January 21, 2022

Analysis of Force Principle of Deformation Measurement of Fixed Electronic Weighing Capacity

1 Overview
GB/T 7723-2008 “Static Electronic Weighing Apparatus” National Standard Since its implementation on September 1, 2009, the biggest change compared to before is the addition of a new content of bearing capacity deformation test. The implementation of the national standard to date has made more detailed and specific requirements for manufacturers of large-scale fixed weighing instruments, the most important of which is the requirement for more stringent and strict requirements for the selection of materials for the manufacture of large-scale stationary scales; In the type evaluation test, according to the test methods and test conclusions stipulated in the deformation test of the bearing capacity, the material selection of steel has a crucial role.
2 Weighing platform steel work properties
Strength, plasticity, toughness, and hardness are important indicators of measuring the metal properties of the weighing platform's own steel.
2.1 Intensity
Strength is the main test indicator of the mechanical properties of the material. Steel will deform under static load, and the material resistance will begin to be lost, and plastic deformation stress will be generated. When the actual load of the weighing platform steel itself reaches the yield strength point of the steel, the material itself will produce an irrecoverable permanent deformation. Intensity is expressed in material mechanics as [σ] and the unit is MPa.
Understanding the nature of the steel strength of the weighing platform makes it practical for the actual production process.
2.2 Elastic Modulus
Elasticity is the focus of the test of deformation of bearing capacity. The load and the strain of the steel itself are changed under the static load of the steel bearing platform of the weighing instrument. The property of the deformation characteristic in the test is called elasticity. In this stage of deformation, the ratio of stress and strain produced by the steel is the elastic modulus [E], the unit is MPa; the formula is:
[E=σε] ([ε]—Strain)
Elastic modulus is an important indicator to measure the deformation resistance of the bearing platform steel, which is of great significance. The greater the [E], the greater the stress value that causes a certain amount of elastic deformation; in the areas involved in industrial production, the elastic modulus [E] reflects the strength of the steel and is the calculation of the weight of the steel under stress conditions. Taiwan's structural deformation of an important indicator. The elastic modulus of the carbon structural steel Q235B, which is commonly used in the manufacture of scale caps, is [E]=(2.0 to 2.1)*105 MPa.
2.3 Sectional axis moment of inertia
The moment of inertia of steel is a geometric quantity that is often used to characterize the resistance of steel sections to bending. In the GB/T 7723-2008 "fixed electronic scales" with [J] said; international unit of inertia moment (m4). That is, the area second moment, also called the area moment of inertia.
As for the structure of large scales, the type of steel used is also very different, so the moment of inertia of the steel section axis is not the same, as shown in Figure 1.
3 Requirements of national standards
GB/T 7723-2008 "Fixed Electronic Weighing Apparatus," the national standards in the article pointed out: In the field test or prototype test, you need to first check the product random file, and understand the test sample after loading the corresponding weight load deformation value .
Then use the load with the specified weight to load into the middle of the single-section carrier, the length is in accordance with the loading area, the width is the same as the width of the carrier (see Figure 2), and the height vernier or dial indicator will be placed in the middle of the single-section carrier. The deformation of the single-section carrier was measured at this time, and the relative deformation was calculated according to the size of the single-section carrier.
The deformation formula is calculated as follows:
[fmax=qcl3384EJ(8-4γ2+γ3)]
Where: [q] - the average load on the length of the local unit; [c] - the length of the local unit; [l] - the distance between two support points of the single-section carrier; [γ] - [cl]; [E] - Elastic modulus; [J] - Sectional axis moment of inertia.
The formula for calculating the stiffness is: stiffness=[fmaxl≤1800] or [1600]. According to Table 1, it can be concluded whether the deformation test of the carrier is qualified.
4 Conclusion
For the forming fixed electronic weighing instrument, in the test process, the elastic modulus [E] and the sectional axis moment of inertia [J] are the material properties of the steel used by the scale, and the other quantities are fixed values ​​of the scale itself and the test.
It is not difficult to see from the formula that the elastic modulus [E] and the moment of inertia of the section axis are the important basis for the determination of the amount of deformation [J] from the material selection. Therefore, more detailed and specific requirements have been put forward for manufacturers of large-scale fixed weighing instruments. , Including: (1) full understanding of the provisions of GB/T 7723-2008 "Fixed Electronic Weighing Apparatus"; (2) Selection of Steels for Weighing Instruments; (3) Satisfying Technical Requirements for Type Evaluation of Fixed Electronic Weighing Apparatus.
references
[1] GB/T 7723-2008 Fixed Electronic Scale [S].
[2] Nie Yiqin, Meng Guangwei. Materials Mechanics [M]. Beijing: Mechanical Industry Press, 2009.
[3] Zhang Yue, Wu Xiaojie. Steel Structure [M]. Hangzhou: Zhejiang University Press, 2016.
About the Author
Wang Baochen, specialist and assistant engineer, is mainly engaged in the research of weighing instruments and calibrators.
Liu Xu, undergraduate, assistant engineer, is mainly engaged in the research work of weighing instruments.
Author: Wangbao Chen Liu Xu Source: Brand and standardization of 2017 4

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