Coupling element for extruder

Abstract

The invention relates to a coupling element (10) for connecting an extruder screw (14, 16) to a drive unit (12) of a twin-screw extruder (2), comprising two receiving bushings (18, 20) which are connected to each other in a connection region (22), a first receiving bushing (18) being provided for receiving a shaft end of the drive unit (12) and a second receiving bushing (20) being provided for receiving a shaft end of the drive unit (12). And a second receiving bushing (20) is provided for receiving one of the extruder screws (14, 16). In the event of a torsional load, the connection region (22) forms a predetermined breaking point that fails in the event of an overload, thus protecting other system components.

Description

TECHNICAL FIELD

[0001] The invention relates to a coupling element for each connecting one extruder screw to a drive unit of a twin-screw extruder, comprising two receiving bushes which are connected to each other in a connection region, wherein the first receiving bush is provided for receiving a shaft end of the drive unit and the second receiving bush is for receiving one of the extruder screws. BACKGROUND

[0002] Extruder systems are used for mixing, conveying and compacting various materials. The materials are usually heated in the process. The process is achieved via one or two rotating extruder screws arranged parallel to each other. Thus, a distinction is made between single-screw extruders and twin-screw extruders. In the case of twin-screw extruders, the power split principle is used in the transmission, and the resulting motor torque is distributed between the two output shafts. Ideally, the output torques of the two shafts are identical. The output shaft of the transmission then drives both extruder screws. There are extruder systems with unidirectionally rotating screws and counter-rotating screws. Furthermore, the rotation angles of the two screws are usually synchronized with each other.

[0003] Faults in standard operation, for example caused by impurities or other inhomogeneities in the starting material or by cooling material residues from previous extrusion processes, can lead to an uneven load distribution of the torque to the output shafts. The system or process requires the extruder screws to be at a defined axial distance from each other, which limits the outer diameter of the transmission output shafts. The torque density in the components is therefore high, even at rated load. If load peaks are added due to the aforementioned effects, overloading of the individual components can result. There is therefore a constant need to protect the components of the extruder system from overloading during standard operation.

[0004] EP 2939943 A1 discloses an electronic control system for protecting a system from overload. Torque is measured at the output shaft of the drive unit. If a torque limit, a torque gradient limit, or unacceptable high vibration is detected, the switchable connection between the motor and the drive unit is disconnected, and the motor speed is reduced via a frequency converter. EP 3 378 624 A1 describes a safety coupling with two coupling halves, with a shear pin arranged between the two coupling halves. In the event of overload, the shear pin forms a predetermined break point, shearing and thereby interrupting the transmitted torque. The shear pin can be replaced, and the safety coupling operates again. However, the safety coupling requires a certain radial mounting space, which is typically not provided due to the axial distance defined between them, especially in the case of twin-screw extruders. WO 2010 / 109486 A1 describes a coupling adapter for connecting a drive shaft to an extruder shaft, wherein the adapter has a weakened region to cut off upon reaching a predetermined torque. The safety connector described in DE 20 2019 106 047 U1 should also be mentioned. Summary of the Invention

[0005] The object of this invention is to disclose measures that can provide connecting elements for twin-screw extruders considering a limited axial distance.

[0006] This objective is achieved by a connecting element having the features of claim 1. Preferred improvements are specified in the dependent claims and the description below, and in each case may represent an aspect of the invention individually or in combination. If one feature is presented in combination with another feature, this is only for the purpose of simplifying the description of the invention and is in no way intended to imply that the feature could not be a development of the invention without the other features.

[0007] One embodiment relates to a coupling element for each drive unit connecting an extruder screw to a twin-screw extruder, the coupling element comprising two receiving bushings connected to each other in a coupling region, wherein a first receiving bushing is provided for receiving the shaft end of the drive unit, and a second receiving bushing is used for receiving one of the extruder screws. Under torsional loads, the coupling region has a reduced breaking moment relative to adjacent structural regions of the receiving bushings. In particular, it can be provided that the coupling region has a plurality of circumferentially distributed and radially extending holes or circumferentially extending welds, wherein the reduced breaking moment is indirectly applied via the holes or welds.

[0008] The receiving bushings are arranged coaxially with each other and are preferably cylindrical with a profile on their inner surface for transmitting torque between the receiving bushing and the drive unit on the one hand, and between the receiving bushing and the extruder screw on the other hand.

[0009] The drive unit may include a drive motor and a gear ratio stage or transmission. Power splitting is typically performed via the transmission. Upstream of the transmission, a belt drive may also be connected between the motor and the transmission to achieve a larger gear ratio. The drive unit can be used to distribute or split the torque provided between the two extruder screws. Preferably, the torque is evenly distributed between the extruder screws. Each shaft end of the drive unit is assigned to a specific output shaft of the drive unit.

[0010] The connecting region forms a transition between the two receiving bushings. Due to the connecting region, the two receiving bushings are designed as a single component, i.e., a single piece. This does not affect the fact that the two receiving bushings can exist as two separate workpieces, separate from each other, during the production process. The connecting region typically includes the same material as the adjacent structural regions of the receiving bushings, for example, in embodiments with multiple circumferentially distributed and radially extending holes. In embodiments with circumferentially extending welds, the connecting region may also include the material of the weld.

[0011] During standard operation of a twin-screw extruder, torsional loads are generated due to the driving torque applied by the drive unit on the one hand and the resistance resisted by the extruder screw on the other hand due to the extruded material to be processed.

[0012] An embodiment of a connecting element having circumferentially distributed and radially extending holes or circumferentially extending welds forms a predetermined fracture point that fails under overload conditions, thereby protecting other system components. However, no additional shearing elements, such as shear pins, are used; instead, the connecting element itself has a weakened region. This region is designed in such a way that it can be modified with minimal adjustments, allowing the defined fracture moment to be achieved through calculation.

[0013] Implementations of coupling elements with circumferentially distributed and radially extending holes or circumferentially extending welds enable more compact constructions than conventional designs allow. In particular, no additional axial mounting space is required compared to conventional designs. The coupling elements can also be used to retrofit existing systems because the required mounting space and connection dimensions can be selected to be the same.

[0014] In a preferred improvement, the connecting region forms a reduced cross-section compared to the adjacent structural region due to the hole or weld. This allows a predetermined fracture point to be inserted into the connecting region. Specifically, the connecting region can be configured to be designed relative to a fracture moment, which is achieved through the hole diameter and the circumferential distance between the holes and / or the inner and outer diameters (especially the weld).

[0015] In embodiments with circumferentially distributed and radially extending holes, preferably, the circumferential distance between the holes is at most 1.5 times the hole diameter, and particularly at most 1.2 times. This ensures that defined crack propagation occurs in the fracture plane because the torsional shear stress acts at an angle of 45°.

[0016] This objective is also achieved by a twin-screw extruder having 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 connecting element, each as claimed in any of the preceding claims. Attached Figure Description

[0017] The invention will now be explained by way of example based on preferred exemplary embodiments and with reference to the accompanying drawings, wherein the features presented below may individually or in combination represent an aspect of the invention in each case. In the drawings: Figure 1 : This shows a perspective and partially exploded view of a twin-screw extruder; Figure 2a ) and 2b): show perspective and cross-sectional views of the first embodiment of the connecting element, and Figure 3a 3a) and 3b) show perspective and cross-sectional views of a second embodiment of the connecting element. Detailed Implementation

[0018] Figure 1 The twin-screw extruder 2 is shown in perspective and partially exploded view. The twin-screw extruder 2 structurally includes a drive unit 12, which in this case consists of a motor unit 4 and a transmission unit 6. The transmission unit 6 can transmit the drive torque of the motor unit 4 to two output shafts 8 arranged parallel to each other in a power-splitting manner. In each case, the first extrusion screw 14 and the second extrusion screw 16 are connected to the two output shafts 8 via a coupling element 10. Depending on the output shafts 8, the two extrusion screws 14, 16 are spaced a small axial distance from each other. However, other components of the system may include cylinders, a filling hopper, a heating belt, nozzles, and a machine frame (not shown).

[0019] Figures 2 and 3 illustrate two embodiments of the coupling element 10 according to the invention in perspective and cross-sectional views a) and b). In each embodiment, the coupling element 10 includes two receiving bushings 18, 20 connected to each other in a connecting region 22. The two receiving bushings 18, 20 are preferably designed identically and are placed concentrically to each other and connected to each other via the connecting region 22. The first receiving bushing 18 is provided for receiving the shaft end of the drive unit 12, and the second receiving bushing 20 is used for receiving one of the extruder screws 14, 16. Here, the inner circumference of each receiving bushing 18, 20 forms longitudinal teeth that can form a form-fit connection with the corresponding longitudinal teeth 30 of the drive shaft of the drive unit 12 and the extruder screws 14, 16 for torque transmission. The connecting region 22 has a plurality of circumferentially distributed and radially extending holes 24 – see Figure 2a ) and 2b) - or circumferentially extended welds 26 - see Figure 3a (3b) and (3c). In any case, under torsional loads, the connecting region has a reduced breaking moment compared to the adjacent structural region 28 of the receiving bushings 18, 20.

[0020] exist Figure 2b )and Figure 3b As can be seen in the cross-sectional view of the weld 26, the connecting region 22 has a smaller cross-section compared to the adjacent structural region 28 due to the holes 24 or weld 26. The connecting region 22 is designed relative to the breaking moment, which is achieved by the hole diameter and the circumferential distance between the holes 24, as well as the inner and outer diameters of the weld 26. As shown here, preferably, the radial dimension of the connecting region does not exceed the radial dimension of the interconnected receiving bushings. The circumferential distance between the holes 24 is preferably at most 1.5 times the hole diameter, and particularly at most 1.2 times.

[0021] List of reference numerals 2. Twin-screw extruder 4 motor units 6. Transmission Unit 8 Output shafts 10 Connecting elements 12 drive units 14 Extruder screw 16 Extruder screw 18 Receiving bushing 20 Receiving bushing 22 Connecting Area 24 holes 26 Welds 28 Structural Regions 30 longitudinal teeth

Claims

1. A connecting element (10) for connecting an extruder screw (14, 16) to a drive unit (12) of a twin-screw extruder (2) for each connecting element, said connecting element comprising: Two receiving bushings (18, 20) are connected to each other in a connecting area (22), wherein the first receiving bushing (18) is configured to receive the shaft end of the drive unit (12), and the second receiving bushing (20) is configured to receive one of the extruder screws (14, 16). Its features In the case of torsional load, the connecting region (22) has a reduced breaking moment relative to the adjacent structural region (28) of the receiving bushing (18, 20).

2. The connecting element (10) according to claim 1, characterized in that, The connection area (22) has a plurality of circumferentially distributed and radially extending holes (24) or circumferentially extending welds (26).

3. The connecting element (10) according to claim 2, characterized in that, Due to the hole (24) or the weld (26), the connecting region (22) forms a smaller cross-section compared to the adjacent structural region (28).

4. The connecting element (10) according to any one of claims 1 to 3, characterized in that, The connection area (22) is designed relative to the fracture moment, which is achieved via the hole diameter and the circumferential distance between the holes (24) and / or particularly the inner and outer diameters of the weld.

5. The connecting element (10) according to any one of claims 1 to 4, characterized in that, The breaking moment is in the range of 11,000 Nm and 14,000 Nm.

6. The connecting element (10) according to any one of claims 1 to 5, characterized in that, The circumferential distance between the holes (24) is at most 1.5 times the diameter of the hole, and in particular at most 1.2 times.

7. The connecting element (10) according to any one of claims 1 to 6, characterized in that, The radial dimension of the connection area (22) does not exceed the radial dimension of the interconnected receiving bushings (18, 20).

8. A twin-screw extruder (2) having a drive unit (12) and two extruder screws (14, 16) driven by the drive unit (12) in a power split manner, characterized in that, The drive unit is connected to the extruder screws (14, 16) via a connecting element (10) for each extruder screw, the connecting element being the connecting element as described in any of the preceding claims.

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