Technical Report Tribological properties of polymer-based journal bearings Bekir Sadık Ünlü a, * , Enver Atik b,1 , Sinan Köksal b,1 a Celal Bayar University, Vocational High School, Department of Machinery, 45400-Turgutlu-Manisa, Turkey b Celal Bayar University, Engineering Faculty, Department of Mechanical Engineering, 45140-Muradiye-Manisa, Turkey article info Article history: Received 14 August 2008 Accepted 14 November 2008 Available online 28 November 2008 abstract Polymer-based materials are widely used due to their good corrosion resistance, self lubrication, and wear resistance properties at low speeds and but are not suitable for lubrication in journal bearings. High performance engineering polymers ensure desired properties for journal bearings and give good tribolog- ical results. In this study, tribological behaviors of polymer-based PE, PA, POM, PTFE, and Bakelite bear- ings have been investigated and evaluated. As a result, the highest wear resistance has occurred in PA and POM bearings. Ó 2008 Published by Elsevier Ltd. 1. Introduction For the past few decades, polymeric materials have been widely used in industry. Some of these materials are thermoplastics (poly- propylene (pp), polyethylene (pe), polyoxymethylene (pom), poly- tetrafluoroethylene (ptfe) ve polyamide (pa) etc.). The main advantage of these polymers is high wear and corrosion resistance. These materials (ptfe) are especially used due to their good tribo- logical properties and solid lubricant properties in the food indus- try and due to their good performance at non-lubricated dry conditions in journal bearing materials. PE has low density, high elasticity, and strength. (Pa), (Pom) and (Ptfe) have good sliding and wear properties at low frictions. Polyoxymethylene (POM) is a material which is generally used in engineering applications and is highly self lubricating. Previous research has generally ad- dressed the lubricating mechanism of POM rubbing against steel under adhesive conditions [1–8]. Polymeric materials can show very good wear resistance in spite of their modest surface stiffness and the shear strength. Many elastomeric polymers, such as cross-linked rubbers and reinforced ductile polymers are reported as good wear resistant materials [9]. PTFE bearings are frequently used on various machines due to their low friction coefficients in boundary lubrication conditions. The major problems in designing polymer bearings are to decide the optimal dimensions and material type for a long life and for obtaining lower friction and wear losses. Tribological properties of polymer radial bearings are affected by the adhesion on the sur- faces of steel–polymer, cohesive characteristics of the polymers used and thermal effects in the friction area at high p.v. (pressure Á velocity) values [10–12]. This p.v. value is not valid for polymeric materials. Velocity is affected by applied pressure at these materials [13,14]. Even though some filler materials are added to the polymers, their effects on tribological properties are not clearly known. There are different opinions in literature on how fillers affect polymer wear. These filler materials decrease wear by modifying the opposite surface and supporting the load. This increasing effect on wear is due to increased adhesion. They also reduce wear of the PTFE composites and they can induce abra- sive wear of the counterface [15–19]. If polymeric materials are worn at abrasive conditions, wear rate decreases with an increase in grit grade number [20]. Polymer-based materials can be used as journal bearings at low speeds [21]. The objective of this study is to investigate tribological behaviors of the pure PE, PA, POM, PTFE, and bakelite journal bear- ings at low speeds (v = 0.13 m/s) and to compare the treatment combinations among themselves for tribological properties. 2. Experimental studies 2.1. Preparation of experimental materials In this study, the pure PE, PA, POM, PTFE, and Bakelite materials have been used as journal bearing and SAE 1050 material as shaft. The chemical compositions of the journal materials used in the experiments were given in Table 1. Dimensions of bearing speci- mens were as follows: inner diameter (d = 10 +0.05 mm), width (B = 10 mm), outer diameter (D = 15 mm). The specimens have been worn and friction coefficient have been measured at radial journal bearing wear test rig at dry condi- tions as described by Atik et al. [22] and Ünlü and Atik [23]. The wear losses have been measured at dry conditions of 20 N loads, 250 rpm (v = 0.130 m/s velocity) and every 30 min for 2.5 h (1177.5 m sliding distance). The specimens were cleaned by ace- tone. In addition, macro-hardness has been measured using a 0261-3069/$ - see front matter Ó 2008 Published by Elsevier Ltd. doi:10.1016/j.matdes.2008.11.018 * Corresponding author. Tel.: +90 2363124888; fax: +90 2363144566. E-mail addresses: bekir.unlu@bayar.edu.tr (B.S. Ünlü), enver.atik@bayar.edu.tr (E. Atik), sinan.koksal@bayar.edu.tr (S. Köksal). 1 Tel.: +90 2362412144; fax: +90 2362412143. Materials and Design 30 (2009) 2618–2622 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes