Wear 271 (2011) 86–91 Contents lists available at ScienceDirect Wear journal homepage: www.elsevier.com/locate/wear A study of airborne wear particles generated from the train traffic—Block braking simulation in a pin-on-disc machine Ulf Olofsson ∗ Royal Institute of Technology (KTH), Department of Machine Design, SE 100 44 Stockholm, Sweden article info Article history: Received 24 August 2010 Accepted 3 October 2010 Available online 11 November 2010 Keywords: Airborne particles Wear Block brake abstract Recently, much attention has been given to the influence of airborne particles in the atmosphere on human health. Sliding contacts are a significant source of airborne particles. In this study airborne particles from railway block brakes are studied using cast iron and composite block material on railway wheel steel. A pin-on-disc tribometer equipped with airborne particle counting instrumentation was used as experimental set-up. The result shows differences for the two tested block brake material combinations in particle size distribution, morphology and elemental content. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The main concerns about airborne wear particles are environ- mental. They include their health effects, visibility problems and the soiling of surfaces. The settling velocity of airborne spheri- cal particles with a larger diameter than 1 m is approximately proportional to its density and the square of the diameter [1]. For example a 1 m particle with a density of 1 g cm -3 has a settling velocity of 0.03 mm s -1 and may be transported several hundred kilometers. Many studies have shown an association between adverse health effects and the concentration of airborne particles in the atmosphere [2–4]. The size of the inhaled particles is an impor- tant factor for particle effect on health since it is crucial for where they deposit in the respiratory tract. For example nano-particles (particles smaller than 100 nm) are deposited deep in the lungs (in the alveolus) and are reported to cause a greater inflamma- tory response as reported by Donaldson et al. [5] and Oberdorster et al. [6]. Airborne particles in the size range 1–5 m deposit in the mouth and noise region, and the trachero-broncial and are more swiftly removed. Also the elemental content of the airborne parti- cles influences the health effects and especially the metal content has been suggested to be the reason for high toxicity as discussed by Ghio et al. [7] and Karlsson et al. [8]. Limit levels for PM10 (air- borne particles with an aerodynamic diameter smaller than 10 m) are set in EU by the EC [9] to an average of 50 g/m 3 per day. This limit level may be exceeded at most 35 days per year. Also, the ∗ Corresponding author. Fax: +46 8 7231730. E-mail addresses: ulf.olofsson@itm.kth.se, ulfo@md.kth.se annual average is not permitted to exceed 40 g/m 3 . These levels can be compared to the very high particle mass concentrations (in the range 300–1000 g/m 3 ) that have been found in the under- ground systems in Stockholm [10], London [11], Budapest [12] and Prague [13]. There are only few studies investigating the emission of wear particles from railway above ground. According to Bukowiecki et al. [14] the emissions from railways were analyzed by the content of Fe, Mn, Cr and Cu in aerosol samples outside a railway station. The study concludes that the exposure above ground can be about an order of magnitude lower than in a subway station. A problem with measuring airborne brake particles in field tests is to distinguish them from the background noise. Therefore, it may be preferable to use laboratory test stands that allow control- ling of the cleanliness of the surrounding air. Recently, Olofsson et al. [15,16] used a pin-on-disc material test stand with a clean air supply to measure the number and size of airborne wear particles online. With this in mind, a test series has been run in the pin-on-disc material test stand previously used in Refs. [15,16]. The purpose of this paper is to characterize the size and number distribution of airborne particles generated from tests with the material combina- tions; block brake against railway wheel. Also the morphology and the material of the particles are studied by collecting wear particles on filters for geometry and material analysis. 2. Experimental set-up The test set-up was the same as that used in Refs. [15,16], supple- mented with an additional aerosol spectrometer that measured size distributions of particles between 0.01 and 0.52 m and a pump that captures airborne wear particles on a filter. Nuclepore 0.4 m 0043-1648/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2010.10.016