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Babbitt, also called Babbitt metal or bearing metal, is any of several alloys used for the bearing surface in a plain bearing. The original Babbitt metal was invented in 1839 by Isaac Babbitt in Taunton, Massachusetts, USA. He disclosed one of his alloy recipes but kept others as trade secrets.〔Isaac Babbitt, ("Mode of making boxes for axles and gudgeons," ) U.S. patent no. 1,252 (issued: July 17, 1839). Babbitt did not patent his alloy, although he does state its formulation: "The inner parts of the boxes are to be lined with any of the harder kinds of composition known under the names of britannia metal or pewter, of which block tin is the basis. An excellent compound for this purpose I have prepared by taking about 50 parts of tin, five of antimony, and one of copper, but I do not intend to confine myself to this particular composition."〕 Other formulations were later developed.〔.〕 Like other terms whose eponymous origin is long since deemphasized (such as ''diesel engine'' or ''eustachian tube''), the term ''babbitt metal'' is frequently styled in lowercase.〔〔American Heritage Dictionary, 4th ed, headword ''babbitt metal''.〕 It is preferred over the term "white metal", because the latter term may refer to various bearing alloys, lead- or tin-based alloys, or zinc die-casting metal. Babbitt metal is most commonly used as a thin surface layer in a complex, multi-metal structure, but its original use was as a cast-in-place bulk bearing material. Babbitt metal is characterized by its resistance to galling. Babbitt metal is soft and easily damaged, which suggests that it might be unsuitable for a bearing surface. However, its structure is made up of small hard crystals dispersed in a softer metal, which makes it a metal matrix composite. As the bearing wears, the softer metal erodes somewhat, which creates paths for lubricant between the hard high spots that provide the actual bearing surface. When tin is used as the softer metal, friction causes the tin to melt and function as a lubricant, which protects the bearing from wear when other lubricants are absent. Internal combustion engines use Babbitt metal which is primarily tin-based because it can withstand cyclic loading. Lead-based Babbitt tends to work-harden and develop cracks but it is suitable for constant-turning tools such as sawblades. ==Traditional Babbitt bearings== In the traditional style of a babbitt metal bearing, a cast iron pillow block is assembled as a loose fit around the shaft, with the shaft in approximately its final position. The inner face of the cast iron pillow block is often drilled to form a key to locate the bearing metal as it is cast into place. The shaft is coated with soot as a release agent, the ends of the bearing are packed with clay, and molten metal poured into the cavity around the shaft, initially half filling the pillow block. The bearing is stripped, and the metal trimmed back to the top surface of the pillow block. Hardened babbitt metal is soft enough to be cut with a knife or sharp chisel. A steel shim is inserted to protect the face of the lower bearing and to space the cap of the pillow block away from the shaft. After resealing the ends with clay, more metal is then poured to fill the cap of the pillow block through the hole in the top of the pillow block cap that will eventually be a lubrication hole. The two halves of the bearing are then split at the shim, the oil holes cleared of metal and oil ways are cut into the surface of the new bearing. The shaft is smeared with engineer's blue and rotated in the bearing. When the bearing is disassembled the blue fills the hollows and is rubbed off the high spots. The high spots are scraped down, and the process repeated, until a uniform and evenly distributed pattern of blue shows when the shaft is removed. The bearing is then cleaned and lubricated, and shimmed up such that the shaft is held firmly but not binding in the bearing. The bearing is then "run in" by being run heavily lubricated at low load and revolution, completing the process of exposing the hard bearing surface. After final adjustment of the shimming, a very reliable and high load capability bearing results. Before the advent of low cost electric motors, power was distributed through factories from a central engine via overhead shafts running in hundreds of Babbitt bearings. The expression a "run bearing" also derives from this style of bearing, since failure of lubrication will lead to heat build up due to friction in the bearing, eventually leading to the bearing metal liquefying and running out of the pillow block. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Babbitt (metal)」の詳細全文を読む スポンサード リンク
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