Bearings

Campus Summer 2001


Eureka on Campus sponsor feature

Where there's a wheel there's a way

SKF discusses its involvement in a unique engineering project which heralds back to the old days of transportation

By the end of this year, the Falkirk Wheel will open to carry boats. The Wheel, which will be located close to the Scottish town after which it is named, is a new giant rotating boat lift and will be the only structure of its kind in the world.

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It is the centre piece of the Millennium Link, a 78 million project led by British Waterways, which reopens and reconnects the Forth and Clyde Canal, and the Union Canal between Glasgow and Edinburgh. The wheel measures 35m in diameter, with an axle length of 28m, and will transfer boats between the two canals, over a vertical gap equivalent to the height of eight double decker buses.

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Up until the 1930s, the two canals were linked by a series of 11 locks. However, along with the demise of the canals, the locks fell into disrepair, were in-filled and remain unusable. As a result, the idea of connecting the canals via a rotating boat lift was put forward. It was originally conceived as a giant Ferris wheel with suspended gondolas. For this design, SKF proposed large, double-row, spherical roller bearings and specially designed bearing housings to support the wheel. The final design has, however, evolved over the years of planning into the radical concept currently under construction. In Scottish eyes, the Falkirk Wheel is expected to double as a new national landmark.

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The new design, now being fabricated, came from the successful collaboration of several designers led by the Morrison Bachy Soletanche Joint

Venture. It follows on from the much-acclaimed initial design by Dundee Architects Nicoll Russell Studios and the exemplar designs by Engineers Binnie Black and Veatch.

Situated in a natural amphitheatre, the design itself is considered to be a form of contemporary sculpture and is endorsed as such by the Royal Fine Art Commission for Scotland. It takes the shape of a Celtic-inspired, double headed axe, in which two axe-shaped arms rotate in a continuous circle, 180 degrees at a time. It will simultaneously lift and lower two 22m long caissons which each hold a payload of 300 tonnes, comprising of water and up to four boats, and uses a series of synchronous gears to positively keep the caissons in the horizontal plane.

Butterley Engineering, of Ripley, Derbyshire, won the contract to build the wheel and its engineering design consultant, Bennett Associates, of Rotherham, Yorkshire, invited SKF to provide a new bearing solution. To support the wheel, SKF developed a solution which uses a pair of purpose-designed, 4m diameter, three-row, slewing bearings – one positioned at either end of the wheel – with outer rings bolted to the support structure and inner rings bolted to the arms. The inner ring of one of the bearings is equipped with gear teeth to transmit the drive to the wheel.

The use of the slewing bearings was an unusual solution, as these bearings are normally used in applications with heavy axial loads, such as those encountered in the rotational movement of large cranes. However, SKF specially designed these slewing bearings to be positioned on a horizontal axis and to cope with the specified combination of radial and axial loads. When the wheel is fully loaded, it weighs 1,800 tonnes, which results in a radial load of 9,095kN per bearing. Each slewing bearing has three rows of cylindrical rollers, one for the radial load and two with smaller rollers for the axial loads.

The wheel is rotated by ten hydraulically driven gearboxes, via the geared slewing bearing. It turns at a rate of around 0.125rpm, which sees it lift and lower boats at an average rate of 4m/min. With consideration given to the time taken for loading boats, the wheel is expected to complete a half turn about once every 15 minutes.

In operation, the wheel will be maintained close to perfect balance. With the caisson and the canal watertight doors open for loading and unloading, the water levels in the caissons will depend on the level in the canals to which they are then open. Any vessel which enters a caisson will automatically displace it’s own weight of water back into the canal and therefore has no nett effect. When the caisson and canal watertight doors are closed, a pump system will be brought into action to equalize the water levels in the two caissons to establish near perfect balance. The wheel drive system has, of course, been designed to handle a degree of imbalance due to differing water levels in the caissons. However, even allowing for this potential out of balance, the very low friction torque of the SKF antifriction bearings means that a rated torque of only 2,972kNm is required to rotate the wheel.

Although the bearings come with their own integral seals and have been designed to have a life expectancy of 120 years, SKF is also supplying extra CR seals of 4 and 2.5m diameters. This type of seal is specifically designed to withstand the conditions found in heavy-duty applications and, in this instance, will virtually guarantee the prevention of any ingress of water.

SKF has also provided bearings, in the form of SKF cross roller bearings, to support the idler gears, which will keep the caissons level at all times. The caissons themselves will run on a wheel arrangement on circular rails, with each wheel mounted on two SKF sealed spherical roller bearings.

The project is the second instance of SKF's involvement in the development and construction of a 'wheel' that will become an international landmark, having already provided the bearing arrangements for the capsules on the London Eye. The Falkirk Wheel provides a further example of SKF's continued involvement and expertise in providing bearing solutions for the moving parts of what are primarily civil engineering projects, other recent examples of which include bearing assemblies for bridges, roof supports, door assemblies and docking facilities.

As the centrepiece of the Millennium Link project, the Falkirk Wheel is part of the largest canal restoration project currently underway in the UK. The Millennium Link will see the removal of over 30 obstructions on the Forth and Clyde and Union Canals to make the 200-year-old waterways navigable once again. Although the canals will be reconnected by the end of 2001, this is just the beginning of the story. It is expected that over the coming years, the regenerated network will attract increasing numbers of boaters, and visitors to the area with the waterways acting as a catalyst for further economic regeneration and the revitalisation of communities across central Scotland. The potential of the project has gained it a 32 million grant from the Millennium Commission, and financial backing from the European Regional Development Fund, seven local authorities, Scottish Enterprise, five local enterprise companies, and, of course British Waterways which is also project managing the construction.

Jim Stirling, Director of British Waterways, Scotland, said: "We always said that the Falkirk Wheel should be something special, we wanted to create something elegant that people would want to come and see. The wheel will be a symbol for Scottish innovation and ingenuity as well as a unique, thrilling experience for visitors."

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