• Ojala, Niko

Abstract

Demanding industrial wear problems cannot be properly simulated in the laboratory with standard methods using, for example, diamond indenters or fine quartz abrasives, as many standard or conventional wear testing methods do. The main reason is that most of the commonly available testing methods are based on low-stress wear conditions, while in mining high-stress wear conditions dominate. For this reason, several wear testers that can also utilize large sized abrasive particles to produce high-stress wear have been developed at Tampere Wear Center. In this work, one of such testers, a high speed slurry-pot, was developed with a possibility to conduct tests in both slurry and dry conditions. One of the main tasks of this thesis was to study how to set up the test method and the test device for simulating real mining related applications, and how the obtained results finally correlate with real-life material behavior in the applications. Another part of the work was to study and compare the wear mechanisms created by the low and high-stress testing methods, as well as the role of the microstructure and chemical composition of steels in the industrial wear processes.<br/><br/>In the comparison of the wear performance of steels and elastomers with each other, abrasive embedment was also observed to have a great influence on the comparison outcome, which needs to be taken into account when assessing the relative performance of these different types of materials in different wear conditions. For elastomers, especially, the effect of abrasive embedment is important in both low-stress and high-stress conditions, while steels show a particle size effect that limits the embedment in the low-stress conditions.<br/><br/>The wear resistance of steels in low-stress wear conditions does not essentially increase in the course of the process due to the lack of plastic deformation and, consequently, due to the lack of work hardening. On the other hand, in high-stress wear conditions work hardening can almost double the hardness of the wear surfaces, thus in general also increasing the material’s wear resistance. Yet, it is also shown that the hardness, neither the initial nor the hardened one, of the steel is not the only factor determining the material’s wear performance. Elastomers perform quite differently, i.e., they tolerate quite well the low-stress conditions but suffer from increasing wear when the stresses become higher. With the pot tester, the transition from the low-stress to the high-stress condition was observed to occur around the particle size of 1-2 mm.<br/><br/>To be able to simulate mining wear with a laboratory wear tester, proper material response during the test is crucial. To achieve that, the correct stress state in the wear process is required. For steels, the deformation, tribolayer formation and work hardening are important phenomena, which strongly influence the wear performance in high-stress wear conditions. In low-stress conditions, these phenomena are mostly absent or have a minimal effect at best. For the above reasons, good (if any) correlation between low-stress laboratory wear tests and high-stress industrial applications is not usually observed. On the other hand, with a wear tester that can sufficiently reproduce the wear environment of a mining application, good correlation between laboratory and field test s is possible to achieve.

Topics

• impedance spectroscopy
• microstructure
• surface
• wear resistance
• wear test
• steel
• hardness
• chemical composition
• elastomer