Vertical shaft impactors
The Vertical shaft impactors is also know as Vertical shaft impact crusher or VSI Crusher, it represent a recent development to exploit the advantage of cubical product shape whilst overcoming the problem of wear when crushing abrasive rocks. Particularly popular applications are crushing of oversize flint gravel in situations where an increased yield of sand is desired, 'shaping' of crushed gritstone in the final stage of comminution to produce roadstone surface chippings and the 'manufacture' of sand from hard rock.
The machine comprises a horizontal table or rotor that revolves rapidly about the vertical axis of the drive shaft. Crushed rock fed into the centre of the rotor is ejected at high speed by 'centripetal forces' and breaks by impact upon the hardened alloy anvils surrounding the rotor and by inter-particulate collision. The rotor is lined with extremely hard materials such as carbides where appropriate. Wear of the casing may be reduced by the addition of a low ledge or shelf forming a 'rock-box' within which broken rock accumulates thereby obscuring and protecting the internal surface of the casing. Rock particles thus impact upon similar material and not upon the liner plates. These two designs are referred to as 'stone on metal' and 'stone on stone' respectively. The former can produce a greater reduction ratio.