How Does It Work?
A spring in the probe projects the tungsten carbide ball tipped indenter at the test piece. Impact velocity is measured immediately prior to impact and then on rebound. The quotient is computed and displayed as the Leeb Hardness Value. On hard materials, the rebound velocity will be higher than that from softer materials, which will absorb more of the impact energy.
For a correct and repeatable measurement, certain conditions must be met:
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- The material must be smooth and free of paint, rust, oxide, etc...
- The grain size of the test part must be small in relation to the indentation size.
- The material cannot move or be deflected by the impact of the indenter.
- Correction factor must be applied for the material's elastic modulus.
- Correction for the effect of gravity must also be made.
Surface: The test piece surface needs preparation by filing, sanding or grinding. As a general rule, if you drag your thumbnail across the surface and it drags, the surface is too rough.
Grain Structure: Materials such as cast iron, that have a coarse (large) grain structure, will cause inconsistent measurements. The use of a much large identer "G" probe will often correct for this condition.
Thickness & Mass: Test parts that have a low mass or thickness need to be supported to prevent movement or deflection.
Material: Selection of the material corrects for material type. The following materials can be selected: Steel / Cast Steel, Gray Cast Iron, Nodular Cast Iron, Cast Aluminum, Brass, Bronze, Copper, Stainless Steel, Forged Steel and Tool Steel*
Probe Position: Set; Up, Down, Sideways, 45° up or 45° down
*Leeb measurements are affected by the material elasticity. To a large degree this is taken care of by selecting the most similar material type from the Material list. If you find that your measurements are a bit high or low, it is because the built-in correction factor does not match your material. You can try a different material to see if this gets you closer to a correct measurement. You can also use a known hardness sample of your test material (having enough mass and thickness) to determine the +/- error and then adjust the reading to match using the Calibration facility.