widely first rate quality vibrating screen classifier

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widely first rate quality vibrating screen classifier

Structural Failures in Vibrating Screeners at a Petrochemical ...

Detailed investigations of two of the eight vibrating screeners were performed at the facility to identify the root cause of the screener failures, and to reach an effective, practical solution to the machinery problem for the customer. While the screeners operated in the typical manner, a multiple channel spectrum analyzer was used to record detailed vibration data from the main structural components of the screener, which included the hopper and the base structure. Operating Deflected Shapes of the screener were created from this data to visualize the motion of the screener accurately during its normal manner of operation. A modal impact test of one of the screeners also was conducted to establish the natural frequencies of vibration and the mode shapes of the screener assembly. Because compliant connections facilitated relative motion between the hopper and the support structure, separate sets of impacts were performed on the hopper and on the support structure of the scree...

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Simultaneously, a three dimensional finite element model of the screener, which included the base structure, was created. Drawings of the screener were supplied by the customer, from which 3D solid geometry models were produced using the Pro/Engineer solid modeling software package. The 3D solid model geometry was translated into the ANSYS finite element analysis software environment, where it was distilled into a mesh of elements that represented the mechanical structure of the screener. The appropriate element properties, material properties, and boundary conditions were assigned to the elements in order to create the comprehensive finite element model of the vibrating screener. The 3D finite element model of the screener was used to conduct a detailed modal analysis that accounted for gravitational acceleration in the vertical direction, along with lateral and longitudinal accelerations which simulated the motion that was induced by the gearbox. The finite e...

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The mode shapes that had been predicted analytically through the FEA were compared with the ODS model, which represented the experimentally identified mode shapes of the screener. For both the hopper and the base structure, the analytically predicted vibration modes occurred at frequencies that were approximately 1.5 times greater than the vibration modes which had been identified experimentally. The results of the comprehensive modal evaluation indicated that the structural stiffness of the screeners which had been tested at the facility had diminished significantly, to a magnitude that fell well below the analytically predicted stiffness of the nominal design of the vibrating screener. Using standard equations for the vibration of flat plates, the welded plates that formed the structure of the screener were analyzed to gauge the influence of the edge boundary conditions on the plates natural frequencies of vibration. Modeling the edges of the plates as clamped boundaries resulted...

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To solve the problem of the failing vibrating screeners, it was recommended that any existing cracks in the main welded joints of the structure should be repaired immediately, both to restore the overall structural stiffness of the screener to approximately that of the theoretical design, and to prevent additional potential failures from occurring that would have been caused by the weakened joints. In addition, damping of the plate modes of the structure was recommended to reduce the amplification factor, and hence, the detrimental vibration response of the screener. This was implemented in a practical manner by the application of commercially available constrained layer damping material to the panels of the screeners hopper . To improve the service life of the structural beams and the support cables, it was recommended that the twisting and bending mode frequencies of the screener should be increased, to shift them further away from the driving frequencies of the vibrati...

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