Wire rope is used across many end applications, each with their own specific demands and protection requirements (load carrying, shock loading, fatigue protection, corrosion, excessive heat, etc..). Keeping these wire ropes at peak performance is essential for any operation or project relying on secure, strong, consistent and safe performance.
Studies show that a well lubricated wire rope can increase operational life >4 times that of an unlubricated rope and while lubricants are generally introduced at the build stage, rope manufacturers and rope distributors selection does not always align with the interests of the end user. Differing lubricants can offer a large variety in protection benefits, while all lubricants will eventually deteriorate, dissipate, and leave your rope unprotected. The ability to apply a secondary/dressing lubricant gives us the opportunity to introduce both protections tailored to our needs and replenish lost performance as existing lubricants dwindle.
Let’s take a recent example of a steel mill ladle crane. During manufacture the rope producer used a standard wax-based build lubricant with a typical melting point of 120oC. Now, for a steel mill ladle crane reaching temperatures >300oC it’s obvious this lubricant was unsuitable, offering limited, if any, protection. Its use would create further safety concerns with oil and grease dripping to the floor below. Identifying this early, the build lubricant was removed while the rope was still with the manufacturer and replaced with a specialised heat resistant wire rope lubricant, which subsequently gave a 30% increase on rope life from the competitor product and no loss of material.
This is just one example of the extended rope life that can be achieved simply through lubricant awareness and selection. A dressing, or secondary lubricant also allows us to replenish lost lubricant maintaining rope performance and operational life. This can be particularly relevant to biodegradable lubricants that are becoming commonplace but are designed to naturally breakdown over time.
In this blog post, we will discuss typical applications used, when best to use each method and some of the considerations to keep in mind.
Our application method is inherently linked to lubricant selection (based on the demands of the end application), access, rope length, build lubricant and current rope condition. Our goal is to achieve maximum protection for prolonged rope life while balancing costs, time and maintaining safety.
Pressurised units are now commonplace, typically used in offshore and marine environments where maximum protection is a requirement given the potential for corrosion coupled with heavy lifting. Pressurised units have been on the market for ~40 years with the method of application essentially remaining the same. The rope is traversed through an enclosed housing with seals fitted at the rope entrance and exist to maintain a level of pressure within. Lubricant is then pumped into this enclosure where the pressure aids the lubricant to penetrate the rope strands. Several brands are commonly used, each with their own claims – save up to a 90% reduction in labour requirements – increase lubrication speed, greater penetration, etc… The level of penetration is dependent on setup and operation, rope speed, rope design, diameter, seal selection, seal condition, lubricant and lubricant flow rate, although, generally, penetration will be better than brushing alone though dry spots can occur if system balance is not maintained. These units also introduce the option of cleaning the rope of debris and old lubricant as it enters the housing. As generally the unit is fixed in place while the rope traverses through it, with sufficient space you can also take this opportunity to inspect the rope either visually or with MRT as part of the same operation. There is an initial outlay for these units and seals do wear over time. Seals will also be specified to a given rope diameter so multiple seals and housings could be required for varying ropes. Alternatively, companies now offer this service to avoid the initial CAPEX costs. The ropes must run at a steady speed for what can be prolonged periods of time, while for fixed ropes and short ropes the setup time and operation may not be suitable or cost effective. Access can also be a constraint with a requirement to fix the housing in place, connect it to a pump and supply of lubricant.
With adequate setup lubricant waste should be minimal, while excessive lubricant, not penetrating the rope, is captured in an overflow pail. Suitable area protection should still be used, and excessive lubrication avoided. A drum or pail is also generally used to capture debris and old lubricant as the rope enters the unit, (if a rope cleaning procedure is in place).
This method of application also allows for a stiffer/thicker/more viscous lubricant to be used, which has the capability of offering greater resistance to wash-off, corrosion, load and shock load protection. Though, again, these lubricants should not be applied to excess to avoid fling-off. Typically aim for a lubricant of NLGI 0.5-2 with a proven thixotropic feature.
Brushing lubricant into the rope is still a requirement in certain situations, although other methods like the pressurised units and sprays offer greater penetration and protection of the rope internals. Generally, the ‘thicker’ the lubricant applied the greater the level of protection that can be incorporated into its structure. For areas where pressurised units are not feasibly brushing can be used in a tight circular pattern with a short stiff brush proportionate to the rope diameter. This will give the greatest amount of coverage and penetration while avoiding excessive build up. Ensure all sides of the rope are treated. This practice can be time consuming and additional access equipment maybe required. A softer lubricant will provide greater penetration and quicker application, but performance carrying abilities could then be limited.
Still seen but not common and additional safety requirements need to be considered. This is a basic application where an excess of lubricant is held between the wire rope and cloth and traversed along the rope until the lubricant is used. The level of penetration is limited (only an outer coating may result), while a greater degree of waste and fling-off could be an issue if excess is not removed. Contact with a running rope should be avoided, especially near to drums and sheaves where entrapment can easily occur and any broken wires within the rope can act as snag points. Typically, this system could be employed where surface corrosion is an issue as penetration and load carrying capacity will be minimal.
Spray applications exist as a standalone process distinct from aerosols. These come in two general options, solvent based fluids – widely available, or increasingly common solvent free options. These fluids, although they can be poured, are generally transferred to spray system, typically handheld or backpack sprayers.
- Solvent-based products do offer a better spray pattern with cheaper spray systems, but solvents can have a detrimental effect to any remaining build lubricant so their use should be limited to when the build lubricant has all but gone. The solvent also raises safety, storage and environmental considerations.
- Non-solvent, or zero-solvent products are generally slightly thicker and the selection of a spray system needs to be more considered. The lack of solvent does mean no detrimental effect on the build lubricant, so they act only to boost current performance. Manually pressurised equipment is now readily available that provides suitable spray patterns while the lack of solvent also means environmentally friendly are available, while use, storage and transport is less restricted.
Only the smallest spray pattern will avoid a loss of lubricant to surrounding areas. It is generally advised that sprays be limited to the drum area, where the broad surface area accommodates the wider spray pattern and prevents excessive loss of material. Given the ‘light’ nature of sprayed products they generally offer more corrosion protection and limited performance towards lifting and shock loading. However large sections of rope, i.e., the drum, can be treated quickly and frequently.
Aerosol use is generally limited to small diameter, small lengths of rope in none demanding environments. They will offer limited protection against any excessive conditions but can be ideal for applications such as light overhead factory cranes and warehouse cranes. If several aerosol cans are being used, consider the spray option discussed above.
Aerosols contain solvents as a propellant, so consideration needs to be given towards storage, safety and environmental requirements. Also, dripping from the rope can easily occur as the aerosol is applied.
Remember wire ropes can last >4 times longer when a correct and adequate lubricant is used. Whether the rope is new, has been in storage or is under regular use, consider if its existing lubricant is right for your application and what options do you have for relubricating. It maybe easier to relubricate prior to or during installation.
Implement regular checks and relubricate as per above for prolonged rope life, following individual product instructions.