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Correct use of Rockwell hardness testers

Jun June, 2018

In practical applications, the hardness value of the material being tested can be directly read from the corresponding scale C or B on the Rockwell hardness testers dial, and does not need to be calculated according to the formula. During the test, the following table can be used to select the indenter and load value, the symbol and the effective measurement range.

The most common combinations of indenter and load applications are:

A scale: The indenter is a cone diamond indenter with a vertex angle of 120°. The total load is 588.399N. For the determination of high hardness metals (such as tungsten carbide, etc.), or specimens for hard sheet material and thin surface layer should not use HRC occasions.

C scale: The top angle is 120° cone diamond indenter with a total load of 1471N. Used to determine the hardness of hardened steel products after heat treatment. Application range HRC20-67, if the hardness of the sample is lower than HRC20, the indenter presses deep into the test piece, and the error caused by the incorrect shape of the indenter increases, so the measured result is not accurate. If the hardness of the sample is higher than HRC67, the depth of the indenter pressed into the test piece is very shallow, a large pressure will be generated at the tip of the indenter, and the indenter will be easily damaged.

B scale: Steel ball indenter with a diameter of 1.588mm and a total load of 980.665N. For the determination of soft or medium hardness metals and unhardened steel products. The application range is HRB20-100. When the hardness of the sample is lower than HRB20, the creep phenomenon begins to occur in most cases, and the contact surface between the steel ball and the test piece is too large and the measured result is inaccurate. When the hardness is higher than HRB100, the steel ball is greatly deformed, the depth of the pressed test piece is too shallow, and the measured result is not accurate.

Use the operating method (HR-150A) as follows:

1. Preparation

The certified Rockwell hardness tester is used; the thickness of the test specimen is greater than 10 times the depth of the indentation; Zhangzhou Europe Spectrum selects the appropriate workbench according to the specimen shape; select the appropriate indenter and the total load value.

2. The specific steps of the experiment

A. Place the test piece on the worktable, rotate the handwheel to slowly raise the worktable, and lift the pressure head 0.6mm. The small indicator of the indicator dial points to "3", and the large pointer to marks C and B. (A little bit can turn the dial until it is aligned.)

B. After aligning the pointer, you can pull the loading handle forward so that the main load is applied to the indenter.

C. When the indicator pointer turns to a standstill, the unloading handle can be pushed back to remove the main load.

D. Read the corresponding scale value from the indicator. When using a diamond indenter, read the black dial reading on the outer ring of the dial. When using a steel ball indenter, read the value in the red dot on the inner ring of the reading dial.

E. After loosening the hand wheel and lowering the work bench, you can move the test piece slightly and select a new location to continue the test.

It should be noted that the distance between the centers of the two indentations should not be less than 3mm; for the same test piece, it is better to carry out no less than 3 tests in different places so that the actual conditions can be reliably ascertained.

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