Dimensioning of a cutter wheel bearings

Sammanfattning: Mobile Miner 40V is a machine used for rock excavation and developed by Epiroc. This machine is equipped with a large cutter wheel to perform the excavation. After a test run, some surfaces associated with bearings within the cutter wheel were found to be damaged due to scuffing - severe sliding wear. There is a static load applied to the surfaces due to gravity. However, the reason for this damaged issue was believed that there is a large dynamic load applied to the surfaces during the excavation. This dynamic load was not found in a previous FE model used to verify safety issues. Therefore, a new FE model that is more in line with reality, and a failure analysis were required. Additionally, a feasibility study for a cutter wheel with a larger dimension was also needed since a larger cutter wheel is desirable. Firstly, wear mechanisms were reviewed, and some theories were chosen to analyze the damaged issue. Since it was unknown whether the surfaces were well-lubricated or not, both cases were investigated. The Archard wear equation was used to analyze the poor-lubricated situation, while the lubrication number and the Reynolds equation were used to analyze the well-lubricated case. Secondly, contact mechanisms between the surfaces were also investigated. The investigation of the contact mechanisms involved several theories, such as the Hertzian contact theory and the impact load factor. Besides these theoretical analyses, a numerical analysis was performed. Lastly, a new FE model was established in Ansys. Both the cutter wheel which was subjected to scuffing(existing cutter wheel), and the cutter wheel with a larger dimension(larger cutter wheel) were analyzed by the use of the new FE model. The maximum and minimum wear rates obtained by the Archard wear equation are approximately 1.9・10-2mm3/m and 4.8・10-3mm3/m, which are considered as a completely unacceptable level in engineering applications. The maximum and minimum critical loads obtained by the Reynold equation are approximately 1.8kN and 24.8kN, which both are larger than the static load applied to the surfaces. The maximum and minimum critical mean contact pressures obtained by the lubrication number are approximately 65MPa and 240MPa, which both are larger than the mean contact pressure generated by the static load. No evidence shows that there is a large dynamic load applied to the surfaces during the excavation. The largest possible contact pressure on the bearings in the existing cutter wheel is very close to the limit of severely damaged. The largest possible contact pressure on the bearings in the larger cutter wheel is believed to exceed the limit of severely damaged. The previous assumption that the surfaces were damaged due to a large dynamic load was wrong. The obtained results support that the surfaces were only subjected to a static load and were damaged due to inadequate lubrication. The existing cutter wheel is operated safely with the current load cases. However, the forward thrust force is suggested to decrease when the cutting angle is large. There is a high risk if the larger cutter wheel is operated with the current load cases.