic product according to Claim 27, characterized in that the barrier plastic is aliphatic polyketone. 31. A plastic product according to any one of Claims 27 to 30, characterized in that the matrix plastic is cross-linked polyethylene. 32. A plastic product according to any one of Claims 27 to 31, characterized in that the matrix plastic and the barrier plastic do not intermix. 33. A multilayer plastic product having a thicker outer layer made of cross-linked polyethylene and an inner layer of barrier plastic, characterized in that the barrier plastic is arranged to prevent the migration of the rest products of the cross-linkage of the outer layer to the inner surface of the product. 34. A plastic product according to Claim 33, characterized in that the barrier plastic is aliphatic polyketone. 35. A plastic product manufactured with an apparatus of Claim 12, characterized in that the plastic product mainly consists of cross-linked polyethylene having a molecular weight of over 200 000 g/mol, preferably over 300