Wire ropes are used for a variety of maritime operations. Applied onboard all types of marine vessels including ships, large boats, drilling units, etc. these ropes are chosen for their flexibility, breaking strength, resistance to deformation and bending, anti-corrosion and anti-frictional properties. Wire ropes are mostly utilised for mooring, towing, handling heavy lifts and similar other operations.
Due to such profound 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. Such adverse work conditions can lead to untimely breakdown of the wire ropes if proper care is not maintained. In order to avoid premature failure of wire ropes, understanding onboard maintenance requirements such as their lubrication is very important.
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Construction of a steel wire rope
Steel wire ropes are heavy duty wires wrapped around jointly to form strands. These strands are firmly twisted over the wire rope core to form a final rope. The core of the wire rope is made up of different materials namely nylon, hemp, etc. The construction of the wire rope is primarily specified by the number of strands and the number of wires in each strand. The arrangement of wires in the strand, type of lay and outer and core material depend on the rope’s indispensable application for onboard usage.
Lubrication of Wire Ropes
To avoid corrosion, entail a longer life and evade subsequent damage due to consistent wear and tear of the wire ropes, regular and proper lubrication is vital. Although, marine 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.
Steel Wire Rope
A lubricant used for wire ropes must therefore:
- Be free of additives and compounds which result in corrosive reactions or degeneration
- Be water-resistant and non-emulsifying
- Not contain grit, sand, other abrasives, water, chlorine, or similar impurities
- Have high-quality layering properties
- Be able to penetrate easily to the core of the wire
Why Re-lubrication is needed:
During the manufacturing process of steel wire ropes, lubrication is carried out in order to protect initial damage to the wire due to corrosion during transportion and stowage. This also reduces the initial wear and tear of the wire ropes. Wire ropes once used loose the initial lubrication and start “drying up”. Therefore, to maximize the shelf life of the ropes which are subject to usage and stowage conditions, regular re-lubrication is required. Shipboard maintenance charts such as ‘Planned Maintenance Systems’ should include wire rope lubrication at frequent intervals and also take account of the type of lubricants applicable for the category of wire ropes onboard.
Before lubricating wire ropes onboard one must ensure that grit, sand, old lubricant layers are considerably removed using wire brushes, compressed air, or relevant solvents. Brushing, painting and swabbing are the most common application techniques used onboard. These methods, however, do not provide adequate penetration to the wire rope core. In order to provide good penetration to the core of the rope, pressurised lubricators are used.
Types of Lubricants
Lubricants most commonly used on board for maintenance purposes have a high penetration rate and melting point, rust protection and inhibition properties, adhesive and semi-drying film when applied, and be used in all climates. These lubricants that are used for various shipboard applications are easily available in the market.
Wire rope eye splice
‘Asphalt’ based lubricants that are the most frequently used lubricants on ships are viscous in nature. These types of lubricants are often premixed with an inflammable solvent, which can be applied easily and has penetrating properties. These products are applied on the wire ropes by way of brushing, swabbing or painting. Some of the ‘Asphalt’ based lubricants require heating which are prone to becoming frail when in low temperatures and may lead to ‘dripping’ in heated climates.
‘Paraffin Wax’ based lubricants are another set of products that can be used for wire rope maintenance. These wax based products are generally used without additives or solvents which means they are to be melted before application. They too are applied over the wire ropes by either brushing or swabbing.
‘Synthetic Oil’ based lubricants are considered to be the best of them all. They are high performance multi-fits generally applied with lithium based additives / solvents for providing adequate viscosity and thickness, contain anti-corrosive compounds with rust inhibitors and are water-resistant. These special lubricants are applied over wire ropes using pressurised lubricators for forced penetration.
In addition, there are other excellent products used lubricating wire ropes depending on the application methods and their overall structure and composition. Choosing the right lubrication for wire ropes on ships is as important as scheduled planned maintenance.