The bearings were designed in close cooperation with German tower clock manufacturer Perrot. 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.
Only Federal-Mogul’s self-lubricating deva.bm was able to handle the combination of extreme loads, low rotational speed, intermittent motion and harsh operating environment.
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,” says 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.
“The material has proven its worth a thousand times over, especially under conditions of high load, intermittent motion and dusty or abrasive environments. This is exactly what was required for the tower clock in Mecca,” explains August Stadlmayr, managing director of Federal-Mogul’s DEVA bearings business.
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.
“The very low shaft speeds and extremely high loads mean classic bronze bearing solutions with grease or oil lubrication would soon reach their limits under these conditions,” explains Stadlmayr. “These heavily loaded bearings are expected to operate maintenance-free over decades in spite of extremely difficult conditions.”
Following successful year-long trials at Perrot that included lightning strike tests, the first of the four movements was installed in late summer 2010. At that time only one of the four sides of the fibre-reinforced concrete tower had been completed. All construction work has now been completed. All four movements of the world’s largest tower clock are now ticking in sync.
Clock Tower Facts
- At 601 metres (approx. 1,969 feet), the clock tower is six times higher than Big Ben’s clock tower in London.
- The dials on the four sides of the tower have a diameter of 43 metres (approx. 141 feet).
- The minute hands are 22 metres (approx. 72 feet) long and weigh around 7.5 tonnes each.
- The hour hands are 17 metres (approx. 55 feet) long and weigh around 7.5 tonnes each.
Because DEVA sliding contact bearings work so well in demanding conditions such as extreme heat or icy temperatures, or conditions with heavy loads, dirt and dust, they have been used in the toughest of applications. Federal-Mogul’s experience includes heavy duty, wind turbines, hydro-electric plants, construction, the marine and offshore industry and the iron and steel making industry.
Monday, February 13- 2012 @ 13:12 UAE local time (GMT+4) Replication or redistribution in whole or in part is expressly prohibited without the prior written consent of Mediaquest FZ LLC.