1, ball mill introduction
1.1 Working principle
The ball mill is mainly composed of a transmission device, a cylinder device, a feeding device, a discharging device and an electric control device, and is divided into a feeding portion, a discharging portion, a rotating portion, a transmission portion (a reduction gear, a small transmission gear, a motor, and an electric control). And other major parts. The main body is a simplified low-speed swivel mounted horizontally on two large bearings. The ball mill is driven by the motor through the reducer and the surrounding large gears, or by the low-speed synchronous motor directly through the peripheral large gear reduction drive, driving the rotary part to rotate, and the cylinder is equipped with a suitable grinding medium-steel ball. Under the action of centrifugal force and friction force, the grinding medium is lifted to a certain height and falls down in a falling or falling state. The falling grinding body crushes the material in the cylinder like a projectile.
1.2 Analysis of the movement of the ball mill
The movement state of the grinding body in the ball mill is related to the rotation speed of the cylinder and the friction factor of the grinding body with the inner wall of the cylinder. The movement state of the grinding body in the cylinder can be divided into three types:
1.2.1 sloping motion state
When the rotation speed of the ball mill is low, the steel ball and the material rise with the inner wall. When the angle between the steel ball and the material rises is greater than the natural inclination angle, the steel ball slides down the inclined surface to form a sufficient drop, and the material and the steel ball in the cylinder are presented. In the escaping operation state, the grinding efficiency is very low.
1.2.2 throwing motion state
When the rotation speed of the ball mill is high, the grinding body is thrown down like a projectile after the cylinder rises to a certain height. In the state of the throwing motion, the material is mainly the impact action when the grinding body is thrown off and part of the Grinding under the action of grinding, the grinding efficiency in this state is high.
1.2.3 Centrifugal motion state
When the rotation speed of the cylinder is too high, due to the centrifugal force, the grinding body "attaches" on the inner wall of the cylinder to perform a rotary motion together with the cylinder without being thrown off. In the centrifugal movement, the grinding body no longer has a collision and grinding effect on the material, and the material is of course not crushed.
Comparing the above three states, it is known that in order to achieve a higher efficiency of the grinding effect, it is necessary to adjust the appropriate cylinder running speed to keep the material in the cylinder in the throwing operation state. Insufficient speed and too fast speed can result in reduced efficiency of the ball mill.
2, ball mill transmission program
2.1 asynchronous power frequency transmission
At present, the transmission mode of most ball mills is driven by a three-phase asynchronous motor, and the transmission process is as follows.
The ball mill is a heavy-duty device, and the power of the matching motor is large. The asynchronous scheme has the following shortcomings:
a, high power capacity requirements
The ball mill belongs to the heavy-duty high-power equipment. The power-frequency starting current of the asynchronous motor is 4-7 times of the rated current. The requirements for the power supply capacity are very large. After starting the star-delta, the current should reach about 3 times of the rated current.
b, poor control of the process
The asynchronous motor running at power frequency is fixed in speed, which is easy to cause excessive grinding, can not achieve stepless speed regulation, and has poor process control capability.
c, low efficiency
The hydraulic coupler in the asynchronous scheme has low transmission efficiency, which affects the efficiency of the whole system. At the same time, most of the asynchronous motors are not ultra-efficient motors, and the efficiency of the motor itself is also low. More importantly, the power frequency regulation is not convenient and cannot be Ensure that the system is operating at its most efficient state.
3, Sanjing Electric S3000 synchronous servo drive
3.1 program introduction
In order to improve the shortage of asynchronous power frequency scheme and improve the efficiency of the ball mill system, the synchronous servo scheme is used for transformation. The system block diagram is as follows:
The scheme adopts energy-saving control cabinet for easy installation and debugging;
Using an ultra-efficient servo motor instead of an asynchronous motor, removing the hydraulic coupler in the original system further improves efficiency;
Using the variable frequency speed control technology of the servo drive, the ball mill works in the best efficiency state;
The process parameter setting is completed by the touch screen, and the touch screen can monitor the running status and data to improve the user experience.
3.2 Program Features
3.2.1 Servo motor
The shape of the base is the same as that of the original asynchronous motor, which is easy to install and replace;
The power factor of the motor can reach more than 0.98, which is much higher than that of the asynchronous motor;
Higher transmission efficiency, the overall power under rated load is more than 3% higher than that of asynchronous motor;
3.2.2 servo drive
Adopting the most advanced frequency conversion technology to realize the stepless speed regulation of the servo motor, so that the motor runs in the most efficient state;
The built-in 16-speed simple PLC function of the drive can fully meet the needs of the ball mill production process;
With 210% overload capability, it meets the torque demand when the servo motor starts;
Built-in standard Modbus communication protocol for easy integration with touch screen control system;
3.2.3 System advantages
The soft start function of the servo drive ensures that the starting current of the system is less than 2 times of the rated current, which greatly reduces the impact of the power grid.
The system can provide all-round monitoring and protection of voltage, current, temperature, speed, etc., and the equipment runs more reliably.
Parameter setting and operation data monitoring can be completed through the human interface, which is easy to operate and has a better user experience.
3.3 program application effect
Through the modification of the synchronous servo scheme of the ball mill, the power saving rate can reach 12%-20%;
High return rate, all investments can be recycled within 1 year;
Reduce equipment maintenance and maintenance costs and extend equipment life;
Improve the working environment, the synchronous servo motor running noise is significantly lower than the asynchronous motor;
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Xinxiang Zhenying Mechanical Equipment Co., Ltd , https://www.zhenyinggroup.com