Planetary gearboxes cut weight of drilling head

Edited by the Engineeringtalk editorial team Jan 16, 2002

Roger Bullivant has exploited the smaller frame sizes and even lighter assemblies offered by some planetary gearboxes on a massive 60 tonne crawler-mounted mobile piling machine

The performance of the latest Series 2000 planetary gearboxes from Reggiana Riduttori may permit smaller frame sizes and even lighter assemblies, but it is not immediately apparent how that would be an advantage on a massive 60 tonne crawler-mounted mobile piling machine.

Yet market leader Roger Bullivant, specialists in foundation engineering, exploited just those characteristics on its latest rig, substantially reducing the weight of the rotary drilling head and facilitating an extra 3 metres of mast height.

Bradford-based Reggiana Riduttori UK recently supplied four RR2700D female shaft 17.42:1 ratio gearboxes to the Roger Bullivant headquarters in Burton-on-Trent, for installing on its new 7003 Continuous Helical Displacement Piling Rig.

The compact epicyclic units, with a maximum torque capacity of 24kNm, replaced comparable planetary boxes from a major competitor and enabled a weight saving of 72kg each, contributing substantially to an overall reduction of 460kg in the rotary head.

Established in 1971 and now one of the top three foundation companies in the UK, Roger Bullivant designs and builds all of its specialised plant and equipment in-house, at its 40 acre Drakelow site, and enjoys a unique standing in the marketplace.

It has produced more than 80 piling and mini-piling machines, encompassing both displacement and replacement auger techniques; the 7002 model, on which the new 7003 rig is based, is powered by a massive 700hp Cummins diesel engine, which enables it to produce up to 18 tonne.metres of torque at the boring end, double the power of most competitive machinery.

The 7003 was developed in response to a customer requirement for an extra 3m of boring depth, which dictated a commensurate increase in mast height.

In order to maintain stability without increasing overall weight, RB's design engineers lightened the boom, mast and other front-end components, then turned their attention to the rotary head at the top of the mast, where further savings were especially critical.

The continuous helical displacement piling technique, employed on this rig, displaces and compacts the soil through which it bores, creating no appreciable arisings and minimal spoil for disposal.

This method is preferred for many ground conditions, especially contaminated sites, but it requires tremendous torque and traditionally RB used four industrial planetary gear units to provide primary speed reduction and a conventional ring gear of its own design for the final reduction stage.

For the 7003 rig, the designers chose Reggiana Riduttori's Series 2000 reduction gear units, enabling them to move down a complete frame size, and coupled these with smaller Rexroth hydraulic motors of 200cc/rev capacity.

These are mounted vertically above the ring gear, one in each quadrant, and drive it by means of smaller pinion gears.

Exploiting the modular configuration of planetary gearing, the boxes were specified with female output shafts, saving still further weight in the torque element, and instead additional bearings were included on both sides of the pinions to support axial loads.

This revised mounting geometry is better suited to the application, say the designers, and, combined with 288kg weight savings on the gearboxes and 104kg on the motors, enables an overall reduction to the rotary head of 460kg, which also means that less ballast is required at the rear of the rig to keep it stable.

Moreover, these savings were achieved without sacrificing performance, the 7003 generating 19 tonne.m at 20rpm and 8 tonne.m at 60rpm, comparing favourably with speeds of 8rpm normally seen at the auger.

Dependability is naturally a factor when choosing components, since such rigs represent a major capital investment and are typically expected to be idle only 27 days in a full year.

Thus RB erred on the side of caution when sizing the gearboxes, with added load, life and service factors, and confidently expect that this new lightweight drive solution will meet the company's 95% plus reliability target.