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 Manufacturing of Balls:
Balls may be manufactured by any material. The manufacturing process for precision balls differs primarily in the geometry of the original blank. The predominant shape of the blank is wire for metal balls, sticks for sintered materials (such as tungsten carbon steel), steel balls < 30 mm, plastic balls, and glass balls. Other blanks have the shape of a dice or come in pressed spherical forms.
The number of different materials for balls and quality levels has led to specializations in the ball manufacturing industry. In the course of miniaturization, JSK Nanoball, for instance, has concentrated its efforts on developing and constructing miniature balls. It all began around the year of 1950, with the invention of the ball pen.
The Manufacturing Process of Balls is Illustrated in the Following:
The raw metal wire has a slightly larger diameter, than the finished ball. I a cold forming process, the wire is continuously being cut into small cylindrical pieces, which immediately afterward will be compressed between two spherical calottes to gain a spherical shape with an equatorial ring.
This process is also called upsetting. The second manufacturing stage, the so-called flashing, is meant to remove the equatorial ring. For this end, the cut blanks are positioned between two lathe-machined grinding wheels. The grinding wheels are either horizontally (horizontal grinding machines) or vertically (vertical grinding machines) seated. The lower plate rotates while the upper plate is being pressed upon the blanks. By adding lubricating and grinding fluids and abrasives (powdery grinding media, such as diamond powders), the equatorial ring is being abraded. The resulting ball has now a rather rough surface. The second grinding stage, the so-called rough grinding, grinds the balls close to the final diameter by adding rough abrasives. After the rough grinding process, the steel balls undergo a hardening to provide the steel with the required hardness. The following grinding processes are being carried out on grooved grinding plates. The groove is milled into the grinding plates by a lathe. There are centric ball ways, which serve as a guidance for the balls between the grinding plates. The balls take a 360 degree turn in heir grove and are then being moved to another inner and outer groove. This provides the balls with the required roundness. Depending on their degree of accuracy (quality grade), after the hardening process the balls will be worked in 2 to 3 further stages by grooved grinding plates. The last grinding processes differ in the grinding material used, that is, the abrasives and grinding liquids. The balls are cleaned, dried, and sorted between the single stages of grinding. This sorting process prevents inaccurate balls from disturbing the succeeding grinding.
Due to the numerous grinding parameters (such as materials used, grinding pressure, or rotation speed of the grinding plates), the ball grinding processes can hardly be automated.
Quality Grades for Balls:
Balls are categorized into different grades of quality. An international standard (ISO 3290) combines many national standards (such as DIN 5401, German standard, AFBMA American standard, or JIS Japanese standard). These standards classify the tolerances of the geometrical parameters of balls: diameter tolerance, roundness, form deviation, roughness of surface.
Balls are also classified into different types. The classification into different types plays a major role in applications for high speed bearings.
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