Relevance of Laboratory Wear Experiments for the Evaluation of In-Service Performance of Materials

In high-stress abrasion, rocks or minerals are being crushed between two moving bodies. In the mining industry, this kind of wear occurs for example in the haulage and grinding of minerals. Wear of materials causes also significant economic and ecological losses in the mining business, because the replacement of wear parts causes interruptions in the mining operations, and production of new wear parts creates a big carbon footprint for the mines. Therefore, the selection and development of better materials for the demanding wear environments is worth the effort.

Although the results of field wear tests are readily applicable for example for materials selection, such tests are challenging to conduct, overly expensive, and very time consuming. Thus, it is important to create substitutive application oriented wear test methods and research methodologies that produce relevant and repeatable results and are well controllable, unlike the in-service conditions. However, the relevance of the test method should also be somehow traceable and verifiable.

This thesis elucidates the relevance of laboratory wear experiments for the evaluation of the in-service performance of materials. Two cutting edges of underground mining loader buckets and two feed hopper wear plates were tested in the in-service conditions, and their wear rates were recorded using 3D scanning. Moreover, a used wear plate of a dumper truck body and a grooved roller from a hoist system were received for characterization. A novel method for testing impact wear of steels in Arctic conditions was also used and analyzed. The wear conditions in these in-service cases were simulated using various laboratory wear testing systems, the wear surfaces and cross-sections of the test specimens were carefully characterized, and the results of the wear tests and characterizations were correlated with the in-service cases.

There are two common ways to utilize laboratory wear tests, i.e., testing of different materials using the same test method or device, or testing the same material(s) using different test methods. In both cases, however, the fundamental question is, how do the test results compare with the real application under consideration? Another question that affects the outcome of the testing program is, how should the test results be presented to obtain the correct or best possible answer to the set research question? In this work, normalization of the test results using the mass loss of a reference sample proved to be a good methodology, when comparing the wear rates of different steels. Even the small differences between the different test cycles were corrected in this way. However, when different test methods are compared to each other or to the in-service data, the normalization should also take account of the differences in the contact time and the contact area in different cases. In addition to the numerical correlation, it is essential to characterize and compare the wear mechanisms and deformation of materials during wear. Only by combing these two different types of results, the relevance of the used test method can be assessed and confirmed.