Materials bearing

Plain bearings are the oldest form of bearing. They may be manufactured completely from a single bearing material or composition of materials, or, alternatively, a thin layer of bearing material can be attached to a backing which is usually of a stronger materiaL 

Where a metal bearing material is used with a metal shaft, metal-to-metal contact must be avoided to prevent seizure of the two metals. This is done by providing a film of lubricant between the two surfaces. Where it is not possible to provide a film of lubricant, a non-metallic bearing material will have to be used. 

Ideally a bearing material should possess the following properties  

Cast phosphor-bronze bearings possess high strength to support heavy loads at low speeds and have excellent corrosion-resistance. The bearing and shaft must be accurately aligned. 

Lubrication is required and must be plentiful and reliable - oil grooves or indents are usually provided in the bore of the bearing to give good distribution over the complete surface. 

For many centuries the application of materials for low friction and wear in sliding and rolling contacts primarily involved wood, stone, leather, iron, and copper. Almost all engineering materials have since been employed at one time or another in the continuing search for the best bearing material. Final selection is commonly a judgment based on the most essential material properties, ease of appHcation, and cost. 

Production trends for bearings and bearing materials closely parallel general industrial activity. 

Ball and roUer bearings represent the largest business segment with worldwide production estimated at 14 biUion in 1988 (1). U.S. production, forecast for 3.6 biUion in 1991, has fallen 5% aimuaHy for several years (2). This decrease is attributed largely to the slump in the automotive industry which represents 31% of the market for rolling-element bearings (3). 

Despite this past downward trend, which has persisted in the United States since 1979 with modernization of large suppHers in Japan and Europe, growth of 2 to 2.5% is now expected into the mid-1990s. This reflects increased demand for some military appHcations and commercial aircraft, plus growing needs for farm and constmction machinery (2). U.S. production of the relatively new ceramic ball bearings is expected to increase distinctively by about 50% yearly to reach 17 million in 1993 (3). 

Some other bearing materials find extensive use for which production volume is less well defined. EiHed plastics such as nylon, acetal resin, PTEE, and phenoHcs are formed and molded into bearings in a wide variety of mechanical stmctures. Tin, lead, and bronze alloys are used for oil-film bearings in heavy industrial and power generating equipment, frequently in custom bearings manufactured directly as machine components. 

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COPPERALLOYS-WROUGHTCOPPERANDWROUGHTCOPPERALLOYS] (Vol7) -as bearing materials pEARING MATERIALS] (Vol 4)... 

Plastic bags Plastic beads Plastic bearing materials Plastic cements Plastic drums Plastic electronic package Plastic encapsulant... 

Solvent Extraction. Treatment of oil-bearing materials with solvent can effect virtually complete removal of oil from meal. However, the... 

Uses. Indium s first commercial use was in the production of dental alloys (see Dental MATERIALS), but its first significant use was in the production of bearings for heavy-duty and high speed service (see Bearing materials). The advent of jet engines has reduced this use, but indium is still used in high performance engines. 

Because shear and compressive strengths s andp depend in a similar way on material properties such as lattice stmcture and bond strength,yis often in a rather narrow range of about 0.20—0.35 for a wide variety of materials. The following are typical data for sliding on steel with bearing materials varying several hundredfold in yield pressure ... 

Hydrometallurgy. The treatment of ores, concentrates, and other metal-bearing materials by wet processes, usually involving the solution of some component, and its subsequent recovery from solution. 

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