Rotary grinding mill

Abstract

The present application relates to a rotary grinding mill. The rotary grinding mill comprises a mill housing, a drive shaft rotatably arranged within the mill housing and a mill drive coupled to the drive shaft at a first end thereof in order to drive the drive shaft in rotation. A plurality of grinding rotors are arranged on the drive shaft, the grinding rotors being spaced apart from each other along a length of the drive shaft. At least one torque sensor is arranged on the drive shaft on both sides of each grinding rotor, each torque sensor measuring a torque exerted on the drive shaft during a rotation thereof. Each torque sensor is electrically connected to a control unit of the rotary grinding mill, the control unit being configured to calculate a power dissipated by each of the grinding rotors to a grinding mix contained within the mill housing based on the difference of the measured torque exerted on the drive shaft on both sides of each of the grinding rotors.

Description

[0001] Rotary grinding mill

[0002] Technical Field

[0003] The invention relates to a rotary grinding mill, preferably for grinding mineral ore particles, which allows to monitor the power dissipated from a plurality of grinding rotors to a grinding mix comprising grinding media as well as particulate mineral ore material to be ground.

[0004] Background Art

[0005] Rotary grinding mills, specifically rotary grinding mills for grinding mineral ore particles are known in the art. Such mills typically comprise a usually cylindrical mill housing, which may be arranged in a vertical or horizontal direction. A drive shaft is rotatably arranged within the mill body. A plurality of grinding rotors are connected to the drive shaft. Particulate mineral ore material as well a grinding media are filled into the mill body through an inlet opening, which is usually situated at a first end of the mill body. In the case of a vertical arrangement of the mill body, the inlet opening is typically located at a lower end of the mill body. The particulate mineral ore material and the grinding media form a grinding mix. The rotation of the grinding rotors induces a circular flow of the particular mineral ore material and grinding media within the mill body. This leads to attrition between the grinding media and the particulate mineral ore material which brakes up the latter into smaller mineral particles. The ground mineral particles exit the mill housing through an outlet opening located at a second end of the mill body. In the case of a vertical arrangement of the mill body, the outlet opening is typically located at an upper end of the mill body. Direct contact of the grinding material on the grinding rotors produces a high wear on the grinding rotors, which makes it necessary to replace the grinding rotors when they are worn down. However, as the mill housing typically comprises relatively thick metal walls and the rotary grinding mill is usually filled with the grinding mix, the wear status of the grinding rotors may not so easily be determined. Today, rotary grinding mills for grinding mineral ore particles are thus stopped at regular intervals and their drive shaft removed for inspection and replacement of grinding rotors. However, due to the size and weight of the drive shaft, this operation necessitates a lot of time and man power, thus leading to a relatively long down time of the rotary grinding mill and high costs. Further, if the intervals are not timed adequately, the grinding rotors are either replaced too late or too early. In the former case, the grinding efficiency is diminished until the replacement and in the latter case grinding rotors which would still allow a sufficient grinding efficiency are replaced. The selection of the right intervals is difficult, as grinding rotors may be subjected to different wear depending on their position along the drive shaft.

[0006] Thus, there exists the need for a rotary grinding mill which allows for a continuous monitoring of the status of the grinding rotors during operation of the rotary grinding mill.

[0007] Summary of the invention

[0008] In view of the above, it is thus the object of the present invention to provide a rotary grinding mill, especially for grinding mineral ore material, which allows for a continuous monitoring of the status of grinding rotors during operation of the rotary grinding mill.

[0009] The solution of the invention is specified by the features of claim 1. According to the invention, the rotary grinding mill comprises a mill housing, a drive shaft rotatably arranged within the mill housing and a mill drive coupled to the drive shaft at a first end thereof in order to drive the drive shaft in rotation. A plurality of grinding rotors are arranged on the drive shaft, the grinding rotors being spaced apart from each other along a length of the drive shaft. At least one torque sensor is arranged on the drive shaft on both sides of each grinding rotor, each torque sensor measuring a torque exerted on the drive shaft during a rotation thereof. Each torque sensor is electrically connected to a control unit of the rotary grinding mill, the control unit being configured to calculate a power dissipated by each of the grinding rotors to a grinding mix contained within the mill housing based on the difference of the measured torque exerted on the drive shaft on both sides of each of the grinding rotors.

[0010] By means of the calculation of the power dissipation to the grinding mix for each of the grinding rotors the efficiency of each of the grinding rotors in the milling process can be monitored. Worn grinding rotors usually have a smaller diameter than new grinding rotors e.g. due to material loss. Therefore, the circumference of a worn grinding rotor is smaller compared to a new grinding rotor, which leads to a decrease of its peripheral speed when the drive shaft is moving at a constant rotational speed. This results in a decrease of the power dispensated from the grinding rotor into the grinding mix. Hence, the measurement of the power dissipation may be used as an indicator on the wear status of a grinding rotor. A low power dissipation and hence a low efficiency of a grinding rotor therefore indicates that the corresponding grinding rotor is worn down and should be replaced. Hence, a replacement of grinding rotors may be performed exactly at a time point where at least one of the grinding rotors reaches a wear making its replacement necessary.

[0011] The power dissipated by a grinding rotor to the grinding mix is understood as the amount of power which is transferred from the grinding rotor into the grinding mix.

[0012] By using torque sensors arranged on both sides of a grinding rotor on the drive shaft the setup for monitoring the condition of the grinding rotors is simple and easy to implement, so that it may also be retrofitted to existing rotary grinding mills.

[0013] Preferably, the mill housing has a substantially cylindrical shape with a length axis and a circumferential mill wall. The mill wall thereby encloses an interior space. The length axis of the mill housing preferably is arranged in the vertical direction. Alternatively, however, the length axis of the mill housing may also be oriented in the horizontal direction. As is known in the art, the mill housing preferably comprises an inlet opening and an outlet opening. The inlet opening allows to introduce material, notably the particulate mineral ore material to be ground into the interior space of the mill housing. Concurrently, the outlet opening allows the removal of ground material from the interior space of the mill housing. In the case that the length axis of the mill housing is oriented in the vertical direction, the inlet opening preferably is located at a lower end of the mill housing and the outlet opening at an upper end thereof.

[0014] The mill housing preferably is made of a metal, especially of steel. Preferably, the mill housing comprises two half bodies which may be separated, for example in order to replace the drive shaft or the grinding rotors as well as for inspection of the interior space of the mill housing. In the case that the mill housing is cylindrical, the half bodies are preferably configured as half cylinders, one of which is preferably connected to an actuator means, in order to move this half cylinder away of the other half cylinder, preferably in a horizontal direction.

[0015] In the case of a vertical arrangement of the mill housing, the mill housing comprises at least a lower end face closing the interior space at the lower end of the mill housing. Further, an upper end face at least partially closing off the interior space at an upper end of the mill housing may be provided. Alternatively, the upper end of the mill housing may remain open.

[0016] Preferably, the rotary grinding mill according to the present invention is used for grinding particulate ore material. However, the rotary grinding mill could also be used to grind other material, such as for example grain.

[0017] Besides the material to be ground, a grinding media is also introduced into the interior space of the mill housing. The grinding media are preferably spherically shaped elements, preferably made of a ceramic material. Alternatively, the grinding media may also be made of a metal, alloy or polymer material. A rotation of the grinding rotors induces a circular flow of the material to be ground and the grinding media within the mill body leads to attrition between the grinding media and the material to be ground which brakes up the latter into smaller particles. The mixture of material to be ground and grinding media is also references as "grinding mix" in the present application. It is noted that in the preferred case where particulate mineral ore material is to be ground with a rotary grinding mill according to the present invention, the material to be ground is usually introduced into the rotary grinding mill as a slurry comprising the particulate mineral ore material as well as process water.

[0018] The drive shaft is preferably cylindrical, preferably a full cylinder with a length axis and an outer shell. The length axis of the drive shaft is preferably arranged to be congruent with the length axis of the mill housing, so that the drive shaft is arranged centrally within the interior space of the mill housing. The drive shaft may be supported in rotation by means of at least one bearing. In this case, the at least one bearing preferably is located in the area of the first end of the drive shaft, i.e. in the area of the end of the drive shaft where the drive shaft is coupled to the mill drive. In the case of a vertical arrangement of the mill housing, the at least one bearing is preferably arranged above the mill housing and supported by means of a scaffold. In this case, the drive shaft therefore is arranged in a hanging configuration within the interior space of the mill housing.

[0019] The mill drive comprises a motor, preferably an electric motor. The drive shaft may be directly coupled to an output of the motor, however, preferably, the drive shaft is coupled by means of a gear element to the motor. Provision of a gear element allows a reduction or increase of the rotation frequency of the drive shaft compared to the rotation frequency of the motor. Appropriate gear elements for rotary grinding mills are known in the art. In the case of a vertical arrangement of the mill body, the mill drive preferably is arranged vertically above the mill housing. In this case, the mill drive is preferably supported on a separate scaffold and not on the mill housing. Preferably, the drive shaft is supported only by the gear element without any further bearing. This simplifies the construction and maintenance of the grinding mill, as not separate bearing for the drive shaft is present.

[0020] The grinding rotors preferably include a disc shaped base element. Further, the grinding rotors may include further elements, such as protection elements, protective coatings and the like. For example, the grinding rotors may be configured in the shape of an impeller. The disc shaped base element preferably is made of a metal, such as steel, and preferably comprises a coating made of a polymer material. The term "plurality of grinding rotors" is understood to mean that the rotary grinding mill comprises two or more grinding rotors, such as three, four, five, six, seven, eight, nine, ten or more grinding rotors. The grinding rotors are spaced apart from each other along the length of the drive shaft. Thereby, the grinding rotors may be evenly spaced apart from each other. Alternatively, the grinding rotors may be unevenly spaced apart from each other. In this latter case, the drive shaft may include several zones, the grinding rotors of each zone being spaced apart from each other evenly, while this spacing varies from zone to zone.

[0021] All grinding rotors may have the same shape and dimensions. Preferably, however, the shape and dimensions of the grinding rotors varies, especially depending on the position of each specific grinding rotor along the length of the drive shaft. For example, grinding rotors positioned on an area of the driving shaft which lies in an area closer to the outlet opening of the mill housing may have a bigger diameter than grinding rotors lying closer to the inlet opening. In this case, the grinding rotors closer to the inlet opening may comprise protective elements, while grinding rotors closer to the outlet opening may lack protective elements.

[0022] Preferably, the torque sensors are affixed on an outer shell of the drive shaft. Thereby, the torque sensors are arranged such that there is at least one torque sensor on the drive shaft on both sides of each of the grinding rotors. This means that, when seen along the length axis of the drive shaft, each grinding rotor is flanked with at least one torque sensor. With other words, the arrangement along the length axis of the drive shaft from the first end to a second end of the drive shaft is always (torque sensor - grinding rotor - torque sensor). Thereby, preferably, one torque sensor may be arranged on the drive shaft between two grinding rotors and its measured torque be used for calculating the power dissemination of both grinding rotors. In this case, the arrangement is (torque sensor - (grinding rotor - torque sensor)n; n being the total number of grinding rotors present on the drive shaft. The minimal number s of torque sensors present on the drive shaft thereby is s = (n+ 1). For example, if 8 grinding rotors are present on the drive shaft, the minimal amount of torque sensors is 9. Preferably, only one torque sensor is arranged on the drive shaft on both sides of each grinding rotor. The power dissipated by a grinding rotor to the grinding mix is the amount of power the grinding rotor inputs into the grinding mix, i.e. the mixture of material to be ground and the grinding media. If the power dissipated by a specific grinding rotor drops below a predetermined value, the corresponding grinding rotor exhibits a degree of wear which makes its replacement necessary, as otherwise the overall grinding efficiency of the rotary grinding mill is insufficient.

[0023] The control unit preferably comprises at least one microchip or microcontroller. Preferably, the control unit further comprises at least one volatile or non-volatile memory. The control unit preferably comprises an output means, such as e.g. a display or monitor on which the calculated power dissipation of each of the grinding rotors may be displayed. Further, the control unit may also comprise at least one interface for data exchange with further electronic devices, such as e.g. a connector for a databus, an Ethernet connector, a WiFi or Bluetooth® module. This allows the transmission of the calculated power dissipation of each grinding rotor to an external device, such as a mobile device, notebook or the like. Preferably, however, the control unit is connected to a databus of the grinding mill, such as to allow the transmission of the calculated power dissipation of each grinding rotor to a central control of the rotary grinding mill.

[0024] The control unit is electrically connected to the mill drive in order to control the electric motor of the mill drive, especially in order to set a defined rotation speed of the electric motor, and preferably to receive data from the electric motor, especially data about the rotation speed and / or the output power thereof.

[0025] The control unit calculates the dissipated power of each of the grinding rotors by subtracting the measured torque below a grinding rotor of the measured torque above the same grinding rotor when viewed along the length axis starting from the first end of the drive shaft. By multiplying this torque difference with the rotation speed of the drive shaft, the power dissipation of this grinding rotor is calculated. The calculation of the power dissipation P of a specific grinding rotor k is hence calculated according to below formula [I]: where

[0026] (j^shaft is the angular rotation speed of the drive shaft [s’1];

[0027] Mk is the torque measured above the grinding rotor k [Nm];

[0028] Mk+i is the torque measured below the grinding rotor k [Nm];

[0029] Pk is the dissipated power of grinding rotor k [kW],

[0030] The angular rotation speed of the drive shaft is preferably measured by means of an appropriate sensor which is connected to the control unit. Alternatively, the angular rotation speed of the drive shaft may be calculated based on the rotation speed of the electric motor of the mill drive and the gear ratio of the gear used in the mill drive. This calculation may be carried out according to formula [II] given below: where co is the angular rotation speed of the electric motor [s’1]; k is the gear ratio.

[0031] The angular rotation speed of the electric motor may be calculated based on the rotation speed of the electric motor according to formula [III] given below: where n is the rotation speed of the electric motor [rpm].

[0032] Further, based on the uppermost torque sensor, i.e. the torque sensor arranged above the uppermost grinding rotor and hence closest to the first end of the drive shaft, the control unit may further calculate the total shaft power according to formula [IV] as given below: where

[0033] Pshaft is the total shaft power [kW];

[0034] Mi is the measured torque of the uppermost torque sensor [Nm];

[0035] Pshaft is the angular rotation speed of the drive shaft [s’1].

[0036] Preferably, the control unit is further configured to calculate a wear of each of the grinding rotors based on the calculated dissipated power. Preferably, this wear is calculated and most preferably output in a percentage value, i.e. a value which gives an indication of the degree of wear of a specific grinding rotor. Alternatively, the control unit may also convert the calculated wear into an integrity value of the grinding rotors, e.g. such that a value of 100% indicates that a grinding rotor exhibits no or almost no wear and a value of 0% indicates that a grinding rotor has reached its maximal tolerable wear.

[0037] In order to calculate the wear of each of the grinding rotors by the control unit, the power dissipation of each grinding rotor as a percentage of the total drive shaft power input has to be measured in an initial calibration run when all grinding rotors are new. This percentage value is then stored for each of the grinding rotors in a non-volatile memory of the control unit as reference value. This calibration run has to be repeated in the case that the arrangement of the grinding rotors on the drive shaft is altered or if other grinding media is used (as the power dissipation of the grinding rotors changes depending on the grinding media used).

[0038] The wear condition of each grinding rotor may then be calculated by the control unit by calculating the current power dissipation of each rotor and determining the percentage of this power dissipation in relation to the total power input of the drive shaft. This percentage value for each grinding rotor is then subtracted from the reference value for each grinding rotor to determine the wear of each of the grinding rotors. Alternatively, is also possible to determine the wear of a grinding disc based on a proportionality coefficient for each of the grinding rotors. In essence, the torque experienced for a grinding rotor in the grinding mix is

[0039] M — c x a>ghajrt[V] where c is the proportionality coefficient;

[0040] (j^shaft is the angular rotation speed of the drive shaft [s’1].

[0041] Hence, the proportionality coefficient may be calculated as where

[0042] M is the torque experienced by the individual grinding rotor, which may be calculated based on the measurements of the torque sensors as elaborated above.

[0043] The proportionality coefficient depends on the fill level of the grinding media in the rotary grinding mill, the flow parameters of the grinding mix as well as the degree of wear of the grinding disc. Hence, when the fill level of the grinding media in the rotary grinding mill and the flow parameters of the grinding mix are known, the degree of wear may be calculated based on the proportionality coefficient.

[0044] The fill level of the grinding media is preferably determined by means of a weight measurement of the mill body. As the weight of the mill body, the weight of the grinding media and the specific average weight of the material to be ground, particularly of the particulate mineral ore material to be ground, are known, the weight of the grinding media present inside the mill body may be calculated based on the weight measurement of the mill body. The fill level may subsequently be determined based on the volume of the mill body, the volume occupied by the drive shaft and the grinding rotors, the volume per weight of the grinding media and the average volume per weight of the material to be ground. This calculation may preferably be performed as follows in the case that particulate mineral ore material is to be ground by the rotary grinding mill: where

[0045] Mgm is the weight of the grinding media [kg];

[0046] Mmsis the weight of the mill shell [kg];

[0047] Vnis the net volume of the interior space of the mill shell [L];

[0048] Ssis the density of the slurry [kg*drrr3];

[0049] Swis the density of the process water [kg*drrr3];

[0050] Sgmis the density of the grinding media [kg*drrr3].

[0051] This fill level may further preferably be transformed into a percentage value of the net volume of the mill shell, for example to be displayed to an operator of the rotary grinding mill: 100

[0052] [VIII] where

[0053] Lgmis the fill level of grinding media [%];

[0054] Mgm is the weight of the grinding media [kg];

[0055] Vnis the net volume of the interior space of the mill shell [L];

[0056] BDgm is the bulk density of the grinding media [kg*dm-3].

[0057] Preferably, the weight measurement of the mill body is performed by means of at least one load cell arranged between the mill body and a support of the mill body. Preferably, the mill body is supported by a scaffold structure arranged on the outside of the mill body, wherein the mill body is supported by the scaffold structure by means of the at least one load cell, i.e. the at least one load cell is arranged between the scaffold structure and the mill body. In the case of a vertical arrangement of the mill body, the at least one load cell is preferably arranged in an upper half of the mill body, more preferably in an area of the top end of the mill body. Hence, the mill body is suspended from the scaffold structure rather than standing on a support.

[0058] Preferably, the weight measurement of the mill body is performed by four load cells arranged essentially at regular angular intervals one to another around the circumference of the mill body. Provision of a plurality of load cells allows to spread the total weight of the mill body and to hence use loads cells with a lower maximal capacity compared to the use of a single load cell.

[0059] As the mill body is fairly stiff, it is not guaranteed that the weight thereof is evenly distributed on all load cells present. Hence, the maximal capacity of each of the load cells is chosen to be at least 25% higher than the maximum expected weight of the fully loaded mill housing divided by the amount of load cells present. For example, if the mill housing is supported by four load cells, each of the load cells would be expected to bear a maximal load of 25% of the maximal weight of the fully loaded mill housing. In order to compensate for an uneven distribution of the weight of the mill housing, the load cells should then have a maximal capacity which is at least 31.25% of the maximal weight of the fully loaded mill housing. Preferably, in the case that the mill housing is weighted by four load cells, each load cell has a maximal capacity which corresponds to 33% of the maximal weight of the fully loaded mill housing.

[0060] Herein, the term fully loaded mill housing is understood to be the total weight of the mill housing and the grinding mixture when the interior space of the mill housing is completely filled with the grinding mix.

[0061] The at least one load cell is preferably electrically connected to the control unit, so that the control unit may calculate the fill level of the grinding mixture within the interior space of the mill housing based on the weight measured by the at least one load cell.

[0062] In an alternatively preferred embodiment, the fill level may also be calculated based on at least one reference table stored in a non-volatile memory of the control unit. Said at least one reference table preferably comprises reference values of the weight of the mill housing correlated to a fill level corresponding to the weight reference values. Use of at least one reference table allows for a fast and reliable determination of the fill level of the grinding mix. Preferably, the control unit comprises a multitude of reference tables, each reference table containing reference values for different types of particulate mineral ore materials which may be ground by the grinding mill and / or different amounts of grinding media used for the grinding operation of the grinding mill.

[0063] A person having skill in the art recognizes that the weight measurement and / or the fill level determination as disclosed above may also be used on a grinding mill with a drive shaft devoid of any torque sensors.

[0064] Preferably, the torque sensors are strain gauges, especially arranged in full Wheatstone bridge circuits.

[0065] Strain gauges are known in the art and are sensors which are able to convert a deformation into a change of electrical resistance which can be measured. Strain gauges usually comprise an insulating flexible backing which supports a metallic foil pattern. Once attached to an object, a deformation thereof leads to a deformation of the strain gauge, causing the electrical resistance of the strain gauge to change.

[0066] Full Wheatstone bridge circuits are known in the art. A Wheatstone bridge comprises four resistors of equal resistances connected and to end to form a square. Across one pair of diagonal corners of the circuit, an excitation voltage is applied and across the other pair, the output of the bridge is measured. In a full Wheatstone bridge circuit all four resistors are substituted by strain gauges.

[0067] For measuring the torque on the drive shaft, the strain gauges of the full Wheatstone bridge circuit are each arranged at a 45° angle relative to the length axis of the drive shaft on a shell thereof. By such an arrangement, when viewed from the side, two strain gauges are arranged on a first side relative to the length axis, one of these strain gauges being oriented at an angle of 45° and the other one at an angle of -45° relative to the length axis. The two other strain gauges are concurrently arranged on the other side of the length axis, one of these strain gauges being oriented at an angle of 45° and the other one at an angle of -45° relative to the length axis.

[0068] Upon rotation of the drive shaft, two of the strain gauges on one side of the length axis are compressed, while the two strain gauges on the other side of the length axis are stretched. Both the compression and stretching of the strain gauges induces a change of resistance in the strain gauges, which generates a voltage change of the excitation voltage which may be detected at the output of the bridge circuit.

[0069] Full Wheatstone bridge circuits provide a good sensitivity and are less sensible to temperature changes and their use hence greatly increases the reliability of the torque measurement.

[0070] Preferably, the drive shaft comprises a slip ring unit arranged at one end of the drive shaft, preferably a the first end of the drive shaft, the slip ring unit comprising a plurality of slip rings, each of the torque sensors being electrically connected to at least one slip ring and the slip ring unit being electrically connected to the control unit.

[0071] Provision of a slip ring unit allows a simple and reliable transfer of electrical signals from the torque sensors located on the rotatable drive shaft to the control unit, which is preferably not located on the drive shaft. Each slip ring of the slip ring units is in contact with a brush affixed on a stator element, the brushes slipping along the respective slip ring when the drive shaft is rotated, as is known in the art.

[0072] Preferably, the slip ring unit comprises a number of slip rings which is larger than the number of torque sensors, preferably by at least three additional slip rings. The additional slip rings may be used to provide a voltage, e.g. an excitation voltage, as well as a grounding to the torque sensors. The torque sensors may be connected to the voltage and grounding in a parallel wiring or in a serial wiring. The electrical connection between the torque sensors and the slip rings may be realized by means of isolated wires, isolated strands or the like.

[0073] The brushes of the stator are preferably connected to the control unit by means of isolated wires, isolated strands, a ribbon cable or the like. Preferably, the drive shaft comprises a shell with at least one channel running substantially parallel to a length axis of the drive shaft on the shell, wherein each torque sensor is connected to the respective at least one slip ring by means of at least one electrical cable arranged within the at least one channel.

[0074] By the provision of the at least one channel, the cables may be arranged therein in a protective manner. Preferably, the at least one channel is closed by means of at least one lid or by filling the at least one channel up with a resin or the like, in order to increase the protection the electric cables.

[0075] Preferably, shell of the drive shaft comprises more than one channel, especially two, three or four channels. In this case, the channels are preferably distributed around the circumference of the shell at regular angular positions, e.g. in the case of three channels, each of the channels is located at an angle of 120° to its two neighbouring channels.

[0076] Preferably, at least one signal amplifier is arranged in the electrical connection between each torque sensor and the control unit. This allows to amplify the signal generated by each torque sensor. Preferably, the amplifiers are further configured to convert the input signal received from the torque sensors, which is a voltage signal, into a current signal. I.e. the amplifiers comprise a V to mA converter. As voltage based signals are vulnerable to ambient conditions and disturbances as well as are not suitable for great distance transmissions, a conversion of the signal to a current signal allows for a more precise signal transmission over greater distances and hence increases the reliability and exactness of the calculations performed by the control unit.

[0077] Preferably, the drive shaft comprises at least one bending sensor arranged in the area of its first end. Provision of a first bending sensor allows to detect any bending stresses exerted on the drive shaft, which may indicate an irregularity or problem during the milling process.

[0078] In the case that the drive shaft includes a slip ring unit, the at least one bending sensor is preferably electrically connected to at least one slip ring thereof. Hence, the slip ring unit may be used to also transmit data from the at least one bending sensor preferably to the control unit. Preferably, the drive shaft comprises four bending sensors arranged at equal distances around the circumference of the shell of the drive shaft. This allows the detection of any bending stresses on the drive shaft in any possible direction.

[0079] Preferably, the control unit is further electrically connected to at least one additional sensor, said at least one additional sensor measuring at least the rotational speed of the drive shaft and / or the power transmitted from a motor of the mill drive to the drive shaft.

[0080] The data provided by the at least one additional sensor may be used by the control unit to calculate absolute values for the power dissipation of each of the grinding rotors to the grinding mix, e.g. based on the power transmitted from the motor to the drive shaft.

[0081] Preferably, the control unit comprises a non-volatile memory, wherein the control unit is configured to store the calculated dissipated power for each grinding rotor at pre-defined time intervals during operation of the rotary grinding mill.

[0082] This allows to build a database with which the changes of the power dissipation for each of the grinding rotors over time may be monitored. Such a database may e.g. allow to calculate an estimated remaining operating time for each grinding rotor before it must be exchanged for excessive wear.

[0083] The present application also relates to a method for monitoring an operation of a rotary grinding mill. In a first step of the method, a torque exerted on a drive shaft of the rotary grinding mill during a rotation of the drive shaft on both sides of at least one grinding rotor arranged on the drive shaft is measured by means of at least one torque sensor arranged on each side of the at least one grinding rotor. In a second step, a control unit of the rotary grinding mill calculates a power dissipated by the at least one grinding rotor to a grinding mix contained within a mill housing of the rotary grinding mill within which the drive shaft is rotatably arranged, the calculation being based on the difference of the measured torque exerted on the drive shaft on both sides of the at least one grinding rotor.

[0084] Based on this method, it is thus possible to monitor the power dissipation of the at least one grinding rotor in real time during the operation of the rotary grinding mill. Thereby, the dissipated power is an indication on the wear of the at least grinding rotor, as a grinding rotor exhibiting a high wear will dispense less energy to the grinding mix than a new grinding rotor.

[0085] The method is preferably carried out with a rotary grinding mill according to the above description. Preferably, the calculation of the power dissipated by the at least one grinding rotor to the grinding mix is calculated as described above, especially according to formulas [I] to [IV].

[0086] Preferably, the control unit further calculates a wear of each of the grinding rotors based on the calculated dissipated power. Preferably, the wear is calculated and output as a percentage value. I.e. 0% wear means that the respective grinding rotor is new and 100% wear indicates that the grinding rotor has reached its maximal tolerable wear and should be replaced. Alternatively, the control unit may also calculate and output indicating an integrity value of the grinding rotors, e.g. such that a value of 100% indicates that a grinding rotor exhibits no or almost no wear and a value of 0% indicates that a grinding rotor has reached its maximal tolerable wear.

[0087] Preferably, the control unit displays the dissipated power for the at least one grinding rotor on a display of the rotary grinding mill.

[0088] Other advantageous embodiments and combinations of features come out from the detailed description below and the entirety of the claims.

[0089] Brief description of the drawings

[0090] The drawings used to explain the embodiments show:

[0091] Fig. 1 shows a schematic view of an embodiment of a rotary grinding mill according to the present invention;

[0092] Fig. 2 shows a cross-section of the drive shaft according to the embodiment of the rotary grinding mill as shown in Fig. 1; Fig. 3 shows a schematic diagram of the connection between the torque sensors with the control unit;

[0093] Fig. 4 shows a second embodiment of a rotary grinding mill according to the present invention;

[0094] Fig. 5 shows an enlarged view of a torque sensor comprising four strain gauges arranged in a full Wheatstone bridge circuit;

[0095] Fig. 6 shows a wiring diagram of the full Wheatstone bridge circuit of Fig. 5;

[0096] Fig. 7 shows a schematic drawing of an embodiment of a weight measurement configuration for a rotary grinding mill, preferably for a rotary grinding mill according to the present invention.

[0097] In the figures, the same components are given the same reference symbols.

[0098] Preferred embodiments

[0099] Fig. 1 shows a schematic view of an embodiment of a rotary grinding mill 1 according to the present invention. The rotary grinding mill 1 comprises a mill housing 2, which is shown in a partially cut-away view. The mill housing 2 has a substantially cylindrical shape with a closed bottom face and an open upper face. The mill housing 2 includes a central axis L as well as an inlet opening 3 close to the bottom face and an outlet opening 4 close to the upper face. The mill housing 2 encloses an open space 5 into which grinding media as well as material to be ground may be filled, i.e. through the inlet opening 3. The grinding media as well as the material to be ground thereby form a grinding mix. Preferably, the material to be ground is particulate mineral ore material, preferably in the form of a slurry comprising the particulate mineral ore material as well as process water.

[0100] The rotary grinding mill 1 further comprises a drive shaft 6 rotatably arranged within the mill housing 2. The drive shaft 6 is cylindrical and has a central axis which coincides with the central axis L of the mill housing 2. The central axis of the drive shaft 6 is simultaneously a length axis of the drive shaft 6. The drive shaft 6 has a connection flange 8 at a first end thereof, which is connected to a mill drive 9. The drive shaft 6 may be driven in rotation by means of the mill drive 9. The mill drive 9 includes a motor, preferably an electric motor, as well as a gear.

[0101] A plurality of grinding rotors 10.1 - 10.n are arranged on the drive shaft 6. The grinding rotors 10.1 - 10. n are arranged spaced from each other along the length of the drive shaft 6. When the drive shaft 6 is driven in rotation by means of the mill drive 9, the grinding rotors 10.1 - 10.n are rotated. The rotation movement of the grinding rotors 10.1 - 10. n is transmitted to the grinding mix. By this movement, the grinding media collide with the particulate material, said collisions braking the particulate material up to smaller particles.

[0102] On each side of the grinding rotors 10.1 - 10. n along the length axis of the drive shaft 6, a torque sensor 11.1 - 11.m is arranged on the drive shaft 6. As such, each grinding rotor 10.1 - 10. n is flanked by a torque sensor 11.1 - 11.m. The drive shaft 6 includes at least one more torque sensor 11.1 - 11.m than the number of grinding rotors 10.1 - 10. n. This means that m = n+ 1 in the embodiment shown.

[0103] The torque sensors 11.1 - 11. m are affixed to the drive shaft 6 within a channel 7 running along a shell of the drive shaft 6 along its entire length. The torque sensors 11.1 - 11.m are arranged to measure a torque exerted on the drive shaft 6 in a direction perpendicular to the length axis L of the drive shaft 6. All torque sensors 11.1 - 11.m are electrically connected to a slip ring of a slip ring unit 13 by means of electric cables arranged along the channel 7. A stator of the slip ring unit 13 is further in electrical connection with a control unit 15 by means of electric cabling 14.

[0104] The control unit 15 is configured to calculate the power dissipated to the grinding mix contained within the mill housing 2 by each grinding rotor 10.1 - 10.n based on the difference of the torque measured by the torque sensors 11.1 - 11.m arranged on both sides of each of the grinding rotors 10.1 - 10. n. For example, for the first grinding rotor 10.1, the control unit 15 calculates the dissipated power of this first grinding rotor 10.1 based on the difference of the first torque sensor 11.1 and the second torque sensor 11.2 flanking the first grinding rotor. Based on the dissipated power for each of the grinding rotors 10.1 - 10.n to the grinding mix, the wear of each of the grinding rotors 10.1 - 10.n may be further calculated by the control unit 15.

[0105] Fig. 2 shows a cross-section of the drive shaft 6 according to the embodiment of the rotary grinding mill 1 as shown in Fig. 1. In this figure, the arrangement of the torque sensor 11.m within the channel 7.1 may readily be seen. It is noted that the drive shaft 6 includes three channels 7.1 - 7.3 on its shell 17. The channels 7.1 - 7.3 are thereby spaced apart from each other at regular angular intervals, here at angular intervals of 120°. The torque sensor 11.m is arranged within the channel 7.1 such as to be able to measure a torque exerted on the drive shaft 6 in a direction perpendicular to the length axis L, as indicated by the double arrow. Next to the torque sensor 11.m, electric cables connecting the torque sensors 11.1 - 11.m to the slip ring unit 13 are arranged within a cable duct 16. In order to protect the torque sensor 11.m and the cable duct 16 from mechanical damages by collisions with the grinding media and the particulate material, the channels 7.1 - 7.3 may be filled with a resin or closed by means of a cover, e.g. a steel lid (not shown).

[0106] Fig. 3 shows a schematic diagram of the connection between the torque sensors 11.1 - 11.m with the control unit 15. As shown in the figure, each of the torque sensors 11.1 - 11.m are connected to a respective signal amplifier 17.1 - 17.m, which amplifies the electric signal from the torque sensors 11.1 - 11.m and preferably converts the signal from a voltage signal to a current signal. The signal amplifiers 17.1 - 17. m are electrically connected to the slip ring unit 13, which allows the transfer of the electric signal from the rotating drive shaft 6 to the static control unit by means of a multitude of slip rings on which static brushes are running in a known manner. The slip ring unit 13 is itself electrically connected to the control unit 15 by means of electric wiring 14. Further depicted in the figure are the grinding rotors 10.1 - 10. n, of which one grinding rotor 10.1 - 10. n is arranged between each pair of torque sensors 11.1 - 11.m.

[0107] Fig. 4 shows a second embodiment of a rotary grinding mill 1 according to the present invention. The second embodiment is substantially similar to the first embodiment as shown in Fig. 1. In the second embodiment, a bending sensor 18 is arranged on the shaft in the area of its first end. Further, the mill drive comprises an additional sensor 19 with which the rotation speed of the drive shaft 6 and / or the power output of the mill drive 9 may be measured. Both the bending sensor 18 and the additional sensor 19 are connected to the control unit 15, preferably by electric wiring, so that the measurement signals of the bending sensor 18 and / or of the additional sensor 19 may be transferred to the control unit 15.

[0108] Fig. 5 shows an enlarged view of a torque sensor 11 comprising four strain gauges 12.1 - 12.4 arranged in a full Wheatstone bridge circuit. The torque sensor 11 is located between two grinding rotors 10.k, 10.1 which could be located anywhere along the length axis L of the drive shaft 6. As may be seen on this figure, a first strain gauge 12.1 and a second strain gauge 12.2 are located on one side of the length axis L on the shell of the drive shaft 6, while a third strain gauge 12.3 and a fourth strain gauge 12.4 are located on a second side of the length axis L. The strain gauges 12.1 - 12.4 are arranged to each be oriented at an angle of 45° relative to the length axis L, whereby the strain gauges 12.1, 12.2; 12.3, 12.4 on each side of the length axis L are at an angle of 90° relative to each other. When the drive shaft 6 is rotated (dashed arrow) the first strain gauge 12.1 and the fourth strain gauge 12.4 are compressed and the second strain gauge 12.2 and the third strain gauge 12.3 are being stretched by the torque exerted on the shell of the drive shaft 6 by the rotation.

[0109] Fig. 6 shows a wiring diagram of the full Wheatstone bridge circuit of Fig. 5. Uo is the excitation voltage and UDis the measurement or output voltage produced when the drive shaft 6 is rotated. Ri, R2, R3 and R4 are the resistances of the four strain gauges 12.1 - 12.4 while RD is the change of resistance experienced by the four strain gauges 12.1 - 12.4 when the drive shaft 6 is rotated. The output voltage UD may be calculated as: where R is R = (R1 + R2 + R3 + 4).

[0110] The voltage signal UD is transmitted to the signal amplifier, where the signal is amplified and preferably converted to a current signal. Fig. 7 shows a schematic drawing of an embodiment of a weight measurement configuration for a rotary grinding mill 1, preferably for a rotary grinding mill 1 according to the present invention. For reasons of simplicity, the drive shaft 6 and the mill drive 9 have been omitted in this figure. As may be seen, the mill housing 2 is connected to two suspension elements 20.1, 20.2 in the embodiment shown. Each suspension element 20.1, 20.2 is supported by two load cells 21.1, 2.1, 21.3, 21.4, respectively. The load cells 21.1, 2.1, 21.3, 21.4 themselves are arranged on a scaffold structure 22, which is represented in a simplified manner in this figure. As may be recognized, the two suspension elements 20.1, 20.1 are connected to the mill housing 2 in an upper half thereof, hence leading to a hanging suspension of the mill housing 2 on the scaffold structure 22. Thereby, a bottom end of the mill housing 2 is spaced apart from a ground on which the scaffold structure 22 resides. Hence, the entire weight of the mill housing 2 and of a grinding mixture filled into the mill housing 2 resides entirely on the load cells 21.1, 2.1, 21.3, 21.4. This allows the load cells 21.1, 2.1, 21.3, 21.4 to measure the weight of the mill housing 2. A weighing signal generated by the load cells 21.1, 2.1, 21.3, 21.4 is transmitted to the control unit 15 of the rotary grinding mill 1 by means of electric cables or wires (represented as lines). This allows the control unit 15 to calculate the weight of the mill housing 2 with the grinding mixture filled therein and to use such a weight e.g. to determine a fill level of the grinding mixture within the mill housing 2. This fill level may then for example be used to determine a wear of the grinding rotors in a rotary grinding mill 1 according to the present invention. Of course, as a person having skill in the art will recognize, the weighing arrangement of the embodiment shown may also be used in connection with any other rotary grinding mill, i.e. a rotary grinding mill not having any torque sensors arranged on the drive shaft.

Claims

AMENDED CLAIMS received by the International Bureau on 13 February 2026 (13.02.2026)1. A rotary grinding mill comprising: a) a mill housing; b) a drive shaft rotatably arranged within the mill housing; c) a mill drive coupled to the drive shaft at a first end thereof in order to drive the drive shaft in rotation; d) a plurality of grinding rotors arranged on the drive shaft, the grinding rotors being spaced apart from each other along a length of the drive shaft; characterized in that at least one torque sensor is arranged on the drive shaft on both sides of each grinding rotor, each torque sensor measuring a torque exerted on the drive shaft during a rotation thereof, wherein each torque sensor is electrically connected to a control unit of the rotary grinding mill, the control unit being configured to calculate a power dissipated by each of the grinding rotors to a grinding mix contained within the mill housing based on the difference of the measured torque exerted on the drive shaft on both sides of each of the grinding rotors.

2. The rotary grinding mill according to claim 1, characterized in that the control unit is further configured to calculate a wear of each of the grinding rotors based on the calculated dissipated power.

3. The rotary grinding mill according to any of claims 1 to 2, characterized in that the torque sensors are strain gauges, preferably arranged in full Wheatstone bridge circuits.

4. The rotary grinding mill according to any of claims 1 to 3, characterized in the drive shaft comprises a slip ring unit arranged at one end of the drive shaft, preferably athe first end of the drive shaft, the slip ring unit comprising a plurality of slip rings, each of the torque sensors being electrically connected to at least one slip ring and the slip ring unit being electrically connected to the control unit.

5. The rotary grinding mill according to claim 4, characterized in that the drive shaft comprises a shell with at least one channel running substantially parallel to a length axis of the drive shaft on the shell, wherein each torque sensor is connected to the respective at least one slip ring by means of at least one electrical cable arranged within the at least one channel.

6. The rotary grinding mill according to any of claims 1 to 5, characterized in that at least one signal amplifier is arranged in the electrical connection between each torque sensor and the control unit.

7. The rotary grinding mill according to any of claims 1 to 6, characterized in that the drive shaft comprises at least one bending sensor arranged in the area of its first end.

8. The rotary grinding mill according to any of claims 1 to 7, characterized in that the control unit is further electrically connected to at least one additional sensor, said at least one additional sensor measuring at least the rotational speed of the drive shaft and / or the power transmitted from a motor of the mill drive to the drive shaft.

9. The rotary grinding mill according to any of claims 1 to 8, characterized in that the control unit comprises a non-volatile memory, wherein the control unit is configured to store the calculated dissipated power for each grinding rotor at pre-defined time intervals during operation of the rotary grinding mill.

10. A method for monitoring an operation of a rotary grinding mill according to any of claims 1 to 9, comprising the steps of: a) measuring a torque exerted on a drive shaft of the rotary grinding mill during a rotation of the drive shaft on both sides of at least one grinding rotor arranged onthe drive shaft by means of at least one torque sensor arranged on each side of the at least one grinding rotor; and b) calculating, by a control unit of the rotary grinding mill, a power dissipated by the at least one grinding rotor to a grinding mix contained within a mill housing of the rotary grinding mill within which the drive shaft is rotatably arranged, the calculation being based on the difference of the measured torque exerted on the drive shaft on both sides of the at least one grinding rotor.

11. The method according to claim 10, characterized in that the control unit further calculates a wear of each of the grinding rotors based on the calculated dissipated power.

12. The method according to any of claims 10 or 11, characterized in that the control unit displays the dissipated power for the at least one grinding rotor on a display of the rotary grinding mill.

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