The loading drive system of the bolt torsion testing machine is mainly divided intoElectric servo and hydraulic types have significant differences in torque output, control accuracy, and applicable scenarios. The advantages and disadvantages are compared as follows:

1 Electric servo loading drive system

Core principle: Using servo motors+The gearbox and precision transmission mechanism (such as ball screws and gearboxes) are used as power sources to achieve torsional loading through precise control of motor speed and torque.

advantage

High precision servo motors can achieve closed-loop control of torque and angle, and the torque measurement accuracy can reach ± 0.5% FS, with a corner resolution of 0.01 °, can accurately capture the yield torque of bolts and the torque corner curve during the elastic deformation stage, suitable for small torque and high-precision testing requirements (such as precision bolts of M3~M20).

Fast response speed: The motor has a short response time for starting, stopping, and reversing, and can quickly switch between various test modes such as fixed torque, fixed angle, and constant speed. It is suitable for dynamic torsion testing or fatigue torsion testing.

Easy to operate and maintain, no need for auxiliary equipment such as hydraulic oil or hydraulic pump stations, compact equipment structure, and small footprint; Daily maintenance only requires regular lubrication of transmission components, with no risk of oil leakage or contamination, and low operating costs.

Good loading stability, no crawling phenomenon during low-speed loading, small torque output fluctuation, able to meet the brittleness of ceramic coated bolts, titanium alloy bolts, etc/Requirements for low rate torsion testing of low plasticity fasteners.

shortcoming

Torque is limited by the motor power and transmission mechanism strength, and the torque usually does not exceed5000N · m cannot meet the testing requirements for large-sized high-strength bolts (such as bolts for wind power and bridges above M20).

The overload capacity of the servo motor is weak, and the overload protection threshold is low. If the bolt suddenly breaks or the load suddenly changes, it is easy to cause the motor to stall or the transmission components to be damaged. A complete overload buffering device needs to be equipped.

High speed loading performance generally results in significant motor heating at high speeds. Prolonged high-speed torsion testing can affect motor life and control accuracy, making it suitable for medium and low speeds（0.1~30r/min) test scenario.

II Hydraulic loading drive system

Core principle: Using hydraulic pump station+The hydraulic motor and hydraulic valve group serve as the power source, and the torque and speed of the hydraulic motor are adjusted by controlling the pressure and flow of hydraulic oil to achieve torsional loading.

advantage

Ultra large torque output capability, hydraulic motor can output tens of thousandsThe torque of N · m (up to 50000 N · m) can easily meet the ultimate torsional failure test requirements of large-sized bolts (such as M20~M100 high-strength steel structural bolts) and anchor bolts.

The hydraulic system has strong overload capacity and natural buffering characteristics. When the bolt breaks or the load suddenly changes, the hydraulic oil can be relieved through the relief valve to avoid damage to the drive system and sensors, and the equipment has high durability.

The hydraulic motor with excellent low-speed and high torque performance can still stably output high torque at extremely low speeds without speed fluctuations, making it suitable for static torsion tests of large bolts (such as load holding tests to determine failure torque).

shortcoming

Low control accuracy is affected by hydraulic oil compressibility and valve group response delay, and the control accuracy of torque and angle is usually ± 1.0% FS, difficult to accurately capture subtle torque changes during the bolt elasticity stage, not suitable for high-precision small torque testing.

The operation and maintenance are complex and require an independent hydraulic pump station, which occupies a large area; Daily maintenance requires regular replacement of hydraulic oil and cleaning of filter elements, which poses a risk of oil leakage and requires high environmental cleanliness, resulting in high usage costs.

The hydraulic system has a slow response speed and a long response time for starting and reversing, which cannot meet the requirements of high-frequency dynamic torsion or fatigue torsion tests. It is mainly suitable for static torsion tests.

Hydraulic pump stations with high energy consumption require continuous operation, and even if the equipment is in standby mode, it will consume electrical energy. Long term use consumes more energy than electric servo systems.

III Summary of Applicable Scenarios for Two Types of Drive Systems