In a carefully choreographed maneuver, three cranes lifted, turned and positioned a 140-mt replacement wheel for one of the world's largest excavators

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With a 200-mt-capacity heavy-load transporter waiting in the wings, three large Liebherr
cranes lifted this 140-mt bucket wheel off its assembly table.

Mobile cranes owned by Breuer & Wasel are a common sight at the Hambach open-cast mine in Germany—in fact, seven units operated by the heavy load logistics company from Bergheim are permanently stationed there, at what is regarded as the largest brown coal open-cast mine in the country. During a recent maintenance event, one of the mine's bucket wheel overburden excavators was scheduled to be fitted with a new 140-metric ton (mt) wheel, and three large Liebherr mobile cranes were sent to the site to assist the on-site fleet in this operation.

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With the assembly base removed, the transporter
approaches as the cranes maneuver the wheel into
position for loading.

Support from Breuer & Wasel was crucial during this procedure, as well as with a similar procedure involving the mine's other bucket wheel excavator three years ago. Replacement of the second excavator's bucket wheel was the culmination of a general overhaul of the giant machine, which took three months after 33 years of service. Weighing in at a total of 13,000 mt and standing 96 m high and 200 m long, 'Excavator 290' is among the largest machines of its kind in the world. Since 1978, the 18 buckets fitted to the excavator—which has a tractive force of 100 mt—have been digging through sand and gravel, and in the process have moved close to 3 billion m3 of material.

The new wheel, 18 m in diameter and weighing 140 mt, was initially delivered in individual parts and assembled at the installation site, minus its buckets. At the completion of this assembly stage, the three Liebherr mobile cranes, comprising an LTM 1500-8.1, an LTM 1400-7.1 and an LTM 1350-6.1, maneuvered into position for turning the wheel—which was still lying in the position it had been assembled—and then moving it onto a heavy-load crawler unit. Special fastening equipment had to be constructed for tilting the wheel during loading.

Next, all three cranes lifted in unison and pivoted the wheel into a vertical position. The two bigger cranes then held the wheel in place while the smaller crane moved to the other side and was re-attached. Once the load was suspended horizontally, the special crawler unit was positioned beneath it, ready to take on the 140 mt of steel.

The loaded crawler had to travel 200 m to reach the excavator. There the process of getting the wheel upright was repeated. Once again, the two bigger Liebherr cranes hoisted it into position for installation.

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Special fastening equipment had to be built to allow the
wheel to be safely tilted for loading onto the transporter,
which then carried it 200 m to the excavator for installation.

"We also had to follow the special safety instructions from the clients, which stipulated that during the tandem lift, the cranes could not be subjected to more than 80% of their maximum capacity," said Jürgen Oprée, technical director at Breuer & Wasel.

Breuer & Wasel operate a number of cranes permanently on site in the largest open-cast mines in the Rhine coalfield, at Garzweiler and Inden as well as Hambach. These units are called "basic load" machines and include two Liebherr telescopic crawler cranes—an LTR 1100 and LTR 1060—that are mainly used for repair and maintenance work on the giant excavators.

The crane fleet at the mine also includes a unique Liebherr model, of which only one was produced. The LTL 1160 off-road machine, 4 m wide and robustly designed, has been in continuous operation at the mine since 1997, and during that period has racked up 16,000 operating hours on the crane chassis and 19,000 hours on the superstructure. The four-axle unit underwent a general overhaul in the early part of the year at the Liebherr Service Center at Oberhausen, and was also partially modernized.

It took two days for the crane experts from Bergheim to turn, transport and install the bucket wheel on the site. The specialists from RWE Power AG, which operates the 38 km2, 370-m-deep mine, had taken two years to plan and prepare for the huge excavator to be overhauled, and the refurbishment cost RWE around €11 million. It will still be some three decades before the brown coal reserves at the Hambach mine are fully exhausted—and the excavator's new wheel assembly is expected to easily last that long.

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