How to Define the quality of a steel ball?
The quality of a steel ball is defined by size, surface hardness, surface integrity and deviation from spherical form. See below instructions:

  • Size is the mean ball diameter, arithmetical mean of the largest and the smallest of the single diameters of a ball.

  • Surface hardness is usually measured on Rockwell scale.

  • Surface integrity is measured as surface smoothness and no defects like flats, pits, soft spots and cuts. Balls must have no such defects on visual inspection.

  • Deviation of spherical form defines whether the ball is out of ball shape.

Other definitions of steel balls:

  • Nominal ball diameter: diameter value which is used for the general identification of a ball size.

  • Single ball diameter: distance between two parallel planes tangential to the actual surface of a ball.

  • Mean ball diameter: arithmetical mean of the largest and the smallest of the single diameters of a ball.

  • Variation of ball diameter: difference between the largest and the smallest of the single diameters of a ball.

  • Deviation from spherical ball surface: various types of deviation from the perfect spherical ball surface, uniformly or non-uniformly distributed and repeated around the ball surface.

  • Deviation from spherical form: radial distance between the smallest circumscribed sphere and the greatest inscribed sphere, with their centres common to the least squares sphere centre.

  • Waviness: surface irregularities of random or periodical deviation from the ideal spherical form.

  • Surface roughness: surface irregularities with relatively small spacings, which usually include irregularities resulting from the method of manufacture being used and/or other influences.

  • Surface defect: element, irregularity or group of elements and irregularities of the real surface, unintentionally or accidentally caused during manufacture, storage, handling or use of the surface.

  • Ball lot: definite quantity of balls manufactured under conditions presumed uniform and which is considered as an entity.

  • Mean diameter of ball lot: arithmetical mean of the mean diameters of the largest ball and the smallest ball in a ball lot.

  • Variation of ball lot diameter: difference between the mean diameters of the largest ball and the smallest ball in a ball lot.

  • Ball grade: specific combination of dimensional, form, surface roughness and sorting tolerances for balls.

  • Ball gauge: amount by which the mean diameter of ball lot should differ from the nominal ball diameter, this amount being one of an established series.

  • Deviation of a ball lot from ball gauge: difference between the mean diameter of a ball lot and the sum of the nominal ball diameter and the ball gauge.

  • Ball subgauge: amount, of an established series of amounts, which is the nearest to the actual deviation from the ball gauge of a ball lot.

  • Hardness: (rolling bearings) measure of resistance to penetration as determined by a specific test method.