Tribological aspects for the shafts and bearings of sugar cane mills

The high rate of wear on top roll shaft journals is an important problem for the Colombian sugar cane mills and it has shown a marked influence in the shaft reliability. The presence of mineral extraneous matter (MEM) added to a low hardness ratio between the shaft and bronze bearing (it was found to range between 1.27 and 4.29) causes rapid abrasive wear rate, which reduces the shaft service life and results in a need to apply submerged arc welding (SAW) to rebuild the shaft journal. Welding of shaft steel requires very careful procedures in order to maintain shaft reliability. This research is based on the identification of wear mechanisms present on the shaft and bearing tribological pair, as well as the analysis of mechanical and tribological properties of the pair elements. Optical microscopy and scanning electron microscopy (SEM) were used to characterize surface phenomena in the tribological pair and a block on ring tribometer was used to test different combinations of bearing materials and lubricants. Two bronze bearing materials, SAE 64 and SAE 67, was probed in the block on ring tribometer using two lubricants, asphaltic oil and high pressure grease. The friction coefficient for SAE 67 was lower than that of SAE 64 with both lubricants used (0.052 for asphaltic oil and 0.076 for high pressure grease) but the block lost higher material weight for SAE 67 than for SAE 64.