How Ball Bearings Are Made
The manufacturing process for ball bearing balls is a blend of precision engineering and time-tested technology.
It all starts with the selection of raw material, usually high-quality steel wire. The wire is then fed into a machine for a cold heading process. During the cold heading process, the wire is cut into sections and the ends are forced toward the center. This process gives the wire a rough spherical shape, but with a ring of excess material around it, called "burrs," which makes it look like the planet Saturn.
Next, the balls are fed into a machine equipped with two heavy, hardened steel plates, called "grooved plates." One plate is stationary while the other rotates. The plates have grooves that guide the balls in a circular path. As the balls pass through these grooves, they spin and tumble. Rough edges are ground off and burrs are gradually removed, giving the balls a more rounded shape. This process also compresses the metal, making the surface harder. Water is poured over the balls and plates during this process to dissipate the heat.
After the initial shaping, the balls may need to be heat treated. This step hardens the balls, but also causes dimensional changes. To achieve the required precision (to within a millionth of an inch), the balls also need to be ground. At this stage, a coolant containing an abrasive is used, and as the balls pass through the grooves again, they are ground to their final dimensions.
Finally, the balls are ground. The grinding process uses a machine with a softer metal plate and uses a polishing paste instead of an abrasive. The grinding process gives the balls a smooth surface without removing any material. Once completed, the balls are carefully inspected using high-precision machinery.
