The Influence of the Operating Conditions on the Lubrication Regimes of Ball Screws

Abstract:

In point contact related applications (ball bearings, ball-screws) the minimum and the central film thickness of lubricant have a particular importance. The literature presents various numerical solutions to determine these parameters in the case of elliptical contacts [1-4]. Most of them refer to the fully developed elastohydrodynamic lubrication regime (EHD). Hamrock [5] proposes four different lubrication regimes depending on the size and importance of two physical phenomena that occur in contact: elastic deformation of the bodies in contact under a given load and lubricant viscosity variation of contact pressure. These four lubrication regimes have specific relations for calculating the two parameters. Also, Hamrock [5] develops a methodology for identifying the lubrication regime in a point contact, depending on three dimensionless parameters: the ellipticity parameter; the viscosity parameter; the elasticity parameter. According to the viscosity and elasticity parameters, for each value of the ellipticity parameter a map of lubrication regimes can be built. These parameters are influenced by the materials and geometry of the bodies in contact and operating conditions. By using the methodology [5] a comprehensive analysis regarding the lubrication regimes in contacts between balls and races of a ball screw drive has been done. Thus, a complex program to draw lubrication regimes maps, starting from an imposed geometry and from given operating conditions, has been developed. The developed maps have revealed the different lubrication regimes that can occur in contacts between the balls and races on the screw and nut. It was also revealed, for a given type of screw, which are the load and speed limits that allow transition from an isoviscous-rigid regime of lubrication (IVR) / hydrodynamic (HD) to an elastohydrodynamic lubrication regime (EHD). For each lubrication regime, relations were used for calculating the appropriate minimum thickness of lubricant film, hence the major importance of accurate knowledge of lubrication regime.

• Periodical: Applied Mechanics and Materials (Volume 371)
• Pages: 581-585
• DOI: https://doi.org/10.4028/www.scientific.net/AMM.371.581
• Online since: August 2013
• Authors: George Constantin Puiu, Vasile Puiu
• Keywords: Ball Screw, Elliptical Contact, Film Thickness, Fluid Film Lubrication, Lubrication Maps, Lubrication Regime

References

[1] J.F. Archard, E.W. Cowking, Elastohydrodynamic lubrication at point contacts, Proc. Inst. Mech. Eng. 180 (1965) 47-56.

[2] B.J. Hmrock, D. Dowson, Isothermal EHD Lubrication of Point Contacts Part III – Fully Flooded Contacts, Trans. of ASME, Journal of Lubrication Technology. 99 (1977) 15-23.

DOI: 10.1115/1.3453074

[3] R. J. Chittenden, D. Dowson, J. F. Dunn and C. M. Taylor, A Theoretical Analysis of the Isothermal Elastohydrodynamic Lubrication of Concentrated Contacts. I. Direction of Lubricant Entrainment Coincident with the Major Axis of the Hertzian Contact Ellipse, Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, 1985, pp.245-269.

DOI: 10.1098/rspa.1985.0014

[4] V. Puiu, D.N. Olaru, Film Thickness in Ball Screw, Buletinul Institutului Politehnic Iasi. secţia V vol. XLV (XLIX) fasc. 3-4 (1999) 7-20.

[5] B.J. Hamrock, S.R. Schmid, B.O. Jacobson, Fundamentals of Fluid Film Lubrication, second ed., Marcel Dekker, Inc., New York, (2004).

[6] C.G. Puiu, Contributions regarding the performance increase of ball screws correlated with the tribological processes, PhD Thesis, Gheorghe Asachi, University of Iasi, (2012).