Specifications

Document No. DER01122 DESCRIPTION AND OPERATION
Page 4 of 6 Effective Date 30 Aug 07
Conveyor
The conveyor assembly is a hollow, cylindrical auger that receives the inlet slurry into its interior,
disperses it through feed nozzles to the bowl assembly, and transports the solids to the solids
discharge outlet. Rotated by an electric motor through a three-stage planetary gearbox, the
conveyor turns in the same direction as the bowl but at a higher rate of speed. The outer housing
of the gearbox is secured to the bowl, while the shaft is directly connected to the conveyor.
The differential speed setting on the control panel determines the conveyor speed in relation to
the bowl speed. This relationship remains consistent; as bowl speed is varied, the conveyor
speed varies commensurately but maintains the differential relationship. For example, a bowl
speed of 2000 RPM and a conveyor differential speed of 10 results in the conveyor rotating at a
rate of 2010 RPM.
The feed component at the liquid discharge end directs inlet slurry into the interior of the
conveyor, which rapidly disperses the material through feed nozzles into the bowl. Replaceable
inserts line each of the eight feed nozzles to minimize wear due to abrasive action. A roller
bearing supports the conveyor at the liquid bowl head, while at the solid end the conveyor is
supported by the conveyor drive gearbox.
Conveyor Drive Gearbox
The conveyor drive gearbox is a three-stage planetary gearbox that rotates the conveyor at a
faster speed than the bowl assembly. The gearbox is mounted on, and consequently driven by,
the bowl assembly, Input and output shafts of the gearbox are supported by internal bearings.
The conveyor drive motor is coupled to the gearbox input shaft by a flexible coupling, which
permits compliance with slight alignment variations. The gearbox contains a gear system that
transfers rotation from the motor and bowl to the conveyor’s output shaft.
The input shaft end of the gearbox is supported by the solid end main bearing, while the output
end is secured to the bowl. The gearbox ratio of 49:1 turns the conveyor at a proportionally faster
rate than the bowl assembly. The control system ensures that the conveyor’s rotational speed
varies directly with bowl speed, maintaining a consistent differential relationship for solids
conveyance.
During an overload condition, excessive solids in the conveyor may overburden the motor,
causing motor torque to increase and resulting in an overload alarm. If the conveyor’s pre-set
torque limit is reached, the control system automatically reduces the feed rate to enable the
conveyor to clear the excess solids. When the centrifuge is operating at the reduced feed rate, the
Operation screen displays a message to inform the operator of the modified status. Unless the
over-torque condition is removed, the centrifuge will be shut down automatically.
CONTROL SYSTEM
Centrifuge operation is supervised by a programmable logic controller (PLC) that interfaces with
the variable frequency drives (VFDs) supplying power to the bowl, conveyor, and feed pump drive
motors. Monitoring and control of the centrifuge may be performed locally or remotely. The
environmentally hardened PLC also offers short-term data storage and a high degree of operating
flexibility. The graphical interface mounted on the control cabinet facilitates communication with
the VFDs and provides real-time access to system operating characteristics. Through the control
panel, the operator may start up the centrifuge, enter and adjust bowl and conveyor speeds, set
feed rate, and shut down the machine.