Could you explain the most common problems when conducting Rockwell hardness testing?
Here are the remaining four problems and tips from last week’s blog (in no particular order):
5. Readings taken too close together will give false (higher) hardness readings.
a. Indentations should be three diameters apart.
6. The indenter is damaged (chipped or cracked diamonds or flattened balls) and will produce false readings.
a. Periodically remove the indenter from the hardness tester and inspect the tip using a low-power magnification (10-50X) such as a stereomicroscope or loop to check for damage. Flattened balls are sometimes difficult to detect unless you inspect all surfaces – often at an angle.
7. Parts that are not properly supported will give false readings.
a. Large and irregularly shaped parts need to be well supported. Parts that move, even slightly during the test, produce a false reading – even if that reading falls within the desired hardness range.
b. Changing the anvil to one that keeps the part stationary using the variety that should be available with your tester.
c. Additional outside support (such as a Steady-Rest®) may also be required.
8. The sample being tested being too thin will yield false readings.
a. The material being tested should have a thickness at least 10 times the depth of the indentation. Minimum acceptable thicknesses can be found in ASTM E18 Tables 4 and 5.
b. Special (prehardened) anvils can be used when hardness testing thin sheet or foil material.