Need for powerful cranes drives development technologies

Paul Boughton
One of the biggest offshore slewing cranes in the world has just come into operation, driving developments in broader crane technology. Sean Ottewell reports.

Liebherr has delivered the first heavy lift offshore crane type MTC 78000 from its manufacturing plant in Rostock. One of the biggest offshore slewing cranes in the world with a maximum dynamic torque of 78,000 mT, the MTC 78000 is the most powerful machine within the extensive range of cranes and material handling machines offered by the Liebherr group of companies. Four units of the new heavy-lift crane have already been ordered to date. Despite its size, the MTC 78000 has been designed as a slewing crane and is supported by traditional large-diameter anti-friction bearings. With a weight of 70 tons, the swing ring has a diameter of approximately nine metres.

The onsite erection and assembly of the large size crane on the heavy load vessel OSA Goliath presented Liebherr engineers with special challenges - for example, the planning of the individual hoists so that the maximum permitted ground pressure of the pier was not exceeded.

As the assembly starting date depended on the arrival of the heavy load vessel and the required lifting equipment needed to be ready on short notice, Liebherr used its own cranes for the assembly. Two large LHM 600 mobile harbour cranes were used in tandem operation for the heavy duty lifts. Both cranes with their maximum load capacity of 208 tons each enabled parts weighing up to 400tons to be mounted in tandem operation. The machines were equipped with the recently patented Liebherr sycratronic control system. In combination with the dynamic anti-collision system the sycratronic controls the simultaneous operation of the mobile harbour cranes, so ensuring best possible performance and protection for the cranes.

The assembly of the MTC 78000 required several heavy duty lifts. First, the slewing platform was mounted - at 370t, the heaviest of the components. Thereafter, the machinery compartment with the drive components (approximately 240t), the mast lower section (about 250t) and the mast upper section (around 160t) of which the lowest point needed to be hoisted up to over 43m above the pier level. This hoisting height was made possible by equipping the mobile harbour cranes with two corresponding tower extensions.

The last step in the assembly process involved putting the boom in place. In a tandem hoist operation, the 87m boom was positioned at the respective connection points enabling the boom to be pinned to the slewing platform on both sides. The sheer size of the pins required a specially developed hydraulic pinning machine.

Due to precise project planning, the specially trained team of 50 mechanics was able to assemble the MTC 78000 in only 23 days.

Among the many companies involved in construction of the new crane is Teufelberger, who supplied nine ropes with a total weight of 90tons and a length of over 7500metres. The Austrian company employed a permanent team of ten rope installation technicians in order to facilitate the project.

"For the installation of our ropes, we prepared a detailed concept in cooperation with Liebherr in order to ensure compliance with the agreed timetable and make the installation procedures as efficient as possible. In view of the crane's complexity, this installation project posed a major challenge even to our experienced crew. Similar to a piece of furniture, all prefabricated components for the MTC 78000 had to be assembled within tight deadlines into one complete whole. This required highly accurate planning and organisation and careful preparations from both Liebherr and Teufelberger. The smooth interaction and co-operation between all parties involved was a prerequisite for the success of the entire project," said a Teufelberger spokeswoman.

Meanwhile, Demag Cranes & Components has extended its range of industrial drive products with a new travel unit combination. The complete drive solution can be used wherever an optimised travel contour is required. It is designed to be used mainly on portal and semi-portal cranes as well as for travel applications in the general mechanical engineering sector. The 400, 500 and 630 series wheel sets have a load capacity of 28-60t per wheel and have played an important role in the Demag wheel product range for some time. A new shaft has now been standardised for installation on angular gearboxes. The proven shaft and hub connection is optimised for reversing operation as well as for all travel applications. The splined profile is designed to DIN 5480. The ARM 2 torque bracket is a new standard design that makes it possible to install angular geared motors in four different mounting positions. The ARM 2 torque bracket is fitted direct to the customer's travel unit.

Angular geared motors in the upper performance range W70 to W100 with output torques of 2500 to 12,000Nm are used for the new travel unit combination. Demag Cranes & Components offers these units - as required - as cylindrical-rotor and conical-rotor brake motors for line or inverter-fed operation.

The new travel unit saves space and offers an optimised travel contour width. For a combination consisting of an angular geared motor with gearbox size W70 (2500Nm) and an RAE 500 wheel set, the clearance width is reduced by some 60 per cent compared to solutions with an offset geared motor. If two driven wheel sets are arranged opposite each other, this value further increases correspondingly.

The travel units can be installed in hollow profile sections and box girder sections. If preferred, a corner-bearing design is also possible. This makes it possible to benefit from the advantages of the Demag modular drive range with its matching components. The wheel sets are pre-assembled and can be supplied on site as a complete unit. They can then be fitted in prepared travel units without the need for any complicated alignment.

Recent Issues