Working under contract from project manager, Alfred McAlpine Business Services, Brevini has engineered a replacement drive system for ten aerators at Yorkshire Water’s Rawcliffe sewage treatment works. The original drives were regularly being taken out of service due to gearbox failures, largely as a result of excessive mechanical loading and vibration issues. The half-tonne weight of the aerator paddles was being borne by the original helical gearbox end-bearings and because the paddles were not perfectly balanced, they were introducing vibration into the drive train, compounding the loading problem.
Brevini’s solution was to start from the mounting, selecting anti-vibration washers and nylon sleeve locking bolts to reduce the vibration effects. The paddles were dynamically balanced and large taper roller bearings fitted to the final output stages of the new planetary gearboxes. This bearing arrangement is able to take up to ten tonnes thrust load – more than sufficient for this application. Moreover, the in-line configuration of the planetary gearboxes avoids torsional loads on the bearings, ensuring a much longer service life.
The 5.5kW motors that drive the paddles via the gearboxes are inverter controlled for smooth ramp-up and ramp-down. They drive two planetary stages at 20:1 reduction ratio to achieve 70rpm at the output shaft for an optimum 1,440 motor speed. Brevini provided the drive system as a complete package that could be fitted directly to the existing mounting with little or no additional on-site fabrication.