In 2013, many hardness testing devices were updated multiple times, yet the technical articles remained largely unchanged. It was challenging to find up-to-date information on the number of available test positions. Today, we’re sharing some new and essential technical knowledge about Rockwell hardness testers to help you better understand and use them.
First, the accuracy adjustment method for a Rockwell hardness tester: start by opening the upper cover. If the reading is lower than the standard block, loosen the nut and adjust the screw clockwise. If the reading is higher, turn the screw in the opposite direction. This ensures accurate measurement results.
Second, the load change mechanism of the surface Rockwell hardness tester includes knobs, bushings, chucks, cards, cams, brackets, camshafts, and forks. When the device is unloaded, turn the knob clockwise to the desired load position.
Third, common operational errors include improper sample selection and preparation, incorrect installation of the head, wrong test conditions, unskilled handling (such as sudden loading or unloading), and reading mistakes.
Fourth, when using a surface Rockwell hardness tester to measure thin parts on the T-scale, small indentations may appear on the back of the sample, causing material deformation. To avoid this, use a diamond table with a diameter of approximately 4.5 mm. However, this table is not suitable for the Rockwell and N scales, and it should be clearly noted in the report.
Fifth, the mechanical structure of a Rockwell hardness tester typically consists of a body, loading mechanism, measuring system, and indenter. The principle involves applying a set load through the loading mechanism, pressing the indenter into the sample, measuring the indentation depth, and converting it into a hardness value.
Sixth, the surface Rockwell hardness test uses two test forces: initial and total. After maintaining the total force for a while, the main force is removed, and the indentation depth is measured. The difference between the depths indicates the Rockwell hardness value, which is calculated based on 0.001 mm per unit.
Seventh, the tolerance for Rockwell hardness testers is ±2% for accuracy, and the total load tolerance is ±0.5%.
Eighth, the Rockwell hardness test is fast, simple, and widely used in production due to its ability to measure both hard and soft materials. However, it is less accurate than Vickers or Brinell methods due to the influence of the indenter and measuring mechanism.
Ninth, the B scale is used for softer metals with a 1.588 mm steel ball under 100 kg force. It is not suitable for HRB values above 100 or below 20, as creep or deformation can occur.
Tenth, the loading speed affects the results. A faster application can increase indentation depth, leading to lower hardness readings. Slower speeds are recommended for more accurate measurements.
Eleventh, the plastic Rockwell hardness tester has different scales with specific ranges: HRE (70–94), HRL (100–120), HRM (85–110), and HRR (114–125).
Twelfth, the symbol for surface Rockwell hardness is HR followed by the scale, such as HRN or HRT, with specific ranges like HR15N (70–94).
Thirteenth, each Rockwell scale uses a specific combination of load and indenter: A scale (60 kg + diamond), B scale (100 kg + steel ball), and C scale (150 kg + diamond).
Fourteenth, the initial and main loads must be properly adjusted. Any misalignment or wear can affect accuracy. The initial load tolerance should be less than ±2%, and the main load less than ±0.5%.
Fifteenth, if the indicator moves too quickly, the buffer may need oil. Use clean No. 32 oil and move the piston up and down to remove air bubbles.
Sixteenth, regular calibration is essential. Test five points on a standard block and ensure the average deviation does not exceed specified limits. Check the indenter and test force if necessary.
Seventeenth, installing the pressure head requires cleaning the spindle and ensuring proper alignment. Tighten the ram screw after applying the main load.
Eighteenth, the Rockwell hardness value is calculated using constants N and S, depending on the scale. The deeper the indentation, the lower the hardness value.
Nineteen, Rockwell hardness testers come in various types, including manual, electric, and digital models. They also differ in loading mechanisms and applications.
Twentieth, the sheet thickness must be at least 1 mm, and the diameter of round bars should be 3 mm. Small components cannot be tested accurately.
This summary covers key technical aspects of modern Rockwell hardness testers, helping users make informed decisions and improve measurement accuracy.
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