Definition
A torque tester is a precision measuring instrument used to measure and evaluate rotational or torsional moments. Torque is the moment that causes an object to rotate, and its international unit is Newton-meter. In industrial production and scientific research, torque testers are mainly used to determine the mechanical properties of fasteners, transmission parts, material samples or finished products in the torsionized state, such as maximum torque, breaking torque, fastening torque, and the relationship between torque and corner, etc., and are key equipment for quality control, product development and safety evaluation.
Principle
The core working principle of the torque tester is based on mechanical sensing and signal conversion. When the test piece is mounted between the drive and load cells of the instrument and a torsional load is applied, the sensor senses the strain or displacement generated by the torque. At present, the mainstream sensor types include strain gauge type, phase difference type and magnetoelastic type. Take the widely used strain gauge sensor, for example, which works according to Hooke's law and the resistive strain effect. The strain gauge attached to the elastic shaft changes its resistance value as the shaft twists and turns.
This resistance change is converted into a weak voltage signal change through the Wheatstone bridge circuit. The signal is amplified by the instrument's amplifier and then converted into a digital signal through an analog-to-digital converter. Finally, the digital signal is processed, calculated and displayed by a microprocessor or computer system to obtain accurate torque values. The whole process can be expressed as: T = k * Δε, where T represents torque, k is the calibration coefficient of the sensor system, and Δε is the amount of strain change caused by torque.
Measurement method
According to the purpose and object of the test, the following methods are mainly used for torque measurement. Static torque measurement is used to evaluate the torque characteristics of components under constant or slow loading conditions, such as measuring the tightening torque of screws or the torsional strength of materials. Dynamic torque measurement focuses on the real-time change of torque during rotation and is often used to monitor torque fluctuations in motors, engine output shafts, or transmission systems in operation.
In specific operations, common test modes include torque peak testing, which is used to determine the maximum torque that causes a component to fail or reach a specific functional point; Torque attenuation test to evaluate the degree to which the torque loosens over time or vibration after initial fastening; and torque-to-angle testing, which draws curves by simultaneously measuring torque and rotation angle, comprehensively analyzing the elastoplastic behavior of materials or the fit state of the fastening process.
Influencing factors
The accuracy of torque measurement is influenced by a combination of factors. Factors inherent in the instrument include the linearity, hysteresis, and repeatability of the sensor, which are determined by the manufacturing process and materials. The calibration status of the measurement system is critical and needs to be calibrated regularly using a standard torque wrench or weight lever system to ensure the accuracy of measurement transfer.
Test conditions and environmental factors should not be overlooked. Any deviation in the mounting coaxiality of the part under test will introduce additional bending stresses that will affect the reading. Loading speed or rotation rate affects the strain rate response of a material, especially when performing material property testing. Changes in ambient temperature can cause thermal expansion and contraction of the sensor's metal components, resulting in zero drift or sensitivity changes. In addition, the operator's installation technique and loading control method will also affect the repeatability of the measurement results.
Applications
Torque testers are used in many industrial and scientific research fields. In the automobile manufacturing industry, it is used to detect the tightening torque of engine head bolts, wheel nuts, as well as the torsional performance of the drive shaft and steering system. In the aerospace sector, where fastener reliability is demanding, torque testing is a critical part of ensuring structural safety.
In the electronic and electrical industry, the precise measurement of tiny torques such as micro screws, mobile phone vibration motors, and hinges is inseparable from high-resolution torque testers. In materials science research, it is used to test torsional strength, shear modulus, and fracture behavior of metal, plastic, and composite specimens. In addition, torque testing also plays a role in ensuring product performance and consistency in medical devices, packaging industry, new energy battery cover packaging, and other fields.
Selection considerations
Choosing the right torque tester is a systematic project that requires a comprehensive evaluation of multiple technical parameters and usage needs. The maximum measurement range of the selected instrument should cover the expected value of the measured torque with a certain margin, and its indicated error should meet the requirements of the test standard or quality control document.
Resolution determines the smallest torque change that the instrument can discern, which is especially important for small torque measurements. The sampling frequency determines the density of data acquisition, and a high sampling rate is required for high-speed dynamic torque measurements. The interface and functions of the instrument also need to be considered, including whether it supports multiple communication protocols and whether the software provides the necessary analysis functions such as peak hold, curve plotting, statistical calculations, etc.
Finally, it is also necessary to consider the compatibility and scalability of the test accessories, such as whether the type of fixture can adapt to different shapes and sizes of workpieces, and possible changes in future testing needs. By systematically evaluating these factors, the measurement device that matches the specific application scenario can be selected.