tailieunhanh - Mechanical Engineering-Tribology In Machine Design Episode 4

Tham khảo tài liệu 'mechanical engineering-tribology in machine design episode 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 62 Tribology in machine design fmin is recommended. Thus if e c and 0 then r 1 2fi V 11 c 3s 3 v rY _ 7 _ 2 v l - 2 p c J 12tĩ 71 so that r ir 2 p 1 V- c and r2 M fPr V . c If p denotes the load per unit of projected area of the bearing surface and N is the speed in . then p 2p r and V 27irN so that and j rV p - . c In using these expressions care must be taken to ensure that the units are consistent. Numerical example A journal and complete bearing of nominal diameter 100 mm and length 100 mm operates with a clearance of c mm. The speed of rotation is . and 1 20cP. Determine i the frictional moment when rotating without load ii the maximum permissible load and specific pressure . load per unit of projected area of bearing surface knowing that the eccentricity ratio e c must not exceed iii the frictional moment under load. Solution The virtual coefficient of friction when e c is c r and the load per unit length is r 2 p 1 V - . c i when rotating without load eqn will apply namely r2 M 2npV per unit length. Basic principles of tribology 63 To convert from centipoise to Ns m2 we have to multiply z 20cP by 10 3. Thus p 20 X 10 3 Nsm 2 V 2nrN 2 X X X 600 60 m s 2 r c - 50m and so M 2tĩ20 X 10 3 X X 50 Nm per meter length but length of the bearing m thus frictional moment X Nm. ii load per unit length r 2 p 1F - c uVr2 _ _ _ 20x 10 3 X 50 c and so p X 1 478 N m maximum permissible load Px length of bearing 478 N p 478 specific pressure p 0 1 MPa iii frictional moment under load M fPr per unit length where fr X m total frictional moment 478 X Nm. References to Chapter 2 1. E. Rabinowicz. Friction and Wear of Materials. New York Wiley 1965. 2. J. Hailing ed. . Principles of Tribology. Macmillan Education Ltd.