Automatic control of grinding unit

The automatic control of the grinding circuit not only saves the labor problem, but more importantly, stabilizes the operation and controls the working conditions at the optimal level to achieve the purpose of increasing the output and reducing the consumption; especially the self-grinding machine and the semi-self-grinding (or gravel) Grinding machine, because the material level or medium load in the mill changes rapidly, an automatic control system must be installed to ensure high efficiency and low consumption of the mill.
According to foreign reports, the automatic control of the grinding circuit can increase the output by 2.5~10%, and the treatment of one ton of ore can save energy by 0.4~1.4 kW·hour (see Table 1).
Our company Dongfeng fluorite flotation plant and beneficiation plant Shougang Dashi grinding and classification automatic control experience shows that when the automatic control system, fluctuation range of indicators than small grinding operations manual (see Table 2 and Table 3 ).
Since there are many factors affecting the grinding efficiency, especially the nature of the ore, so far, these factors have not been unified to develop a unified mathematical model for production. Generally, according to the specific ore and conditions, the suitable operating range is obtained through experiments. In the production, the mill is controlled to operate within this range. The experience of automatic control of the grinding circuit at home and abroad is based on the expert system. Recently, fuzzy logic control has been adopted.
The main parameters of the automatic control system for grinding operations that are usually measured or controlled are as follows:
1. Power: It is related to the rotation rate of the grinding machine, the concentration of the slurry, the filling rate of the grinding medium, and the state of the lining. The load change of the self-grinding mill can be reflected by the power signal or the axial pressure signal.
2. Sound: The sound intensity is related to the medium motion state and the ball material ratio, which can indicate the size of the mill load. Some extraneous sound frequencies need to be filtered out during the measurement.
3. New ore supply: Place the sensor (electronic scale or nuclear scale) on the ore belt, transfer and record the load weight, and control the grinding machine to add water.
4. The level of the slurry pump tank of the hydrocyclone: ​​the level of the liquid level can indicate the circulating load of the closed circuit grinding and is used to control the flow of the sand pump. The liquid level can be measured by ultrasonic waves, atomic absorption, pressure difference, and pressure of a bubble tube immersed in the slurry.

5. Slurry flow rate: It can be measured by slurry flow meter. The weight flow of the slurry is measured by the calculation of the bulk density and volume flow of the slurry to control the amount of flotation agent added and calculate the mass balance table of the grinding system. The volume flow rate was measured with a magnetic flow meter.
6.pH value: measured with a standard electrode, pH of the slurry was formed on metal hydroxide colloidal particles impact, but also affect the number of colloidal particles of the slurry concentration and grading operations.
7. Water supply: affect the slurry concentration and grinding efficiency.
8. Slurry concentration: measured by a concentration meter.
9. Grinding product particle size: measured by particle size sensor.
The automatic control of the grinding and grading process of the ore dressing can be divided into fixed value control and self-optimization or optimal control. When selecting, it is necessary to fully study the specific conditions of the original ore properties, process flow, equipment configuration and production indicators, and determine the appropriate plan.
Figure 1 shows an example of the automatic control system for grinding in three control sections. These three links are:
2. According to the electronic scale to measure the amount of minerals, proportionally adjust the additional water to the ball mill to adjust the open loop control of the mill concentration;
3. According to the concentration meter, measure the overflow concentration of the classifier, adjust the water supply of the classifier to adjust the closed-loop control of the graded overflow concentration.
Figure 2 is a further example of automatic control of grinding operations. There are two control loops in the figure: one is the loop that controls the particle size of the product, which is used to adjust the water supply amount of the water supply pump pool of the hydrocyclone to adjust the working concentration of the cyclone to meet the requirements of the graded particle size; To control the amount of ore and water supplied by the mill, the control variable is the level of the water supply pump pool of the hydrocyclone.
The feed weight indication, the controller WIC adjusts the belt speed adjuster SC by the signal from the weighing sensor of the feed belt and the remote set value RSP, and the feed weight is recorded on the recorder WR. The water supply amount PW of the mill is regulated by the proportionaler FRa. The proportionaler receives the signal from the weight sensor WT and the feedwater amount signal measured by the orifice plate and processed by the square. After the conversion process, the signal from the proportional controller controls the set value of the flow regulator PIC. The current signal sent by the FIC is changed to the wind pressure by the “current/voltage” transmitter I/P to control the valve, so that the grinding machine The amount of water supplied is proportional to the amount of new feed. [next]

Figure 1 block diagram of an automatic control system for a ball milling classification process
1. Ball mill; 2. Spiral classifier; 3. Pressure sensor of HHG-01 type electronic belt scale; 4. Feeding belt conveyor;
5. Feeding flat belt conveyor; 6. Disc feeding machine; 7. JZT32-4 speed regulating motor; 8. Fine crushing mine bin; 9. Speed ​​regulating motor controller; 10. Synchronous operator; 11. Regulator; 12.XWDI-200 electronic potentiometer; 13.ZAZN-64KD
G50 type electric regulating valve; 14.DKZ-310 type 25m/m electric actuator; 15.DFD-09 type operator; 16. servo amplifier; 17.DTL-121 type regulator; 18. graded overflow concentration indicating ammeter ;; DBC-334Q differential pressure transmitter; 20. differential pressure concentration gauge pressure device; 21. DGF-12 type flow divider; 22. DGA-12 type constant current device;
23. servo amplifier; 24. DFD-09 type operator; 25. DKZ.-310 type 25mm electric actuator;
26. ZAZN-64KDg50 type electric regulating valve; 27. LD50A type electromagnetic flow transmitter; 28. LD-1 type electromagnetic current converter;
29. Water flow indicator ammeter; 30. Electronic scale secondary table

The mine pumping tank of the grinding machine is equipped with a high liquid level HL and a low liquid level LL control device. When the liquid level is higher than HL or lower than LI, the signal sent by the liquid level sensor LT passes through the liquid level regulator LIC, and sends a signal to control the speed controller SC of the ore feeding belt to change the feeding of the grinding machine. At the same time, the proportional device Ra receives the signals of the weight sensor WT and the flow sensor FT, and after processing, changes the water supply amount of the grinding machine according to the same process as described above, so that the liquid level of the discharge pump pool is kept stable.
The implementation of the automatic control system scheme is as follows:
Constant fixed ore closed loop automatic adjustment. As shown in Fig. 1, the electronic belt scale pressure transducer (3) measures the amount of ore, which is converted into a 0~10 mA DC signal representing the ore by its secondary instrument (30), and the signal is sent to the regulator. (11), comparing with the given signal of the regulator, generating a deviation signal, the regulator performs PID calculation on the deviation signal, generates a control signal and sends it to the synchronous operator (10), and then sends it to the speed regulating motor controller (9). The output signal is used to control the speed regulating motor (7), and the rotation speed is changed to change the rotation speed of the disc feeding machine (6), thereby adjusting the ore amount so that the ore amount is constant near a given value. At the same time, the electronic scale secondary instrument uses the electromagnetic counter to accumulate the ore amount, and outputs a signal of 0~10 mA representing the ore amount, and sends it to the electronic potentiometer (12) for indication and recording.

Figure 2 System diagram of automatic control of grinding operation by the concentrator
1. Feeding; 2. Hydrocyclone; 3. Pump; 4. Slurry tank; 5. Ball mill; DP. Concentration meter; PIC. Flow regulator;
FT. Flow sensor; FRa. Proportional station (device); I/P. Current and voltage transmitter; LIC. Level regulator;
LT. level height sensor; PSIC. particle size regulator; PSM. particle size monitor; PSR. particle size recorder;
PW. Additional water; RSP. Remote set value; SC. Speed ​​control; SP. Set value; WR. Weight recorder;
WRC. Weight adjuster; WT. Weight sensor; DR. Concentration recorder

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