2.6

Introduction

Free oscillating systems are either activated in using exciters,

unbalanced motors or unbalanced shafts.

The oscillation amplitude, type of vibration and the direction

of vibration of the screen are determined by the dimension-

ing and arrangement of these actuators. The excitation

force, the angle of inclination of the excitation, the inclina-

tion of the screen-box and the position of the center of

gravity determine the resulting oscillation amplitude of the

device. The oscillation amplitude, and thereby the conveying

speed of the machine, can be optimized by augmenting

these.

ROSTA spring suspensions support the desired oscillation

movement of the screen machine. Through their shape and

function, they help to achieve a purely linear conveyor mo-

tion without unwanted lateral tumbling.

Circular motion screens

Technology of free oscillating systems

with unbalanced excitation

These ideal spring suspensions harmonically support the run-

ning of the vibrating screen. Because of their high spring

deflection capacity, they offer a good detuning of the excita-

tion frequency with a very low natural frequency, which

guarantees a high isolation effect with regard to the ma-

chine substructure. The ROSTA mounts effectively dissipate

the large residual force peaks at start-up and shut-down,

when passing through the natural frequency of the suspen-

sion.

Circular motion screens or circular vibrators are normally

excited by unbalanced weights that create a circular

rotating oscillation of the screening frame. Relatively low ac-

celerations of the screened material are achieved with this

form of excitement. Circular vibrators thereby normally work

with a screening frame inclination of 15° to 30°, so that an

adequate material throughput is ensured.

It is recommended to mount circular vibratory screens of this kind on ROSTA type AB or AB-HD oscillating mountings. Experi-

ence has shown that the positioning of the AB suspensions under circular vibrators should be a mirror-inverted of each other,

which, with the above-mentioned frame inclination, will counteract the tendency of the shifting of the center of gravity. If the

suspension of the screening frame requires two supporting suspensions per brace support for reasons of capacity, these

should also be preferably arranged in mirror-inverted manner for the above-mentioned reason.