The top weight on the motor shaft rotates in plane close to the center of the mass of assembly. Rotation of the top eccentric weight creates vibration in the horizontal plane which causes material to move across the screen cloth to the periphery. Increasing the top eccentric mass increases the horizontal throw causing over size material to be discharged at a faster rate.
The bottom eccentric weight rotates below the center of the vibrating mass creating tilt on the screen causing vibration in vertical & tangential planes. Increasing the vertical component of this motion promotes turnover of material on the screen surface helping maximum quantity of undersize material to pass through the screen. The effective vertical motion helps in minimizing blinding of screen by near size particles.
The tangential component of this motion is controlled by the angle of lead given to bottom weights in relation to the top weight.
Variation in lead angle controls the spiral pattern of material travel over the screen cloth. Typical material travel patterns generated at various lead angles are shown below :
The material is fed on to the centre of top screen. The undersize material passes rapidly through the screen during its travel to the periphery. The oversize material gets continuously discharged through a tangential outlet. Vibroscreens are equipped to handle upto five different screens one on the top of the other with feed trays in between to give six precise sized fractions in single screening operation.