1 traditional single factor detection method
At present, the domestic testing methods for ball mill load mainly include: current method, acoustic method, useful power method, vibration method and other single factor detection methods. These methods have limitations and it is not possible to accurately detect the load of the mill in the entire process.
(1) The current method analyzes the load amount inside the mill according to the magnitude of the current intensity of the mill motor. The current method is greatly affected by the amount of steel balls, and is also susceptible to fluctuations in the grid voltage. The load can be well detected when the steel ball volume and the grid voltage are relatively stable.
(2) The acoustic method estimates the amount of load inside the ball mill by detecting the sound emitted by the ball mill cylinder. There are many factors affecting the measurement of the acoustic method, such as the noise generated by other ball mills around; the hardness of the raw materials, the diameter of the particles; the material load of the ball mill; the medium load of the ball mill; the concentration of the grinding and the change of the cyclic load.
(3) The active power method has a single-peak correspondence relationship between the active power of the ball mill motor and the ball mill load, and the active power is used to determine the load of the ball mill. There are also many problems with the power method. The main performances are as follows: 1 There are many factors affecting the active power, such as the amount of ore, the addition and consumption of steel balls. 2 Single peak curve is not good to determine the load. 3 Active power is mainly determined by the amount of ball loaded.
(4) Vibration method When the rotation speed of the ball mill is constant, the vibration intensity of the ball mill is related to the amount of material. The vibration method indirectly detects the material load of the ball mill by detecting the vibration intensity of the ball mill. The main disadvantages of the vibration method are: 1 The grid voltage change will cause the material load point to drift, affecting the detection; 2 the grinding concentration, the steel ball volume, the material ball ratio and other factors will affect the vibration amount.
2 two-factor detection method
Considering the advantages and disadvantages of the single detection methods, two complementary detection methods are combined to detect the load, and two-factor detection methods such as acoustic-power dual-signal detection and acoustic-vibration dual-signal detection have appeared successively.
Overall, the dual signal detection ball mill load still does not determine the internal state of the ball mill.
3 three-factor method
The sound, power and vibration are jointly detected, and the adaptive network fuzzy inference system is used for analysis and calculation. The experimental results show that the method has the advantages of reducing the complexity of the model and improving the estimation accuracy. But this requires the information provided by multiple sensors to be authentic.
4 force sensor method
The force sensor method is a technical method that uses a force sensor to directly measure the force related to the load of the ball mill to detect the load of the ball mill. At present, there are mainly three situations.
(1) Liner pressure detection method
A sensor capable of measuring radial pressure and tangential pressure is installed under the inner liner of the ball mill cylinder, and the signal measured by the sensor is introduced into the microcomputer for processing to obtain a force map, and the throwing point of the ball mill load can be judged from the figure. By dropping the point, the filling rate of the ball mill can be calculated, and then the radial pressure can be analyzed, and the ratio of the material load to the steel ball load can be calculated. According to this principle, the international control company developed a ball mill monitoring system, which can transmit the measurement signal to the microcomputer through the wireless transmitter-receiver, and analyze and control the load by the microcomputer, but the system is complicated to install and expensive.
(2) cylinder stress detection method
The deformation of the cylinder is caused by the weight of the steel ball and the material in the cylinder, and the amount of deformation is proportional to the load. When the barrel rotates, the lower surface of the barrel will always be subjected to tensile stress and the upper surface will always be subjected to compressive stress. This strain gauge can be measured directly by the strain sensor. However, since the sensor is mounted on the cylinder and rotates with it, it is easily damaged, and it is inconvenient to install and measure. At the same time, the change of stress is not a single-value correspondence with the load, but also affected by the load of the steel ball.
(3) cylinder weighing detection method
The pressure sensor is mounted under the bearings at both ends of the ball mill, and the ball mill is weighed to determine the total amount (load) of the ball medium, ore and water in the ball mill. The advantage of this method is that the implementation is relatively simple, and the disadvantage is that the detection accuracy is not high, and the respective amounts of the ball medium, the ore and the water in the ball mill cannot be accurately detected, and the filling rate of the ball mill cannot be detected, and only the bearing is used. In the case of hydraulic pressure to support.
5 Optimal load point judgment based on data fusion
Data fusion technology is the process of using computer technology to automatically analyze and synthesize the measurement data of several sensors obtained in time series under certain criteria to complete the required decision and estimation tasks. The biggest advantage is that it can comprehensively utilize various support information for the target mode to improve the reliability of judgment.
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