There are some applications where extremely fine particles are required or the solid content is especially difficult to break down and disperse. These requirements need something besides a dissolver disc and that’s where a bead or basket mill is used. High-speed bead mills are very useful in dispersing otherwise difficult materials. All the steps of a standard disperser still apply (wetting, mechanical breakdown, stabilization) but a bead mill consists of a milling chamber and an agitator. The milling chamber contains beads made of glass, steel or zircon oxide and the millbase and the milling vessel has the grinding medium which is kept moving by a motor-driven agitator. The actual dispersion occurs between the grinding beads, rotor, and sides of the container.
A basket mill uses a rotating perforated basket with a disc that contains pegs to permit grinding. The disc remains fixed in place while the basket moves and uses centrifugal force to accelerate grinding. The sieved basket is also filled with grinding beads so the shearing forces that provide dispersion are created between the beads, rotating basket and the fixed disc.