Have you ever heard of “cable shifting”?
As it is likely that many of you know little to nothing about this important task, we decided it was time to shed some light on it. Cable shifting is a task that is carried out every nine years on the Alpin Express tri-cable gondola lift. Primarily, it is an opportunity to inspect, clean and carry out maintenance work on the lift’s suspension cables. On aerial tramways, this task is usually carried out every twelve years.
A huge amount of work goes into the cable shifting process, and it can easily take up to five weeks to complete. Four Saastal Bergbahnen mechanics and six external specialists are responsible for the work.
The first phase is cleaning the cables. For this, a hydraulic cleaning unit of wire brushes is attached to one of the cabins and travels the entire length of all the 3,000-metre cables, cleaning as it goes. Meanwhile a visual inspection is also carried out.
Once this stage is completed, the cables are inspected more closely – this is a vitally important task, as it ensures that any damage to the cable is detected in good time and can be dealt with accordingly. A special magnet-inductive device is used to inspect the cable and detect any damaged or broken wires. The details are then sent to a computer so that the specialist can evaluate how serious the existing damage is. If the damage exceeds the standard safety requirements, the entire cable must be replaced. This costs around half a million Swiss francs per cable.
As soon as the inspection is complete, preparations begin for “shifting” the cable. First, the slack carriers are removed from the haulage cable. There are a total of 18 slack carriers per stretch of cable in each direction. Their purpose is to support the haulage cable and ensure that it doesn’t sag. Once the slack carriers have been removed, the haulage cable must therefore be temporarily supported by other means.
Once this phase is complete, preparations get under way at the valley and mountain terminals to pull in the cable. Clamping plates, pulley blocks, and winches are set up to form a sort of hoist (incorporating 17 pulleys), which hugely reduces the load of the cable and makes it possible to reel in.
At the valley terminal, a hoist for 40 tonnes is set up; at the mountain terminal, one for 70 tonnes. A total of 27 m of cable is released at the mountain terminal, which is then reeled in at the valley terminal. The sections that slide over the cable supports must be greased with a special lubricant to prevent friction. This is hugely important as it ensures that the cable is not exposed to permanent friction at the same point (the cable supports), which would cause considerable damage over time.
Once all the work is finished, the slack carriers are hung back up and the shifting of the first cable is complete. Now, the entire process starts all over again for the remaining five suspension cables.
Once all the suspension cables have been shifted, they are inspected once more with the magnet-inductive device and given a second clean. This ensures that the sections of cable that were on the cable supports before the shift took place have also been inspected and cleaned. To finish off the process, all six cables are lubricated and given a protective coating with special cable oil. Like the other devices, the oil spray is mounted on the back of the running gear. This allows the entire length of cable to be coated and provides the finishing touch to the process.
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