Operating principle

High pressure grinding is achieved by an advanced type of grinding roll. Contrary to conventional crushing rolls, the particles are broken by compression in a packed particle bed, and not by direct nipping of the particles between the two rolls.

This particle bed is created between two choke-fed,counter-rotating rolls. Between these rolls, a particlebed is pressed to a density of up to roughly 85%of the actual material density. This compression is achieved by applying high pressure of up to nearly 300Mpa, exceeding the compression strength of thefeed material. During this compacting process thematerial is ground to a wide particle size distributionwith a large proportion of fines, compacted intoflakes.

The breakage process can be visualized as consistingof two distinct stages. In the first stage, the choke fed material entering the space between the rolls issubjected to an acceleration to meet the peripheralroll speed. As a consequence of the narrowinggap between the rolls, the material is graduallycompacted and the larger pieces and particlesare pre-crushed. Furthermore, a certain degree of particle rearranging occurs, filling the inter particle voids.