The 1937 cranes needed to be updated as the old systems had an unprotected open power supply and various parts of the system were deemed unsafe. Additionally, spare parts were difficult to find and costly.
The hoists, electrical installation and the crane drives were to be replaced but the appearance of the cranes, which are listed, had to be maintained. The Heritage Agency focussed particular attention on the latticework construction of the crane bridge girders (rarely seen nowadays) and the colour.
As in restoring historical buildings, the modification needed to maintain the character of the building structure, a somewhat unusual challenge in crane refurbishment.
As no crane test logbook or technical documentation was available to establish the identity and type of operation of the cranes, the University of Kassel carried out material tests and calculated welding and bolt connections. Documentation comprising crane test logbook, certificate of conformity and CE marking was put together after the job. The static calculation as per DIN 18800 and DIN 4132 resulted in the old rails being replaced.
Rails of a total length of 66m were mounted in the existing bridge construction. Electric wire rope hoists of the SH6 series with a SWL of 10t were used.
The double-grooved rope drum permits true vertical lift with a lifting height of 12.5m. The crabs, meanwhile, were adapted to the existing track gauge while the rope sensors provided protection against overloads.
The toughest challenge was the modernisation of the crane drives. The drive technology 70 years ago, a central drive with drive shafts, had become uneconomic and the ravages of time had caused a great deal of wear.
After dismantling the old wheels, modular wheel blocks were fitted at a height of 13m. The heavy crane bridges did not have to be removed from the crane runway for this work.
The control signals to the hoist are now transmitted without a festoon cable. In its place a modern radio signal transmission was installed, while compact conductor lines carry the power along the crane bridges. They were mounted inside the crane bridges so no visually distracting festoon cables detract from the overall appearance of the historical latticework construction. Similarly, new compact conductor lines supply power to the cranes along the 50m long runways.
stahl 1 stahl 2 stahl 3
