First, human error :
Â Â Â 1. The operator is not skilled enough, has poor practical experience, and is caused by improper operation. It should be led by a person familiar with the operation of the hardness tester;
Â Â Â 2. The load is too fast, the holding time is short, the hardness of the low-hardness parts is high, the loading is too slow, the holding time is long, the hardness is low, and the loading should be smooth during the operation to maintain a certain loading time.
Second, the impact of the tested parts :
Â Â Â 1. Different surface finishes show different effects when tested on Rockwell hardness. The lower the surface finish, the higher the hardness of the high hardness test, whereas the lower the hardness, the rougher surface with the marks, the quickest cooling at the time of quenching, or the very hard surface, the hardness value is high. Conversely, when the tempered parts are tempered at high temperatures, the surface layer with knife marks changes first, the resistance to tempering is small, and the hardness value is low. When testing parts with a surface finish of Î” 7 or less, they must be ground with a waste wheel, then honed with a guillotine, or polished with a thin hand wheel and wiped clean.
Â Â Â 2 , the surface of the heat treatment parts have salt, sand and other objects, when the load increases, the parts will produce slip, if there is greasy existence, when the diamond head presses into the lubrication, reduce friction, increase the pressure depth. Both of these reasons make the tested hardness value low. The hardness value of the thin layer of loose skin and loose skin of the parts tested was reduced, and the hardness value of the dense layer of oxide scale was increased. The parts to be tested for hardness must be descaled, rubbed clean and free of dirt.
Â Â Â 3 , the slope (or taper), spherical and cylindrical parts of the hardness test error than the plane. When the indenter is pressed into the surface of such a part, the resistance around the indentation is smaller than the plane, and there is even a phenomenon of deviation and slip. The pressure depth increases and the hardness decreases. The smaller the radius of curvature, the greater the slope, the more significant reduction in the hardness value. Diamond indenters are also easily damaged. For such parts, a special workbench is designed so that the worktable and the indenter are concentric.
Third, the impact of hardness tester head :
Â Â Â 1. The diamond indenter does not meet the technical requirements or wear out after a certain period of time. If the operator can not judge the quality of the diamond, the diamond indenter can be calibrated by the measurement testing agency.
Â Â Â 2 , steel ball head strength and hardness is not enough, easily deformed. After the steel ball is flattened and flattened, it becomes elliptical after permanent deformation. When the minor axis is perpendicular to the surface of the part, the indentation is shallow and the indication value is high; when the long axis is perpendicular to the surface of the part, the indentation is deepened, the indication value is reduced, and the steel ball tolerance is small 0.002. Mm .
Fourth, the load :
Â Â Â 1 , the initial load: friction between the spring and the spindle, the lever and the dial indicator, resulting in 100N increase or decrease. Adjust the screw loose and adjust the movement. The starting line is different, causing the initial load to be wrong. If the initial load is not correct, the fit of the spring, spindle, lever, dial indicator, etc., should be adjusted. After the position of the adjustment block is properly moved, tighten the adjusting screw and tighten the position of the ejector lever. The initial load tolerance should be less than Â± 2% .
Â Â Â 2. Main load: Leverage ratio is incorrect. There is error in the weight of the suspender and the weight. The main shaft, lever and weight are skewed. All of them cause errors in the main load. Leverage ratio is incorrect and should be adjusted. The wear of the blade should be repaired or replaced, and the spindle deformation should be straightened. Spindle, lever and weight deflection should be positive. The tolerance of main load for various scales is less than Â± 0.5% .
Fifth, the hardness of the installation is not correct. The hardness tester is not in the horizontal position. When testing the hardness, the value is low. Use a spirit level to measure the level, then level the hardness tester.
6. The surface of a test part of a part is in poor contact with the worktable, or the support point is not stable, and slipping, rolling, and tilting will occur. This not only results in inaccurate results, but also damages the instrument. A suitable table should be designed according to the geometry of the part.
Seven, the impact of the surrounding environment. The hardness tester used in factory production is often affected by the vibration of the surrounding environment, causing the instrument structure to loosen and the indication value to be unstable. The hardness tester should be installed without vibration or away from the source.
Eight, the hardness value is not accurate: There are two conditions leading to inaccurate test hardness, if the indenter used is a diamond indenter, first use the surface of the nail and gently rub the top of the indenter, observe the nails are not out Deep traces, deep traces indicate that the indenter has been damaged, and vice versa. The second case is that the fine adjustment of the instrument is not adjusted properly. Open the top of the hardness tester, loosen the two screws of the thimble part with a flat-head screwdriver, and then adjust the trimming iron forward to increase the hardness value, and vice versa.
Professional create value, Dongguan Haida cast quality! Dongguan Haida equipment specializing in the production of carton compression testing machine , burst strength testing machine, drop test bench , vibration testing machine and other packaging testing equipment, welcome to call!
For more detailed product series and related technical parameters, please contact:
National Unified Service Hotline: 400-0711-808
Haida International Instrument: 0769-89280808
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