FAG Bearings (Germany, a division of Schaeffler Group, Germany) said it has finished manufacturing two massive high-precision spherical roller bearings for the hub of the Great Observation Wheel [website] being constructed just outside Beijing.

The two roller bearings are the largest of their kind ever manufactured; production took 18 months from specification to delivery.

S p e c i f i c a t i o n s         OD ID W rollers each roller assembled weight 3200 mm 2600 mm 630 mm 118 20 kg 10,000 kg

Located in Chaoyang Park, on the main road from Beijing International Airport to the city, the Great Wheel will open as the anchor of a world-class tourist destination in late 2009 or early 2010. It was originally named the Sky Boat and was to open in time for the 2008 Summer Olympics, but engineering challenges and construction delays made that impossible.

At more than 208 meters (682 feet) tall, the observation wheel is being built by the same company and following similar design ideas as the 135 meter (443 feet) London Eye / Millennium Wheel. The London Eye, after some teething pain, is now considered one of Europe's most successful tourism attractions. Beijing's Great Wheel builders say it will eclipse the London structure through sheer size and by, "eradicating its relative weaknesses."

Other than engineering updates and changes, the Great Wheel will offer reserved seat ticketing rather than requiring riders to wait in lines. Also, it will allow boarding the observation pods on both sides.

New York Times graphic comparing various wheels through history
FAG also produced the London Eye bearings, but faced challenges even purposing equipment to produce giant 3200mm OD bearings. By comparison, the London bearings' 2600mm OD is exactly the ID of the Beijing bearings.

Great Wheel bearings had to be significantly larger to accommodate the expected loads. While London is 135 meters high, Beijing is 208. London carries 800 riders, Beijing 1,920. But while the loads are high, the speed is low -- each revolution takes from 20 to 30 minutes.

A recently completed wheel in Singapore, the Singapore Flyer, is larger than the London wheel but less well known as a comparison to the Beijing structure. The original Ferris wheel, built in 1893 for the Chicago World's Fair, was 80 meters (264 feet) and carried a whopping 2,160 riders.

FAG's Henri van der Knokke, Heavy Industries head of Application Engineering, recalled: "When we received the dimensions and specifications from Great Wheel Corporation in black and white, at first we could hardly believe our eyes. We delved deep into the matter but a spherical roller bearing of such dimensions having to meet such demands has never been built before.

Design Engineer Rainer Schroder said: "The first thing we had to do was to find out if our production facilities would be up to manufacturing the bearings at all. It was like a puzzle with many thousands of single pieces."

The company had to research of the machine tools could accommodate the size and if the heat treat furnace could accommodate the rings, or if there was a crane on site with sufficient capacity to safely move the bearings, and finally how to get them safely all the way to China and 108 meters up to the Great Wheel's hub carrier.

The unfinished inner and outer rings were manufactured for FAG in Italy, reportedly by Prosino. Those were then shipped to Wuppertal, where grinding, heat treat and finish grinding took place. Heat treating, where the outer rings barely fit in the furnace, caused the rings to shrink 1cm and meant finish grinding had to be adjusted to achieve the necessary micron range accuracy. Production Manager Gerd Benninghoven noted tooling was a particular challenge: "Just imagine, during a single machining cycle, the tool covers a distance of more than 20km as it cuts through the metal."

Each bearing uses 118 barrel rollers, with a finished weight of 20kg each. The rollers started out at FAG's Eltmann plant, were sent to Wuppertal for heat treating and then back to Eltmann for finish grinding.

All of the components were brought together in Wuppertal for final assembly, 18 months after the Wheel's design specifications were presented.

The bearings were sent to Beijing, successfully installed, and the wheel is being built around them. It is scheduled to open to the public in late 2009 or early 2010; the project's total cost is expected be in excess of USD $200 million.

Beijing Great Wheel ( courtesy Great Wheel )

The same company expects to build similar wheels in Berlin, Dubai and Orlando, so FAG will be making more of these bearings.

Lead engineer on the Great Wheel project is Dutch engineering company IV Bouw; the capsules are made by Poma in France, and the sophisticated drives and control mechanisms are from Bosch Rexroth.