Although rockwell hardness tester is simple in structure and easy to operate, if it is improperly operated for a long time, the quality of products will be greatly affected, and the hardness tester will bring bad consequences. Now we will introduce some common errors and processing methods in the verification as follows:
1. Human error
1. Operators are not skilled enough and have poor practical experience, so they should be used by those who are familiar with the operation of durometer;
2, too fast loading, short load holding time, low hardness parts hardness on the high side, and too slow loading, long load holding time, low hardness, the operation of loading should be flat, maintain a certain loading time.
Ii. Factors affecting the tested parts:
1. Different surface finishes show different effects in rockwell hardness test. The lower the surface finish, the higher the hardness in the high hardness test, and vice versa, the lower the hardness, the rough surface with knife marks, when quenching * fast cooling first, or very hard surface, the hardness value is high. On the contrary, when tempering at high temperature, the surface structure with knife marks changes first, the resistance to tempering is small, and the hardness value is low. Δ surface finish of the test the following seven parts, must use the grinding wheel finishing grinding, reoccupy file file grinding smooth, or with a hand wheel polishing, then wipe and clean;
2, heat treatment parts surface salt, sand and other things, when the load, the parts will produce slippage, if there is greasy, diamond head into the lubrication, reduce friction, increase the depth of pressure. These two reasons make the hardness measured low. The hardness value of the thin oxide peel pinewood layer decreased and the hardness value of the thick oxide peel dense layer increased. To measure the hardness of the parts must be removed from the oxide skin, wipe clean, no dirt;
3, bevel (or taper), spherical and cylindrical parts of the hardness test error than plane. When pressing a head into the surface of this kind of part, the resistance all round pressing place is smaller than plane, have deviation, the phenomenon of slip even, press deepness increase, hardness decreases. The smaller the radius of curvature, the larger the slope, the more significant the decrease of hardness value. Diamond head is also easily damaged. To this kind of spare parts must design the special work table, causes the work table and the pressure head to be homocentric.
Iii. Impact of head:
1. The diamond indenter does not meet the technical requirements or is worn after being used for a period of time. A simple method to determine whether the diamond indenter is damaged: scrape the glass surface with the diamond indenter for several times to see that the glass surface is good if there is no scratch, otherwise the indenter has been damaged. If the operator cannot judge whether the diamond is good or bad, it can be verified by a measuring and testing institution.
2, steel ball head strength and hardness is not enough, easy to produce deformation. When the short shaft is perpendicular to the surface of the part, the indentation is shallow and the indication value is high. When the long shaft is perpendicular to the surface of the part, the indentation deepens, indicating value decreases, and the tolerance of steel ball is 0.002mm smaller.
1. Initial load: there is friction between spring and spindle, lever and dial indicator, resulting in the increase or decrease of 100N. Adjust the screw loose, adjust the movement, the ejector position is improper. The difference of starting line causes wrong initial load. If the initial load is not correct, adjust the spring, spindle, lever, dial indicator, etc. When the position of the adjusting block is moved properly, tighten the adjusting screw and tighten the position of the ejector. The tolerance of initial load should be less than ±2%.
2. Main load: the proportion of lever is wrong, and the balance weight of derrick and weight is wrong; The deviation of spindle, lever and weight will make the main load error. Lever ratio is wrong, should undertake adjusting. Blade wear should be repaired or replaced, spindle deformation to be straightened. The deviation of spindle, lever and weight should be corrected. The tolerance of main load of various scales is less than ±0.5%.
5. Improper placement of hardness tester (rockwell hardness tester). The durometer is not in a horizontal position and its value is low when the hardness is tested. Measure levelness with a leveler and flatten the hardness tester.
Six, the surface of a certain test part and the table contact is not good, or the support point is not stable, will produce sliding, rolling, warping phenomenon. This not only makes the results inaccurate, but also damages the instrument.