Geometry and Basic Dimensions
- Nominal Ball Diameter: The theoretical value used for general identification of the ball size (e.g., 1/4", 6mm). It is the "commercial" size.
- Basic Diameter : The precise dimension ordered, which serves as the reference point for applying diameter tolerances.
- Specific Diameter : The actual mean diameter marked on the packaging, rounded to the nearest standard marking increment.
- Sphericity / Deviation from Spherical Form : A measure of roundness; it is the difference between the largest and smallest diameters measured on a single ball.
Tolerances and Variations (Quality)
- Ball Grade : A specific classification system that combines tolerances for size, shape (sphericity), and surface roughness. The lower the grade number, the more precise the ball.
- Ball Diameter Variation : The difference between the maximum and minimum diameter measurements found on a single ball.
- Lot Diameter Variation : The difference between the mean diameter of the largest ball and the smallest ball within the same production lot.
- Basic Diameter Tolerance : The maximum allowable deviation of the mean ball diameter from the ordered basic diameter.
Surface Finish and Treatments
- Surface Roughness ($R_a$) : Small-scale surface irregularities resulting from the production process (such as grinding or polishing).
- Waviness : Geometric irregularities that are wider than roughness, repeating periodically across the ball's surface.
- Passivation : A chemical treatment used to remove surface impurities and create a protective film (primarily used for stainless steel balls).
- Oxidize : Surface discoloration or alteration caused by external contaminants or reaction with oxygen (rust).
- HFC (Headed, Flashed, and Cleaned) : Refers to a ball that has not undergone lapping. These are unhardened and can be easily machined.
Physical Properties and Materials
- Hardness (Rockwell C) : The resistance of the ball's surface to penetration, measured using standardized methods (such as Rockwell).
- Case Depth : Specifically for case-hardened balls (like carbon steel), this is the distance from the surface of the ball to the point where the hardness drops below a specified level.
- Crushing Strength : The maximum load a ball can withstand before fracturing (often measured using the three-ball method).
- Density : The mass per unit of volume (usually expressed in lb/in³ or kg/m³).
- Chemical / Physical Certification : Official documentation guaranteeing the material's composition analysis and mechanical properties.
Manufacturing and Testing Processes
- Forge : The process of creating the initial shape of the ball by heating and hammering or compressing the metal.
- Annealing : A heat treatment used to soften the metal and relieve internal stresses.
- EDM (Electric Discharge Machining) : The use of electrical sparks to drill or thread a ball that has already been hardened.
- Eddy Current Tester : A machine used during final inspection to detect cracks or surface flaws that are invisible to the naked eye.