The planning of the elastic element, shell, diaphragm and upper pressure head and lower pressure pad of the load cell is necessary to ensure that the function does not shake in the structure after loading, or the function shakes very little.
1. The structure of the load cell
It is necessary to ensure that the function of the structure does not shake after loading, or the function shakes very little, so that in the planning of the load cell, the force in the strain zone should be as single as possible, and the stress should be uniform and common; The patch part should be flat; Structurally, it ensures that it has a certain ability to resist eccentric loads and lateral loads; The force of the device is far away from the strain zone, and the displacement of the load bearing point should be prevented when measuring. Although the load cell is an installation product, it is planned as a monolithic structure as much as possible in order to ensure optimal technical functions and long-term stability.
2. Metal material of elastic element
The metal material of the elastomeric element plays a key role in the comprehensive functionality and long-term stability of the load cell. Materials with high strength limit and elastic limit, good elastic modulus at time and temperature, small elastic hysteresis, and small residual stress during machining and heat treatment should be selected. There is a material indication: as long as the plasticity of the material after quenching is good, its residual stress after machining and heat treatment is small. Special attention should also be paid to the stability of the elastic modulus with time, and it is required that the elastic mold of the material does not change during the service life of the load cell.
3. Machining and heat treatment process
In the process of machining of elastic elements, due to the uneven surface deformation, large residual stress occurs, the larger the amount of cutting, the greater the residual stress, and the residual stress occurs in grinding is the largest. Therefore, a reasonable machining technology and rules should be formulated, and the appropriate cutting amount should be formulated. In the heat treatment process of elastic elements, due to the uneven cooling temperature and phase transformation of metal materials, residual stresses in different directions occur in the core and surface layers, and the core part is tensile stress and the surface layer is compressive stress. It is necessary to go through the tempering process, and the opposite direction of stress occurs inside it, and the residual stress cancels each other out, reducing the effect of the residual stress.
4. Resistance strain gauge and strain binder
The resistance strain gauge should have the best function, requiring good stability of sensitivity coefficient, small heat output, small mechanical hysteresis and creep, fatigue life up to 108 when the strain variable is 1000×10, small resistance value error, good batch quality uniformity, etc. The strain binder should have high bond strength and high shear strength; The modulus of elasticity is large and stable; Good electrical insulation function; Have the same or similar coefficient of thermal expansion as the elastic element; Low creep and hysteresis; When curing, the volume of the adhesive line shrinks small, etc. The thickness of the adhesive layer must be strictly controlled, because the adhesive strength decreases with the addition of the thickness of the adhesive layer.
This is due to the fact that the thin adhesive layer needs greater stress to deform, is not easy to flow and creep, the internal stress on the interface is very small, the probability of bubbles and shortcomings is relatively small, the strain transmission function is good, and as long as the protective seal is reasonable, it can reach a higher level of stability.
5. Production process
The operating principle and overall structure of the strain gauge load cell determine that some processes in the production process are necessary for manual operation, and human factors have a great impact on the quality of the load cell. Therefore, it is necessary to formulate a scientific, reasonable and repeatable production process, and add computer-controlled automatic or semi-automatic processes to it, so as to reduce the impact of human factors on product quality as much as possible.
6. Circuit compensation and adjustment
Due to the unavoidable occurrence of some internal shortcomings and the influence of external environmental conditions, some functional indicators of the load cell can not meet the planning requirements, so it is necessary to carry out various circuit compensation and adjustment, and improve the stability of the load cell itself and the stability of the external environmental conditions. The perfect and precise circuit compensation process is an important part of improving the stability of the load cell.
7. Protection and sealing
Protection and sealing are the key processes in the production process of load cells, and they are the fundamental guarantee for the load cells to withstand the influence of the objective environment and the sensing environment and operate safely and reliably. If the protective seal is poor, the resistance strain gauge and strain binder adhesive layer attached to the elastic element will absorb the moisture in the air and plasticize, resulting in a decrease in bond strength and stiffness, causing zero drift and irregular change in output until the load cell fails.
Therefore, effective protective sealing is the fundamental guarantee for the long-term stable operation of the load cell, otherwise the process effect will be wasted.
8. Stability treatment (artificial aging experiment)
In addition to dealing with the influence of the above-mentioned factors, the most important way to improve the stability of the load cell is to adopt various technical measures and technological means, simulate the application conditions for effective artificial aging experiments, and release as much residual stress as possible to minimize the shaking of its function.
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