Timely repair thanks to good cooperation
Dortmund, March 27, 2015. The repair of a 45-tonne hydraulic cylinder had to take place within 3.5 weeks. Meeting this deadline was a real challenge due to incalculable difficulties, yet was achieved thanks to good coordination and collaboration between Montanhydraulik Reparatur und Service and the parent company Montanhydraulik in Holzwickede.
Repair of steering cylinder for 13,500-tonne excavator
It was the first repair to the steering cylinder since the bucket wheel excavator BG 285 was built in 1975. Wear and enormous impacts had completely destroyed the piston sealing system and the sealing material. The axial retaining rings for the piston seal had completely come loose from the piston and become stuck in the cylinder tube. Due to the large amount of leakage via the piston sealing system that had come apart, the forces necessary to move the steering shaft could no longer be achieved. The excavator was not manoeuvrable.
“It is already the third steering cylinder that we have repaired for this customer,” reports Heinz-Peter Kupiek, Managing Director at Montanhydraulik Reparatur und Service. “This time, the rod eye assembly was the biggest challenge. Once shrunk onto the rod through heating and cooling, it had to be removed again in a similar manner in order to dismantle the 45-tonne cylinder. In both cases, we had to play with time, as we simply cannot estimate all uncertainties that influence the dismantling and assembly in advance.”
Hand in hand with Montanhydraulik Holzwickede
It actually required three attempts, ten hours of patience and a degree of technical creativity before the six-tonne rod eye came loose with the help of hydraulic pressure and heating the rod head to 300ºC. In the process, it was discovered that the 610 mm-long and 500 mm-large fitting diameter of both parts was highly grooved and displayed many deep seizure marks. However, thanks to support from Montanhydraulik in Holzwickede, Germany, the repair duration was only extended by one day. Using the latest equipment for large cylinders, the technicians in Holzwickede performed the necessary machining work in just three days. This work required the utmost precision, as the force fit according to the original design had to be produced to transfer the tensile forces of 10,000 kN in full once more without any problems.
High tension at the final cylinder assembly
The final hurdle was to shrink-fit the rod eye onto the piston rod again in such a way that the force fit is used for the full length and the repaired steering cylinder guarantees the fault-free operation of the bucket wheel excavator. The piston rod including rod and cylinder head was also attached to the hook of a 300-t mobile crane, lowered through the opened hall roof, and inserted into the rod head centimetre by centimetre. Following successful functional and compression testing, along with filling with 3,500 litres of hydraulic oil, the steering cylinder was finally transported back to the customer on a special low-loader – on time and restored in mint condition.
Additional details about the repair process and the technical specifications can be found under References.