The crusher crushes via radial vanes on a rotor (6). These engage with lumps (12) of coal which are fed in between the rotor and a reinforced edge (5) of the crusher's spiral housing (1). The crushed coal and coal dust travel, due to the centrifugal force, along the inner wall of the housing. The wall carries an inward facing obstruction (8) which is located half way between the twelve o'clock and six o'clock positions. The sloping face of the obstruction guides any lumps, which are still too large, back into the crusher.
