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Actively Lubricated Hybrid Journal Bearings Based on Magnetic Fluids Actively lubricated hybrid journal bearings based on magnetic fluids for high-precision spindles of machine tools Luis Lopez de Lacalle, Harkaitz Urreta, Gorka Aguirre, Pavel Kuzhir, Luis Norberto López de Lacalle To cite this version: Luis Lopez de Lacalle, Harkaitz Urreta, Gorka Aguirre, Pavel Kuzhir, Luis Norberto López de Lacalle. Actively lubricated hybrid journal bearings based on magnetic fluids for high-precision spindles of machine tools. Journal of Intelligent Material Systems and Structures, SAGE Publications, 2019, 30 (15), pp.2257-2271. 10.1177/1045389X19862358. hal-02426104 HAL Id: hal-02426104 https://hal.archives-ouvertes.fr/hal-02426104 Submitted on 1 Jan 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Page 1 of 53 Journal of Intelligent Material Systems and Structures 1 2 3 4 5 6 7 Actively lubricated hybrid journal 8 9 10 11 bearings based on magnetic fluids for 12 13 14 high precision spindles of machine tools 15 16 17 1 1 2 18 Harkaitz UrretaFor*, Gorka Peer Aguirre Review, Pavel Kuzhir , Luis Norberto 19 20 Lopez de Lacalle 3 21 22 23 24 1 IK4-IDEKO, Arriaga 2, E-20870 Elgoibar, Spain 25 26 27 2 University Côte d’Azur, CNRS UMR 7010 Inst. of Physics of Nice, Parc Valrose 28 06100 Nice, France 29 30 31 3 EHU-UPV Dept. Mechanical Engineering, Alameda Urquijo S/N, E-48013 Bilbao, 32 33 Spain 34 35 36 * Corresponding author [email protected] ; Tel: +34943748000 ; Fax: +34943743804 37 38 39 Abstract 40 41 42 43 The research work reported in this paper is focused on the use of magnetic fluids as 44 active lubricant for improving the performance of hybrid journal bearings, with 45 46 application to high precision machine tools. Prototype design was optimized following 47 48 numerical computation of Reynolds equation and computational fluid dynamics (CFD) 49 50 calculations, in both cases with Herschel-Buckley model for the magnetorheological 51 52 fluid. This fluid (LORD Corp. MRF 122-2ED) was experimentally characterized in 53 detail. The improvement of the hydrodynamic effect in journal bearings was 54 55 demonstrated with 50% higher load capacity and stiffness, mainly at half of shaft 56 57 eccentricity 0.4<ε<0.7. Active hydrostatic lubrication achieved quasi-infinite stiffness 58 59 60 http://mc.manuscriptcentral.com/jimss Journal of Intelligent Material Systems and Structures Page 2 of 53 1 2 3 within working limits (load and speed), at low frequencies. For high dynamic response 4 5 the active lubrication based on magnetorheological valves did not show good response. 6 7 The feasibility of using magnetic fluids for developing high performance machine tool 8 9 spindles and the validity of the simulation models was demonstrated experimentally. 10 11 12 Keywords 13 14 15 Magnetorheological fluid, MR valves, active bearing, CFD, machine tool, spindle. 16 17 18 For Peer Review 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 http://mc.manuscriptcentral.com/jimss Page 3 of 53 Journal of Intelligent Material Systems and Structures 1 2 3 4 5 6 7 Nomenclature and main variables 8 9 10 b Recess width [m] S Stiffness [N/m] 11 B Magnetic flux density [T] t Time [s] 12 C Radial clearance [m] T Temperature [ºC] 13 14 F Force [N] W Load capacity [N] 15 Ff Friction force [N] x,y,z Linear coordinates [-] 16 h Film thickness [m] r, θ,z Cylind. coordinates [-] 17 H Magnetic field strength [A/m] u,v,w Fluid velocity [m/s] 18 l Recess lengthFor Peer[m] Review Shear rate [1/s] 19 ʖ 20 L Bearing length [m] θ Angular coordinate [º] 3 21 n Number of pockets [-] ρ Density [kg/m ] 22 p Pressure distribution [Pa] σ Stress [Pa] 23 P Recess pressure [Pa] Shear stress [Pa] 24 r τ 25 Pp Pumping pressure [Pa] µ Dynamic viscosity [Pa·s] 3 2 26 Q Flowrate [m /s] ν Kinematic viscosity [m /s] 27 R Radius [m] φ Attitude angle [º] 28 R Shaft radius [m] Angular abscissa [º] 29 a ψ 30 Rc Bearing raius [m] Ω Angular speed [1/s] 3 31 Rh Hydraulic resistance [Pa·s/m ] 3 32 Ro Hydraulic resist. bearing [Pa·s/m ] 33 R Hydraulic resist. restrictor [Pa·s/m 3] 34 i 35 1 Hydraulic resistance ratio L Length to = λ = diameter ratio 36 ͌ 2R 1 + $Ɵ 37 ͌* 38 39 e Relative eccentricity * τ 0C Dimensionless ε = τ 0 = 40 µ Rω yield stress R 0 41 ∆x Dimensionless element h Dimensionless 42 ∆X = size in tangential H = gap size 43 R C 44 direction 45 ∆h Dimensionless element p(C R)2 Dimensionless ∆Y = P = 46 h size in radial direction pressure 47 ω 48 ∆z Dimensionless element d P dp (C R)2 Dimensionless 49 ∆Z = size in axial direction = pressure gradient L d X dx ω 50 tangential 51 Dimensionless velocity 2 Dimensionless 52 vx d P dp (C R) u = in tangential direction = pressure gradient 53 ωR dZ dz ω 54 axial 55 vz Dimensionless velocity 56 w = in axial direction 57 ωR 58 59 60 http://mc.manuscriptcentral.com/jimss Journal of Intelligent Material Systems and Structures Page 4 of 53 1 2 3 4 5 6 7 INTRODUCTION 8 9 10 The introduction to this research work has three sections, 1) a brief introduction to 11 12 classic lubricated bearings with hydrostatic and hydrodynamic lubrication, 2) active 13 14 bearings and 3) active hybrid journal bearings with magnetic fluid. 15 16 17 Hydrostatic and hydrodynamic lubrication bearings 18 For Peer Review 19 20 Pressurized lubricated bearings, commonly known as hydrostatic or hydrodynamic 21 22 bearings, are quite widely used and known by manufacturers of high-precision machine 23 24 tools. Most influencing authors in the machine tool building field, for instance M. Weck 25 26 (Weck, 1984), agree that between the available technologies for guiding systems, namely 27 sliding, rolling and pressurized lubricant technologies, the latter offers better properties, 28 29 considering resolution, damping and smoothness in the movement. Lubricated bearings 30 31 can work in either hydrostatic or hydrodynamic regime, in function of the boundary 32 33 conditions, i.e.: external oil pressurization, geometry of the bearing, fluid viscosity and 34 35 applied load. 36 37 38 Hydrodynamic bearings, where pressure is generated by relative motion between the 39 bearing surfaces (Frêne et al., 1997), are suitable for applications where working 40 41 conditions are quite stationary. Thus, with a proper design of the bearing, a stable and 42 43 safe pressurized oil thin film can be achieved between the moving parts, the shaft and the 44 45 bearing, avoiding any contact, friction and therefore wear. The pressure in the bearing 46 follows the classic equation in thin fluid films proposed by Osborne Reynolds (Reynolds, 47 48 1886). The main hydrodynamic bearing drawback are the starting and deceleration 49 50 stages, where fluid velocity is so low that lubricant film cannot support the load, leading 51 52 to contact, friction and wear of surfaces. 53 54 55 To avoid contact and wear whatever is relative movement speed, hydrostatic 56 lubrication (Bassani and Piccigallo, 1992) is the proper solution. In this case, lubricant 57 58 59 60 http://mc.manuscriptcentral.com/jimss Page 5 of 53 Journal of Intelligent Material Systems and Structures 1 2 3 fluid pressure is provided by an external hydraulic pump, which ensures a fully 4 5 developed thin lubricant film between bearing and shaft. The bearing behaviour is 6 7 strongly dependent on the selection of compensation valves, commonly known as 8 9 restrictors . Restrictors determine fundamental mechanical properties of the bearing, like 10 11 stiffness and force. With increasing shaft speed, hydrodynamic pressure appears in the 12 hydrostatic bearings, as described by Reynolds equation. Hydrostatic bearings can thus, 13 14 in function of the geometry, oil viscosity and operational conditions, become in a “hybrid 15 16 bearing” with mixed hydrodynamic and hydrostatic lubrication regime. Figure 1 scheme 17 18 shows the bearing Forhydrodynamic Peer pressure governed Review by Reynolds equation (1). 19 20 [insert figure 1] 21 22 23 24 Figure 1 Hydrodynamic pressure in journal bearings. 25 26 ∂ ρ h3 ∂ p ∂ ρ h3 ∂ p ∂h ∂ 27 + = 6ρ ()U1 +U 2 + 6ρ h ()U1 −U 2 +12ρ V +12ρ& h (1) ∂ x µ ∂ x ∂ z µ ∂ z ∂ x ∂ x 28 29 Figure 2 shows the implementation of hydrostatic lubrication ruled by the basic 30 31 equations (2). 32 33 34 [insert figure 2] 35 36 37 Figure 2 Hybrid journal bearing and hydraulic circuit 38 39 ͮ ͮ_ 40 u (2) ͊- = · ͊+ = ċ ·͊+ ͑ = Ȅ Ȅ ͤ · ̻͘ ͍ = 41 u~ ĜƠ ͯ ͯ_ T ċĢ 42 The improvement of the performance of journal bearing with hybrid lubrication by 43 44 means of active magnetic fluids will be discussed in this paper. 45 46 47 Active bearings for smart systems 48 49 50 Following Reynolds and hydrostatic lubrication basic equations, see Eqs.
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