Liebherr will introduce the 81 K fast-erecting tower crane at Bauma in 2010.
Based on the concept of the 71 K model, the new fast-erecting 81 K lifts loads more than 25% higher at the end of the jib, Liebherr said. The 6t capacity crane has a maximum hook height of 40.4m and 55m at a 30˚ jib angle.
Transport dimensions haven’t change much from the 71 K, but the 81 K now has a 2.75m slewing radius. Tower sections measure 2.4m-long, allowing them to be carried sideways on a truck. These new sections can be used with the 71 K, and vice versa.
The tower is raised and telescoped out with a single continuous erecting rope and the process is supported by jib guying rods and by semi-automatic, quick-connection locking between the tower and the slewing platform. Separate hoisting and erecting winches also help simplify the erecting procedure, Liebherr said. Pairs of ballast slabs can be secured together by threaded couplings, so that only eight lifting movements are needed to install the ballast and make the crane ready for operation.
With eleven variable hook heights, various configurations are possible without using the climbing facility to insert additional tower sections: four additional intermediate hook heights, a 30˚ steep angle jib position and a 45˚ angle to keep the jib clear of obstructions. With a 45m working radius the 81 K has a 1.4t capacity, or at a 31m radius it can handle a 2.9t load. Inserting further tower sections with the climbing mechanism, six more hook heights up to more than 40m are available with the jib horizontal.
Another new development on the 81 K is its double-reeving only operation. It’s the first crane in its class to offer this, according to Liebherr, and can operate both at the maximum speed lifting the maximum possible load, and at high speeds without a load on the hook.
The bottom-slewing 81 K uses driveline and control system technology previously found only on top-slewing cranes. All drive assemblies on the 81 K are continuously variable, using the frequency control principle. To ensure accurate movement of every load, the range of control lever movement always corresponds to the maximum possible speed. The push button selected fine positioning mode reduces rope speed to 25%, so that even heavy loads can be positioned accurately without the hoist gear brake being applied, Liebherr added.