The effects of shear stress on the lubrication performances of oil film of large-scale mill bearing

Transcription

1 Universit of Wollongong Researc Online Facult of Engineering - Papers (Arcive) Facult of Engineering and Information Sciences 9 Te effects of sear stress on te lubrication performances of oil film of large-scale mill bearing Zengi Jiang Universit of Wollongong, jiang@uow.edu.au A K. Tieu Universit of Wollongong, ktieu@uow.edu.au Jianmei Wang Universit of Wollongong Q.X. Huang Taiuan Universit of Science and Tecnolog ttp://ro.uow.edu.au/engpapers/887 Publication Details Wang, J., Huang, Q., Jiang, Z. Tieu, A. K. (9). Te effects of sear stress on te lubrication performances of oil film of large-scale mill bearing. Advanced Materials Researc, Researc Online is te open access institutional repositor for te Universit of Wollongong. For furter information contact te UOW Librar: researc-pubs@uow.edu.au

2 Te Effects of Sear Stress on te Lubrication Performances of Oil Film of Large-scale Mill Bearing Jianmei Wang 1, a, Qingxue Huang 1,b, Zengi Jiang,c, Kiet A. Tieu,d 1 Taiuan Universit of Science and Tecnolog, People s Republic of Cina Universit of Wollongong, Australia a wjmdb@13.com, b qx@tust.edu.cn, c jiang@uow.au, d ktieu@uow.au Kewords: Oil film bearing. Finite difference metod. Boundar element metod. Sear stress Lubrication performance. Viscosit Abstract. A new coupling numerical algoritm as been developed to integrate Finite Difference Metod (FDM) wit Boundar Element Metod (BEM) to analze sear performance of oil film b iterativel solving a series of equations suc as te film flow velocit and sear stress equations for contact bodies in bearing sstem. Wit consideration of te variations of viscosit and densit wit pressure and temperature, te effects of sear stress of oil film laers on lubrication performance of contact surfaces under different loadcases were discussed. Moreover, German-made Anton Paar MRD (Magnetic Reologic Device) was used to determine te relationsip between te viscosit and sear stress of lubricating oil. Te conclusions were verified to be beneficial to te furter stud on lubricating performance of eav contact components and to prolong teir service lives. Introduction To prolong te service life of large-scale eav bearing, teoretical and experimental researc as to be compreensivel done for overall assessment on on-line bearing. Not onl complete ceck and on-line test sould be made, but also te influence of temperature rise on lubricating performance of bearing sould be taken into account to analze te effects of all te factors on bearing performance, tus more refined lubrication teor could be summarized [1]. Te function of oil film is to reduce friction force, but it alwas produces tangential force to inder movement [,3]. Even if te friction force is reduced to te minimum, te existing friction consumption could still decrease maciner efficienc [4,]. Sear stress of oil film is correlated wit film flow velocit. It is te perquisite to calculate te friction resistance between te sear stress and contact bodies. So, te effects of sear stress of oil film in mill bearing as been teoreticall analzed in detail, wic as great meaning to furter understand and grasp te lubricating performance of contact components under eav load, as well as to prolong te bearing service life. Calculating Model on Sear Stress of Lubricating Film. Wen oil-film bearing works, te lubricating oil will be brougt into te wedge clearance to form into draulic film b te rotation of roll neck. Fig.1 sows te coordinate sstem of Reonlds equation. During te wole calculation process, bearing was regarded as elastic bod 1, roll as elastic bod and bearing cock as elastic bod 3. Meanwile, it is supposed tat te rotating roll and still bearing ad no axial misalignment. Matematical Model on Sear Stress of Lubricating Film. Sear stress formula can be deduced from te definition of Newtonian fluid. u v x, (1) z z According to te rotation relationsip between te bearing and te roll [], velocit boundar conditions can be expressed as below, were U, U are respectivel te velocit components in x direction at z and z.

3 z, uu, v z, uu, v () Z Roll neck Bus O V U X Y Neglecting te influence of curvature, setting te viscosit along te film tickness as a constant, te fluid velocit on contact surface is equal to te velocit of contact bod. Bearing was fixed to bearing cock b position pin, and roll neck is supposed to ave no axial misalignment, so U = V = V =ten te fluid velocit in x and directions at an point of lubricating film can de deduced as follows. z 1 P u U, v g ( z z) (3) z Were u is mainl consisted of te sear flow velocit defined as us U. Te velocit gradient along te film tickness is far greater tan tose in axial and circumferential directions, so te velocit gradient can be deduced below. U Fig. 1 Generalized coordinates for Renolds u v 1 P, ( z ) z z g (4) Substitute Eq. 4 into Eq. 1, ten 1 p 1 p x z U, z x On roll neck surface z, te sear stress can be deduced below. () p x, U p () x On bearing surface z, te sear stress can be deduced below. p x, U p x (7) Matematical Model. Substituting te following dimensionless parameters into te above equations, X x/ R Y L/, P P / ur /, e, /, v v/ u, u u/ U, x x /, /, ten te dimensionless sear stress equations can be deduced. On roll neck surface z, te dimensionless sear stress can be deduced below. u p x U, p u X Y On bearing surface z, te dimensionless sear stress can be deduced below. (8)

4 u p x U, p u (9) X Y Main Input Parameters. Table 1 sows te main working and geometrical parameters of bearing, and te main parameters of lubricant are sown in Table. Table 1 Main parameters of oil-film bearing Name Value Bearing diameter [mm] 111 Lengt-to-diameter ratio [mm].7 Relative clearance.4-3 Elastic modulus [ Kg/ cm ].11 Poisson ratio.3 Initial temperature [ o C] 4 Table Main parameters of lubricants Name Value Viscosit (4 o C)[ Pa s ] Densit [ kg / m ] 89 Specific eat [ J / kg K] Termal conductivit[ WmK / ].14 Viscosit-pressure coefficient[ m / N] 8.1 Inlet oil pressure [ MPa ].1 Calculating Results on Sear Stress of Lubricating Film. Te dimensionless sear stress of oil-film bearing is mainl circumferential sear stress x and axial sear stress. Te dimensionless sear stress on te bearing surface Z and roll surface Z 1 at different velocit is respectivel sown in Figs. -3. Te circumferential sear stress on bot contact surfaces could increase rapidl wit te roll velocit, since suc sear stress generall includes te sear stress b pressure flow and te sear stress b sear flow. Wit te improvement of roll velocit, more and more lubricating oil will be brougt into wedge clearance, and te sear stress b sear flow is far larger tan tat b pressure flow. So, te circumferential sear stress is mainl determined b te sear flow, because te film viscosit increases rapidl wen te oil film pressure increases wit velocit. circumferential sear axial sear stress (a) circumferential sear stress at rps (b) axial sear stress at rps circumferential sear axial sear stress (c) circumferential sear stress at rps (d) axial sear stress at rps Fig. Te circumferential and axial sear stresses of oil film at bearing surface Z

5 It can be seen from above, te roll rotates and te bearing is fixed, te oil flow on bearing surface at te transient region from oil inlet zone to pressure peak zone needs to overcome larger oil film resistance, so a larger axial sear stress is required. Meanwile, te oil flow from pressure peak zone to oil film rupture zone can be accelerated wit pressure, so a smaller axial sear stress of oil film is needed. circumferential sear axial sear stress (a) circumferential sear stress at rps (b) axial sear stress at rps circumferential sear axial sear stress (c) circumferential sear stress at rps (d) axial sear stress at rps Fig. 3 Te circumferential and axial sear stress of oil film interface at roll surface Z 1 As sown in Fig. 4, te rotation of roll makes te distribution laws of axial sear stress of oil film at different region justl contrar to te above explanation in Figs. -3. (Oil film region) Here, te axial sear stress of oil film is onl determined b pressure flow, wic generall increases wit te roll velocit. At te same time, te axial sear stress on bot contact surfaces Axial sear stress vector Axial center (a) Smmetr feature of spectrum profile (b) Asmmetr feature of vector plot Fig. 4 Te distribution features of axial sear stress on roll surface Z 1

6 displas asmmetr feature along te cross section of axial center, as sown in Fig. 4, and te distribution feature of axial sear stress on te roll surface and bearing surface is contrar to eac oter. Terefore, te rapid increasing sear stress would worsen te stress state of materials, ten result in microcrack, and ten fasten te expansion of crack, ultimatel result in pitting damage on materials. Measurement on Propert Parameters of Oil Film. German-made Anton Paar Magneto Reological Device MRD-31 was used to measure te oil film propert parameters suc as te viscosit and sear stress, wic could provide teoretical references to furter analsis on lubricating film performance of oil-film bearing in large-scale mill. Te Variation of Oil Film Sear Stress Under Different Film Tickness. As sown in Fig., te viscosit of lubricating oil decreases wit an increase of temperature, and te sear stress to overcome te lubricating oil flow also obviousl decreases as te temperature increases. Moreover, te sear stress of oil film under no normal stress decreases wit a decrease of oil film tickness. Sear Sear stress (Pa) (Engine Te variation of sear stress oil-3c) wit film tickness (3 o C) Measurement point point 1um 8um um um 1um Sear Sear stress (Pa) Te variation of sear stress wit film tickness (4 o C) 1 1 (Engine oil- 4C) Measurement point point 1um 8um um um 1um Fig. Te variation curves of sear stress under various oil film tickness Sear stress (Pa) (Pa) Te variation of sear stress wit velocit (Engine oil-3c) under different film tickness (3 o C) Velocit (1/min) (1/min) 1um 8um um um 1um Te variation of sear stress wit velocit (Engine oil- 4C) under different film tickness (4 o C) Sear stress (Pa) (Pa) Velocit (1/min) Velocit (1/min) 1um 8um um um 1um Fig. Te variation curves of sear stress wit roll speed under various oil film tickness Te Variation of Sear Stress wit Roll Velocit at Different Film Tickness. As sown in Fig., te lubricating oil wit iger viscosit will produce iger sear stress due to oil flow, and te sear stress is generall iger under te tin film tickness during te lower velocit range. Altoug te sear stress of oil film increases wit te roll velocit, te full film can be maintained onl under ticker oil film tickness. However, te tinner film could rupture at iger roll velocit. So, te variation range tat te sear stress varies wit roll velocit under te tin film tickness seems muc sorter tan tat under te tick film.

7 Summar Te effects of sear stress on different oil film laer ave been analzed. Te circumferential sear stress on contact surfaces increases rapidl wit roll velocit, te axial sear stress of oil film is onl related to pressure flow, and increases wit roll velocit. Meanwile, te axial sear stress on te contact surfaces displas te asmmetric feature along te cross section of axial center, and te sear stress on roll surface as te same value as tat on bearing surface wit opposite direction. Moreover, German-made Anton Paar MRD-31 was used to measure te lubricating oil properties, te distribution laws on te variation of viscosit wit sear stress, roll velocit and temperature ave been proved to be consistent wit te teoretical results, wic could provide references for furter researc on lubricating performance of oil film bearing in large-scale mill. Acknowledgements Te autors would like to express teir appreciation to te support of te project of te National Natural Science Foundation (71), Sanxi Generalization Project of Science and Tecnolog Acievements (77171), and Sanxi Overseas Scolarsip Fund (8171). References [1] S.Z.Wen, P.R.Yang: Elasodrodnamics Lubrication (Tsingua Universit Press, Cina 199). [] X.Q. Guo, S.Q. Li. Modern Large-scale Mill Oil-film Bearing (Macine Press, Cina 199). [3] Z.Y. Jiang, A.K. Tieu. J. Tribol. Int. Vol. 37 (4), p. 18 [4] G.Z. Ding. J. Taiuan Sci & Tec Univ. Vol. (4), p. 1 [] J. M. Wang, Q. X. Huang, C.J. Zao and J. B. Yao: Ke Eng. Mater. Vol. 34-3(), p. 33 [] J.M. Wang, Q.X. Huang, in: Te Proceeding of te 1 st International Smposium on Digital Manufacture, Cina, (), p. 18

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