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Download Article Selecting the Right 28 powertransmissionengineering february 2010 www.powertransmission.com www.powertransmission.com february 2010 powertransmissionengineering Precision Ball Material FOR AGGRESSIVE ENVIRONMENTS Jim Peta alls are a common mechanical balls to resist aggressive environments for applications where the balls are only component used in nearly all and help in selecting the right one. required to withstand a medium load. B complex—and many simple— Brass Balls Brass provides excellent electrical con- mechanical products. The criti- Brass balls provide excellent resis- ductivity, so it is well suited for many cal nature of balls is illustrated by the tance to corrosion by water, including electrical applications. A silver coat- fact that ball bearing factories were one seawater, and also resist the corrosive ing is sometimes applied to brass balls of the primary targets for Allied bomb- effects of fuel oil, gasoline, butane, to improve their electrical conductivity ers seeking to disrupt the German war dry carbon oxide, benzene and similar and corrosion resistance to even higher industry during World War II. While chemical agents. However, it should be levels. the vast majority of balls are made of noted that brass can be unstable in the Brass balls’ combination of resis- some type of steel, steel’s relatively weak presence of acids and bases. tance to corrosion from water and high resistance to chemical attack means Another key advantage of brass balls hardness make them suitable for water that applications involving aggressive is their cost, which is substantially lower valves, including high-pressure applica- environments generally require a more than other corrosion-resisting balls. tions. Brass valves are even used in fire exotic material. This article will exam- Brass balls have a Rockwell B hardness nozzles where they must withstand high ine the major materials used to enhance of 75 to 87, which makes them suitable continued powertransmissionengineering february 2010 www.powertransmission.com www.powertransmission.com february 2010 powertransmissionengineering 29 ® pressures and flow rates. Brass balls pump, valve and metering applications water, they are ideal for valves in the oil are frequently used in electrical equip- in water treatment and chemical plants and gas industry. The added hardness of ment, most often in the role of connec- because they resist attacks by a wide k-monel makes them well suited for use tors that make an electrical circuit. For range of chemicals, and because their in bearings that must survive aggressive example, brass balls are used in wireless strength enables them to withstand environments. power devices, data storage equipment, high flows and pressures. In particular, Tungsten Carbide Balls heating units and kitchen applications. monel balls’ ability to withstand ammo- Tungsten carbide is a homogenous Another common application is the use nia makes them particularly useful in mixture of tungsten carbide grains in of brass balls in the pumps of sprayers wastewater treatment and chemical a binder matrix, with cobalt being the used to apply fertilizer and pesticides to plants. Monel balls’ corrosion resistance most commonly used binder matrix. lawns and crops. The tungsten carbide grains are fused Monel Balls into a solid matrix of cobalt metals Monel balls provide an even high- under extreme heat and pressure in a er resistance to corrosion than brass process called sintering. There are many balls. Monel is composed primarily of different grades of tungsten carbide nickel and copper, and also has smaller available, making it possible to provide amounts of other elements such as balls that are tailored for most any iron, silicon, manganese, carbon, alu- application. In general, a higher per- minum, titanium and sulfur. Monel centage of cobalt will provide a tougher balls are impervious to the effects of but softer grade, while a lower percent- fresh water, salt water, steam, petro- age of cobalt will provide a harder but leum products, ammonia, acids, many less tough grade. bases and calcium chloride. Monel also The hardness of tungsten carbide has a relatively high tensile strength is evidenced by the fact that it is com- of 79 to 90 Kpsi and yield strength of monly used for tools used to cut steel 24 to 40 Kpsi. Monel has a hardness enables them to provide longer life than and other metals, and for armor pierc- of 85 to 95 Rockwell B, while its sis- chrome or stainless steel balls in water ing ammunition. Its abrasion resistance ter alloy, k-monel can be hardened to supply, wastewater and hydroelectric and resistance to shock are both excel- about Rockwell 27 C. K-monel also applications. They are used in meters lent. Tungsten carbide is also practically offers superior resistance to bases. On that measure the flow of liquid and inert so it is able to resist corrosion in the other hand, monel balls are rela- gases because their ability to withstand nearly any environment. But it should tively expensive because of the difficulty most any chemical makes for a more be noted that bases with a pH below involved in machining them. versatile instrument. Since monel balls 4 have a tendency to attack the binder. Monel balls are frequently used in are resistant to both petroleum oils and Tungsten carbide is also one of the most 30 powertransmissionengineering february 2010 www.powertransmission.com www.powertransmission.com february 2010 powertransmissionengineering costly ball materials. not magnetic. Aluminum oxide or alu- that must survive in aggressive environ- Naturally, tungsten carbide balls mina balls resist very high temperatures ments requires special ball materials are used in applications where extreme and can survive most corrosive materi- that can survive chemical attack and hardness and wear resistance are als, with the exception of hydrochloric other hazards. Brass, monel, tungsten required. Tungsten carbide balls are or hydrofluoric acid and strong bases. carbide, ceramic and titanium pro- used in heavy machinery applications Ruby sapphire balls provide the high- vide excellent performance in the vast because of their wear resistance and est possible resistance to temperature majority of these applications. strength. They are frequently used in and also excellent corrosion resistance. Work with a ball supplier who can the down-hole tool industry for hard Zirconia balls provide excellent corro- help carefully examine the requirements banding, which refers to covering the sion resistance. of your application to select a material outer surface of the lower portion of a Ceramic balls are often used in that will provide the required level of tool with a wear material to enhance aircraft braking assemblies. These sys- corrosion and temperature resistance at its life. Other common applications tems must be able to withstand a very the right price. for tungsten carbide balls include ball high amount of heat and pressure, yet screws, bearings, valves, flow meters, in any aircraft application weight is an For more information: pivots, detents and tips. For example, important factor. Ceramic balls provide Jim Peta tungsten carbide balls are often used as weight savings over hollow steel balls Product Manager tips for ballpoint pens and instruments sufficient to save many thousands of Thomson Industries, Inc. used to test the hardness of materials. dollars in fuel costs per year and per Phone: (540) 633-3549 Ceramic Balls plane. Ceramic balls are also frequently wwwthomsonprecisionball.com [email protected] Ceramic balls provide excellent cor- used in wind turbines used to generate rosion resistance, abrasion resistance electricity because of their high strength and resistance to high temperatures, and abrasion resistance, as well as their along with exceptionally low weight. inherent insulating properties that pre- The melting point of silicon nitride, vent arcing. one of the most common ceramic Bioinert ceramics, such as alumi- ball materials, is 1,900°C compared na oxide and zirconia, also provide to 1,370°C for stainless steel. Some the important advantage of being types of ceramic balls are capable of non-reactive to biological organisms. withstanding temperatures in excess of Bioinert ceramics are used as load- 3,200°F. There is little or no increase in bearing implants, such as implants for bearing friction as temperature increas- finger and toe joint replacement. One es in most applications. Ceramic balls surgeon using a ceramic ball and socket also show very little deformation under to replace toe joints reported a success pressure, as their hardness reduces the rate of 95% relief of pain and 80% for coefficient of friction, thus maximizing restoring mobility similar to compa- the amount of energy that is converted rable good joints. to work. Titanium Balls A number of different ceramic Titanium balls are desirable for materials are used in ball applications. their low density, anti-corrosive proper- Silicon nitride balls provide excellent ties, and high tensile and compression performance in applications involving strength. Titanium isn’t easy to form, high speeds, high loads and high tem- but manufacturing processes have been peratures. The material does not require developed that can make a 0.125-inch- lubrication in most applications, and is diameter titanium ball round to with- in 10 millionths of an inch. High- performance bearings are one common application for titanium balls. Another application is medical implants such as hip implants. Titanium has a weight advantage over its main competitor in the implant field—Cobalt-Chrome- Molybdenum. But Cobalt-Chrome- Molybdenum generally offers longer life. Other applications include connec- tors for cables, check valves for pump sprayers and body jewelry. Precision balls play a critical role in a wide range of equipment. Equipment powertransmissionengineering february 2010 www.powertransmission.com www.powertransmission.com february 2010 powertransmissionengineering 31.
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