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Smooth operator

By Masayuki Yonezawa
DuPont Engineering Polymers, Japan

Ball tables are industrial conveyors that use fixed balls to transport products and materials by rolling instead of using a moving belt or chain. The ball tables are made up from multiple ball transfer units, each consisting of a large, load-bearing ball which sits atop smaller balls inside a semispherical main body. Both ball tables and ball transfer units are designed for industrial and commercial applications that require the transportation of bulk materials, boxes, packages, or parts in a predetermined path, and that have fixed or selective points for loading and discharging. The components of the ball transfer units are usually made of steel, carbon steel, or stainless steel.

It was when considering the development of ball transfer units for the alignment of flat panel displays and solar panels, that Japanese company ISB (Iguchi Kiko Co., Ltd. Tokyo), a supplier of quality ball bearing systems, discovered the requirement for a tailor-made solution for use in cleanroom environments. “Conventionally, solid pins are used to support the glass alignment process, which generate particles and result in high friction due to repeated, abrasive motion. There was a strong need to improve the process,” explains Hiroshi Kawai, marketing department director at ISB. “But nobody believed that ball transfer units would solve the problem because of the number of metal parts moving within them, which was seen as the source of contamination by cleanroom process engineers.”

The solution lay in the adoption of different families of Vespel® parts for components in ISB’s ISC range of ball transfer units for cleanroom applications. Due to the high surface hardness and stiffness of the Vespel® parts – including the main body, small balls and large ball – their elastic deformation, caused by the weight of the transported material, can be controlled. Similarly, the high heat deflection temperature of the Vespel® parts (above 300 °C or 572 °F) also helps limit deformation. Consequently, frictional resistance to movement of the transported material is minimized, allowing it to be moved both smoothly and accurately by a small external force. The elimination of metal components from the ball transfer units helps remove the source of foreign matter (e.g. metal powder resulting from abrasion) which can potentially damage the delicate panels. The excellent erosion resistance of the Vespel® parts prevents the depositing of chemical substances, further reducing the risk of contamination. Excellent resistance to UV light or chemical resistance are additional benefits, as Hiroshi Kawai confirms: “By selecting Vespel® as the key material for our ISC range of ball transfer units, we have obtained particularly good results when using the units in pretreatment devices for a liquid-crystal panel substrate glass, such as a vacuum chamber, or a heating oven.”

Over a six-year period, DuPont in Japan worked with ISB on selecting the best material and technical solution to meet the needs of flat panel display and solar panel manufacturers. A range of Vespel® series are used in the ISC ball transfer units, including those from the Vespel® TP-8000 family of finished parts and shapes, whose high purity and resistance to plasma and heat makes them well suited for uses within the semiconductor industry. The material is weldable and wear resistant and maintains its good dielectric properties even at permanent operating temperatures of up to 200 °C (392 °F). Other Vespel® series used include Vespel® SP-202, which decreases electrostatic loading in the manufacturing and handling of flat glass panels for liquid crystal displays and is ideal for use with products that are handled in high-temperature, vacuums or reactive environments. Vespel® SCP-5000, whose benefits include ultra-high purity and high stiffness, and Vespel® SP-1, delivering exceptional wear resistance, insulation, and a low coefficient of friction, complete the list of DuPont materials used.

“The proven performance of Vespel® parts and shapes in highly demanding semiconductor applications, in terms of their purity, wear resistance and wide range of thermal resistance, was one principal reason to work with DuPont,” explains Kaoru Iguchi, president of Iguchi Kiko (ISB). “The other is the strong emphasis on development support for the material and testing. With the cooperation of DuPont, we were able to accelerate development faster than ever before.”

According to Iguchi, flat panel display and photovoltaic manufacturing engineers have boosted their productivity by using the ISC range of ball transfer – indeed their application has extended from flat panel display and photovoltaic manufacture in Asia to parts of North America. In 2005, Nikkan Kogyo Newspaper awarded the ‘ISC Ball Transfer for Cleanrooms’ with the “Japanese Brand Award” for its innovative solution in flat panel manufacturing. In 2007 ISB & DuPont’s joint patent for the ball transfer unit and ball table was granted in the U.S. “With DuPont as a key development partner, we will continue to develop new products, new applications, and new markets,” concludes Kaoru Iguchi.