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Helping Turn the Wheels of Industry with Ball Bearings

Ball bearings can be found almost everywhere in modern life; from jet engines, motors and power drills to gearboxes, pumps, washing machines, lawn mowers and even the humble yo-yo. The most common rolling bearing is the Deep Groove Ball Bearing. A single row deep groove ball bearing consists of 4 main components: An inner ring, an outer ring, a ball set and cage The balls are retained by the cage and run in the inner and outer raceways. Most often, deep groove ball bearings are also sealed and greased for life.

How are ball bearings made?

The process for making steel ball bearings involves several different stages:

Creating the ball

To manufacture the balls for standard bearings a high quality grade of steel wire is used. The wire is cut into blanks, and then pressed into balls between hemispherical dies. Any surplus metal is removed by filing plates in a deburring machine. The balls are machined in re-filing machines. Concentric grooves in the plates make sure that the whole ball surface is machined equally and achieves a spherical form. After re filing the balls are hardened and tempered in automatic furnaces. The hardened balls are then ground in ball grinding machines wheel. This process brings all the balls in a batch to the same size. The balls are then honed in order to achieve the correct size, roundness and surface finish. At all stages of ball production continuous inspections are carried out. A final inspection is performed at random on each batch under microscopes and other precision equipment to examine size, form and surface finish.

The raceways

These are machined from tube on multi – spindle lathes. After washing and gauging they are transferred to a furnace to be hardened and tempered to give them the required hardness and strength. The final machining operations are then carried out in parallel lines of grinding and finishing machines – one for inner rings and one for the outer rings. The next step is honing which is to achieve a high surface finish. High and consistent quality is extremely important – the finish of the raceways must not vary by more than a fraction of a micron. The rings are finally washed to ensure they absolutely clean ready for assembly.

Cage making

The function of the cage is to hold the ball set together. It consists of 2 halves that are made from cold rolled steel strip which is processed in a number of operations. Presses with progressive tools are used to produce cage halves from the strip. This operation consists of piercing and blanking, forming the ball pockets and piercing the rivet holes. Following surface treatment and cleaning the cage halves are coated with a preservative and are ready for assembly. Other cage materials such as Polyamide and brass are also used.

Bringing it all together

Firstly the raceway diameters of the inner and outer rings are measured. Selecting a suitable combination of ring and ball sets gives the required internal clearance. Balls are fed between the paired inner and outer rings and the two cage halves are fitted and riveted together. The final inspection checks running accuracy, vibration level, bore and outside diameter and radial clearance. The bearings are then washed, coated with preservative and if applicable greased and fitted with shields or seals before being packed The low cost of ball bearing prices and their relatively simple design mean that ball bearings and especially stainless steel ball bearings will be here for some time, continuing to keep industry on the move.