A wet milling process refers to mechanical shear and grinding that reduces the primary solid particles of a slurry to smaller sizes. A slurry is simply a mixture of solids, or aggregates, within a liquid medium. Some mechanical shearing device is used to grind up particles or agglomerates between solid mechanical components moving or rotating at high speed. Bead mills use spherical balls or beads that tumble inside a rotating housing as a slurry passes through. Colloid mills are typically used as well and tend to be more efficient than bead mills.
Wet milling process equipment is very mechanical in nature and tends to operate at low flow rates and has more wear than say propeller agitation, but propeller mixers provide lengthy mix times to achieve decent particle sizes.