10
7.3 Other Conditions for Testing
- The angle of test force should be within 90L K2L.
- A hardened steel ball (at least 810 Vickers hardness) may only be used on a
material of hardness less than 450 and with a tungsten carbide ball on materials
under HB 650.
- The test force should be applied smoothly and for 10 to 15 seconds.
- To improve the ability to measure an impression, the test site is often ground down
slightly so a smoother edged, easily measured test impression can be made.
7.4 Measurement of the Brinell Impression & Obtaining a Brinell Value
The impression should be measured with a Brinell scope (usually around 20x power with
a fixed measuring scale in millimeters and a source of light to facilitate measurement) at
perpendicular axes to within 0.05 mm. The average value is used for calculation of the
Brinell value by looking up the Brinell scale (load and indentor size) in the Brinell Conver-
sion Chart. This averaged measurement gives the corresponding hardness value.
All Brinell Values should be reported with the load, ball size, ball material, and time-
at-load if it is not the most common 3000kg, 10mm tungsten ball, and 10-15 seconds
time-at load. The test result is often abbreviated such as HB5 400 for Hardness Brinell,
500 kg., test value 500.
7.5 Calibration
There are two methods of calibration of the tester: direct and indirect. The direct meth-
od should be used for checking a new or rebuilt tester. Indirect calibration should be
used for routine checking.
Before a tester is calibrated, it should be checked to make certain that it is set up prop-
erly, the indenter assembly is not damaged and a new ball is properly installed, and the
test force is applied without shock or vibration.
Direct verification involves direct measurement of the indentor, test load, and scope.
Indirect verification involves the use of a standardized test block where testing is done
with all the different forces, balls and hardness ranges being used. For information,
please refer to the most recent revision of ASTM E-10 available.
Daily calibration is performed by making two impressions on a test block, averaging
the values and comparing it with the test block value. If the averaged test value falls
within the test block tolerances, then the tester is suitable for testing.