ROTORDYNAMIC CHARACTERISTICS AND VIBRATION REDUCTION OF AN INDUSTRIAL DECANTER CENTRIFUGE

A rotordynamic analysis was performed to the decanter type centrifuge utilized in the dewatering of waste sludge. The decanter-type centrifuge system is composed of the screw and bowl rotors, driving motor, gear box and support rolling element bearings, having a rated speed over than 4,000 rev/min. Rotordynamic design goals are to achieve wide separation margins of lateral critical speeds and favorable unbalance responses in the operating range. A complex rotordynamic analysis had been carried out to evaluate its critical speeds/whirl natural frequencies and mode shapes, and unbalance responses under various balance grades. Early results indicated that the analyses performed by separating the screw and bowl rotors from each other might induce some substantial errors in predicting critical speeds of the system. Therefore, in this study the coupled analyses of the screw and bowl rotors were performed in order to more accurately estimate dynamic characteristics of the decanter-type centrifuge in hand. Results also indicated that rolling element bearings with suitable stiffness should be selected to ensure enough separation margins. Further, for the balance grades the ISO G2.5 would be more recommended rather than the ISO G6.3. Particularly, a balance correction of the screw rotor, based on the ISO G2.5, would be strongly recommended.