Lubrication mechanism investigation of alkali polyphosphate glass in hot rolling

Increasing competition in steel industry facilitates high demands for high efficient, low cost and environmentally friendly lubricant in hot rolling so that better strip quality at the minimum cost can be manufactured. In this thesis, a type of inorganic alkali polyphosphate glass has been recommended as a lubricant in hot metal forming, with a particular attention being paid to hot rolling. Before hot rolling tests, laboratory-scale ball-on-disc tribometer was used to evaluate the tribological performance of alkali polyphosphate glass. Firstly, the physical and chemical properties of the sodium polyphosphates aqueous solution were studied by SEM&EDX, TG&DSC, XRD as well as a high temperature laser microscope with a CCD camera. The result shows that some intermediate reactions such as hydrolysis and depolymerization in the aqueous solution have produced short-chained phosphates. However, once the polyphosphate solution is heated to 600oC, the dehydration and polymerization reaction causes these short-chained dihydrogen ortho- or pyro-phosphate to re-polymerize into desired long-chain polyphosphates. Therefore, the dissolution of alkali polyphosphate in the aqueous solution exerts little impact on the structure and properties of alkali polyphosphate glass at high temperatures...