Designing granules for abrasive cleaning (using high-shear granulation)
This work investigates the granulation of fine calcium carbonate powder to form microgranules (less than lOOf.lll1). The influence offormulation and operating conditions on granule properties was investigated. This work analyses experimental data using a database approach to relate granulation conditions to granule properties, to fmd propertyto-property relationships and to investigate the influence on the abrasion of Perspex. It was found that the granulation was undertaken in an unstable regime dictated by the need to produce small granules. As a result, it was not possible to achieve reproducibility in making the granules. For the range of granules produced it was difficult to determine variation in abrasiveness within the experimental errors, a detailed error analysis was carried out. A theoretical relationship between strength and porosity is developed and the factors influencing abrasive wear are investigated. Two theoretical models are presented: 1) Impact Failure model and 2) Granule Consolidation model. The impact failure model relates dynamic impact strength to static strength, which enables the prediction of a failure distribution curve (how many particles will fail per hundred impacts as a function of velocity). This is done using a "critical normal impact velocity" determined from the properties of the granule, properties of the impact surface and experimentally measured granule static strength. The granule consolidation model allows the qualitative prediction of the rate and extent of consolidation from granulation conditions. It models the compaction of a granule by descnbing the packing of its primary particles within an imaginary internal granule. Sphere packing is discussed with implications for determining the maximum packing of a primary particle size distribution.