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Steel Ball Glossary
  • Lot
    A specified number of balls taken as a unit. Balls in a lot are manufactured under presumed uniform conditions and should have very similar characteristics.

  • Grade
    The guaranteed roundness of a ball identified in millionths of an inch. The grade designation is based on a combination of tolerances including dimension, surface roughness, and sphericity. The lower the grade value, the higher the precision of the ball.

    • Surface Roughness
      A measure of the texture of the surface of the steel ball. It is quantified by a measure of the vertical deviations of a real surface from its ideal form. Irregularities on the surface of balls having height, width, and direction.

    • Sphericity (Deviation from Spherical Form)
      A measure of how spherical or the roundness of the steel ball. This is measured by the radial distance from the maximum peak of a perfect circle to the maximum valley from the perfect circle.

    • T.I.R. (Total Indicated Runout)
      A measure of the concentricity of a drilled ball usually measured by a dial indicator.

  • Nominal Ball Diameter
    The value used to make a general identification of a ball size. Eg…1/8” ball.

  • Ball Diameter Variation
    The difference between the largest and smallest actual single diameter measurement.

  • Lot Diameter Variation
    The difference between the mean diameter of the largest ball and the mean diameter of the smallest ball in the lot.

  • Case Hardening
    A heat treatment or a combination of heat treatments of surface hardening involving a change in the composition of the outer layer of an iron-base alloy in which the surface is made substantially harder by inward diffusion of a gas or liquid followed by appropriate thermal treatment. Typical hardening processes are carburizing, cyaniding, carbo-nitriding and nitriding.

    • Case Depth
      The thickness of the case of a hardened steel ball.

    • Surface Hardness
      The ball surface’s ability to withstand penetration by a specific indenting shape. Rockwell testing is one method of measuring surface hardness. It uses a dial reading which indicates the depth of penetration of a steel ball for softer steels and a diamond cone for heat treated and harder steels when a load is applied.

    • Core Hardness
      The ball core’s ability to withstand penetration by a specific indenting shape. The core of the ball is the volume of the sphere below the case of the ball.

  • Microstructure
    The structure of a prepared surface or thin foil of material as revealed by a microscope above 25× magnification. The microstructure of a material can strongly influence physical properties such as strength, toughness, ductility, hardness, corrosion resistance, high/low temperature behavior, wear resistance, and so on, which in turn govern the application of these materials in industrial practice.

  • Surface Condition
    The existence of cracks, pits and rust on the surface of balls when examined visually without magnification.

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