Application of grinding machine in VFD (Variable-frequency Drive) machining outer circle

1 Introduction:

Grinding machines and grinding wheel motors used in standard mechanical processing operate according to the traditional starting circuit. After the motor is started, it runs at the rated speed. Due to the fluctuation of the grid voltage, the friction load between the grinding wheel and the workpiece grinder is constantly changing, which will affect the speed error of the motor grinder. The standard grinding wheel motor starting circuit generally has only one processing speed, which is difficult to adapt to different workpiece sizes. Grinding machines require different grinding machines to process relative linear speeds, so that it is difficult to guarantee the processing precision of workpieces processed by grinding machines. Therefore, from the aspects of improving processing quality and processing efficiency, saving energy, etc., applying frequency conversion speed regulation technology to grinding machines can receive satisfactory grinding machine results.

There are many types of grinding machine products processed by grinding machines in the machining industry. The workpieces are of different sizes and require different processing precision. Relative to the grinding machine, the speed of the grinding wheel is different from the linear speed of the spindle grinder. It is difficult to adjust the speed of the spindle grinder to meet the processing line speed of the workpiece grinding machine to an ideal state. In addition, due to the stress bending of the grinding machine produced by the shaft during the processing process, the grinding wheel feed torque will be different during the grinding process, which will cause the output speed/torque of the grinding wheel to vary, and the corresponding grinding machine will produce vibration patterns/ Burnt grains, etc., the grinding accuracy is difficult to guarantee, resulting in low production efficiency and low quality rate.

With the development of power electronics technology grinding machines, frequency conversion speed regulation technology grinding machines are becoming more and more popular, and the application of VFD (Variable-frequency Drive) grinding machines in the machining industry has received good grinding machine results. VFD (Variable-frequency Drive) grinding machine has stepless speed regulation, soft start, and constant torque output. The grinding machine meets the requirements of mechanical processing equipment for constant speed/constant torque grinding machines.

2. Grinding machine processing Grinding machine load characteristics:

According to the size of the diameter of the shaft of the grinding machine, the speed of the main grinding wheel motor is equal to the output speed of the grinding wheel. The size of the grinding force of the grinder depends on the output torque of the grinder motor grinder. In the high-speed section of the spindle motor of the rotary grinding machine that drives the workpiece, the output speed of the grinding wheel remains unchanged, and the diameter of the workpiece to be processed is small, and the grinding feed is small; The feed rate of the grinding wheel is large, the grinding force of the grinding wheel is also increasing, and it is difficult for the motor to run at constant torque/constant speed. Changes in the speed of the grinder produce changes in the grinder such as vibration knife lines/burning lines/processing accuracy. Frequency conversion speed regulation motor grinding machine stepless speed regulation, constant torque output can just make up for the above defects.

3. VFD (Variable-frequency Drive) grinding machine selection:

According to the characteristics of the grinding machine running in the system, considering meeting the requirements of the grinding machine for mechanical processing and equipment investment costs, etc., the vector type VFD (Variable-frequency Drive) of the grinding machine with automatic torque boost function is selected. Taking the SANCH-S2000 series as an example, 18.5KW/15KW grinding machine VFD (Variable-frequency Drive) is selected according to the power of the grinding wheel motor grinding machine. Taking 15KW as an example, the rated voltage is three-phase 380V, the output current is 32A, the frequency control is 0.5-400HZ, the speed Control 0.1%, overload capacity 150%/60S. With automatic torque boost function, flexible PWM control, can achieve lower noise operation, more than 10 stages of grinder speed control.

4. System grinding machine startup and speed regulation:

Grinding machine The starting circuit of the main grinding wheel motor of the grinding machine mostly uses a star-delta conversion starting circuit. Replace the original circuit with VFD (Variable-frequency Drive), use the normal open contact of the original contactor grinder to control the operation of the VFD (Variable-frequency Drive) grinder, consider the inertia of the grinding wheel to start the grinder, and the soft start time of the VFD (Variable-frequency Drive) The setting is 10S, the stop braking time is 15S, and the starting torque of the grinding wheel of different types of grinding machines can be adjusted between 50%--80%. The system speed is adjusted by an external adjustable potentiometer, and the grinding machine adapts to the speed adjustment according to the diameter of the workpiece. Due to the mechanical strength/noise/vibration and other factors of the grinding machine when the motor is at high speed, the maximum frequency of the motor is set to 60HZ; due to the heat dissipation of the motor at low speed The effect is poor, considering the variable speed factor of the workpiece rotary grinder and the actual maximum workpiece size, the minimum frequency is set to 35HZ, and the reference frequency is set to 50HZ. From the previous analysis of the load characteristics of the grinding machine, it can be seen that the high-speed section is of constant power, and the low-speed section is of constant torque. At low speed, the load requires large torque and strong overload capacity. For motors above the reference frequency, in order to ensure that the motor does not overvoltage, constant voltage frequency conversion speed regulation is adopted. According to the motor theory, when the voltage is constant and the frequency increases, the magnetic flux per pole of the motor decreases with the increase of the frequency; when the motor current is the rated current, the maximum allowable output torque decreases, and the allowable output The power is constant, which belongs to constant power speed regulation, and is suitable for constant power loads. Below the base frequency, in order to ensure that the magnetic flux of each pole of the motor remains unchanged, V/F=constant variable voltage and variable frequency speed regulation is adopted. When the motor current is the rated current, the allowable output torque of the motor remains unchanged, which belongs to constant torque regulation. speed, suitable for constant torque loads. But when the speed is low, the internal resistance of the motor cannot be ignored. If the V/F is still kept constant, the motor torque will decrease, which cannot meet the load requirements at low speeds. The torque of the grinding machine is large, and the overload capacity is strong. (Variable-frequency Drive) Grinding machine torque automatic compensation function, select the V/F curve of the grinding machine after compensation to correct it.

5. System Design Grinding Machine Notes:

The precision of the grinding wheel balance grinding machine should be improved: run the motor at the rated speed. In order to reduce the vibration of the grinding machine at high speed, the dynamic balance of the motor rotor and the grinding wheel grinding machine should be improved and corrected.

Heat dissipation of the grinder at low speed: Since the motor is cooled by a self-cooling fan, the heat dissipation condition becomes worse at low speed, and the load torque is large, and the temperature of the motor will increase. Therefore, the minimum speed of the grinder is set so that the surface temperature difference of the motor does not exceed the allowable value in accordance with.

When VFD (Variable-frequency Drive) output contains high-order harmonics during frequency control, electromagnetic noise will be generated in the motor. Therefore, a zero-phase noise filter should be installed at the output end to reduce auxiliary radio interference and induced noise.

VFD (Variable-frequency Drive) grinding machine parameter setting items are important to lock the functions such as reverse rotation/maximum frequency/stall!

This paper analyzes in detail the application of VFD (Variable-frequency Drive) on grinding machines in the mechanical processing industry. As the main motor of the grinding wheel of power grinding machines, frequency conversion speed regulation technology is introduced to meet the needs of grinding machines for various shaft grinding machines and improve the performance of grinding machines. Work efficiency improves the processing quality of the shaft grinding machine and saves energy. Combined with the actual on-site grinding machine application, the operator's response is more handy, the surface is smooth and the imaging degree is high, and the yield rate is greatly improved.