METHOD AND DEVICE FOR RELEASING A STUCK LOAD FROM THE INSIDE OF A GRINDING PIPE OF A PIPE MILL

Description

[0001] The invention relates to a method and a device for releasing a stuck load from the inside of a grinding tube of a tube mill. Furthermore, the invention relates to a tube mill.

[0002] Tube mills are primarily used for grinding materials such as ores. It is not uncommon for the operation of a tube mill to be interrupted for an extended period of time. During this time, the tube mill is idle. During idle time, the material in the grinding tube can solidify and adhere to the inner wall of the grinding tube. Such solidified material is referred to as a frozen charge.

[0003] If the tube mill is put back into operation after a long period of downtime, there is a risk that the stuck solution will detach from the grinding tube at a great height (e.g. after half a turn or after a rotation of approximately Phi=160° of the grinding tube), fall down and cause considerable damage to the tube mill when it subsequently hits the inside of the grinding tube.

[0004] Therefore, devices exist that detect the presence of the stuck load, as described in DE 35 28 409 A1.

[0005] EP 2 353 724 B1 proposes a method for releasing a stuck load from the inner wall of a grinding tube, wherein the grinding tube is abruptly braked at least once at a predetermined angle of rotation.

[0006] A method for releasing a stuck load is disclosed in WO 2011 / 089067 A1.

[0007] The object of the invention is to operate tube mills without damage caused by a stuck load.

[0008] This object is achieved by a method according to claim 1.

[0009] Furthermore, the object is achieved by means of a device according to claim 10 and a tube mill according to claim 15.

[0010] To release the stuck load from the inner wall, it is proposed to apply a disturbance, for example in the form of a vibration, to the rotational movement of the grinding tube. A motor current is provided to move the vessel.

[0011] In other words, a disturbance, particularly a vibration, is to be imposed on the motor current, particularly one that is adapted to the component structure. The disturbance can be of any frequency, both harmonic and aharmonic, and both periodic and non-periodic. The disturbance can also be imposed as a pulse.

[0012] Preferably, the disturbance continues until the stuck charge has detached from the inner wall of the vessel.

[0013] The disturbance can take the form of a periodic or non-periodic oscillation, repeated force impulses, repeated abrupt deceleration of the rotational movement, and / or repeated force impulses in the direction of rotation or perpendicular to the surface of the vessel. The force impulses are preferably designed as abrupt increases in torque and / or speed. Mechanical disturbances, for example force impulses on the surface of the vessel, are preferably applied to the vessel using a mechanical disturbance element or a mechanical excitation unit.

[0014] Advantageously, a recurring disturbance can be caused by a mechanical effect on the vessel and thus on the (stuck) load.

[0015] The mechanical disturbance can be effected by a vibrator, which is preferably connected directly to the vessel. The mechanical action on the vessel or another element of the industrial plant is effected by means of a disturbance element. The disturbance element is preferably connected to a control device, which triggers the disturbance element to perform the recurring mechanical disturbance, particularly in the case of a stuck load. The disturbance element can be designed as a hydraulic cylinder, and when the actuator is extended, the actuator transmits a force impulse to the vessel.

[0016] With the help of a frequency converter, the disturbance is applied by means of a disturbance signal that is applied to the motor current. The motor current is usually a three-phase alternating current.

[0017] The basis for three-phase alternating current is a three-phase alternating voltage. A disturbance can therefore be a disturbance voltage added to the three-phase alternating voltage. For the sake of simplicity, the following refers only to the motor current and a disturbance current.

[0018] In the method according to the invention for releasing a stuck load from the inner wall of a grinding tube of a tube mill, a drive device is used to release the stuck load and to move the grinding tube, wherein the drive device comprises two operating modes, wherein in the first operating mode the drive system carries out the rotary movement of the grinding tube for grinding, wherein in the second operating mode the drive system releases the stuck load from the inner wall of the vessel, wherein in the second operating mode a motor of the drive system is repeatedly disturbed in its rotary movement due to a recurring disturbance.

[0019] After the tube mill has started, the drive device can initially operate in the second operating mode. This second operating mode is particularly useful after a stuck load has been detected, preparing for a safe first operating mode.

[0020] The term "rotational" movement generally refers to the rotational movement of the grinding tube. This rotational movement preferably occurs at a constant speed. In the event of a disturbance, the speed of the grinding tube's rotational movement is altered over time.

[0021] In the first operating mode, the grinding tube usually rotates around its axis of rotation without any rotational acceleration.

[0022] A recurring disturbance is a deviation from a uniform rotational movement or a uniform acceleration movement. A recurring disturbance can be characterized by a temporally non-constant acceleration.

[0023] The disturbance of the rotary movement occurs preferably through an interference signal impressed on the motor current.

[0024] The method described above makes it particularly easy to release a stuck load.

[0025] In an advantageous embodiment of the invention, the interference signal leads to a recurring jerky movement of the grinding tube.

[0026] The interference signal is preferably a short-term increase in voltage and / or motor current. The interference signal can also be an alternating current, with the frequency of the alternating current being different from the frequency of the three-phase motor current.

[0027] The use of a disturbance signal applied to the motor current allows for very simple modulation of the grinding tube's rotational movement. This allows a stuck load in a grinding tube to be easily and simply released.

[0028] In a further advantageous embodiment of the invention, the interference signal is periodic.

[0029] A periodic disturbance signal is either a sinusoidal signal or a regularly recurring current increase and / or a regularly recurring current decrease.

[0030] A periodically recurring disturbance allows the inside of the grinding tube to be freed from a stuck load in a particularly gentle manner.

[0031] In a further advantageous embodiment of the invention, the disturbance is modulated onto the movement up to an adjustable point in time.

[0032] Typically, freeing the grinding tube from a stuck load takes between one and approximately 30 minutes. Therefore, it makes sense for the drive unit to automatically return to the initial operating state after this time, provided no stuck load is detected.

[0033] To further increase operational safety, the transition between the operating states preferably only occurs if no stuck load can be detected.

[0034] This makes it easier to operate the tube mill.

[0035] In a further advantageous embodiment of the invention, the disturbance occurs with a variable time interval t.

[0036] The time between the individual interference signals decreases over time, so that the time interval of the recurring interference is shortened.

[0037] This protects the grinding tube and the drive system of the tube mill.

[0038] Preferably, the disturbance occurs through torque shocks that are imposed on the rotational movement of the grinding tube by the respective disturbance signal.

[0039] In a further advantageous embodiment of the invention, the disturbance increases in its amplitude.

[0040] Preferably, the second operating phase starts with a low amplitude. The amplitude then increases to a maximum amplitude during the second operating phase and then remains at the maximum amplitude or decreases again. The amplitude can be increased by changing the interference voltage or current.

[0041] Since it's often not immediately clear how strong a disturbance is needed to remove the stuck charge from the inner wall of the grinding tube, a temporal increase in the amplitude of the disturbance is advantageous. An increase in amplitude is beneficial for protecting the grinding tube and / or the drive system.

[0042] In a further advantageous embodiment of the invention, the disturbance causes a modulation of the rotational movement of the grinding tube or a modulation of the torque acting on the grinding tube.

[0043] The disturbance signal can be used to control and regulate both the rotational speed and the torque.

[0044] By disturbing the torque as well as the rotational speed, a particularly precisely adjustable operation of a tube mill is preferably achieved, in particular in the second operating mode.

[0045] In a further advantageous embodiment of the invention, the disturbance is modulated by an additional voltage or an additional current on the motor of the drive.

[0046] It is particularly easy to cause recurring disturbances to the rotational speed or torque.

[0047] An additional current or voltage is applied to the motor current or voltage.

[0048] The additional current or voltage is preferably provided by means of the frequency converter.

[0049] Preferably, the additional motor current is sinusoidal. By modulating a three-phase alternating current with an additional oscillating voltage, a particularly simple and effective disturbance of the grinding tube's rotational movement is achieved.

[0050] Preferably, the additional interference current or the additional interference voltage can be impressed on the motor current or the motor voltage by switching off a filter in the frequency converter.

[0051] By applying an additional voltage or current, especially a sinusoidal voltage or current, a particularly simple way to remove a stuck charge is to use the voltage or current as a reference.

[0052] In a further advantageous embodiment of the invention, the recurring disturbance occurs through a mechanical effect on the grinding tube.

[0053] The mechanical disturbance is preferably provided by a mechanical disturbance element. The disturbance element can be hydraulically or electrically driven. The mechanical disturbance preferably occurs through a force impulse on the grinding tube. The mechanical disturbance can also occur through a sudden increase in torque. The respective force impulse can occur in a tangential direction to the rotational movement of the grinding tube, for example onto an attachment of the grinding tube. The mechanical disturbance, in particular the respective force impulse, can also be directed towards or away from the axis of rotation. Preferably, the mechanical disturbance, in particular the respective force impulse, is directed directly at the (stuck) load, such that the mechanical disturbance acts directly on the load and releases it through mechanical action from the inside of the grinding tube.

[0054] A combination of mechanical impact on the grinding tube and a recurring disturbance caused by the drive is also possible.

[0055] By using a mechanical disturbance, it is advantageous to directly release the stuck charge from the inside of the grinding tube.

[0056] In a further advantageous embodiment of the invention, the disturbance is modulated up to a predetermined maximum angle of rotation.

[0057] Limiting the angle of rotation in the second operating mode ensures that a suddenly released, stuck load does not cause damage to the grinding tube. A maximum angle of rotation of approximately + / - 150° is advantageous for securing the grinding tube.

[0058] In a further advantageous embodiment of the invention, the movement is only disrupted when a load is detected stuck in the grinding tube.

[0059] A stuck load can be detected by the torque function of the rotation angle of the grinding tube. Thus, upon detection of a stuck load, the drive system of the tube mill can switch to the second operating mode.

[0060] It is advantageous to adapt the recurring disturbance based on the mechanical properties of the tube mill or the drive system.

[0061] Preferably, the recurring disturbance is adapted to the type of loading of the tube mill and / or to the amount of load located in the grinding tube.

[0062] These two adjustments allow for particularly effective release of a stuck load.

[0063] In the device for releasing a stuck load from a grinding tube, the device comprises a motor and a control device and optionally a frequency converter, wherein the motor is provided for rotating the grinding tube, characterized in that the device is designed to carry out a method described here.

[0064] In a further advantageous embodiment of the invention, the device has a locking device for locking the stuck load.

[0065] The detection device is used to detect whether a load is stuck in the tube mill, particularly on the inside of the grinding tube. The detection device is preferably assigned to the frequency converter or the control device. The detection device can determine the torque required to rotate the grinding tube from its initial position. If a certain torque is exceeded, it can be assumed that the load is stuck. In this case, the stuck load is released, for example, using the second operating mode of the tube mill.

[0066] Since a load is not baked or stuck to the inside of the grinding tube every time a tube mill is started up, this design considerably protects the drive system of the tube mill.

[0067] In a further advantageous embodiment of the invention, the device has a mechanical brake.

[0068] The mechanical brake can effectively counteract the disturbance in the rotational movement. A recurring disturbance signal can accelerate the rotation of the grinding tube, while the mechanical brake can decelerate it again.

[0069] The mechanical brake thus increases the service life of the drive system.

[0070] In a further advantageous embodiment of the invention, the motor is designed as a segment motor.

[0071] A segment motor enables particularly gentle and low-maintenance operation of the tube mill. Preferably, both the stator and the motor are designed as segment motors.

[0072] In a further advantageous embodiment of the invention, the motor drives the grinding tube via a gear.

[0073] The use of a gearbox allows for the use of smaller drives for a tube mill. Furthermore, a particularly high torque can be applied to the tube mill. Furthermore, this solution with a gearbox is particularly cost-effective.

[0074] Thus, the device has a gear, wherein the gear is arranged between the motor and the grinding tube.

[0075] The gearbox can be assigned to the motor and / or the grinding tube.

[0076] Preferably, an industrial plant, in particular a tube mill, has such a device.

[0077] Such a system is understood, in particular, to be a tube mill for grinding rock and ore. However, the invention can also be applied to other systems in the processing industry.

[0078] Preferably, the interference voltage or current is applied to the motor voltage or current in such a way that one of the grinding tube's resonances is excited. For this purpose, a resonant frequency is determined, for example, and this resonance is excited with the recurring disturbance. A shift in the resonant frequency can also be used to determine whether a stuck charge is present.

[0079] The invention is further described and explained below with reference to figures. FIG 1 a tube mill with a drive system, FIG 2 a voltage or a current as a function of time, FIG 3 a modulation of the current or the voltage, FIG 4 to FIG 6 different disturbances, FIG 7 a resonance curve and FIG 8 a grinding tube which is subjected to a mechanical disturbance.

[0080] FIG 1 shows a tube mill 1 with a drive system. The tube mill 1 comprises a grinding tube 2, wherein the grinding tube 2 has a load 3. The grinding tube 2 and the load 3 are set in rotary motion by a motor 5. The motor 5 is supplied with current or voltage by an inverter 9. The inverter 9 is connected to a control device 7. The control device 7 serves to control the movement of the grinding tube 2 of the tube mill 1. The control device 7, with the aid of the inverter 9, serves to repeatedly disrupt the rotary movement of the grinding tube 2 of the tube mill 1. Optionally, a disturbance device 9a can also modulate the motor current I of the motor 5 using an interference voltage ΔU or an interference current ΔI. The motor 5 is preferably a segment motor, although only one segment of the motor 5 is shown schematically here. Alternatively, a conventional motor 5 can also be used with the aid of a torque converter to rotate the grinding tube.

[0081] The converter 9 optionally serves to determine whether the load 3 is stuck to the inside of the grinding tube 2. For this purpose, the motor current I is determined and compared with a specified motor current.

[0082] FIG 2 shows the voltage or current as a function of time t. Shown is a motor current I for motor 5 as a function of time t. For clarity, the drive current I is shown as a straight line. A disturbance current ΔI is modulated or impressed onto the motor current I. The modulation of the motor current I with the disturbance current ΔI can be performed in different ways and can be either periodic or non-periodic.

[0083] FIG 3 shows a modulation of the current I or a voltage U with a disturbance voltage ΔU or a disturbance current ΔI as a function of time t. Here, the motor current I is shown as a sinusoidal section. The disturbance current ΔI is modulated or impressed onto the sinusoidal motor current I, so that a motor current I with a higher-frequency disturbance is conducted to motor 5. The disturbance current ΔI or the disturbance voltage ΔU serves to disrupt the movement of motor 5 and thus the movement of the grinding tube 2.

[0084] FIG 4, 5 and 6 show different disturbances. The disturbances shown in each case result from the FIG 4 bis 6 shown interference currents ΔI or the shown interference voltages ΔU.

[0085] FIG 4 shows a disturbance of a speed n or a torque D as a function of time t or a rotation angle ϕ of the grinding tube 2. The speed n or the torque D initially increases linearly. At a time interval dt, disturbances are modulated onto the speed n or the torque D.

[0086] FIG 5 shows a disturbance current ΔI as a function of time t or the angle of rotation ϕ of the grinding tube 2. The disturbance current ΔI is shown as an arbitrarily formed rectangular current. The respective edge of the respective disturbance current rise is generated by adding a constant disturbance current ΔI to the motor current I.

[0087] FIG 6 shows a disturbance voltage ΔU or a disturbance current ΔI as a function of time t or the angle of rotation ϕ. The disturbance voltage ΔU or the disturbance current ΔI is sinusoidal, with the period of the disturbance current ΔI or the disturbance voltage ΔU decreasing with increasing time t. Thus, the frequency of the disturbance voltage ΔU or the disturbance current ΔI increases with time t. Such an increase in the frequency of the disturbance voltage or the disturbance current can lead to a resonance Res, as in FIG 7 shown.

[0088] FIG 7 shows the influence E of the disturbance as a function of the inverse temporal separation of the disturbance. Shown is a resonance curve with a resonance Res at approximately the center of the inverse temporal separation 1 / dt.

[0089] FIG 8shows a grinding tube 2, which is subjected to a mechanical disturbance ms. According to this embodiment, the grinding tube 2 has an attachment 11a, wherein the attachment 11a is repeatedly subjected to a mechanical disturbance ms by a mechanical disturbance element 11. The mechanical disturbance ms can be caused by a recurring forward and backward movement of the mechanical disturbance element 11, as indicated by the arrow next to the mechanical disturbance element 11.

[0090] The mechanical disturbance ms is implemented here as a recurring force pulse. The mechanical disturbances ms are spaced apart by a time interval dt.

[0091] The mechanical disturbance element 11 is controlled by a control device 7. The control device 7 preferably controls the amplitude and the time interval dt between the mechanical disturbances ms.

[0092] In summary, the invention relates to a method and a device for releasing a stuck charge 3 from the inner wall of a grinding tube 2. To release the stuck charge 3, also referred to as a "frozen charge," a recurring disturbance is imposed on the rotational movement of the grinding tube 2. The recurring disturbance is preferably generated by a disturbance current ΔI imposed on the motor current I. The disturbance current ΔI is preferably selected based on the type of charge and / or the physical properties of the tube mill. The invention at least greatly simplifies the release of the stuck charge 3. The recurring disturbance can also be caused by a mechanical disturbance.

Claims

1. Method for detaching a frozen charge from the inner wall of a grinding tube (2) of a tube mill, wherein a drive device is used to detach the frozen charge (3) and to move the grinding tube (2), wherein the drive device comprises two operating modes, wherein, in the first operating mode, a drive system rotates the grinding tube (2) for grinding, wherein, in the second operating mode, the drive system removes the frozen charge from the inner wall of the vessel (2), characterised in that, in the second operating mode, a motor (5) of the drive system is repeatedly disturbed in its rotational movement by a repeated disturbance, wherein the disturbance occurs with a variable time interval and wherein the time interval of the repeated disturbance is shortened.

2. Method according to claim 1, wherein the disturbance signal produces a repeated jerky movement of the grinding tube (2).

3. Method according to claim 1 or 2, wherein the disturbance signal is periodic.

4. Method according to one of the preceding claims, wherein the disturbance is modulated onto the rotational movement up to a settable point in time.

5. Method according to one of the preceding claims, wherein the disturbance increases in amplitude.

6. Method according to one of the preceding claims, wherein the disturbance causes a modulation of the rotation of the grinding tube (2) or a modulation of the torque (D) acting on the grinding tube (2).

7. Method according to one of the preceding claims, wherein the disturbance is modulated onto the drive motor (5) by an additional voltage (ΔU) or by an additional current (ΔI).

8. Method according to one of the preceding claims, wherein the disturbance is modulated up to a predetermined maximum angle of rotation starting from a rest position.

9. Method according to one of the preceding claims, wherein the movement is disturbed only when a frozen charge (3) is detected.

10. Device for releasing a frozen charge (3) from the inside of a grinding tube (2) of a tube mill, comprising a motor (5) and a control device (7), optionally a frequency converter (9), wherein the motor (5) is designed to rotate the grinding tube (2), characterised in that the device is designed to carry out the method according to one of the preceding claims.

11. Device according to claim 10, further comprising a detection device for detecting the frozen charge (3), the detection device being designed in particular to provide the disturbance signal as long as a frozen charge is present in a grinding tube (2).

12. Device according to claim 10 or 11, further comprising a mechanical brake.

13. Device according to one of claims 10 to 12, wherein the motor (5) is a segment motor.

14. Device according to one of claims 10 to 13, further comprising a gearbox, wherein the gearbox is disposed between the motor (5) and the grinding tube (2).

15. Industrial system for processing a base material, in particular a tube mill comprising a device according to one of claims 10 to 12.