TAILIEUCHUNG - Hydrodynamic Lubrication 2009 Part 2

Tham khảo tài liệu 'hydrodynamic lubrication 2009 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 2 Foundations of Hydrodynamic Lubrication The essence of hydrodynamic lubrication was first clarified experimentally by British railroad engineer Beauchamp Tower 1845 -1904 in 1883 1 2 . Based on Tower s experiments Osborn Reynolds 1842-1912 the physicist formulated a theory of lubrication in 1886 3 . Since then Reynolds theory has been the foundation of the theory of hydrodynamic lubrication. Recently developed theories of elastohy-drodynamic lubrication thermohydrodynamic lubrication turbulent hydrodynamic lubrication and others are regarded as extensions of Reynolds theory. The pioneering works of Tower and Reynolds are reflections of Britain s advanced technology at that time. In this chapter Tower s experiment will be explained first and then Reynolds theory will be derived. Tower s Experiment Figure which is a simplification of a drawing from Tower s famous paper of 1883 1 shows the main part of Tower s friction test rig for a bearing used in rolling stock. The bearing is a partial bearing and bearing bush A covers the upper half of the journal. A load weight of the vehicle acts on the journal from above through bearing cap B and bearing bush A. The lower part of the journal is immersed in lubricating oil and the oil adhering to the journal surface is pulled up by rotation of the journal and is supplied to the bearing clearance. Such a method of lubrication is called oil bath lubrication. The frictional resistance frictional moment of the bearing can be obtained by measuring the frictional moment acting on the bearing cap. Using this test rig Tower found the frictional characteristics of a journal bearing with oil bath lubrication to be as follows. 1. Frictional resistance is nearly constant regardless of the bearing load. 2. The frictional coefficient is very small usually of the order of 1 1000 . 3. Frictional resistance increases with sliding speed. 10 2 Foundations of Hydrodynamic Lubrication Fig. . Tower s test rig. A bearing bush B bearing .

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