Torque wrench running speed The running speed of the torque wrench has a certain influence on the test result. Many testing organizations use the manual to realize the running speed of the torque wrench during the testing process, which will result in unstable loading: the speed is too slow. The final tightening torque lags behind the force response, and the value is too small; the speed is too fast, the final tightening torque depends on the inertia at the end of the test, and the value is too large, so the tester is required to operate at a uniform and moderate speed, or use a loadable torque wrench. The detector can improve the accuracy of the test.
Pre-selection value In the actual operation process, the tester will bring different test results to the test if the selection of the pre-tension force given range value is different. The author has done two sets of tests on the same batch of the same specification bolt: the specification is M24×85-10.9s high-strength bolt pre-tension value range is 206-250 (kN) Test 1: When the pre-tension selected value is relatively close The following table: Test 2: When the pre-tension selected value fluctuates greatly, the following table: the average bolt torque coefficient given in the standard is 0.110~0.150, and the standard deviation is 0.010. Obviously, the above two test results meet the specified requirements. However, the relative error between the two standard deviations is relatively large. Based on Test 1, the value is 25%. The main reason for the above situation can be obtained from the data analysis in the table. The mid-pre-tension values ​​are not much different, so the magnitude of the torque coefficient result is directly affected by the applied torque. The medium pre-tension value fluctuates greatly, and then it affects the torque coefficient together with the value of the torque, and the error source increases, so the error value increases.
The author also carried out the same test on high-strength bolts of other specifications, and found that the pre-tension value is close to the standard deviation obtained, which is always smaller than the standard deviation obtained by the fluctuation of the pre-tension value. This can have two self-contradictory results for bolts of somewhat poor quality. Therefore, the selection of the approximate pre-tension value can reduce the final test error and improve the accuracy of the test.
The measuring instruments should be calibrated before each test. Accurately select the torque wrench range according to different bolts to ensure that the measured value is within 20% to 80% of the range. A selection of high-quality materials to produce test tools with high stiffness. Zero the instrument before the test. The torque wrench runs evenly and moderately. The tester selected the pre-tension values ​​in the test to be equivalent.
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