Evaluation of compressive strength and shear strength of the adhering layer of granules in iron ore sintering

A thorough understanding of the mechanical properties of the adhering layer of iron ore granules is necessary to optimize green bed permeability and improve sinter plant productivity. With this in mind, tablets simulating the granule adhering layer were manufactured using proportions of components in each size range based on Litster's granulation model. Uniaxial compression tests and direct shear tests were performed to characterize the compression and shear strength of the simulated tablets respectively. A variety of granulation conditions including moisture levels, hydrated lime addition levels as well as magnetite concentrate substitution levels were tested. The results of compression tests show that the granule adhering layer becomes more compliant and weaker with the increase of concentrate substitution level due to the increased spread in the size distribution of the embedded particles. In direct shear tests, hydrated lime addition could improve the cohesion constant from ~1kPa to ~3kPa for the base blend, but the extent of this improvement decreased when more concentrate was added to the blend. When micro-particles such as hydrated lime and concentrate particles are introduced into the blend, the mechanical response of the granule adhering layer becomes much more complex. The hydrated lime could act as solid binder and increase the strength of granule adhering layer while the concentrate plays an opposite role and deteriorates the adhering layer strength. The internal friction angle of the adhering layer in direct shear tests ranges from 30° to 38° and could somehow represents the resistance to deformation during packing. Combining the friction angle data with the previous granulation and packing results, a more mechanistic model of green bed voidage [formula could not be replicated] was proposed, in which the term representing the extent of deformation in the adhering layer was given a more reasonable physical explanation.