Steel balls are the main components of bearings. From a macroscopic perspective, a steel ball appears as a perfect sphere. Even under microscopic observation, it still exhibits a regular spherical shape.

From a more microscopic perspective, are steel balls truly perfect spheres in the strict sense? With this question, the surface conditions at two different positions of a steel ball were examined.

                   Steel ball under test

First steel ball inspection

    Through the white light interferometry image, the interference fringes can be seen as regular concentric circles. Through software processing, the three-dimensional surface profile of the steel ball is obtained, which is a smooth spherical surface.

                  Interferogram obtained from white light interferometry inspection of a steel ball

                       Software interface

 Second steel ball inspection

                      White light interferometry inspection image

       The interference fringes of the second steel ball are elliptical, which is significantly different from those of the first steel ball. This indicates that the surface shapes at these two positions are different.

                      Software interface

     Through software analysis, the three-dimensional images in the software interface show that the surface morphologies of the two steel balls are completely different: the first is nearly spherical, while the second is an ellipsoid.

Inspection results

       Steel balls are not ideal spheres, and the surface shapes at different positions vary greatly. Using ordinary microscopes, one can only see whether there are scratches on the surface of the steel ball, but cannot accurately detect its surface shape.

       The experiment used a CR-100V white light interferometer, with non-contact detection and nanometer-level measurement accuracy. The three-dimensional effect of the surface morphology is automatically calculated by the software, making it more intuitive.