1.Overview
Strain gauge load cells are technology-intensive and skill-intensive high-tech products with diversity, marginality, comprehensiveness and technicality. They require multiple disciplines in the design and manufacturing process, multi-technology cooperation and support technology, basic technology, core technology, scientific application and integration of special processes. The most important mechanical part of the load cell is the elastic element that is subjected to external loads. Its function is to counteract the applied load, and at the same time concentrate the effect of the load on an independent, uniform strain field for the resistance strain gauge measurement. The accuracy, stability and reliability of the load cell are inseparable from the performance of the metal material constituting the elastic element, that is, the weight information is detected by the strain-switching element resistance strain gauge using the inherent characteristics of the metal material. Therefore, the design and manufacture of the load cell is mainly the structure and boundary design of the elastic component and the selection of the elastic component metal material and its heat treatment process. The best structural design and manufacturing process is to combine the performance of the elastic component with the properties of the metallic material. One of the difficulties in accomplishing this task lies in the computational and economical limitations of the elastic component structure and the boundary design. Only by following the development and production rules of the load cell can this limitation be solved; the second is to select the load cell accurately. It is only in this way that the comprehensive performance of the elastic component metal material and its heat treatment specification can be overcome to overcome the comprehensive influence of various factors, and produce a load cell with the least fluctuation in performance. Under the rated load, the strain degree of the strain zone of the load cell elastic element has a great influence on the linearity, hysteresis, creep and fatigue life of the elastic component. The degree of strain mentioned here is actually a strain range that ensures the strain stability of the elastic element and has a stricter linear relationship with the load, which is closely related to the metal material used for the elastic element and its heat treatment process.
The influence of the metal material characteristics of the elastic component on the performance of the load cells is mainly the influence of the elastic modulus, hysteresis effect and the moelastic effect of the material.
Effect of elastic modulus of metallic materials
The stability and temperature coefficient of the elastic modulus of the elastic component metal material directly affect the accuracy and stability of the load cell. It is generally considered that the metallic material is within the proportional limit and the elastic modulus E is constant, which is not critical. In fact, the elastic modulus is only close to a constant within a certain range. Different heat treatment specifications are applied to metal materials, and the strain range in which the elastic modulus is constant is also different. The production practice proves that the medium carbon alloy steel 40CrNiMoA, which is widely used in China's weighing sensor manufacturing enterprises, has a hardness of about HRC39 after quenching and tempering; the hardness of 35CrMnSiA is about HRC42, and the stability of elastic modulus is the best. Close to a constant. The elastic modulus of most metal materials decreases with the increase of temperature. In the relationship between elastic modulus and temperature, it is required that the elastic modulus changes linearly with temperature and is very stable. Load cell sensitivity temperature compensation. The load cell used in the dynamic weighing state also requires that the elastic modulus of the elastic element material does not change or change little under vibration and shock.
