MXPA98008171A - An extrusion method, an extruder and a product prepared with the method - Google Patents

Abstract

The extruder comprises at least one conical stator (1, 2) and at least one rotatable conical rotor (3). The rotor (3) is mounted from its widest point with bearings (12a, 12b) in such a way that the first bearing (12a) receives the forces acting in one axial direction of the rotor (3) and the second bearing (12b) receives the forces acting in the opposite axial direction of the rotor (3). The invention provides a very firm bearing arrangement, whereupon it is also possible to produce an extruded product that contains at least 0.5%of a slip agent and substantially no weld lines.

Description

A METHOD OF EXTRUSION. AN EXTRUDER AND A PRODUCT PREPARED WITH THE METHOD DESCRIPTION OF THE INVENTION The invention relates to an extrusion method, wherein the material to be extruded is fed to an extruder comprising at least one stator and at least one rotor, wherein the stator has a conical surface at least on the side of the rotor, and the rotor has a conical surface at least on the side of the stator, the ratio of the length of the stator has its largest diameter being almost five times, and where the rotor rotates, the rotor rests on bearings provided at its point wider as it rotates. The invention further relates to an extruder comprising at least one stator and at least one rotor, the stator having a conical surface at least on the rotor side, and the rotor having a conical surface at least on the side of the stator, the ratio of the length of the rotor to its largest diameter being almost five times, and the rotor is mounted in bearings from its widest point to the extruder. The invention also relates to a product prepared with the method. The length of the screw in the extruder is typically rather large with respect to the diameter of the screw. It is very difficult to mount a long screw in bearings. No matter how tight the screw is mounted on the bearings from one end, in difficult situations the screw can be flexed to such an extent that it touches a cylinder placed outside, which immediately leads to rapid wear. Such arrangements have been described wherein a long screw is mounted in bearings from the end near the nozzle such that the molten plastic flows through the bearing. Said bearing arrangement prevents the screw from bending, but leads to disadvantageous welding lines in the plastic mass, thus producing a point of wear on the product to be extruded. When products that have a very slippery surface are to be prepared, a large amount of slip agent must be mixed with the plastic mass that will be extruded. However, a large amount of slip agent, such as silicone oil, which does not dissolve in the plastic mass also results in friction between the screw and the plastic mass being small, so that only little heat is generated through friction. The small friction results in the slip of the mass in some places of the screw groove against the cylinder with perfect sliding. However, since the plastic mass sticks in other places, a very strong bending movement occurs in the screw in an easy way. Therefore, the use of the very slippery plastic mass described above surprisingly leads to a situation where the screw wears enormously and the screw must be firmly mounted in the bearings. DE 1 961 078 discloses an extruder comprising a conical stator and rotating conical rotor positioned outside the stator. The material that will be extruded is fed between the stator and the rotor. The outer edge of the rotating rotor is mounted to the frame with roller bearings in such a way that the bearings receive axial forces which are directed downwards in the figure. The rotor is also mounted with roller bearings, which receive radial forces. The extruder can not be used in a situation where the rotor is subjected axially to a force directed upwards in the figure. In addition, it is not possible to verify the forces acting on the rotor, nor to control or regulate them. EP 89 906 779 describes an extruder comprising at least three conical stators and at least two conical rotors placed between the stators. The material to be extruded is fed between the rotor and the stator through supply ducts. The lower surface of the rotors is mounted in bearings against a lower stator. This bearing arrangement receives the forces directed downwards, that is, when the external pressure of the rotor is greater than the internal pressure. This bearing arrangement can not receive radial forces or forces that are directed upwards. It is not possible to verify or regulate in any way the forces acting on the rotor. The purpose of the present invention is to provide an extrusion method and an extruder which does not comprise any of the aforementioned disadvantages. The method according to the invention is characterized in that as the rotor rotates, it rests on at least two bearings, whereby the first bearing receives the force acting in an axial direction of the rotor and the second bearing receives the forces acting in the opposite axial direction of the rotor, and the bearings are positioned diagonally with respect to the axial and radial direction of the extruder, the bearings receiving together the forces acting in the radial direction. In addition, the extruder according to the invention is characterized by the rotor being mounted with at least two bearings, whereby the first bearing receives the forces directed in an axial direction of the rotor and the second bearing receives the forces directed in the direction opposite axial rotor, and the bearings are placed diagonally with respect to the axial and radial direction of the extruder, the bearings receiving together the forces acting in the radial direction. In addition, the product prepared with the method according to the present invention is characterized in that at least 0.5% of slip agent has been mixed with the material of the product, and the product is substantially without welding lines, and the thickness tolerance wall of the product is less than 2%. Efforts to solve the problem have surprisingly indicated that the sufficient length of the screw passage that is necessary to melt and homogenize the mass can be fixed to the shape of a shorter screw, if the same screw has a strongly conical shape. In such a case, the length of the screw in proportion to its diameter can be much shorter, which allows a firmer bearing arrangement. The essential idea of the invention is that the extruder comprises at least one conical stator and at least one rotating conical rotor, and that the rotor is mounted with at least two bearings in such a way that the lower bearing receives forces directed axially towards below and the upper bearing receives forces directed upwards. Furthermore, the idea of a preferred embodiment is that the bearings are placed diagonally with respect to the axial and radial directions of the extruder, so that the bearings receive a radial force together. The idea of another preferred embodiment is that the bearing arrangement comprises means for measuring the elastic displacement of the rotor, whereby this measurement reveals the forces acting on the rotor and the stator. The invention has the advantage that the bearing structure can be made very strong, so that products containing a greater amount of sliding agent can be produced. Furthermore, by measuring the elastic displacement of the rotor, it is possible to control the forces acting on the extruder. With the arrangement according to the invention, the tolerances of the product walls can also be kept very small. The invention will now be described in greater detail with reference to the accompanying drawings, in which: Figure 1 is a schematic, cross-sectional side view of an extruder according to the invention; Figure 2 is a schematic side view; , in cross section, of a part of another extruder according to the invention; and Figure 3 is a schematic side view of the extruder of Figure 1 during maintenance. Figure 1 is a cross-sectional side view of an extruder according to the invention. The extruder comprises an internal stator 1 and an external stator 2 positioned outside the internal stator. At least the internal surface of the internal stator 1 and the internal surface of the external stator 2 are conical. Between the internal stator 1 and the external stator 2 there is a conical rotor 3. The ratio of the length of the rotor 3 to the diameter of its widest part is almost 5 times. The rotor 3 is adapted to move rotationally between the internal stator 1 and the external stator 2. The rotor 3 is rotated through a motor 5. The motor 5 can be, for example, a hydraulic motor, an electric motor or some other motor that is known per se and that is suitable for the purpose. The motor 5 is adapted to rotate the rotor 3 through a gear system 4. The rotation speed of the rotor 3 can be adjusted in a desired way through the gear system 4. On the other hand, for example, when an electric motor is used, the gear system 4 is not necessary, since the rotational frequency of the rotor 3 can be adjusted easily by adjusting the rotational speed of the motor 5 in a manner known per se. The above-described components of the extruder are known per se, so they have not been described in great detail in this regard. The extruder further comprises a first supply conduit 6 along which the material to be extruded can be fed to the outside of the rotor 3 between the rotor 3 and the external stator 2. The extruder also comprises a second supply conduit 7, along which the material can be fed into the rotor 3 between the rotor 3 and the internal stator 1 through an opening or openings 8 provided in the rotor 3. The material that will be fed to the first supply conduit 6 is supplied with a first feeding device 9. Correspondingly, for the purposes of feeding materials into the second supply conduit 7, the arrangement comprises a second feeding device 10. The feeding devices 9 and 1 0 can be, for example , feed screws, pumps or other devices known per se. With this feeding device, the flow velocity of the material to be fed into the supply conduit can be adjusted. The rotor 3 is mounted to the gear frame 1 1 with bearings 1 2 a and 1 2 b. The bearings 1 2a and 1 2b are positioned in such a way as to restrict the movement of the rotor 3 in both directions in the axial direction of the extruder. The bearings 1 2a and 12b can be, for example, sliding bearings, ball bearings or other similar bearings. However, the bearings 12a and 12b are most preferably conical bearings, as shown in the accompanying drawings. The axes of the bearings 12a and 12b, which are shown with a dotted line in the accompanying drawings, are preferably positioned diagonally in both the radial and axial directions of the extruder. Therefore, the upper bearing 12a receives the forces acting upwards on the rotor 3 and which result from the feeding of a larger material flow with the second feeding device 10 along the supply conduit 7 through the openings 8 between the rotor 3 and the internal stator 1 that with the first supply device 9 along the supply conduit 6 between the rotor 3 and the external stator 2. In the opposite case, the lower bearing 12b receives a directed force down on the rotor 3. The bearings 12a and 12b collect together a force acting radially on the rotor 3. Therefore, the bearing arrangement of the present provides firmer bearings. Between the gear frame 1 and the external stator 2 there is an upper clear ring 13a. Correspondingly, between the internal stator 1 and the gear frame 1 1 there is a lower clearance ring 1 3b. The clear rings 1 3a and 1 3b can be changed, so they can be used to adjust the free play between the rotor 3 and the stators 1 and 2. The external stator 2, the gear frame 1 1 and the stator r internal 1 are connected together through a clamping bolt 14. An upper measuring rod 15a and a lower measuring rod 15b are also connected to the gear frame 11. The upper measuring rod 15a is connected to a higher measuring sensor 16a, and the lower measurement bar 15b is correspondingly connected to a lower measurement sensor 16b. The clear rings 13a and 13b can flex a little, if required, and on the other hand the clamping bolt 14 is also stretched to a certain degree. Therefore, it is possible to detect with the measuring sensors 16a and 16b the elastic displacement of the measuring rods 15a and 15b and thus the displacement of the gear frame 11 and the stators 1 and 2 The measurement sensors 161 and 16b they can be, for example, pressure indicators or some other measuring devices known per se. The elastic displacement is typically of the micrometer magnitude. The light rings 13a and 13b can also be of the spring type, ie they can be flexed rather easily, so that the elastic displacement is also greater and thus can be measured more easily In addition, the clear rings 13a and 13b can be equipped with force sensors that directly provide information regarding the magnitude of the forces acting over the clear rings 13a and 13b When the extruder is discharged, the signal from the measurement sensors 16a and 16b can be defined as When the pressure caused by the material that will be supplied between the rotor 3 and the external stator 2 is greater than the pressure acting between the rotor 3 and the internal stator 1, the clamping bolt 14 is subjected to a force that causes the bolt is stretched. In such a case, the upper measurement sensor 16a provides a signal S1 which can be defined, for example, as positive and which describes the elastic transfer work which is thus proportional to the elongation of the clamping bolt 14, i.e. , to the force acting on the bolt. Simultaneously, the gear frame 11 is subjected to a force that is directed downwards, whereby the lower measurement sensor 16b provides the elastic transfer work S2, which can be defined as negative and which in this way is proportional to the force acting down on the gear frame 1 1. Correspondingly, when the pressure between the rotor 3 and the internal stator 1 is greater than the pressure between the rotor 3 and the external stator 2, the elongation of the clamping bolt 14, that is, the force acting on the bolt, can be oriented from the elastic transfer work S2 of the lower measurement sensor 16b, which in this case is positive, and the force acting upwards on the gear frame 1 1 can be determined with the signal of the upper measurement sensor 16a , which describes the work of elastic transfer? S1 and which in this case is negative. Therefore, it is possible to accurately determine the forces acting on the extruder through the signals provided by the measurement sensors 16a and 16b, and the material flowing from the materials that will be supplied to the extruder can be adjusted based on this measurement, if required. In conjunction with the extruder frame assembly, the fastening bolts 14 are preferably pretensioned with a hydraulic rotation device to provide sufficient pre-tension. This pre-tension is preferably provided in such a way that the fastening bolts 14 are hollow and contain a heating resistor. When the clamping bolts 14 are then tightened at an elevated temperature, the pre-tensioning can be provided by reducing the temperature to the normal working temperature. The gear frame 11 and the bearings 12 a and 12 b are connected to the rotor 3 with the holding bolts 1 7. The gear frame 1 1 and the bearings 1 2 a and 1 2 b in this manner constitute a unit which can be separated from the rest of the extruder. The attached drawings show, with a broken line, a space to which lubrication oil is supplied in order to lubricate the gear and the bearings 1 2a and 1 2 b. By heating the lubrication oil it is possible to heat the extruder and, correspondingly, by cooling the lubrication oil it is possible to cool the extruder very easily and effectively. The rings of light 1 3a and 1 3 b must be heat conductors in order to ensure heat transfer to the entire extruder. Since the extrusion screw according to the invention does not flex and this bearing arrangement is very fi rm e, and since the process can be controlled with the method of the present, the extruder according to the invention can be used to prepare products of low tolerance also in case of at least 0.5% of a slip agent is mixed with the material. The plastic matrix of the product may be, for example, polyethylene or polyolefin, and the slip agent may be polyolefin wax, silicone wax or a fluoroplastic compound. The product to be extruded may be, for example, a plastic pipe, a cable jacket, a film or some other similar product. In conventional pipe extrusion, the wall tolerance is in practice about 5%, while the standard normally allows a variation of about 10%. The tolerance of the wall thickness of the product according to the invention can easily be reduced to less than 2%. Correspondingly, the tolerances of the center and diameter of the opening can also be small. For example, when the supply flows of material to be extruded are controlled based on the measurement that results from the forces acting on the extruder, it is possible to provide a wall tolerance that is less than 1%. On the other hand, adjusting the amount of the slip agent in the material to be extruded makes it possible to affect the forces acting on the extruder. For example, it is possible to supply a soft mass towards the outside of the rotor and a rigid mass towards the inside of the rotor, and a required amount of sliding agent can be mixed with the material that will be supplied inwards, so the forces that acting on the extruder can be balanced by varying the amount of slip agent. On the other hand, a substantially large constant amount of slip agent, for example about 5%, can be added to the material that is fed inwardly, which thus provides, for example, a cable pipe where a cable can be easily installed, that is, the distance in which the cable can be pulled into the pipe can be very long. When said product is prepared, it is possible to adjust the forces acting on the extruder by regulating the concentration of the sliding agent in the material that will be supplied to the outside. Furthermore, the apparatus according to the invention allows the preparation of products containing a large amount of sliding agent and substantially no welding line, which is very important since due to the effect of the sliding agent, the welding lines do not they close well. Figure 2 is a cross-sectional side view of a part of an extruder according to the invention. The reference numbers in Figure 2 correspond to those in Figure 1. Instead of the clear rings 1 3a and 1 3b, the clear piece can be, for example, a 1 3 'clear weld. The light weld 13 'consists of a welding carrier 1 8 and a welding section 1 9 and a clamping screw 20 and an adjusting screw 21. The weld carrier 1 8 is connected to the gear frame 1 1, for example, with screws. The clamping screw 20 in turn is connected in movably to the welding carrier 18. The clamping screw 20 and the adjusting screw 21 are positioned in such a way that they remain motionless with respect to each other but the adjusting screw 21 is able to rotate around its axis. When the adjusting screw 21 rotates, it remains in place and simultaneously moves the welding section 19 with respect to the weld carrier 18. Therefore, by rotating the adjusting screw 21, it is possible to adjust the clearance between the rotor and the stator in a very easy and simple way. Figure 3 shows an extruder according to the invention during maintenance. The reference numbers of Figure 3 correspond to those of Figures 1 and 2. The end of the extruder in a conventional extrusion apparatus comprises a tool, which rests on its own support. The apparatus is usually disassembled so that the tool rotates to a vertical position and the parts are removed from each other by lifting with a lifting device. Since the structure of the extruder according to the invention is very simple, the disassembly operation can be carried out intelligently in a completely new way. The external stator 2 and correspondingly the unit formed by the rotor 3 and the gear frame 11 are placed on separate wagons 22. The wagons 22 in turn are arranged to move on a rail 23. In addition, wagons 22 can be placed partially one inside the other. In this way, after the fastening bolts have been loosened, the different parts can be pulled along the rail 23 provided in the axial direction of the extruder for the purpose of cleaning and maintenance. With this simple method, it is possible to avoid dents that occur easily during assembly. Compared with the disassembly of a conventional tool and the cleaning of an extruder, the apparatus of Figure 3 saves time more than ten times. The drawings and description related thereto are only illustrative of the inventive idea. The details of the invention may vary within the scope of the claims. Therefore, there are more than two stators and more than one rotor, so it is possible to prepare, for example, products with several layers. In addition, there may be more than one measurement arrangement, for example, preferably four arrangements that are placed on the circumference of the extruder at 90 ° intervals, whereby comparison of the signals of each measurement point provides information with respect to the forces acting on different parts of the extruder, and the temperatures in the different parts of the extruder can be adjusted as the need arises, so that the tolerances of the product can be kept as low as possible. It is also possible to leave one of the stators of the extruder, so that the material to be extruded is naturally supplied only to one side of the rotor between the rotor and stator.

Claims (16)

1 .- An extrusion method, wherein the material to be extruded is fed to an extruder comprising at least one stator (1, 2) and at least one rotor (3), so that the stator (1, 2) has a conical surface at least on the side of the rotor (3), and the rotor (3) has a conical surface at least on the side of the stator, the length ratio of the rotor (3) to its diameter more large being at least five times, and the rotor (3) is rotated, the rotor (3) rests on bearings provided at its widest point as it rotates, characterized in that as the rotor (3) rotates, it is supported on at least two bearings (12a, 12b), whereby the first bearing (12a) receives the force acting in an axial direction of the rotor (3), and the second bearing (12b) receives the forces that they act in the opposite axial direction of the rotor (3), and the bearings (12a, 12b) are positioned diagonally with respect to the axial direction and radial of the extruder, the bearings (12a, 12b) receiving together the forces acting in the radial direction.

2. - A method according to claim 1, wherein the elastic displacement of the rotor (3) and the stator (1, 2) is measured, and the forces acting on the extruder are determined based on the result. of the measurement.

3. - A method according to claim 1 or 2, wherein the extruder comprises at least two stators (1, 2), the internal stator (1) having at least one external surface that is conical and the stator external (2) having at least one internal surface that is conical, that between the stators (1, 2) there is at least one rotating conical rotor (3), and the elastic displacements between the rotor (3) and the internal stator (1) and between the rotor (3) and the external stator (2) are measured separately, and the forces acting on the stators (1, 2) and the rotor (3) are determined based on the measurements.

4. A method according to claim 2 or 3, wherein a sliding agent is mixed with the material that will be supplied between the stator (1, 2) and the rotor (3), and the amount of sliding agent is adjusted based on the measurement result obtained from the elastic displacement.

5. A method according to claim 3, wherein the material to be extruded is fed separately to the outside and inside of the rotor (3), and the amount of slip agent in the material that will be supplied to at least one side of the rotor (3) is adjusted based on the information obtained from the measurements of the elastic displacements.

6. A method according to any of the preceding claims, wherein characterized in that by controlling the temperature of the lubricating oil, which lubricates the bearings (12a, 12b), the temperature of the extruder is controlled.

7. A method according to any of the preceding claims, wherein the extruder frame is assembled with pre-tension that is provided by heating the adjusting bolts (14) from the inside before they are assembled in place. and cooling the bolts to the normal working temperature after assembly.

8. An extruder comprising at least one stator (1, 2) and at least one rotor (3), the stator having a conical surface at least on the side of the rotor (3), and the rotor (3) having a conical surface at least on the side of the stator, the ratio of the length of the rotor (3) to its largest diameter being mostly five times, and wherein the rotor (3) is mounted on bearings at from its widest point to the extruder, characterized in that the rotor (3) is mounted with at least two bearings (12a, 12b), whereby the first bearing (12a) receives the forces directed in an axial direction of the rotor ( 3) and the second bearing (12b) receives the forces directed in the opposite axial direction of the rotor, and the bearings (12, 12b) are placed diagonally with respect to the axial and radial direction of the extruder, the bearings (12a, 12b) receiving together the forces acting in the radial direction.

9. An extruder according to claim 8, characterized in that between the rotor (3) and the stator (1, 2) there are measuring means for measuring the elastic displacement between the rotor (3) and the stator (1, 2). ).

10. An extruder according to claim 8 or 9, wherein the extruder comprises at least two stators (1, 2), the internal stator (1) having at least one external surface that is conical, and the stator external (2) having at least one internal surface that is conical, and at least one rotating conical rotor (3) being provided between the stators (1, 2), and the extruder comprises measuring means for separately measuring the Elastic displacements between the rotor (3) and the external stator (2) and between the rotor (3) and the internal stator (1).

11. An extruder according to any of claims 8 to 10, wherein the bearings (12a, 12b) are tapered bearings.

12. An extruder according to any of claims 8 to 11, wherein the extruder comprises a gear frame (11) which together with the bearings (12a, 12b) constitutes a unit that can be separated from the rest of the extruder.

13. An extruder according to any of claims 8 to 12, wherein at least the gear frame (11) of the extruder and the rotor (3) constitute a unit that is arranged to be moved during maintenance with a wagon (22) along a rail (23) that is parallel to the axis of the extruder.

14. A product prepared with the method according to claim 1, wherein at least 0.5% of a slip agent has been mixed with the material of the product, and wherein the product is substantially without welding lines, and The tolerance of the wall thickness of the product is less than 2%.

15. - A product according to claim 14, wherein the product comprises at least two layers, the inner layer contains from 0.5 to 10% of a slip agent mixed therein.

16. A product according to claim 14 or 15, wherein the product is a protection tube for cables, wherein at least the inner layer is polyolefin and the slip agent is silicone or fluoropolymer agent.