Specifications

Document No. DER01120 DESCRIPTION AND OPERATION
Page 4 of 9 Effective Date 25 May 07
Conveyor
The conveyor assembly is a hollow, cylindrical auger that receives the inlet slurry into its interior,
disperses it through nozzles to the bowl assembly, and transports the solids to the solids
discharge outlet. Rotated by a differential gearbox, the conveyor turns in the same direction but at
a slower rate than the bowl. A drive shaft extending through the bowl head transfers motion from
the gearbox to the conveyor. The feed tube inserted through the conveyor at the solids end
directs inlet slurry against a feed accelerator, which rapidly disperses the material through feed
nozzles in the conveyor. Carbide inserts are installed in the feed nozzles, and carbide tiles are
welded to the edges of the conveyor flights for wear resistance. Ball bearings installed in pillow
blocks having grease fittings support both ends of the conveyor.
Gearbox Drive
The gearbox drive is a differential reduction gearbox that rotates the conveyor at a slower speed
than the bowl assembly. The gearbox, which is available in 52:1 or 125:1 ratios, consists of first-
and second-stage planetary gear systems and a ring gear. The ring gear, which also forms the
gearbox housing, is rotated through its attachment to the liquid bowl gear flange. The planetary
gear system transfers rotation from the ring gear to the second-stage pinion gear, which turns the
conveyor’s splined output shaft.
The gearbox is cantilevered on the bowl assembly; one end is supported by the liquid end
conveyor bearing and the other end is unsupported. The gearbox output shaft, driven by the
second-stage planetary gears, engages internal splines in the conveyor to transmit rotary motion.
As with any differential gear system, rotation of one gear results when another gear is restrained
form turning. For example, if the first-stage pinion is prevented from rotating, the ring gear will
rotate. Conversely, restraining the ring gear results in pinion gear rotation. This characteristic
protects the conveyor from damage due to an excessive feed rate or heavy material feed.
Due to its reduction gearing, the gearbox turns the conveyor at a proportionally lower rate than
the bowl assembly. The conveyor’s rotational speed varies directly with bowl speed, maintaining a
consistent differential relationship for solids conveyance.
During an overload condition, the excessive solids in the conveyor may restrict its rotation,
resulting in a corresponding speed reduction of the ring gear. If the conveyor’s overload release
torque limit is reached (52:1 gearbox - 335 in lbs; 125:1 gearbox - 200 in lbs), the first-stage
pinion begins to rotate. Unless the over-torque condition is removed, the centrifuge will be shut
down automatically.
Overload Release Assembly
If excessive torque is required to rotate the conveyor (335 in lbs - 52:1 gearbox; 200 in lbs - 125:1
gearbox), the overload release assembly (Figure 1120-3) shuts down electric power to the 50 HP
drive motor to protect the conveyor from damage. The torque arm, which is suspended between
stops, is attached to the clutch to prevent it from rotating with the gearbox ring gear. A roll pin
keys the torque cam to the gearbox first-stage sun gear, which can rotate with the conveyor
during excessive torque.
Excessive conveyor torque causes the first-stage sun gear to rotate, moving the cam sufficiently
to move the roller arm, which opens the normally closed over-torque limit switch. The switch
interrupts power to the 50 HP drive motor and feed pump motor, shutting down the centrifuge.
After release, the clutch must be manually reset (refer to Section 5 - Maintenance) before the
centrifuge can be returned to operation.