Investigation of wear behavior of different sliding bearing materials in an alkaline environment

Sammanfattning: In sliding bearing wear is a very common problem and can be affected by several factors. The wear in a bearing can lead to total failure of the component and lower the lifetime. In a sliding bearing used in a machine in the pulp and paper industry large wear has been detected, but no clear evidence of what the wear depends on. The environment in the machine is strong alkaline (pH 14), a solution of white liquor and lime mud. The penetration of this solution into the bearing might lead to increased wear. A wear study and test were done to see if a better material choice could reduce the wear. In this project an investigation of the wear for seven different bearing materials was done. Two cobalt-based alloy Stellite 6 and Stellite 12, two different precipitation hardened martensitic stainless steel with different number of alloying elements, 17-4PH and Endotec 04. The different metals were welded on the pin with a minimum of 3mm. The other material was three different PEEK polymer composites. PEEK HPV reinforced with carbon fiber, PTFE and graphite. PEEK CA30 with carbon fibers and PEEK GF30 with glass fiber. The method used for the wear test was grinding machine that was reconstructed to a pin-on-disc tribology test. The tests were executed in room temperature with sliding speed of 150rpm and duration of 20 minutes. The metals were tested with the solution of white liquor mixed with lime mud, at two different loading conditions of 300N and 550N. The polymer composites were tested at the load of 300N but with different solution present, white liquor mixed with lime mud and with water. All the pins were sliding against a disc of austenitic stainless steel. Equipment used to investigate the wear mechanisms was a scanning electron microscope. The wear rate was measured by weighing of the pin before and after each test. How the material was affecting the roughness of the austenitic steel countersurface was done with the profilometer. The results of this work showed that both Stellite 6 and Stellite 12 was almost wear resistance in the condition similar to the bearing. Endotec 04 also showed low wear and 17-4PH had the highest of the metals. The dominant wear mechanism seemed to be different severity of adhesive wear. The polymer composite showed all higher wear than the metals, the reason to the high wear rate was harder to decide. It might be a combination between adhesive wear, pulverization of fibers, adsorption of calcium carbonate and matrix/fiber interfacial removal. The alkaline liquid was also believed to increase the wear of the polymer and adhere to some of the metals. The metals seemed to increase the roughness of the countersurface, but the polymers seemed to have more of a polishing effect.