COUPLING ELEMENT FOR AN EXTRUDER

Description

[0001] The invention relates to a coupling element for connecting an extruder screw to a drive unit of a twin-screw extruder, with two receiving bushings connected to one another in a connecting region, wherein the first receiving bushing is provided for receiving a shaft end of the drive unit and the second receiving bushing is provided for receiving one of the extruder screws.

[0002] Extruder systems are used to mix, convey, and compact various materials. The materials are usually heated during the process. This process is carried out using one or two rotating extruder screws arranged parallel to each other. Consequently, a distinction is made between single-screw and twin-screw extruders. In twin-screw extruders, the principle of power split is used in the gearbox, and the generated motor torque is distributed between two output shafts. Ideally, the output torque of both shafts is identical. The output shafts of the gearbox then drive the two extruder screws. There are extruder systems with co-rotating and counter-rotating screws. In addition, the angles of rotation of the two screws are usually synchronized.

[0003] Disruptions to normal operation, caused, for example, by impurities or other inhomogeneities in the feedstock or cooled material residues from a previous extrusion process, can lead to an uneven load distribution of the torque on the output shafts. Due to the system or process, the extruder screws have a defined center distance from each other, which limits the outer diameter of the gearbox output shafts. Accordingly, the torque density in these components is already high at rated load. If load peaks occur due to the effects mentioned above, this can result in the overloading of individual components. Consequently, there is a constant need to protect the components of an extruder system from overload during normal operation.

[0004] EP 2939943 A1 describes an electronic control system for protecting a system from overload. The torque is measured at the gearbox output shafts. If a torque limit, a torque gradient limit, or an excessively high vibration is detected, a switchable clutch between the motor and gearbox opens, and the motor speed is reduced via a frequency converter. EP 3 378 624 A1 describes a safety clutch that has two clutch halves with shear pins arranged between them. In the event of an overload, the shear pins form a predetermined breaking point, shear off, and interrupt the transmitted torque. The shear pins can be replaced, and the safety clutch is functional again.However, the safety coupling requires a certain radial installation space, which is often not available, particularly in twin-screw extruders, due to the defined center distance between the two shafts. WO 2010 / 109486 A1 shows a coupling for coupling an extruder screw shaft to the output shaft of a drive device. The coupling and an adapter are configured to engage with the output shaft of the drive device, with the adapter defining a pre-weakened region designed to break at a torque less than a critical torque of the extruder screw shaft. EP 2 179 834 A2 shows a coupling sleeve for a twin extruder that is provided with a strain gauge. US 2009 / 0253521 A1 shows a shaft assembly for a motor vehicle, comprising a first shaft with a first connecting end and a second shaft with a second connecting end.A connecting tube with a shear diameter engages the first connecting end and the second connecting end, respectively. The shear diameter is configured to experience shear failure upon an overload moment.

[0005] It is the object of the invention to show measures with which a coupling element for a twin-screw extruder can be provided taking into account the limited axis distance.

[0006] The object is achieved by a coupling element having the features of claim 1. Preferred embodiments are specified in the subclaims and the following description, each of which, individually or in combination, may represent an aspect of the invention. If a feature is presented in combination with another feature, this merely serves to simplify the presentation of the invention and is in no way intended to imply that this feature cannot also be a further development of the invention without the other feature.

[0007] One embodiment relates to a coupling element for connecting an extruder screw to a drive unit of a twin-screw extruder, comprising two receiving bushings connected to one another in a connecting region, wherein the first receiving bushing is provided for receiving a shaft end of the drive unit and the second receiving bushing is provided for receiving one of the extruder screws. The connecting region has a plurality of circumferentially distributed and radially extending bores or a circumferentially extending weld seam, wherein the connecting region, via the bores or the weld seam, has a reduced fracture moment under torsional loading compared to an adjacent structural region of the receiving bushings.

[0008] The receiving bushings are arranged coaxially to one another and are preferably cylindrical and have a profile on an inner surface for torque transmission between the receiving bushing and the drive unit on the one hand and the extruder screw on the other hand.

[0009] The drive unit can comprise a drive motor and a gear stage or gearbox. Typically, the power is split via a gearbox. A belt drive can also be connected between the motor and gearbox upstream of the gearbox to achieve a higher gear ratio. The drive unit can distribute or split the provided torque between both extruder screws. It is preferred if the torque is distributed equally between the extruder screws. Each shaft end of the drive unit is assigned to a respective output shaft of the drive unit.

[0010] The connecting region forms the transition between the two receiving bushings. Due to the connecting region, the two receiving bushings are designed as a single component, i.e., as a single piece. This does not affect the fact that the two receiving bushings can be present as two separate and distinct workpieces at one point during the manufacturing process. The connecting region can generally comprise the same material as the adjacent structural region of the receiving bushings, as, for example, in the embodiment with the plurality of circumferentially distributed and radially extending bores. In the embodiment with the circumferentially extending weld seam, the connecting region can also comprise the material of the weld seam.

[0011] The torsional load arises during normal operation of the twin-screw extruder as a result of the drive torque applied by the drive unit on the one hand and the resistance of the extruder screws due to the material to be extruded on the other hand.

[0012] The coupling element designs, either with circumferentially distributed and radially extending bores or with a circumferential weld seam, form a predetermined breaking point that fails in the event of overload, thus protecting the remaining system components. However, no additional shear element, such as shear pins, is used; instead, the coupling element itself has a weakened area. This area is designed so that it can be modified with the smallest possible adjustments, allowing a defined breaking moment to be achieved with the help of calculations.

[0013] The coupling element designs, either with circumferentially distributed and radially extending bores or with a circumferential weld seam, enable an even more compact design than conventional designs. In particular, no additional axial installation space is required compared to conventional designs. The coupling element can also be retrofitted to existing systems, as the required installation space and connection dimensions can be selected identically.

[0014] In a preferred embodiment, the connecting area forms a reduced cross-section compared to the adjacent structural area due to the holes or the weld seam. This creates a predetermined breaking point in the connecting area. In particular, it can be provided that the connecting area is designed with respect to the desired breaking moment based on the hole diameter and the circumferential distance between the holes and / or the inner diameter and outer diameter, in particular of the weld seam.

[0015] In the embodiment with circumferentially distributed and radially extending bores, it is preferably provided that the circumferential distance between the bores is at most 1.5 times, in particular at most 1.2 times, the bore diameter. This ensures that a defined crack path develops in the fracture plane, since the torsional shear stresses act at an angle of 45°.

[0016] The object is also achieved by a twin-screw extruder with a drive unit and two extruder screws driven by the drive unit in a power-split manner, characterized in that the drive unit is connected to the extruder screws via a coupling element according to one of the preceding claims.

[0017] The invention will be explained below by way of example with reference to the accompanying drawings using preferred embodiments, wherein the features presented below can represent an aspect of the invention both individually and in combination. They show: Figure 1 : a perspective and partially exploded view of a twin-screw extruder; Figures 2a ), 2b): a perspective and a sectional view of a coupling element in a first embodiment and Figures 3a), 3b): a perspective and a sectional view of a coupling element in a second embodiment.

[0018] The Figure 1 shows a perspective and partially exploded view of a twin-screw extruder 2. The twin-screw extruder 2 structurally comprises a drive unit 12, which in this case is composed of a motor unit 4 and a gear unit 6. The gear unit 6 can transmit the drive torque of the motor unit 4 in a power-split manner to two output shafts 8 arranged parallel to one another. A first and a second extrusion screw 14, 16 are each connected to the two output shafts 8 via a coupling element 10. The two extrusion screws 14, 16 have a small center distance from one another, corresponding to the output shafts 8. Other components of the system can be cylinders, filling hoppers, heating bands, nozzles, and a machine frame, although this is not shown.

[0019] The Figures 2 and 3 show, in a perspective and a sectional view a) and b), two embodiments of a coupling element 10 according to the invention.

[0020] The coupling element 10 comprises, in each embodiment, two receiving bushings 18, 20, which are connected to one another in a connecting region 22. The two receiving bushings 18, 20 are preferably identical and are concentrically placed and connected to one another via the connecting region 22. The first receiving bushing 18 is provided for receiving a shaft end of the drive unit 12, and the second receiving bushing 20 for receiving one of the extruder screws 14, 16. An inner circumference of each of the receiving bushings 18, 20 forms a longitudinal toothing, which can form a positive connection with a corresponding longitudinal toothing 30 of the drive shafts of the drive unit 12 and the extruder screw 14, 16 for torque transmission. The connecting region 22 has a plurality of circumferentially distributed and radially extending bores 24 - see Figures 2a) and 2b ) -or via a circumferential weld seam 26 - see Figures 3a) and 3b). In any case, the connection area has a reduced breaking moment under torsional loading compared to an adjacent structural area 28 of the receiving bushings 18, 20.

[0021] In the cross-sectional views of the Figures 2b ) and 3b) it can be seen that the connecting region 22 forms a reduced cross-section compared to the adjacent structural region 28 due to the bores 24 or the weld seam 26. The connecting region 22 is designed with regard to the fracture moment to be achieved via the bore diameter and the circumferential distance between the bores 24 and the inner diameter and the outer diameter of the weld seam 26. It is preferred, as shown here, that a radial dimension of the connecting region does not exceed a radial dimension of the interconnected receiving bushings. The circumferential distance between the bores 24 is preferably at most 1.5 times, in particular at most 1.2 times, the bore diameter. List of reference symbols

[0022] 2 Twin-screw extruder 4 Motor unit 6 Gear unit 8 Output shaft 10 Coupling element 12 Drive unit 14 Extruder screw 16 Extruder screw 18 Retaining bush 20 Retaining bush 22 Connecting area 24 Bore 26 Weld seam 28 Structural area 30 Longitudinal toothing

Claims

1. Coupling element (10) for connecting in each case one extruder screw (14, 16) to a drive unit (12) of a twin screw extruder (2), comprising two receptacle bushings (18, 20) connected to one another in a connecting region (22), wherein the first receptacle bushing (18) is provided for receiving a shaft end of the drive unit (12) and the second receptacle bushing (20) is provided for receiving one of the extruder screws (14, 16), characterized in that the connection region (22) has a plurality of circumferentially distributed and radially extending bores (24) or a circumferentially extending weld seam (26), wherein the connection region (22) by way of the bores (24) or the weld seam (26) possesses a reduced breaking moment at a torsional load in comparison to an adjacent structural region (28) of the receptacle bushings (18, 20).

2. Coupling element (10) according to Claim 1, characterized in that, due to the bores (24) or the weld seam (26), the connecting region (22) forms a reduced cross section in comparison to the adjacent structural region (28).

3. Coupling element (10) according to Claim 1 or 2, characterized in that the connecting region (22) is conceived in terms of the breaking moment to be achieved by way of the bore diameter and the circumferential mutual spacing of the bores (24) and / or the internal diameter and the external diameter, in particular of the weld seam.

4. Coupling element (10) according to one of Claims 1 to 3, characterized in that the breaking moment is in a range between 11,000 Nm and 14,000 Nm.

5. Coupling element (10) according to one of Claims 1 to 4, characterized in that the circumferential spacing between the bores (24) is at most 1.5 times, in particular at most 1.2 times, the bore diameter.

6. Coupling element (10) according to one of Claims 1 to 5, characterized in that a radial dimension of the connecting region (22) does not exceed a radial dimension of the interconnected receptacle bushes (18, 20).

7. Twin-screw extruder (2) having a drive unit (12) and two extruder screws (14, 16) driven by the drive unit (12) in a power-branched manner, characterized in that the drive unit is connected to the extruder screws (14, 16) by way of in each case one coupling element (10) according to one of the preceding claims.