This decision is made by knowing the type of material you will be working with.
Open Coat – Here, the abrasive granules cover from 50% – 70% of the backing and are set at pre-determined spacing to reduce loading. Used on softer surface materials that tends to load or fill the abrasive surface.
Closed Coat – Here, the abrasive granules cover virtually the entire backing surface. Used where loading of abrasives is less of a problem.
How is fused alumina obtained?
Raw materials containing aluminium oxide are electrothermally melted at a reaction temperature of more than 2,000 °C to produce the various fused aluminas. Different starting materials are used depending on the desired type of fused alumina. For instance,