For maximum process efficiency, large, heavy screening machines, for example for the extraction of the various grain sizes of pebbles in the preparation of ready-mixed concrete, are always positioned at the highest point of the plant – high above the silos, crushers and concrete mixers (Fig. 1). These screening machines weigh several tons, and are accelerated up to 5 g forces by their drives (unbalanced motors, unbalanced shafts or linear exciters), which generates very high dynamic forces.
Neither high reaction forces nor excessive transmission of the vibrations are desirable on the very high steel structures of these processing plants, as they lead to material fatigue in the steel structure and inaccurate functioning of the downstream machinery and controllers. In addition, they make it impossible for the operating staff to work on the various platforms and working stages for longer periods.
When installing screens on such high steel structures, suspensions are thereby demanded that are highly isolating, reaction-neutral and have a controlled runout.
The ROSTA oscillating mountings type AB with the double-arm pantograph arrangement are offering deep spring-deflection, and thereby have a low natural frequency of approx. 2 Hz, which results in levels of isolation of up to 98 % of the vibrations from the drive unit!
ROSTA suspensions harmonically support the linear or elliptical movements of the screen and, through their pantograph construction, create relatively little dynamic rigidity, which can be transferred to the substructure as residual force.
ROSTA oscillating mountings dissipate virtually no lost energy (< 0.5 %) while the screen is running normally. During the resonance transition of the screen, the two rocker arms describe excursions that are 5 to 6 times as great, which generates a high level of energy-loss (hysteresis) in the rubber inserts. The remaining energy in the screen box will thereby be completely dissipated within a few movements! The plant remains motionless.