Wire ropes form an important part of almost every rigging operation. Wire ropes are mostly used for mooring, towing, lifting/hoisting and similar operations. Due to their extreme usage, wire ropes are subject to constant wear and tear. They are exposed to corrosive seawater, dry and heated working temperatures, high and inconsistent pressures / tensions on wires and strands, chafing and internal wear, etc.
Given the kind use it is subjected to, they tend to get damaged very often. It is important to consider appropriate use of wire rope slings that form an important part of any wire rope assembly. The life span of the wire ropes is typically based on its lubrication, inspection, and maintenance.
It is important to choose wire ropes that are appropriate and ensure good service life. Other than trusted manufacturer and cost factors, one should pay closer attention to its quality and strength. Remember that the wire rope’s strength is equal to its size, construction and grade. It is important to consider the load bearing capacity of the wire rope.
The efficiency of wire rope slings are affected by several factors such as:
- The manner in which they are installed
- Rigging methods
- Maintenance of the wire rope
- Maintenance of the rope assemblies
Proper Installation of Wire Ropes
A majority of wire rope problems occur due to improper installation. Proper installation procedures are vital in the protection and performance of wire rope products. Prior to installing a new rope make sure to avoid any twist along the rope lengths. Proper handling of the ropes from reel or coil to the machinery will avoid damage to the ropes.
Another point of concern while installing a new rope on a smooth drum is spooling with wraps that are tighter and closer to the first layer. This layer forms the foundation of the succeeding layers. The closer and tighter the spools, lesser is the risk of twisting or kinking in the wire ropes.
Cross-winding or over-winding can cause crushing of these ropes. Careless winding results in poor spooling and will eventually lead to short service life.
Proper Rigging methods
To ensure longer service life of wire ropes it is necessary to practice appropriate rigging methods. If the loads are rigged inappropriately, this can lead to disastrous accidents. The rigging personnel should be well qualified and properly informed about the correct rigging methods suitable for the load type.
The first step to ensure proper rigging is to use appropriate diameter of wire rope. It is advisable to use the nominal diameter as specified by the manufacturer. The use of larger diameter will result in the rope getting pinched in the sheaves and groove which were originally designed for smaller diameter. While the use of smaller diameter will increase stress on the rope resulting in damage to the strands.
The rigging operations may cause the wire to bend which may cause fatigue failure. Prolonged abuse of wire rope will result in malfunction. Therefore, it is essential to practice proper rigging methods, such as using proper wire rope slings and clamps which are appropriate for that rope and also suitable for the job.
Some heavy loads tend to rotate when they are suspended or hoisted using cranes. Use of rotation resistant wire ropes is advisable in such case. Incorrect calculation of center of gravity may also cause the rope to rotate or swing towards the center of gravity point. Rotation in wire ropes can cause cracking or bird caging.
Inspections should be carried out by a person who has undergone qualified training or has practical experience of the field and who knows how to judge the importance of any abnormal conditions they may detect. It is the inspector's responsibility to obtain and follow proper inspection for each device and also keep record of the repairs and replacements done.
The period and type of inspections will depend on the usage of the wire rope. It is important to inspect the wire rope before and after use to record damages. The commonly found damages are kinking, corrosion, breaks and cuts, bird caging, abrasion, crushing, exposed strands etc.
A wire rope should be removed if there is an increase in wire breaks. Constant abrasion and corrosion can cause reduction in the rope diameter which can lead to rope failure. Such ropes should be discarded immediately. Corrosion can be internal, external, or generalized; this should be taken care with proper lubrication. The wire ropes that are used for long can suffer from deformation, such as waviness, loose ends, loose wires or loop formation. Such deformation can drastically reduce the service life of wire ropes.
Regular inspections should be carried along the full length of the wire rope. Certain areas such as rope zones where the ropes tend to bend over sheaves and drums and also lifting points where the load is attached to the rope are places where wire ropes are affected the most. These places should be taken care of, during inspections.
Lubrication of Wire Ropes
It is important to secure the wire ropes with proper lubrication to decrease the effect of possible damage. To avoid corrosion, consistent wear and tear of the wire ropes, regular and proper lubrication is vital.
Although, wire rope lubricants are available in abundance, the selection of these lubricants has to be with respect to the type of wire ropes to be lubricated. Different lubricants have diverse properties and characteristics.
A lubricant used for wire ropes must be free of additives and compounds which result in corrosive reactions or degeneration. These should have high-quality layering properties that can penetrate easily to the core of the rope.
It is important to make sure that the rope is free from grit, sand, other abrasives, water, chlorine, or similar impurities while applying lubrication. Wire brushes, compressed air, or relevant solvents can used to clean the rope.
Brushing, painting and swabbing are the most common application techniques used for lubrication. Pressure lubricators allow lubrication to reach the core of the wire, which is important. Proper lubrication will protect the wire ropes from corrosion and abrasion.
There are many excellent products used for lubricating wire ropes depending on the application methods and their overall structure and composition. Choosing the right lubrication for wire ropes is as important as scheduled planned maintenance.
Wire ropes are heavy duty equipment which requires proper care and maintenance. The above methods are essential factors that affect the service life of wire ropes. Better maintenance of the wire ropes will directly increase their service life.