How Are Ball Bearings Made?
The majority of ball bearings are made from steel as it’s a strong metal which can withstand intense pressure. Ball bearing cages are also made of steel but plastic can also be used and it is a popular choice as it’s cheaper than steel. Ball bearings are made up of four main parts so as well as the actual bearing balls and the cage, there is also the inner race and outer race which need to be manufactured.
The inner race and outer race are made in the same way as they are both rings of steel and differ only in their size. Machines which work in a similar way to lathes are used to cut the shape of the race before they are heat treated at around 843 degrees Celsius and then cooled which reinforces their strength. The races are then tempered and cooled in air to toughen them up further before being ground into shape on grinding wheels to finish them.
The actual bearing balls start out as steel wire which is formed into balls during what’s called the cold heading process. Cold heading means that the wire is cut up and hit at each end to form a rough ball shape which has a ring (also called a flash) around it. The flash is then removed by a machine which has two cast iron discs which smooth the bearing balls into a spherical shape. To toughen the ball bearings up they are heated and tempered before being put into a grinding machine which wears them down to the exact spherical size required.
The ball bearing cage is also made of steel and is cut out of thin sheet metal. The cages are given their final shape in a die which consists of two pieces of steel which have a hole carved inside them which shapes the finished cage. Cages made from plastic are made by injection moulding, where melted plastic is injected into a mould and then hardened. The parts of the bearings are then ready to be assembled.
Other topics in the ACORN Bearing Compendium series include:
Building a ball bearing - Part 1
Building a ball bearing - Part 2