Mill and method of milling

A milling apparatus for milling material, the apparatus comprising:

• at least two axially extended members eccentrically mounted one within the other so as to define a chamber therebetween;
• the interior surface of the outer member being centred on the axis of that outer member;
• the exterior surface of the inner member being centred on the axis of that inner member;
• both inner and outer members being rotatable about their respective axes;
• an inlet for introducing material to be milled into the mixing chamber, and an outlet for removing milled material from the mixing chamber;
• whereby, for any given axial position, the variation in radial distance between the two members defines a gap that alternately decreases and increases with respect to circumferential movement, for the purpose of applying movement and stress to material entering the gap, such that material passing through the chamber is caused to describe a substantially spiral path with respect to the axial orientation of the inner and outer members;
• and further such that material within the chamber is subjected primarily to mechanically-induced compressive stresses and fluid-induced extensional stresses when both inner and outer members rotate in the same direction, and primarily to fluid-induced shear stresses when both inner and outer members rotate in opposite directions;
• characterized in that a third member extends axially into the chamber for the purpose of extracting the heat arising from the application of stress to the material immediately on exiting from the highly stressed zone.