A study of wear and load behaviour on bucket teeth for heavy-duty cable shovels

Sammanfattning: Many of today’s engineering advancements rely on minerals such as copper, gold and iron. For this reason, the mining industry plays an important role for the development of society and technological wonders. Mining excavators are commonly used tools for extracting the minerals from the mine. Mining excavators are large machines used to breakdown, penetrate and load the rock ores onto trucks that transport the minerals. During the dynamic loading, the excavator bucket experiences significant amount of wear and tear that negatively affects the production by increasing the downtime. The bucket teeth are arguably the most worn parts of the bucket and are responsible for significant amounts of downtime. This thesis aims to provide a better understanding of the load and wear on the bucket teeth of large scale mining excavators used in Bolidens Aitik copper mine in Sweden. Because of how much wear and tear the bucket teeth are exposed to, there is a need to better understand the wear behaviour of the teeth and for the whole bucket in general. This understanding can then be used to improve the service life of the teeth and other parts of the bucket and thus increase work efficiency and reduce downtime. This project was divided into two parts. The first part consisted of regular field measurements to follow the wear on the bucket for about two weeks of digging and loading. The gathered data was then analysed to provide a better understand about the wear behaviour. The second part was to develop a numerical model that could predict the wear on the bucket and could be verified by the field measurements. The field measurements consisted of seven 3D laser scans of the bucket starting with brand new teeth. At the time of the last scan, the buckets total loaded tonnage was approximately 542 kton and the excavator had operated in total of approximately 195 hours. After the raw data from the scans was gathered and analysed, various information about the wear behaviour on the teeth was achieved. The 3D scanned data was also used to provide a complete wear development cycle which allowed to track the wear of any point in the bucket. The method could also be used to create animations of the teeth as they were being worn. From the results, it was concluded that the wear rate for the teeth slowed down and even converged as the geometry changed due to wear. When comparing all nine teeth on the bucket, it was also found that the middle teeth on the bucket were most exposed to wear. The most worn tooth was found to lose around 50 kg of weight after approximately 117 operating hours, which accounts for 40 % of the original weight. The animations from the complete wear development results also showed how the individual teeth and the whole leading edge with all nine teeth were being worn as the buckets loaded tonnage increased from 0 to 542 kton. The numerical model consisted of simulations of loading with the rocks being modelled with the Discrete Element Method (DEM). These were divided into four cases, the first being with the bucket with all new teeth. The second bucket with a mixture of new and worn teeth. The third bucket with all worn teeth and then finally the fourth bucket in which a new tooth geometry was tested. The numerical model showed promising results and potential for being a reliable way to predict the wear on the bucket. The results showed that both the penetration force and wear for the middle teeth was higher than the other neighbouring teeth. It also showed that the completely worn teeth had a lower wear rate than the new teeth which is in agreement with the results from field measurements. Other factors such as tooth shape and length were also observed to have a significant impact on the wear and penetration force. Lastly, the new teeth geometry also showed potential for design improvements in terms of wear resistance but can be further optimised. From the new teeth geometry, a suggestion was given for using an existing tooth system that might be more wear resistant.