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how do they get the balls in ball bearings so perfectly round and smooth?

by:QY Precision      2019-08-31
If you \'ve ever rolled several small metal balls found in ball bearings in your hands, you\'ll notice how perfectly round and incredibly smooth they are.
You might think, how can you be perfect?
This is actually a very neat process, starting with a metal line and ending with a perfect shiny ball.
The first stage of this process is cold or thermoforming operations.
The metal wire about the same diameter as the finished ball is fed through the heading machine.
The machine has a metal cavity in the shape of a hemisphere on each side.
It slammed and closed on the wire, forcing the metal sheet into the shape of the ball.
This process leaves a metal ring (called flash)
So the ball coming out of this machine looks a bit like Saturn.
Next, the ball enters a machine that removes the flash.
This machine rolls the ball between two very heavy hardened steel plates (called the gutter steel plate.
One groove plate is stationary, and the other is rotating.
These plates have been machined into grooves to guide the ball in a circular path.
You can see that part of one of the plates has been cut off;
This is where the ball enters and exits the groove.
The groove is fully filled with balls when the machine is running.
Once the ball passes through the groove, it falls into the open part of the plate and rolls over for a while before entering a different groove.
By making sure that the ball passes through many different grooves, even if there is a difference between the grooves, all the balls will come out of the machine in the same size.
When the ball goes through the groove, it rotates and rolls, the rough edges fall off and the ball is squeezed into a spherical shape, a bit like rolling a ball of dough between your hands.
The extrusion of the ball makes the metal compressed, making the surface of the ball very hard.
Because the ball is metal, this operation generates a lot of heat, so the water will overflow out of the ball and the plate to cool them.
The variables in this process are the pressure to squeeze the plate together, the speed at which the plate rotates and the duration of the ball remaining in the machine.
Setting these variables correctly results in balls of the right size.
After this operation, the ball may heat uptreated.
This harden the ball but also changes the size of the ball.
The size of the bearing ball must be perfect, sometimes within one inch, so more operation is required after heatingtreating.
Next, the ball will be ground.
The same machine is used, but this time the coolant contains an abrasive.
The ball passes through the groove again, landing and compressing to the final size.
Finally, the ball is ground.
Similarly, the same machine was used, but this time the plates were made of softer metal, and the machine squeezed the plates together with less pressure.
In addition, the machine uses a polishing paste, not an abrasive agent.
Without removing any material, this process gives the ball a perfectly smooth glossy surface.
The last step of the process is to check.
Measure the balls with very precise machines to determine if they meet the required tolerances.
For example
Association of friction bearing manufacturers (AFBMA)
A set of grades with bearing balls.
The three-stage ball must be spherical within 3 parts of inches, and the diameter must be accurate within 30 parts of the inch.
This means that for a third-grade student
Inch ball, the diameter must be between 0. 24997 and 0.
The inch 25003 and minimum diameter measured on the ball must be within 3 parts of the maximum diameter.
Manufacturers use very similar processes to make metal particles for air guns, plastic balls for bearings, and even plastic balls for rolling-on deodorant.
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