The Rockwell hardness tester uses a standard hardness block for indirect testing. The range of the standard hardness block for each scale is shown in the relevant list. In each hardness range that needs to be checked, first make two indentations on the corresponding hardness standard block to ensure that the hardness tester is in the Normal working status, and make the positioning of the standard block, indenter and test bench reliable.
Note that these two indentations are not included in the results, and then make 5 indentations evenly distributed. The Rockwell hardness tester has a simple structure and is easy to operate. It is currently widely used in many industries. However, if done improperly, inaccurate hardness testing will greatly affect product quality and lead to adverse consequences. Let’s introduce several common errors and treatment methods in Rockwell hardness tester calibration:
- Human error in Rockwell hardness tester calibration.
(1) Operators with insufficient technical proficiency and poor practical experience should be used by personnel who are familiar with hardness testers.
(2) Parts that are loaded too quickly and have a short load holding time will have a low hardness, while parts that are loaded too slowly and have a long load holding time will have a low hardness. During operation, the loading should be smooth and a certain loading time should be maintained. - Factors affecting the parts being tested in Rockwell hardness tester calibration.
(1) Different surface finishes will show different effects on the Rockwell hardness test. The lower the surface finish, the higher the hardness during high hardness testing; conversely, the lower the hardness. When quenching a rough surface with knife marks, let it cool down the fastest first, because a very hard surface layer has a high hardness value. On the contrary, when the quenched and tempered parts are tempered at high temperature, the surface structure with knife marks will change first and have less ability to resist tempering, so the hardness value will be low. When testing parts with a surface finish below Δ7, it is necessary to use a waste grinding wheel to finely grind, then file it smooth with a file, or polish it with a fine hand grinding wheel and then wipe it clean.
(2) There are salt stains, sand and other substances on the surface of heat-treated parts, and the parts will slip when a load is applied; if there is greasy, the diamond head will act as a lubrication when pressed in, reducing friction and increasing the pressure depth. These two reasons make the measured hardness value low. The hardness value of the parts tested where the oxide skin layer is thin decreases, and the hardness value of the part where the oxide skin layer is dense increases. The parts to be measured for hardness must be removed from scale and wiped clean without any dirt.
(3) The error in hardness testing of inclined surfaces (or tapers), spherical surfaces and cylindrical parts is larger than that of flat surfaces. When the indenter presses into the surface of such a part, the resistance around the indentation point is smaller than the flat surface, and may even deviate or slip. The indentation depth increases and the hardness decreases. The smaller the radius of curvature, the larger the slope, and the more significant the reduction in hardness value. The diamond indenter is also easily damaged. For such parts, a special workbench must be designed to make the workbench and the indenter concentric. - The influence of the indenter in Rockwell hardness tester calibration.
(1) The diamond indenter does not meet the technical requirements or is worn after being used for a period of time. If the operator cannot judge the quality of the diamond, it can be verified by a measurement and testing agency.
(2) The steel ball indenter has insufficient strength and hardness and is prone to deformation. When the steel ball is flattened and permanently deformed, it becomes an ellipse. When the short 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 becomes deeper and the indication value decreases. The steel ball tolerance is as small as 0.002. mm. - Load aspect.
(1) Initial load: There is friction between the spring and the spindle, the lever and the dial indicator, causing an increase or decrease in 100N. The adjustment screw is loose, the adjustment block moves, and the ejector rod is in an improper position. There is a difference in the starting line, causing the initial load to be incorrect. If the initial load is incorrect, the coordination of springs, spindles, levers, dial indicators, etc. should be adjusted. After the position of the adjusting block has moved appropriately, tighten the adjusting screw and the position of the ejector rod at the same time. The tolerance of the initial load should be less than ±2%.
(2) Main load: The lever ratio is wrong, the balance weight of the boom and the weight is wrong; the spindle, lever and weight are deflected, which will cause the main load to have errors. The leverage ratio is wrong and should be adjusted. If the blade is worn, it should be repaired or replaced, and if the spindle is deformed, it should be straightened. The spindle, lever and weight deflections should be corrected. The tolerance of the main load of various scales is less than ±0.5%. - The surface of a certain test part of the part is in poor contact with the workbench, or the supporting point is unstable.
This will cause slipping, rolling, warping and other phenomena, which will not only make the results inaccurate, but also damage the instrument. A suitable workbench should be designed based on the geometry of the part. - The hardness tester is not installed correctly.
The hardness tester is not in a horizontal position, and when testing the hardness, its value is on the low side. Use a spirit level to measure the level and then level the hardness tester. - The influence of the surrounding environment during Rockwell hardness tester calibration.
Hardness testers used in factory production are often affected by vibrations in the surrounding environment, causing the instrument structure to become loose and the indication value to be unstable. The hardness tester should be installed in a place without vibration or far away from the source of vibration.
