Plain Bearing Materials Machinery's Handbook, 31st Edition
2435
9) Operating number.
. 5 614 475 14510 18 10 400 186 × 10 7 6 # # # # = = − − . , .
O
10) Minimum film thickness. From Fig. 13, α = 0.30 × 10 −3 . . . . h 0 00030 4 75 0 0014 inch min # = = 11) Coefficient of friction. From Fig. 14, f = 0.0036. 12) Friction power loss. , . , , . P 33 000 0 0036 70 000 10 400 79 4 hp f # # = = 13) Oil flow. . . . , .
Q 00591 6 030 10 4 475 10 400 2102gpm 3 # # # # # # = = −
14) Temperature rise.
. 030 10 35 0 0217 0 0036 614 45 7 3 # # # # . . . . = ° −
F
t
∆ =
Because this temperature is less than the 50 ° F, which is considered as the acceptable maximum, the design is satisfactory. Plain Bearing Materials Materials used for sliding bearings cover a wide range of metals and nonmetals. To make the optimum selection requires a complete analysis of the specific application. The import ant general categories are: Babbitts, alkali-hardened lead, cadmium alloys, copper lead, aluminum bronze, silver, sintered metals, plastics, wood, rubber, and carbon graphite. Properties of Bearing Materials.— For a material to be used as a plain bearing, it must possess certain physical and chemical properties that permit it to operate properly. If a material does not possess all of these characteristics to some degree, it will not function long as a bearing. It should be noted, however, that few, if any, materials are outstanding in all these characteristics. Therefore, the selection of the optimum bearing material for a given application is at best a compromise to secure the most desirable combination of properties required for that particular usage. The seven properties generally acknowledged to be the most significant are: 1) Fatigue resistance; 2) embeddability; 3) compatibility; 4) conformability; 5) thermal conduc tivity; 6) corrosion resistance; and 7) load capacity. These properties are described as follows: 1) Fatigue resistance is the ability of the bearing lining material to withstand repeated applications of stress and strain without cracking, flaking, or being destroyed by some other means. 2) Embeddability is the ability of the bearing lining material to absorb or embed within itself any of the larger of the small dirt particles present in a lubrication system. Poor embeddability permits particles circulating around the bearing to score both the bearing surface and the journal or shaft. Good embeddability will permit these particles to be trapped and forced into the bearing surface and out of the way where they can do no harm. 3) Compatibility or antiscoring tendencies permit the shaft and bearing to “get along” with each other. It is the ability to resist galling or seizing under conditions of metal- to-metal contact such as at startup. This characteristic is most truly a bearing property, because contact between the bearing and shaft in good designs occurs only at startup. 4) Conformability is defined as malleability or as the ability of the bearing material to creep or flow slightly under load, as in the initial stages of running, to permit the shaft and bearing contours to conform with each other or to compensate for nonuniform loading caused by misalignment.
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