Tribology in coal-fired power plants

Material wear and degradation is of great importance to the economy of South Africa especially within the mining, agriculture, manufacturing and power generation fields. It has been found that unexpected and high rates of fly-ash erosion occur at certain sections of power plants, this is particularly evident at the Majuba power station. The loss of small amounts of material due to erosion can be enough to cause serious damage and significantly reduce the working lifetime of, for, e.g. hopper liners.This study investigated the long-term solid particle erosion of a range of oxide and nitride-fired SiC-based ceramics and alumina with the aim of reducing erosive wear damage in power plants. This entailed carrying out experimental tests on an in-house built erosion testing machine that simulate the problems encountered in the industry. The target materials were eroded with 125–180 μm silica sand at shallow and high impact angles. The surface wear characteristics were studied using both light and scanning electron microscopy (SEM).The results obtained indicate that the erosion rates of the materials remain fairly constant from the onset. It was found that prolonged exposure to erosion results in the progressive removal of the matrix and subsequent loss of unsupported SiC particulates. The fact that the particles were relatively small did not have a significant effect on the erosion rate. This would explain the observed constant rates of erosion for longer periods. These behaviours can be further explained in terms of the composition and mechanical properties of the erodents and target ceramics.     

Tribology in microforming

As the tribological conditions between tool and workpiece in metal working are of greatest importance for process feasibility and process quality this is even more true when the process is scaled from conventional down to micro dimensions. As can be shown by scaled friction tests the friction is increased by a factor of 20 and more which will have a distinct impact on all factors characterising the process. This cannot be described by the conventionally used friction laws but can be explained by the model of open and closed lubricant pockets characterising the surface topography. In the present paper, it will be shown that - starting from this model - the size effect in friction can be described by the general friction law developed by Wanheim/Bay.