The bowl classifier incorporates a two-stage baffled-return separating action, and it consists of a straight classifier with the usual reciprocating rakes, upon which is superimposed at the lower end a shallow circular bowl with a revolving rake mechanism. The general construction of the Dorr Bowl Classifier is shown in Fig. 20.
The feed enters at the centre of the bowl, and, falling on to a baffle-plate placed at the level of the surface of the pulp, is directed radially outwards. In passing from the centre to the periphery the coarser particles settle and only the fines overflow into the annular launder provided for the purpose. The oversize, as it settles, is ploughed to the centre by the revolving rakes and discharged through a rectangular opening into the second stage or reciprocating rake compartment, where it is dragged up along the sloping bottom of the tank exactly as in a straight classifier.
The movement of the rakes in the restricted space beneath the bowl is regulated to give enough agitation to throw the finer solids into suspension. The diluting water is added in the reciprocating rake compartment ; it flows back towards the bowl ….Read more