JPH0368738B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for controlling the operation of a mill, and in particular,
The present invention relates to an operation control method that allows operation at the maximum grinding rate at all times.

(Prior art) As a method of controlling the operation of a mill such as a ball mill,
BACKGROUND ART Conventionally, a method has been widely adopted in which the amount of material to be ground to be ground is controlled to be supplied to a mill so that the sound pressure value of the mill and the drive current value of a bucket elevator attached to the mill are constant. That is, the particle size of the powder leaving the mill is
The residence time varies depending on the residence time in the mill and the grindability of the material to be crushed, and it is necessary to adjust the residence time in order to obtain granules with a constant particle size. Now, assuming that the amount of powder held up in the mill (the amount of powder retained in the mill) is w (Kg) and the flow rate of powder passing through the mill is F (Kg/min), the average residence time τ is as follows: τ=w/F ...It is expressed as (1). Therefore, in order to obtain powder with the target particle size, there is a method of keeping the amount of powder held up in the mill constant and controlling the flow rate of powder passing through the mill with the amount of material to be crushed, or vice versa. An effective method is to keep the powder flow rate constant and control the amount of powder held up in the mill by the amount of material to be crushed. In order to realize such control, it is necessary to measure the actual in-mill powder hold-up amount w or the in-mill powder flow rate F by some means. Conventionally, this measuring method involves detecting a physical quantity related to the in-mill powder hold up amount w or the in-mill powder flow rate F. Specifically, the method involves inserting a pressure measuring tube into the mill and utilizing the fact that the differential pressure across the mill changes depending on the amount of powder inside the mill, and detecting the noise generated by the mill with a microphone. A method that takes advantage of the fact that the noise intensity of the mill changes depending on the amount of powder, a method that takes advantage of the fact that the mill powder exit temperature changes depending on the amount of powder in the mill, and a method that uses the fact that the load current of the motor that drives the mill changes. A method that uses the fact that the vibration value of the mill changes depending on the amount of powder inside the mill, a method that takes advantage of the fact that the vibration value of the mill changes depending on the amount of powder inside the mill, a method that uses the fact that the driving current of the bucket elevator, the return amount, etc. A method that takes advantage of changes depending on the powder flow rate has been adopted. In the conventional control method, the sound pressure value and drive current value at which the mill's grinding efficiency is highest are measured in advance under the condition that the rotational speed of the mill is constant, and these are given as set values. The supply amount of the material to be crushed is controlled so that the pressure value and drive current value match set values.

(Problems to be Solved by the Invention) The conventional operation control method described above can, in principle, perform operation with high pulverization efficiency.
However, it is not always the case that the mill is operating at maximum grinding efficiency. That is, in the conventional operation control method, it is a condition that the rotational speed of the mill is kept constant. This rotational speed typically reduces the internal diameter of the mill to D
(m), theoretically calculated N=
Around 75% of 42.3/√ is considered good and is set to these values. However, the rotational speed set in this way is an ambiguous value based on experience, and there is no guarantee that it is necessarily the best value. Moreover, when the mill is actually operated continuously, the optimum rotation speed is also likely to change due to changes in the properties of the feed ore, changes in the balls in the mill over time, and other various disturbances. Therefore, with conventional operation control methods, the mill is not always operated under optimal conditions, that is, at maximum grinding efficiency.

Therefore, an object of the present invention is to provide a mill operation control method that allows the mill to be operated at maximum grinding efficiency at all times.

(Means for Solving the Problems) The control method of the present invention introduces the idea of varying the rotational speed of the mill. That is, in the control method of the present invention, the amount of grinding of the mill is controlled so that the physical quantity related to the amount of powder retained in the mill or the flow rate of powder passing through the mill is equal to a set value, and the amount of grinding of the mill per unit time is controlled. The rotation speed of the mill is controlled to maximize the amount.

(Function) Taking as an example the case where a ball mill with a return circuit is provided and a predetermined sound pressure value is given as a set value, the situation will be as follows. That is, the ball mill is continuously supplied with the total amount of the material to be crushed, which is the material returned via the return circuit and the new material introduced via, for example, a belt scale. In this case, since the set value is given as described above, the amount of material to be crushed that is supplied via the belt scale is controlled so that the actual sound pressure value of the ball mill matches the set value. For example, when the actual sound pressure value changes to exceed the set value (when the amount of material to be crushed that passes through the mill starts to decrease), the amount of material to be crushed that is supplied via the belt scale is increased, and When the actual sound pressure value turns lower than the set value (when the amount of material to be crushed that passes through the mill starts to increase), control is performed to reduce the amount of material to be crushed that is supplied via the belt scale. This control maintains the highest pulverization efficiency (amount of pulverization) under the operating conditions of the ball mill at that time. In addition to the above-mentioned control, the present invention performs the following control. That is, for example, the rotation speed of the ball mill is increased by one step. Calculate the amount of the material to be crushed per unit time fed via the belt scale in the increased state. Then, this calculated value is compared with the previous calculated value, and if the current calculated value has increased, the rotation speed of the ball mill is further increased by one step. Then, the comparison is made in the same manner again, and if the calculated value this time is higher, the rotation speed of the ball mill is further increased by one step. When the number of revolutions of the ball mill is increased sequentially in this way, a state is reached where the current calculated value is smaller than the previous calculated value, considering the condition that the set value is constant as described above. In this way, when the current calculated value becomes smaller, the number of revolutions of the ball mill is decreased by one step. Then, the current calculated value is compared with the previous calculated value again, and if the current calculated value is smaller, the rotation speed of the ball mill is further lowered by one step, and if the current calculated value is larger, the ball mill rotation speed is Increase by one step. By performing such control, the ball mill can be operated at a rotation speed that maximizes the grinding efficiency (maximum grinding amount) while taking into account changes in the properties of the feed ore and other various disturbances.

(Example) FIG. 1 is a schematic diagram of a ball mill apparatus to which the operation control method according to the present invention is applied.

In the figure, 1 is a ball mill main body, and this ball mill main body 1 is rotationally driven by a rotational drive device 2 mainly composed of a motor. The pulverized material discharged from the pulverized material discharge port 3 of the ball mill main body 1 is conveyed to the separator 5 by a bucket elevator 4. The separator 5 classifies the conveyed pulverized material, discharges a portion as a product, and sends the remainder to the pulverized material introduction port 7 of the ball mill main body 1 via the return circuit 6. A belt scale 8 is provided near the introduction port 7 for the material to be crushed, for feeding new material to be crushed into the introduction port 7 while maintaining a constant thickness.

On the other hand, microphones 9a and 9b for detecting the sound pressure value of the ball mill main body 1 are provided near the ball mill main body 1, and a current detector 10 for detecting the drive current is provided in the bucket elevator 4. is provided. Further, the rotational drive device 2 includes a rotational speed detector 11 and a belt scale 8.
A feed rate detector 12 is provided at each of the feed speed detectors 12 . The outputs of the microphones 9a and 9b, the output of the current detector 10, the rotation speed detector 11 and the feed speed detector 12 are input to the control device 13, and the rotation speed of the rotation drive device 2 and the output of the belt scale 8 are inputted to the control device 13. The feed rate is controlled by the control device 13 according to the relationship described below.

The control device 13 is mainly composed of a microprocessor, and includes an interface 14 with a built-in analog-to-digital converter, a central processing unit (hereinafter abbreviated as CPU) 15, and memories 16a and 16b. It consists of CPU1
5 performs various calculations such as PID calculation as described later based on the above-mentioned signals introduced through the interface 14 and the setting values stored in advance in the memories 16a and 16b, and the results obtained are as follows. A rotation speed control signal X is applied to the rotary drive device 2 via an interface 14, and a feed rate control signal Y is applied to the belt scale 8 via the interface 14.

Next, the operation of the ball mill device configured as described above will be explained with reference to the flowchart shown in FIG. 2 as appropriate.

First, in the memory 16a of the control device 13, the sound pressure value under the conditions that can maximize the grinding efficiency of the ball mill main body 1 is stored as a set value, and the memory 16a
6b stores the drive current value of the bucket elevator 4 under the above conditions as a set value.

Assuming that the ball mill main body 1 starts operating and switches to automatic operation when the entire system becomes stable to some extent, the CPU 15 controls the feed rate detector 12.
PID calculation is performed based on the current grinding amount value obtained from the output of the microphone 9a, 9b or the current characteristic value obtained from the output of the current detector 10, and the stored setting value, and the feed rate control signal is generated. Y
Correct. Through this control, the feed speed of the belt scale 8 is corrected in a direction that brings the characteristic value of the ball mill body 1 into agreement with the set value. Therefore, the amount supplied from the belt scale 8 is controlled so that the most efficient grinding amount can be obtained at that rotation speed. Further, the CPU 15 integrates the amount of crushing over a certain period of time based on the output of the feed rate detector 12. CPU15 is 1 after automatic operation starts.
When the integral time ends, the rotary drive device 2
The rotational speed control signal X is forcibly modified to increase the rotational speed of the motor by one step. Therefore,
The rotational speed of the rotary drive 2 increases by one step. On the other hand, at the end of the above integration time,
The CPU 15 calculates the amount of crushing per unit time and stores it in the first register, and also transfers the contents of the first register to the second register. With this operation, the previous amount of pulverization Fi' per unit time is always stored in the second register, and the current amount of pulverization Fi per unit time is stored in the first register. Next, the CPU 15 subtracts the previous grinding amount Fi' from the current grinding amount Fi, and when this subtraction value is positive or zero, the CPU 15 sends a rotational speed control signal X to increase the rotational speed of the rotary drive device 2 by one step.
and, when the subtraction value is negative, the rotational speed control signal X is modified so as to reduce the rotational speed of the rotary drive device 2 by one step. Thereafter, the above-described operation is repeated.

As can be seen from the above-mentioned operation, this control method compares the current amount of grinding per unit time with the previous one, and if the current amount of grinding per unit time has increased, the ball mill The rotational speed of the main body 1 is further increased by one step. Then, a similar comparison is made again, and if the current amount of pulverization per unit time has increased, the number of revolutions of the ball mill main body 1 is further increased by one step. As the rotational speed of the ball mill body 1 is increased sequentially in this way, given the condition that the set value is constant as described above, the current grinding amount will eventually become smaller than the previous grinding amount per unit time. It will definitely come. At this point, the rotational speed of the ball mill main body 1 is decreased by one step. When such an operation is performed, the setting value is used as a reference and the setting value is matched.
Furthermore, the ball mill main body 1 is always automatically operated at a rotation speed that maximizes the amount of pulverization per unit time.

FIG. 3 shows the above-mentioned control form more clearly. Now, when operating at the optimum rotational speed S1 at which the amount of crushed per unit time is maximum at time t0, if the optimum rotational speed changes to S2 due to changes in the properties of the feed ore, etc., the operation control method of the present invention is applied. If there is, it is possible to quickly shift to the optimum rotational speed S2 through the speed change indicated by P in the figure.

Note that the present invention is not limited to the embodiments described above. That is, in the above embodiment, the rotational speed of the rotary drive device 2 is forcibly increased by one step at the beginning of automatic operation, but it may be increased by two or more steps, or conversely, the rotational speed of the rotary drive device 2 can be forcibly increased by one or more steps. It may also be possible to reduce the Further, the present invention is applicable not only to ball mills but also to various types of mills. In addition, the physical quantity determined as a set value is not limited to the sound pressure value of the mill body or the driving current value of the bucket elevator, but can be any value that changes in relation to the amount of powder retained in the mill or the flow rate of powder passing through the mill. good.

(Effects of the Invention) As described above, according to the operation control method of the present invention, the mill is operated at a rotation speed that maximizes the amount of grinding per unit time, so the grinding efficiency is always maximized. Can run a mill.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of a ball mill apparatus to which the operation control method of the present invention is applied, Fig. 2 is a flow diagram for explaining the operation of the apparatus, and Fig. 3 is for explaining the control form in the apparatus. This is a diagram. 1...Ball mill main body, 2...Rotation drive device,
4...bucket elevator, 5...separator,
8... Belt scale, 9a, 9b... Microphone, 10... Current detector, 11... Rotation speed detector, 12... Feed speed detector, 13... Control device.

Claims (1)

[Claims] 1. Detecting a physical quantity that changes in relation to the amount of powder retained in the mill or the flow rate of powder passing through the mill during operation of the mill, and controlling the physical quantity to the mill in order to keep this physical quantity constant. In addition to controlling the supply amount of the material to be crushed,
A method for controlling the operation of a mill, characterized in that the rotational speed of the mill is controlled to a maximum rotational speed under the condition that the physical quantity is constant. 2. In controlling the rotation speed of the mill,
The amount of material to be crushed per unit time supplied to the mill is sequentially calculated, and the rotational speed of the mill is increased or decreased depending on the difference between the current calculated value and the previous calculated value. A method for controlling the operation of a mill according to claim 1. 3. The mill operation control method according to claim 1, wherein a sound pressure value of the mill or a drive current value of a bucket elevator attached to the mill is used as the physical quantity.