Influence of quartz particles on wear in vertical roller mills. Part I: Quartz concentration Lucas R.D. Jensen a, * , Henrik Friis d , Erling Fundal b , Per Møller c , Per B. Brockhoff e , Mads Jespersen a a FLSmidth A/S, Vigerslev Allé 77, 2500 Valby, Denmark b Fundal Consult, Østergade 4, 4140 Borup, Denmark c Technical University of Denmark, Kemitorvet, Bygning 204, 2800 Kgs Lyngby, Denmark d Århus University, Department of Earth Sciences, Høegh-Guldbergs Gade 2, 8000 Århus C, Denmark e Technical University of Denmark, Richard Petersens Plads, Bygning 305, 2800 Kgs Lyngby, Denmark article info Article history: Received 6 July 2009 Accepted 23 November 2009 Available online 4 February 2010 Keywords: Comminution Limestones Particle size Wear Vertical roller mills Quartz Wear mechanisms abstract The standard closed circuit comminution process commonly employed in industrial vertical roller mills has been analyzed to determine the influence of typical abrasive minerals on wear rates. With the main focus on raw mixes used in cement plants, synthetic mixtures imitating were prepared. Using statistical planning, a total of 10 tests were carried out with two different limestones and one type of quartz sand. The size distributions were kept constant and only the mixing ratios were varied. It appears from the investigation that mixtures consisting of minerals with different grindabilities result in an increased concentration of abrasive particles in the grinding bed ðR 2 > 0:99Þ. The present study shows that the quartz concentration in the grinding bed is determining the wear rate. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Quartz is a hard mineral frequently being part in cement raw mixes. Hence it is of interest to correlate its content in the mixture with the wear rates experienced in vertical roller mills (VRM). From the experience of numerous laboratory VRM tests, it is known that the measured wear rates might not correlate with wear rates in full scale VRMs. So far it has not been possible to ob- serve the material flow inside VRMs and thus wear rate discrepan- cies have been accepted without any acceptable explanation (Private Communication with FLSmidth R&D Department, 2009). The abrasive mechanism of quartz will physically change the geometry of the mechanical parts thus lowering the performance of machinery and further increase the operating costs. The replace- ment of wear parts is both time consuming and laborious and will often require a shut-down of the entire plant with the consequence of high economic losses (Röhrig, 1971). Ozkahraman (2005) has studied two different limestones and observed that there is a relation between the physical mechanical properties (such as point-load-test) and their grinding properties (such as bond work index): Two limestones might have the same physical mechanical strength but highly different energy require- ments when ground to the same final product size. Tavares and das Neves (2008) have studied the relations between rock textures and different physical mechanical properties; however the same difficulties arise as the rocks behave differently when processed on different types of laboratory mechanical testing equipment. Several authors have stated that quartz is the most important abrasive found in cement raw mixes, because the hardness ratio of this mineral is higher compared to most alloys used as wear resistant materials (Jung, 2000). A VRM test is very costly and time consuming and requires ap- prox. 600 kg of raw materials for one single test. Thus, there is a need to develop a simplified characterization procedure to predict the wear rates. The first necessary step is to determine a relation- ship between quartz concentration in the new feed raw mix and the wear rate. 1.1. VRMs On a large scale, the mining, cement and coal industry are the three industries being highly dependent on mineral size reduction equipment. The mining industry is based on wet-grinding of ores and the fi- nal comminution stage is typically a SAG-mill or a ball mill. In this 0892-6875/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2009.11.014 * Corresponding author. E-mail address: lje@flsmidth.com (L.R.D. Jensen). Minerals Engineering 23 (2010) 390–398 Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng