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How are balls made?
This is a common question received by many who are wondering how balls are manufactured to such incredibly smooth and shiny precision.
It is actually a very interesting process that starts with a metal wire and ends with a perfectly round, shiny ball.
The first stage in the process is Heading. Ball blanks are cold or hot headed from rolls of wire or bar stock depending on their size and the material. The heading machine cuts off a short cylinder of the material and a moving die with a concave spherical cup drives the cylinder into a matching cup in a fixed die. The result is a spherical shape which is the ball blank. This process leaves a ring of metal around the ball; looking similar to the planet Saturn.
Next the balls are transferred to a machine that removes the ring. This process is called Flashing. The flashing operation removes the slight belt and small protrusions left on the surface faces by rolling the balls between two very heavy hardened alloy plates under high pressure. The plates are called rill plates. One rill plate is stationary and the other one spins. There are grooves machined into each plate which guide the balls around in a circular path. As the balls travel through the grooves, they spin and tumble until the rough edges are removed and the ball is squeezed into a more spherical shape.
After flashing, the balls enter a Heat Treating process. Heat treating is performed to harden the balls, when required. The balls are hardened by heating them to a high temperature (over 1500 degrees Fahrenheit) in an atmospherically controlled furnace and then quenched into a liquid bath. They are then tempered to reduce their brittleness by heating them to a low temperature (around 325 Fahrenheit). Samples are checked for hardness. The grain size and metallurgical structure are inspected under a high power microscope. This process of hardening also changes the size of the balls. The size of the balls have to be perfect; sometimes within millionths of an inch; therefore a few more steps are required to achieve a perfectly round ball.
The hardened balls are then precision ground in a process called Grinding. This process uses the same kind of machine which rolls the balls between two fixed iron plates, but in this operation, one plate contains an abrasive or has a fine-grit grinding wheel.
Next, the balls enter the Lapping phase. Again, the balls are rolled between two cast iron plates. One plate is fixed while the other plate rotates at a very low speed. The real secret of the extreme quality of precision balls happens here. At this stage the sphericity and size have been established and are carefully inspected by the customers requirements.
A Polishing operation is generally added which produces the shinny luster to the finished ball. Finally, the balls are inspected by Aviko and/or visually.
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