Ropes or lift cables are integral for a lift to function, playing a critical role in controlling the speed of a lift and supporting the weight of a car. These ropes are often made from high tensile steel wires woven together to form incredibly robust lengths of metal rope. The size and speed of a lift will dictate the number of wire ropes required, with multiple cables in place to ensure the safe use of a lift. In the event that one rope snaps (which is extremely rare), the other ropes will be able to support the lift. While this makes lifts extremely safe, there are still things you should be aware of when it comes to wire ropes.
Wire rope damage
While a rope is unlikely to snap, there are early signs of damage that can be spotted, especially on older lifts, to give you time to update them. One of these signs is broken strands caused by continual wear and stress on the rope as it runs around the sheaves (pulleys). This constant traction around a lift sheave can also cause severe wear at specific points on the rope – either flat spots or crushing. Another sign of damage is corrosion, easily identifiable by rust patches on the rope. While this is visible to the eye, internal corrosion is very difficult to judge, making corrosion one of the most dangerous causes of rope failure.
When installing equipment on a lift project, it is important that the equal amount of weight is added to the counterweight. Failure to do this means there is a risk the lift will break traction (when the ropes are pulled over the sheave without being driven) between the ropes and drive sheave. If this happens, the lift could start to run up, if the counterweight has too much weight, and slip down, if the car has too little weight.
Preventing rope problems
Regular inspection of both wire ropes and lift sheaves will help determine the condition and replacement (if required) to prevent incidents. To avoid rope slippage, the correct operation of the installed equipment should be checked prior to use. This should be based on the traction ratio, area of contact of hoist ropes on the drive sheave and rate of acceleration and deceleration. In particular, the car and its counterweight must be within a certain weight of each other, based on the size of the lift and type of drive sheave fitted. If you are removing equipment from the lift car on a modernisation project, it is important to ensure the equal amount of weight is removed from the counterweight. Similarly, if you are installing new equipment, estimate the weight of the removed equipment and then place half that amount in filler weights from the counterweight inside the lift car.
Lift safety should be the top priority when it comes to any form of maintenance or installation of a lift. Correct installation and operation is therefore paramount when it comes to wire ropes, without which, problems are likely to occur that could have otherwise been avoided.