Dust in Grinding Paste Form in Plant Equipment.
Three-body abrasion is used to create a mirror finish to copper brooches in jewellery using rouge smeared onto a leather strop. The particles in the rouge are a few micrometers in size, very fine and angular and it takes only a few passes to create a mirror finish. This is a highly controlled form of three-body abrasion with a hard, angular particle being used as the abrasive and the two surfaces of the leather strop as the two opposing surfaces.
Dry dust may appear to be a passive material but in reality it is never truly ‘dry’ at the point of contact with plant walls. The presence of a thin film of moisture, condensation or oil in suspension in the dry particulate material is sufficient to ‘wet’ the particles and for them to adhere to the plant wall surface. The geometry of enclosed plant equipment, for example the curved surfaces of pipe work (e.g. bends) and the angled faces of hoppers and chutes, can concentrate the ‘paste’ thus formed on the plant wall surfaces that are subjected to the greatest mechanical stress. This is discussed in HSE guidance on how abrasive dust concentrations build inside an enclosed plant. There is more on Ceramic Wear Liners at kingfisher-industrial.com/wear-protection/ceramics.
The Mohs hardness of a material is a useful measure here. The mild steel used in the majority of chutes and hoppers has a hardness of around 4 to 4.5 on the Mohs scale. The cement dust, fly ash and silica dust all have a hardness of around 6 to 7 on the Mohs scale. Thus the paste is harder than the surface it is trying to wear.
Ceramic wear liners on the other hand are designed to deal with dust in a different manner. High-alumina ceramics have a Mohs hardness of 9 or thereabouts, so virtually all dust is less hard than the wear liner. However, the dense, low-porosity surface of a ceramic has a very low coefficient of surface wetting, so the paste of dust and water cannot adhere to it. Thus three-body abrasion is denied the interface between the surface and the wear particle, and most of the abrasive action is removed.
