Calotte grinding method

Ball-cratering device with three balls.
© Fraunhofer IST, Jan Benz

Ball-cratering device with three balls.

The calotte grinding method is used to precisely determine the wear resistance of films and surfaces. A steel ball wetted with abrasive fluid rotating against the specimen grinds a calotte (spherical segment) in the film being examined. The wear coefficient can be calculated from the volume of the calotte. This method is suitable for the examination of films with layer thicknesses ≥ 1 μm. Abrasive wear responds with great sensitivity to changes in the layer composition and structure, which is why it can be used as a parameter for evaluating the quality of films in production.

 

More information about the Calotte grinder

Calotte wear (abrasive)

Results of the calotte grinding method
© Fraunhofer IST

Results of the calotte grinding method. Wear coefficients of steel and hard material films.

Calotte crater profilometer

Calotte crater imaged with profilometer.
© Fraunhofer IST

Calotte crater imaged with profilometer.

Calotte grinding for film thickness determination

If the calotte is ground through the layers down to the substrate, the thickness of the layers can be determined according to the diameter of the rings. Here the layer thickness t is calculated using the following formula: t = (D2-d2)/8R, where D, d = outer and inner ring diameter and R = the ball diameter. The accuracy of the film thickness measurement is approximately 0.1 µm depending on the surface.