Crane wire ropes are considered consumable parts and we need to take good care of them to ensure their service life and durability. Their safety and long-term use depends on the maintenance they receive.
This article includes 6 main parts: handling, storage, pre-installation, installation, commissioning, maintenance, and replacement of wire ropes.
1. Maintenance of wire rope during unloading and storage
To avoid accidents and/or damage to the rope, it should be unloaded carefully.
The rope drum or coil must not be dropped or hit by the metal hook or fork of the forklift or any other external force that may damage the rope or deform the rope.
Ropes should be stored in a cool, dry building and should not be allowed to come into contact with the floor. They should not be stored where they may be affected by chemicals, chemical fumes, steam or other corrosive agents.
If outdoor storage cannot be avoided, the rope should be covered to prevent moisture from causing corrosion.
Ropes in storage should be checked regularly for any signs of deterioration, such as surface corrosion, and if deemed necessary by the competent person, they should be coated with a suitable preservative or lubricant that is compatible with the rope manufacturing lubricant.
In warm environments, the drum should be rotated half a turn regularly to prevent the lubricant from escaping from the rope.
2. Maintenance of wire rope before installation
Before installing the rope, it is best to check the rope and its certificate upon receipt to ensure that the rope corresponds to what was ordered.
The minimum breaking tension of the installed wire rope should not be less than the value specified by the crane manufacturer.
The diameter of the new rope should be measured on a straight section without tension on the rope and the value (dm) recorded.
If the wire rope has been stored for a period of time, during which corrosion may have occurred, it may be more beneficial to perform a visual inspection and MRT.
Check the condition of all pulley and drum grooves to ensure that they can accommodate the size of the new rope, do not contain any irregularities (such as corrugations), and have sufficient residual thickness to safely support the rope.
The pulley groove diameter should be between 5·% and 10·% larger than the nominal diameter of the wire rope. For best performance, the groove diameter should be at least 1·% larger than the actual diameter of the new rope.
Wire rope installation
When unwinding and/or installing wire rope on a crane, all precautions in the wire rope installation procedure should be taken to avoid causing the wire rope to be spooled in or out. Allowing this to occur may cause the rope to form loops, kinks or bends, making it unusable.
To prevent any of these conditions, the rope should be paid out in a straight line with the minimum slack allowed.
The coiled rope should be placed on the turntable and paid out straight; however, if the coiled length is short, the outer end of the rope can be released and the rest of the rope rolled along the ground.
When the coil or reel is lying flat on the ground, the rope must not be paid out by swinging the spool or rolling the reel along the ground.
For rope lengths supplied on reels, keep the supply reel and its support frame or bracket as far away from the crane or hoist as possible to limit any fleet angle effects to an absolute minimum and thus avoid any undesirable rotational effects.
The rope can be protected from any potential ingress of sand or other contaminants by running the rope over a suitable mat (such as a used conveyor belt) rather than letting it run directly on the ground.
Note that a rotating rope drum may have a high inertia, in which case it will need to be controlled to pay out the rope slowly. For smaller reels, this is usually achieved by employing a single brake. Larger reels will have a lot of inertia once they start rotating and may need to be braked heavily.
Where practicable, ensure that the wire rope is always bent in the same direction during installation, i.e. the wire rope is paid out from the top of the supply reel to the top of the drum on the crane or hoist (known as "top-to-top"), or from the bottom of the supply reel to the bottom of the drum on the crane or hoist (known as "bottom-to-bottom"). Take "bottom-to-bottom" as an example.
For multi-layered ropes, apply a back tension equal to approximately 2.5% to 5% of the rope's minimum breaking force to the rope during installation. This helps ensure that the bottom layer of rope is tightly wound, forming a solid foundation for subsequent layers.
Secure the rope ends to the drum and outboard anchorage according to the crane manufacturer's instructions.
During installation, prevent the rope from rubbing against any part of the crane or hoist.
Break-in of new wire ropes
Before putting the rope into full service on the crane, make sure that all lifting limits and indicators related to the crane operation are working properly.
In order to allow the components of the wire rope to better adapt to normal operating conditions, the crane should be operated for several operating cycles at reduced speed and load [i.e. reduced to 10% of the working load limit (WLL)].
Maintenance of wire ropes
The care and maintenance of wire ropes should be carried out according to the type of crane, frequency of use, environmental conditions and type of wire rope.
The wire rope should be dressed from time to time during the life of the wire rope before any signs of dryness or corrosion appear (particularly on the length that passes through the sheaves and enters and exits the drum and the portion that coincides with the compensating sheave) at a time determined by a competent person. In some cases, it may be necessary to clean the rope before applying the dressing for it to be effective.
Rope dressings should be compatible with the original lubricant used by the rope manufacturer and should have penetrating properties. If the type of wire rope dressing is not indicated in the crane manual, the user should seek guidance from the wire rope supplier or wire rope manufacturer.
Lack of maintenance may result in a shortened rope life, especially when the crane or hoist is used in a corrosive environment or when the rope cannot be dressed for some reason. In this case, the inspection intervals should be shortened accordingly.
When the section protrudes excessively from the rope and covers other sections as it passes through the sheave, it can be removed by grasping the protruding end and bending the wire back and forth until it finally breaks (always in the valley between the strands). When a broken wire is removed from a rope as part of maintenance work, its location should be recorded for the reference of the rope inspector. If such action is taken, it should be considered a broken wire and taken into account when assessing the rope condition according to the broken wire scrap criteria.
When a wire break is evident near or at the termination, but the rope is not affected elsewhere along its length, the rope may be shortened and the terminal fittings refitted. Prior to this, the remaining length of the wire rope should be checked to ensure that the minimum number of wraps required remains on the drum when the crane is at its most extreme operating limits.
Wire Rope Replacement
Unless an alternative rope has been approved by the crane manufacturer, rope manufacturer or other qualified person, only ropes specified by the crane manufacturer of the correct length, diameter, construction, type and lay direction, and strength (i.e. minimum breaking force) should be used and should be installed on the crane. Records of rope replacements should be kept on file.
In the case of larger diameter, rotation-resistant ropes, additional methods may be required to secure the rope ends, such as by the use of steel bands or straps, particularly when preparing test specimens.
If the length of rope to be used is cut from a longer length, such as from a mass-produced rope drum, service should be applied on both sides of the intended cut point to prevent the rope from unraveling (i.e. unraveling) after the cut has been made.
The figure below shows an example of how a single-ply rope should be treated before cutting.
For rotation-resistant and parallel-closed ropes, multiple uses may be necessary. The figure below shows an alternative method for larger diameter, rotation-resistant ropes. Ropes that are only lightly preformed are more likely to unravel/come apart after cutting if insufficient or inadequate shares are used.
Note: The serve is sometimes also referred to as a "catch"
Unless an alternative rope end has been approved by the crane manufacturer, rope manufacturer, or other qualified person, only one of the types specified by the crane manufacturer in the operator's manual should be used to attach the rope to a drum, hook block, or anchor point on the mechanical structure.
It is beneficial to test the rope before or as soon as possible after installation, with a base trace for the MRT.
