Development and testing of HVOF-sprayed tungsten carbide coatings applied to moulds for concrete roof tiles

Corrugated steel moulds, so-called ‘gliders’ used to shape, densify and burnish concrete roof tiles are subject to severe abrasive sliding wear caused by the action of hard quartz grains in the moving concrete mass. Hard surface coatings based on tungsten carbide (WC) applied to the gliders are thought to reduce substantially the friction between concrete slab and forming tool and hence the loss of tool material, and also to improve their burnishing (smoothing) capability. Various HVOF-sprayed WC-based coatings on hardened X210Cr12 tool steel substrates were evaluated with respect to their performance in abrasive wear tests. Three tests were performed that stressed the coating surfaces in different ways: a 2-body Taber® Abraser abrasive-rolling integral wear test, a 2-body dry sand/rubber wheel abrasion test according to ASTM G65-91, and a 3-body ring-on-block sliding wear test. Volumetric losses and changes in the surface roughness parallel and perpendicular to the direction of the movement of the concrete slab showed that coatings with a low surface roughness level but high roughness anisotropy, i.e. preferential ‘grooving’ parallel to the loading direction, performed best in ASTM G65-91 wear tests as well as in service tests under real operating conditions.