Figure 6-4.-Secondary unit.
Secondary Unit
The secondary unit (fig. 6-4) consists of a
reciprocating feed hopper, an overcrusher conveyer, a
two-deck vibrating screen, a dual roll crusher (fig. 6-5)
or hydrocone crusher (fig. 6-6), an undercrusher return
conveyer, a revolving elevator wheel, a diesel power
unit, and the running gear. The dual roll or hydrocone
crusher can be driven by a diesel engine or an electric
motor. All other components are driven by individual
electric motors and power is normally supplied by a
200-kW generator.
Material to be processed is introduced into the
hopper of the reciprocating feeder. The rate of flow is
controlled by the adjustable gate opening. Material is
deposited onto the overcrusher conveyer and carried to
the feed end of the top screen. Material that has been
crushed down to product size by the jaw crusher passes
the top screen. Oversized material is retained on the top
screen and directed through a dual roll crusher or
hydroccme crusher for further reduction.
The dual roll crusher consists of a set of rolls that
revolve toward each other at a constant rim speed. Stone
particles are reduced in size as they are drawn between
the two rolls. Product setting is determined by the
Figure 6-5.-Dual roll crusher.
6-4
