Notes on the calibration of hardness testers

Before calibrating the HR-150 Rockwell hardness tester, do not use a hardness block to measure the reading error of the hardness tester. First, determine whether the working state of the verified hardness tester is in normal working state. This requires attention to the following issues
1. To determine if the installation position of the hardness tester is horizontal, the method is to open the back cover of the weight and check if the weight is free to hang vertically. During the loading process, do not touch the inner sides or the bottom support.
2. Check if the position of the suspension rod is normal. Method of judgment: Use HRC high hardness blocks or other materials. When adding initial test force, the pointer has already rotated three times. At this time, press upwards and let the pointer rotate another half circle, within three and a half plus or minus 10 grids, indicating that the suspension rod position is normal. If it is not normal, adjustment method: ① Adjust the length of the weight suspension rod, adjust the two adjustment screws on the suspension rod up and down, and adjust it to the normal working position; ② The method of adjusting the height of the lever is to open the upper cover plate, remove the dial indicator at the front, loosen the screws that fix the height of the lever at the front and top, and then adjust the two screws in the top sink hole. It is obvious that the lever is moving up or down, and can be adjusted to the appropriate position. Then, tighten the four positioning screws.
3. Check if the buffer device of the hardness tester is fully loaded within 4-6 seconds. Adjustment method: Open the back cover and see that the buffer device has an adjustable button inside. Adjust it to adjust the speed of the buffer. If there is no oil in the buffer or there is an impact sound when loading due to oil shortage, add hydraulic oil to the buffer. When adding oil, pry up the dust ring and use oil to grab the oil. The amount of oil added is sufficient.
4. Is the loading action normal. All of the above are normal, and it also depends on whether the loading action is normal. It can be normal during load conversion, with conversion between 60, 100, and 150. If not, the weight position needs to be adjusted. This is necessary for measuring HRA HRB hardness has an impact. The HRA and HRC pressure heads are the same, When measuring HRB, it should be noted that the hardness value of HRB is very small and the tested object is very soft. If measured normally, The HRB hardness value is relatively high, which may be due to the deformation of the steel ball with a diameter of 1.588mm. It needs to be replaced. In case it cannot be replaced, the steel ball can be removed and reinstalled to test the HRA During HRB and HRC, attention should be paid to load to load conversion.
5. The above is normal and formal calibration work can begin.
If it is found during calibration that the high hardness and low hardness of HRC are not linear errors, it is generally caused by the damage of the diamond indenter. At this time, the indenter needs to be replaced. If the error is linear, the adjustment method is as follows: open the upper cover plate, adjust the small cover plate on the top needle, adjust it inward, and the indicated hardness value will increase, adjust it outward, and the indicated hardness value will decrease. Repeat the adjustment until the hardness tester is qualified.
Analysis and Troubleshooting of Three Rockwell Hardness Testers
If the hardness tester shows an unqualified value: There are many factors that can cause the HR-150 Rockwell hardness tester to fail calibration, such as: indenter, preload, main load, frame and specimen support mechanism, measurement and indication mechanism, specimen, test conditions, operator, etc. We will analyze and troubleshoot some common faults as follows:
1. At the beginning of preloading, there is shaking of the pointer on the Vickers hardness tester
Main reason: Loose fit between the long keyway of the flat key and the lifting screw.
Troubleshooting method: Tighten the fastening screws of the flat key or replace the flat key.
2. After the main load is added, the pointer shakes
Main reason: There is oil on the weight tray; The buffer is not level relative to the workbench; The body is not level.
Troubleshooting method: Remove oil stains from the towing tray; Adjust the screws connecting the buffer to the body to make it horizontal; Correct the level on the workbench.
3. Pointer jumping when starting to load the main load
Main reason: The loading handle is loose; The oil level of the buffer is insufficient.
Troubleshooting method: Tighten the loose top screw; Refuel and exhaust the air.
4. After applying the main load, the pointer takes a long time to move
Main reason: The weight suspension rod is too long.
Troubleshooting method: Shorten the suspension rod.
5. After adding the main load, the pointer does not move
Main reason: The main load was not added; The buffer oil needle has closed the oil hole.
Troubleshooting method: Shorten the length of the suspension rod; Open the buffer and adjust the oil needle.
6. When adding the main load, the pointer moves too fast
Main reason: The adjustment oil needle of the buffer is in the large opening position; The buffer is free of oil.
Troubleshooting method: Adjust the oil needle to the appropriate position; Refuel and exhaust the air.
7. When adding the main load, the pointer moves too slowly
Main reason: The adjustment oil needle of the buffer is too small; Buffer oil is too dirty or has excessive viscosity; The dial gauge measuring rod has significant friction; The spindle system has resistance.
Troubleshooting method: Adjust the oil needle to the appropriate position; Replace oil with appropriate viscosity; Eliminate friction; Clean the spindle system.
8. When adding the main load, the pointer will move and stop at different times, and it will be fast and slow at different times
Main reason: There is air in the oil cylinder of the buffer; The unevenness of the fuselage causes collisions or friction between the weights and the fuselage.
Troubleshooting method: Remove the air from the oil cylinder; Adjust the body level. Vickers hardness tester
9. The pointer jumps after the main load is removed
Main reason: There is oil stains on the ball head and ball socket of the connection between the weight suspension rod and the large lever.
Troubleshooting method: Clean the oil stains.
10. When the main load is unloaded to the end, the pointer suddenly rises or falls
Main reason: The control handle is loose.
Troubleshooting method: Adjust and tighten the fixing screws of the control handle.
11 A. B and C scales have regularly high hardness values
Main reason: The testing leverage ratio is too high; The preload is too high; The main load has not been fully loaded; The main load weight is lighter.
Troubleshooting method: Loosen the fixing screws of the adjustment plate and move the adjustment plate forward to the appropriate position; Adjust the preload accurately; Shorten the suspension rod; Weigh each weight.
12 A. The hardness values of the B and C scales are regularly low
Main reason: The testing leverage ratio is too small; The preload has decreased; The main load weight is heavy; Incorrect installation of the pressure head; The workbench is not installed correctly; The tightness between the workpiece and the workbench is poor.
Troubleshooting method: Loosen the fixing screws of the adjustment plate and move it backwards to the appropriate position; Adjust the preload accurately; Adjust the weight mass; Reassemble the pressure head; Reinstall the workbench; Reposition the workpiece.
13 A value is qualified, C-value unqualified
Main reason: The upper conical surface of the top of the pressure head is not smooth or the conical angle is too large; The upper conical surface near the top of the pressure head is damaged.
Troubleshooting method: Repair or replace the pressure head.
14 A. The C value is qualified, B value unqualified
Main reason: The steel ball is loose in the ball socket; The size deviation of the steel ball of the pressure head B is large or rusted and damaged.
Troubleshooting method: Reinstall; Replace with a new steel ball.
15 A. Both B and C scale values are unstable
Main reason: There is resistance in the spindle system; The end face of the spindle is uneven; The blade and fulcrum blade on the large lever have changed or become blunt in contact.
Troubleshooting method: Clean the spindle system; Flatten the end face; Readjust the position or polish the blade with an oilstone.
16 The high value in the C value is qualified, while the medium and low values are unqualified
Main reason: Inappropriate testing leverage ratio; The surface of the pressure head cone angle is not smooth. Vickers hardness tester
Exclusion method: Adjust the leverage ratio; Repair or replace the pressure head.
17 The high, medium, and low values of C are all unqualified
Main reason: Incorrect leverage ratio during testing; The adjusting screw tip on the testing lever is severely worn; The main load has not been fully loaded; Damaged diamond pressure head; Poor coaxiality between the spindle and the workbench; The dial gauge is faulty.
Exclusion method: Adjust the leverage ratio; Replace with new adjustment screws; Shorten the suspension rod; Pressure change head; Adjust the position of the lifting screw; Repair the dial gauge.