13 - Chapter 13 Lubrication and Sliding Bearings 13.1. Type...

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1 Chapter 13 Lubrication and Sliding Bearings 13.1. Type of Lubricants When relative motion occurs between the surfaces, it is usually desirable to minimize friction and wear. Any interposed substance that reduces friction and wear is a lubricant. Lubricants usually are liquid (oil), but can be solid (graphite), TFE (Teflon) or gas (pressurized air). Liquid lubricants that are oils are characterized by their viscosity. Greases are liquid lubricants that have been thickened to stay in position. 13.2 Types of Sliding Bearings Sliding bearings require direct sliding of the load-carrying member on its support, as distinguished from rolling-element bearings. Sliding bearings: 1. Journal or Sleeve bearings 2. Thrust bearings Fig. 13.1 shows a crankshaft supported in a housing by two main bearings, each consisting of a cylindrical sleeve portion plus a flanged end that serves as a thrust bearing. Figure 13.1 (p. 518) Crankshaft journal and thrust bearings. The crankshaft is supported by two main bearings and attaches to the connecting rod by the connecting rod bearing . All three are journal (or sleeve ) bearings . Integral flanges on the main bearing inserts (commonly called merely bearings ) serve as thrust bearings, which restrain axial motion of the shaft.
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2 13.3 Types of lubrication Lubrication is commonly classified according to the degree with which the lubricant separates the sliding surfaces. Fig. 13.2 illustrate three cases. 1. Hydrodynamic lubrication, the surfaces are completely separated by the lubricant film. The load tending to bring the surfaces together is supported entirely by fluid pressure generated by relative motion of surfaces. There is no surface wear and minimum friction within the lubricant film. Typical film thicknesses at the thinnest point, called h 0 are 0.008 to 0.020 mm (0.0003 to 0.0008 in.). Typical friction coefficient values are, f , 0.002 to 0.010. 2.
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13 - Chapter 13 Lubrication and Sliding Bearings 13.1. Type...

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