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Common errors and processing methods in Rockwell hardness tester
Browse: Release Date: 2019-08-02
虽然结构简单,操作方便,但如果长期操作不当,检验硬度失准,将使产品质量受到很大影响,带来不良后果。 Although the Rockwell hardness tester has a simple structure and is easy to operate, if it is improperly operated for a long time and the hardness is incorrectly tested, it will greatly affect the product quality and bring adverse consequences. Now we introduce several common errors and processing methods in our test:
1. Human error.
(1) The operator is not technically proficient and has poor practical experience, and should be used by personnel familiar with hardness testers;
(2) The loading is too fast, the holding time is short, and the hardness of the parts with low hardness is too high, while the loading is too slow, the holding time is long, and the hardness is low. The loading should be flat during operation to maintain a certain loading time.
Second, the factors affecting the tested parts.
(1) Different surface finishes show different effects during Rockwell hardness testing. The lower the surface finish, the higher the hardness during the high hardness test. Conversely, the lower the hardness, the rougher the surface with knife marks, the faster the first cooling during quenching, or the harder the surface, the higher the hardness value. On the contrary, when the tempering part is tempered at high temperature, the surface structure with knife marks is transformed first, the ability to resist tempering is small, and the hardness value is low. When testing parts with a surface finish of Δ7 or less, they must be finely ground with a waste wheel, smoothed with a file, or polished with a fine hand wheel, and then wiped clean.
(2) The surface of heat-treated parts has salt, sand, etc. When the load is applied, the parts will slip. If there is greasy, the diamond head will lubricate when pressed in, reducing friction and increasing pressure depth. These two reasons make the measured hardness values low. The hardness value of the thin oxide and vegetable pine layer at the part tested decreases, and the hardness value of the dense oxide thick layer increases. The scale to be tested for hardness must be removed and wiped clean without dirt.
(3) The error of the hardness test of the inclined surface (or taper), spherical surface and cylindrical part is larger than that of the flat surface. When the indenter is pressed into the surface of such a part, the resistance around the indentation is smaller than that of the plane, and there is even a phenomenon of deviation and slippage. The pressure depth increases and the hardness decreases. The smaller the radius of curvature, the greater the slope, and the more significant the decrease in hardness value. Diamond indenters are also easily damaged. For such parts, a special workbench should be designed so that the workbench and the indenter are concentric.
Third, the impact of the indenter.
(1) The diamond indenter does not meet the technical requirements or is worn after a period of use. If the operator cannot judge the quality of the diamond, it can be verified by a metrological testing agency.
(2) The strength and hardness of the steel ball indenter is not enough, and it is easy to deform. When the steel ball is flattened, it will become oval after permanent deformation. When the short axis is perpendicular to the surface of the part, the indentation is shallow and the value is high. When the long axis is perpendicular to the surface of the part, the indentation is deepened and the value is reduced. mm.
Fourth, load.
(1) Initial load: There is friction between the spring and the main shaft, the lever and the dial indicator, causing an increase or decrease of 100N. The adjustment screw is loose, the adjustment block is moved, and the ejector rod is improperly positioned. The starting line is different, causing the initial load to be incorrect. If the initial load is incorrect, adjust the fit of the spring, spindle, lever, dial indicator, etc. After the position of the adjustment block is properly moved, tighten the adjustment screw and the position of the ejector. The tolerance of the initial load should be less than ± 2%.
(2) The main load: the ratio of the lever is incorrect, the counterweight of the boom and the weight is wrong; the main shaft, the lever and the weight are deflected, which will cause the main load to be wrong. The leverage ratio is not correct and should be adjusted. The knife edge should be repaired or replaced if it is worn, and the main shaft deformation should be straightened. The spindle, lever and weight deflections should be set correctly. The tolerance of the main load of various scales is less than ± 0.5%.
Fifth, the placement of the hardness tester is incorrect.
The hardness tester is not in a horizontal position and its value is low when testing hardness. Measure the level with a spirit level, then flatten the hardness tester.
6. The surface of a test part of the part has poor contact with the workbench, or the support point is not stable.
This will result in slippage, rolling, tilting, etc., which will not only result in inaccurate results, but also damage the instrument. A suitable workbench should be designed according to the geometry of the part.
Impact of the surrounding environment.
The hardness tester used in factory production is often affected by the surrounding environment, which causes the structure of the instrument to become loose, and the displayed value is unstable. The hardness tester should be installed in a place without vibration or far away from the source.

佛山市精测计量仪器设备有限公司 总部 Company Name : Foshan City Precision Measurement Instruments Co., Ltd. ( Headquarters )


广东省佛山市顺德区陈村镇顺联机械城 17座二层2008室 Address : Room 2008, 2nd Floor, Block 17, Shunlian Machinery City, Chencun Town, Shunde District, Foshan City, Guangdong Province
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