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Tham khảo tài liệu 'friction and lubrication in mechanical design episode 2 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 430 Chapter ì I Dominating Frequency in the Noise signal kHz Figure 11.4 Correlation between speed of surface wave and dominating frequency. 11.3 EFFECT OF LUBRICATION ON NOISE REDUCTION It is generally accepted that frictional noise reduction can be achieved through lubrication. This section provides a rational framework for quantifying the role played by the lubricating film between the rubbing surfaces in reducing the intensity of sound generated by relative motion. The hypothesis considered in this section is that frictional rubbing noise is the result of asperity penetration into the surface. The movement of the asperity therefore disturbs the surface layer and generates surface waves. The intensity of the sound can be assumed to be dependent on the depth of penetration which can in turn be assumed to be proportional to the real area Friction-induced Sound and Vibrations 431 of contact. As discussed in Chapter 4 the real area as well as the frictional resistance change in an approximately linear function with the normal load. It can therefore be assumed that the real area of contact between the lubricated solids can be used as a quantitative indicator of the intensity of the sound generated during sliding. The roughness profile data given by McCool 11 for five different surface finishing processes are used to determine the input parameters for the Greenwood-Williamson microcontact model 12 . The model is then used to compute the ratio of the real area of contact to the nominal area for the given normal load and the thickness of the lubricant film separating the surfaces. The model used for the illustration Fig. 11.5 is represented by two rollers with radii 7 I R2 10 in. subjected to a load of 2000 Ib in. The lubricant viscosity and speed are changed to produce different ratios of film thickness to surface roughness ranging from 0 to 3.0. The considered surface roughness conditions are given in Table 11.2. Figure 11.5 Contact model. 432 Chapter lì Table 11.2 .
