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The Schaeffler Group has completed the manufacture of two giant spherical roller bearings for China's Beijing Wheel. In total, around 22 tonnes of steel has gone into producing the two hub bearings.
Each bearing has an outside diameter of 3,200mm, an inner ring bore of 2,600mm and a ring width of 630mm Each bearing incorporates 118 rollers, each of these weighing around 20kg.
The hub bearings for the Beijing Wheel will operate 108m above the ground.
The Beijing Wheel will be 208m high and is designed to accommodate 1,920 passengers.
One revolution of the wheel will take 20 minutes to complete, but will enable guests to see stunning views of the city of Beijing.
Being chosen as a development partner for the Beijing hub bearings placed unique challenges on the engineers at Schaeffler and on the bearings.
Rainer Schroder, design engineer at Schaeffler Group's spherical roller bearing product line, said: 'The first thing we had to do was to find out if our production facilities could actually manufacture the bearings.' Questions needed answering, including whether the machine tools at Schaeffler were suitable for machining such large dimensions, or whether the hardening furnace was large enough.
Could the crane in production support carry such loads? What would be the best method of transporting the bearings to China? And, once delivered to site, how could Schaeffler ensure that the bearings were installed correctly? Henri van der Knokke, head of application engineering at Schaeffler Group Industrial's heavy industries division, said: 'It was like a jigsaw with many thousands of separate pieces, which piece by piece, we had to complete.
'This was made possible only by close collaboration between our application engineering, design, calculation and production departments.' During this process, team members at Schaeffler had to continuously break new ground, improvise and coordinate time schedules.
The bearing rings were forged in Italy.
The barrel rollers were turned at Schaeffler's FAG plant in Eltmann, Germany, then hardened in Wuppertal and returned to Eltmann where they underwent a new grinding process.
Finally, the bearings were manufactured and assembled by FAG's large bearing specialists in Wuppertal.
Gerd Benninghoven, production manager at the FAG plant in Wuppertal, said that the Beijing bearings created one or two surprises.
First, the outer ring only just fitted into the hardening furnace, but nobody could really predict how this process would affect the bearing material.
Indeed, according to Benninghoven, the diameter of the bearing rings shrunk by about 1cm during heat treatment.
During final machining, however, accuracy in the micrometre range had to be restored, which provided a challenge with such large parts.
Benninghoven added: 'Imagine the challenge during the machining process, where the tool is cutting the metal at a speed of more than 20km.' Once delivered to site, the two hub bearings had to be mounted, which required the erection of a 100m tower.
In order to lift the bearings to their mounting position, bores for the eye bolts were also required.
Technicians at Schaeffler had to verify that the threads on these eye bolts were safe and could withstand such high loads.
Schaeffler Group has recently secured further bearing orders from Berlin and Orlando for similar observation wheels.
| Product Model | Inside Diameter | Outside Diameter | Thickness |
| HCB7201C.2RSD.T.P4S bearing | 12 | 32 | 10 |
| B7201E.2RSD.T.P4S bearing | 12 | 32 | 10 |