Planetary Gearboxes for Sewage Treatment Works

Anglian Water sewage treatment works has replaced its obsolete gearboxes for planetary gearboxes. These provide a compact and efficient solution without the need to replace or re-engineer the existing structure.  When a half bridge scraper stopped working and another was found sounding distressed at Benfleet sewage treatment works (STW), Anglian Water, UK, they had to make a decision whether to repair the existing, dated gearboxes or to reengineer the half bridge scraper to accommodate a new gear box. Both of these options were expensive and would have resulted in a lengthy downtime. An alternative solution was provided to drive the bridges using the existing structure. A drop-in solution was designed using a range of planetary gearboxes, providing cheaper running costs and minimal maintenance throughout its long life span. Any standard motor can be directly mounted onto the gear units so the gearboxes can be installed straight into any existing system. Jon Snaith – General Manager of Brevini UK Ltd. visited the site to develop a planetary solution to meet the criteria of the STW and bring the site up to date. The company is well established in the water treatment industry and pride themselves on offering ‘no engineering’. This means that their products can be designed to fit the existing systems making expensive engineering work unnecessary. Planetary gearboxes are capable of producing very large reduction ratios, reaching up to 15,000:1. This means that they are suited for driving large slow moving rotors. Producing up to 800kNM of torque, the gearboxes are able to produce the same power as large ‘worm and wheel’ gearboxes despite being far smaller and often 60% lighter than their equivalent. These gearboxes have a lifetime over 100,000 hours when they are in constant use keeping maintenance down to a minimum; one oil change per year is all that is needed. In the current climate a pressing issue throughout industry is that of energy efficiency. As these gearboxes are smaller than conventional boxes, they are driven by a far smaller motor which reduces running costs. Each stage has three planetary gears, mounted on 2 rows of needle roller bearings, this reduces point pressure and internal friction in the gears, this means that Brevini gearboxes run at 98% efficiency per stage; compared to many other high reduction gearboxes which will run with less than 50% efficiency. For many applications in the water industry gearboxes need to be able to survive in harsh conditions working around the clock. With features such as twin taper roller bearings and extremely high torque ratings, they are capable of surviving in conditions where other transmissions fail. The compact, rigid design of the planetary gearboxes makes them suited to applications within the water industry where very often the drivers are working 24/7 and need to be extremely reliable.