Glass beads are the main points of contact where energy from the mill is transferred to the pigment particles, causing reduction in their size. Since the Glass beads are the actual perpetrators of attrition on the pigment particles, by increasing the number of beads or points of contact in the mill one will increase the opportunity for collision and shearing between the bead and the pigment particle.
The ability to operate a mill with smaller-diameter grinding media greatly increases the mill's efficiency and can overall further increase the quality of product through finer grinding. However, smaller Glass beads are more prone to hydraulic packing due to their decrease in mass per bead. Hydraulic packing occurs when the drag flow from the product pulls the media with the product and ultimately causes media packing around the discharge screen.
Glass beads have replaced the conventional grinding media : Ottawa sand, Steel balls, Pebbles, Ceramic balls etc. in Sand mills, Ball mills, Attrition mills for the following simple reasons :