Analysis and Improvement of Agitator for Drum Filter

Sammanfattning

This project was executed to address the issue LKAB in Svappavaara is facing with failing agitators for the drum filters. The goal was to determine if the stress in the agitator during normal use was high enough to induce fatigue and to propose solutions to mitigate this problem. The project was limited to modifying only the agitator itself, without altering any other parts of the drum filter system. The loads on the agitator were calculated using approximated formulas for similar structures. The stress analysis was performed using the finite element method (FEM). The stress was measured in the critical area where failures have occurred. The conceptual solutions were developed using Ulrich & Eppinger's product development methods. The maximum load magnitude on the agitator was determined to be 4814 N. The resulting stress in that area during the maximum amplitude load was found to be 30 MPa, which is where the largest stress concentrations occur. This stress level is too low to cause fatigue. Even if the engine were to apply its maximum torque, resulting in stresses of 140 MPa, it would still be insufficient to cause fatigue. Three different solutions were proposed. One reinforcement method that can reduce the stresses by 15%. Additionally, two material alternatives with greater fatigue resistance were suggested. One alternative is to switch to Hardox steel, which has proven effective in LKAB's refinement plant in Malmberget. The other is to normalize the steel currently in use. In conclusion, the stress analysis indicates that the current stress levels are insufficient to cause fatigue under normal operating conditions. However, the proposed reinforcement and material changes can further enhance the agitator's durability and operational reliability.