Applications & Tips

The validity period for the calibration of a given hardness reference block is specified in part 3 of the ISO standard published for the respective hardness testing process.

The validity for steel hardness reference blocks should be limited to five years, whereas the validity period can be reduced to two to three years for aluminium and copper alloys.

According to the standard, no subsequent rework may be carried out on the hardness reference blocks.

However, hardness reference blocks do not lose their certified properties on the very day that the calibration certificate expires, recalibration of the respective hardness reference block by an appropriately certified respectively accredited company is possible.
 

The MPA/NRW provides a file for download under the following link in the form of an Excel file for periodic testing and measurement uncertainty. After entering the MPA/NRW number and the hardness value from the calibration certificate, the relevant file becomes available to download.

www.mpanrw.de/downloads/haertevergleichsplatten-dateiabruf-messunsicherheit/
 

Particularly in the case of micro hardness testing, the parts to be tested are often embedded.

Material specimens are embedded in resin to make it easier to handle them until the optimum preparation result has been achieved. Heat-treated and surface-coated specimens should always be embedded.

Note: The best results are achieved when specimens are carefully cleaned before embedding. The specimen surface must always be free of grease, so that the resin adheres optimally to the specimen material. All other contamination must also be removed.

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The standardised period of exposure to the test force in the Brinell method lies between 10 and 15 seconds (s) according to ISO 6506 and ASTM E10.

If the test force exposure period is longer or shorter than the range specified in the standard, then this must be documented in the measurement result.

Example: 170 HBW2.5/187.5/20, means: 20 seconds test force exposure

Period of exposure to test force in the Vickers method
According to  ISO 6507 and ASTM E92 resp. ASTM E384, the standardised period of exposure to the test force is between 10 and 15 seconds (nominal time duration according to ISO: 14 s).

If the exposure period is longer or shorter than the range specified in the standard, then this must be documented in the measurement result.

Example: 650 HV30/25, means: 25 seconds test force exposure

According to ISO 6507, the difference between the lengths of the two diagonals measured during Vickers hardness testing must not exceed 5%.

If the difference is larger, then this must be specified in the test report.

In practice, however, indentations with excessive differences are usually discarded and replaced with a new indentation.
 

If a Rockwell test is conducted on cylindrical parts, then, due to the lower resistance of the test surface with respect to the indenter, the following correction values – depending on the specimen curvature radius and the Rockwell scale used – must be added to the test result (acc. ISO 6508-1).

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There are currently three standardised conversion tables:

DIN 50150
ISO 18265
ASTM E140

Convert your hardness values quickly and easily using the EMCO-TEST Info-App !

• Test date
• Designation of the standard used for the hardness test
• Description of the specimen
• Measurement result
• Temperature during the test, if outside the range 10 °C to 35 °C
• Information about the test, which is not specified in ISO 6507
• Information about any occurrences that may have had an influence on the result
• Conversion table and method used

• Designation of the standard used for the hardness test
• Description of the specimen
• Measured values must be specified in accordance with the specifications stipulated in the standard (Point 4.2)
• Date of test
• Temperature during the test, if outside the range 10 °C to 35 °C
• If the ratio of the indentation diameter to the diameter of the indenter is outside the range 0.24 – 0.60, then this must be specified in the test report.
• If a conversion is used, the conversion process and its underlying algorithm must be specified
• Information about the test, which is not specified in ISO 6506
• Information about any occurrences that may have had an influence on the result

• Designation of the standard used for the hardness test
• Description of the specimen
• Temperature during the test, if outside the range 10 °C to 35 °C
• Measured values must be given in accordance with the specifications set out in the standard (Point 4.2)
• Date of the test
• Information about any test steps undertaken that are not specified in ISO 6507
• Information about any occurrences that may have had an influence on the result
• Details of any conversion process applied and the underlying algorithm must be stated
• Should the exposure time of the overall test duration exceed six seconds, then this must be noted in the test report