Dynamic characteristics of polymer faced tilting pad journal bearings Gregory F. Simmons a,b,n , Alejandro Cerda Varela c , Ilmar Ferreira Santos c , Sergei Glavatskih d,e a Division of Machine Elements, Luleå University of Technology, Luleå 97187, Sweden b LKAB, Kiruna 98186, Sweden c Department of Mechanical Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark d Machine Design, Royal Institute of Technology, 10044 Stockholm, Sweden e Department of Mechanical Construction and Production, Ghent University, Ghent, Belgium article info Article history: Received 24 September 2013 Received in revised form 24 January 2014 Accepted 2 February 2014 Available online 11 February 2014 Keywords: Journal bearing Tilting pad PTFE PEEK abstract Dynamic characteristics of polymer faced tilting pad journal bearings are presented. Investigations are conducted using a single pad, load on pad configuration over a range of shaft speeds and loads. Two polyether ether ketone (PEEK) faced pads, one polytetrafluoroethylene (PTFE) faced pad and two entirely PEEK pads are investigated to determine the effect of varying mean bearing pressure and pivot characteristics as well as different material properties of the polymer layer. Experimental results indicate increased damping and decreased stiffness and slightly increased oil film temperature for entirely PEEK pads compared to pads with a PEEK lining and steel backing. Similar effects were observed by using a softer (PTFE) pad liner with a steel backing. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction Changing demands on the electrical network and growing supply of un-regulated power sources such as wind and solar have resulted in a change of roles for large power generating machines. Machines in hydro-electric and thermal power plants which were originally designed to provide a steady base load are now being operated to fulfill grid regulation and peak power needs. This has resulted in a dramatic increase in the number of starts and stops which machines undergo as well as an increase in operation at non-ideal operating states. Both starting/stopping and non-ideal operation contribute significantly to the wear and tear of machines with components that come into contact with each other such as bearings and seals taking the brunt of the wear [1]. Furthermore, with bearing failures estimated to cause 40% of a hydropower plant's operating losses [2], it is clear that the current technology is inadequate for the markets demands. Current bearing technology consists primarily of white metal faced sliding bearings, technology initially developed at the beginning of the 20th century but little changed since the 1970s. Polymer faced journal bearings have been investigated for use primarily in slowly rotating or oscillating applications by Ukon- saari [3] and Gawarkiewicz and Wasilczuk [4]. While these studies included temperature measurements, the contacts were almost always in boundary lubrication, far from the hydrodynamic lubri- cation regime. Studies conducted by Fleszar [5] investigated a number of bearing liner materials for use in sliding applications finding little performance difference between woven and molded liners made of phenol resins with PTFE additives. Melting temperatures for all materials tested were over 240 1C . Phenol resin based materials with asbestos and carbon fiber reinforcement were investigated by Kim and coworkers [6,7] for use in marine propeller shaft bear- ings. These studies found that carbon fiber provided less wear than asbestos and additionally proposed a method of manufacturing a polymer sleeve bearing with a 4 mm sleeve thickness. Attachment of the sleeve to the backing ring was not discussed. Hydrodynamic sliding bearings utilizing virgin PTFE bonded using a copper mesh have been used in Russia and China for some time, Glavatskih [8], but detailed laboratory studies have only been conducted on thrust bearings utilizing this technology. Reports from industrial installation of these types of bearings have found improved machine operating characteristics as well as potential for reductions of bearing size, Glavatskih et al. [9]. Simulations of such bearings have predicted slightly higher lubricant tempera- tures, Kuznetsov et al. [10], as could be expected by the lower thermal conductivity of polymers in comparison to metals. Recent reports of installed PTFE faced bearings, Simmons et al. [11], Ettles et al. [12] and Dwyer-Joyce et al. [13], report good performance of plain PTFE faced thrust bearings but very little has Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/triboint Tribology International http://dx.doi.org/10.1016/j.triboint.2014.02.001 0301-679X & 2014 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail address: gregory.simmons@lkab.com (G.F. Simmons). Tribology International 74 (2014) 20–27