Method for Starting a Grinding Tube

Abstract

A method for starting a grinding tube with an assigned drive device, wherein during the operation of the grinding tube a grinding mode and a charge release mode can be set such that a particularly reliable monitoring of the state of charge located in the grinding tube is ensured, where the grinding tube is rotated and, at a first rotational angle, a first actual torque is detected, a setpoint torque is calculated for a second, relatively large rotational angle based on the first actual torque, an actually occurring, second actual torque is detected when the second rotational angle is reached, an investigation is performed to determine the difference of the second actual torque from the setpoint torque, and the charge release mode of the grinding tube is set when the second actual torque is within the threshold range, otherwise the grinding tube is operated in the grinding mode.

Claims

1. A method for starting a grinding tube (2) with an allocated drive apparatus (3), wherein during operation of the grinding tube (2) a grinding mode and a charge release mode can be set, wherein, starting from a standstill state of the grinding tube (2): the grinding tube (2) is rotated and, at a first angle of rotation (α.sub.1), a first actual torque (T.sub.1) is acquired, on the basis of the first actual torque (T.sub.1) a target torque (T.sub.2TARGET) is calculated for a second, greater angle of rotation (α.sub.2), when the second angle of rotation (α.sub.2) is reached, an effective second actual torque (T.sub.2ACTUAL) is acquired, with the aid of a predefined threshold range (8), the extent by which the second actual torque (T.sub.2ACTUAL) deviates from the target torque (T.sub.2TARGET) is examined, if the second actual torque (T.sub.2ACTUAL) lies within the threshold range (8), the charge release mode of the grinding tube (2) is set, otherwise, the grinding tube (2) is operated in grinding mode.

2. The method as claimed in claim 1, wherein, to calculate the target torque (T.sub.2TARGET), use is made of the sine of the first angle of rotation (α.sub.1) and the sine of the second angle of rotation (α.sub.2), in particular the ratio of the sine of the first angle of rotation (α.sub.1) to the sine of the second angle of rotation (α.sub.2) is formed.

3. The method as claimed in one of the preceding claims, wherein a quotient is formed from the second actual torque (T.sub.2ACTUAL) and the target torque (T.sub.2TARGET).

4. The method as claimed in one of the preceding claims, wherein the threshold range (8) is defined by a value which in particular is specified as a percentage or as a rational number.

5. The method as claimed in claim 4, wherein the threshold range (8) is defined as a deviation of the second actual torque (T.sub.2ACTUAL) from the target torque (T.sub.2TARGET) by 15%, in particular by 10%, in particular by 5%.

6. The method as claimed in one of the preceding claims, wherein the first and the second angle of rotation (α.sub.1, α.sub.2) lie below 90°, in particular below 70°.

7. A control apparatus (4) for the drive apparatus (3) of a grinding tube (2) for carrying out the method as claimed in one of the preceding claims.

8. A drive apparatus (3) for a grinding tube (2), comprising a control apparatus (4) as claimed in claim 7.

9. A tube mill comprising a grinding tube (2) and a drive apparatus (3) as claimed in claim 8.

Description

[0031] An exemplary embodiment of the invention will be described in greater detail with reference to a drawing. In the figures:

[0032] FIG. 1 shows a schematic and greatly simplified diagram of a grinding tube in four different angles of rotation,

[0033] FIG. 2 shows an evaluation of the torque of the grinding tube in accordance with FIG. 1 as a function of an angle of rotation.

[0034] The same reference characters have the same meaning in the figures.

[0035] In FIG. 1, a grinding tube 2 of a tube mill not shown in more detail here is represented symbolically. Allocated to the grinding tube 2 is a drive apparatus 3 with a control apparatus 4, which actuates inter alia the starting of the grinding tube 2. The grinding tube 2 is charged with a grinding product 6, in particular ore, which is furthermore referred to as charge.

[0036] The grinding tube 2 can be operated both in a grinding mode and also in a charge release mode. The grinding mode represents the normal operation of a tube mill, in which the grinding tube is rotated in view of crushing or pulverizing the charge. The charge release mode is the operating state of the tube mill in which, if a frozen charge is detected, measures for removing the frozen charge from the interior wall of the grinding tube are initiated.

[0037] In FIG. 1, a total of four states of the charge 6 of the grinding tube 2 are shown according to angle of rotation. Z.sub.1 represents a standstill state at 0°, in which the charge 6 is evenly distributed on the bottom on the grinding tube 2. Z.sub.4 represents the position of the caked-on charge at an angle of rotation of approx. 70°. Z.sub.2 and Z.sub.3 represent the caked-on charge 6 at two further angles of rotation α.sub.1, α.sub.2 between 0° and 70°.

[0038] Starting from the standstill state Z.sub.1, the operation of the tube mill is commenced and the grinding tube 2 is driven in the direction of rotation 10, in that it is rotated about a central axis A. At a first angle of rotation α.sub.1, which is smaller than 90°, for example at 45°, a torque T of the drive apparatus 3 is measured. This point is represented by M1 in FIG. 1. At a second angle of rotation α.sub.2, e.g. 60°, the torque T is measured again at point M2. The measurements can also take place at other angles of rotation D between 0° and 90°; only at least two measured values at two different angles of rotation are required.

[0039] The evaluation of the measurements at the measurement points M1 and M2 is shown graphically in FIG. 2. In this context, the torque T of the drive apparatus 3 is plotted as a function of the angle of rotation D. V.sub.1 refers to the increase in the torque T with a frozen charge. V.sub.2 is the effective course of the torque T when starting the tube mill. M refers to the maximum torque occurring.

[0040] In the region B, which is used in the prior art for monitoring the “frozen charge”, lies in the exemplary embodiment shown a minimum deviation of the effective course V.sub.2 of the torque T from the maximum torque M. In this context, the course V.sub.2 has no pronounced torque peaks. At this point, conventional monitoring systems would thus regularly initiate the charge release mode.

[0041] In order to avoid this, the torque T at the measurement points M1 and M2 is determined at α.sub.1 and α.sub.2, respectively. With caked-on grinding product 6, the torque T largely increases according to a sine of the angle of rotation D, as can be seen from the course of V.sub.1. It is therefore possible to determine from the torque T1 at the first angle of rotation (measurement M1), using the relationship

sin (α.sub.1)/sin (α.sub.2),

the theoretical target torque T.sub.2TARGET at the point in time M2 at angle of rotation α.sub.2.

[0042] The effective torque T.sub.2ACTUAL at the measurement point M2 at α.sub.2 is measured in addition and compared with T.sub.2TARGET, by making use of a threshold range 8. In the exemplary embodiment shown, the threshold range is defined as 10%, i.e. it is examined whether T.sub.2ACTUAL deviates more than 10% from T.sub.2TARGET. If T.sub.2ACTUAL is more than 10% below T.sub.2TARGET or is equal to T.sub.2TARGET, it should be assumed that the material has come loose from the interior wall of the grinding tube 2 and the tube mill is continued to be operated without faults. Otherwise, for example, the charge release mode is set, in particular the tube mill is shut down or use is made of a controlled rattling or shaking of the grinding tube 2 by way of adapting the drive torque.

[0043] To compare T.sub.2TARGET with T.sub.2ACTUAL, the threshold range 8 is stored in the controller 4 or use is made thereof on demand in a case-related manner. For the evaluation, in particular the quotient of T.sub.2ACTUAL and T.sub.2TARGET is formed and this is compared with the threshold range 8. In the above exemplary embodiment, in which the deviation boundary is defined at 10%, the condition for initiating the charge release mode is fulfilled when

T.sub.2ACTUAL<T.sub.2TARGET×0.9.

As

[0044]
T.sub.2TARGET=T.sub.1(sin (α(.sub.1)/sin (α.sub.2)),

the following applies:

T.sub.2ACTUAL<T.sub.1(sin (α.sub.1)/sin (α.sub.2))×0.9.

[0045] With the angles of rotation α.sub.1=45° and α.sub.2=60° used in accordance with FIG. 1, the condition for the charge release mode can thus be expressed mathematically by:

T.sub.2ACTUAL<T.sub.1×1.1.

[0046] If T.sub.2ACTUAL is equal to or greater than T.sub.2TARGET by 10%, however, then the normal grinding mode is continued.