Federal-Mogul Corporation has supplied high-performance self lubricating Powder Metallurgy bearings, from its DEVA bearings division, to ensure reliable operation of the world’s largest tower clock, the Makkah Clock Royal Tower at the Fairmont Hotel in Mecca, Saudi Arabia.
The bearings were designed in close cooperation with German tower clock manufacturer Perrot to handle the combination of extreme loads, low rotational speed, intermittent motion and harsh operating environment. The exceptional demands created by the shafts carrying hour and minute hands each weighing around 7.5 tonnes, ruled out any conventional solutions, such as roller or bronze plain bearings, stated Federal-Mogul.
The new clock tower, standing 601 metres (approx. 1,969 feet), is six times the height of Big Ben’s clock tower in London and features four clock faces, each 43 metres (approx.141 feet) in diameter, legible from up to 10 kilometres (approx. 6 miles) away. The hour and minute hands move only once per minute, leading to huge static and inertia loads for the bearings to carry. Sand storms, winter storms, extreme daily temperature fluctuations and the high risk of lightning strikes combine to create a uniquely harsh and abrasive operating environment.
“Federal-Mogul DEVA has refined a proven solution to suit an especially demanding application,” stated Gerard Chochoy, Senior Vice President, Powertrain Sealing and Bearings. “Our application engineers have again demonstrated our technology leadership in the field of self-lubricating bearings.”
Federal-Mogul’s deva.bm is a self-lubricating composite material, produced using a special sintering method. It is maintenance free and features extremely high static and dynamic load carrying capacity and a low friction coefficient, due to homogeneous solid lubricant inclusions such as graphite and PTFE, within the bronze matrix. Bearings featuring this material are ideally suited to sliding contact and greatly outperform conventional roller bearings in applications characterised by heavy loads, low rotational speeds and lack of lubrication.
Federal-Mogul designed the bearings in close cooperation with Perrot to be maintenance-free for several decades. Arranged in quarter segments for easy mounting, each of the 16 bearings required for the four movements carries a self-lubricating contact layer just 1.5mm thick on a 5mm backing. Such minimal thicknesses are sufficient to reliably carry each of the 700mm (approx. 28-inch) diameter hour-hand shafts and the 300mm (approx. 12-inch) diameter minute-hand shafts.
Four clock movements have been constructed, one for each side of the tower. The central elements are two shafts that support the hour and minute hands, driven by servomotors. The motor for the minute hand switches on 15 seconds before the top of the minute, moving the 22-metre (approx. 72 feet) minute hand forward 60 times an hour, 1,440 times a day, 525,600 times a year.
Edited by: Paul Whittaker, Editor ipmd.net, [email protected]