Figure 6-4.-Secondary unit.Secondary UnitThe secondary unit (fig. 6-4) consists of areciprocating feed hopper, an overcrusher conveyer, atwo-deck vibrating screen, a dual roll crusher (fig. 6-5)or hydrocone crusher (fig. 6-6), an undercrusher returnconveyer, a revolving elevator wheel, a diesel powerunit, and the running gear. The dual roll or hydroconecrusher can be driven by a diesel engine or an electricmotor. All other components are driven by individualelectric motors and power is normally supplied by a200-kW generator.Material to be processed is introduced into thehopper of the reciprocating feeder. The rate of flow iscontrolled by the adjustable gate opening. Material isdeposited onto the overcrusher conveyer and carried tothe feed end of the top screen. Material that has beencrushed down to product size by the jaw crusher passesthe top screen. Oversized material is retained on the topscreen and directed through a dual roll crusher orhydroccme crusher for further reduction.The dual roll crusher consists of a set of rolls thatrevolve toward each other at a constant rim speed. Stoneparticles are reduced in size as they are drawn betweenthe two rolls. Product setting is determined by theFigure 6-5.-Dual roll crusher.6-4
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