Getting a handle on the ins and outs of wire rope lubrication can be almost as tough as holding a well-lubricated rope while it's in use.  A collection of experts in the field make the subject a bit easier to understand.

Envision wire rope as a complex mechanical system.  Whether used as a dragline, tow line, elevator cable, or bridge guy line, it is made up of moving parts.  Those parts are forced to continuously adjust to one another during often high stresses in hostile environments.

Consider a hoist rope on a large dragline.  As the rope moves over the sheave, it is pulled, bent and compressed simultaneously.  Metal to metal contact stresses the outside of the rope as it enters and leaves the sheave.  Inside, wires contort and abrade one another.

Sometimes the hoist rope is forced to then move over another sheave in a reverse bend.  The closer the two sheaves are, the more stress the rope will experience because the strands will not re-adjust themselves.

The best lubricant for the job
Almost anyone in the wire rope industry would agree that, with few exceptions, wire rope needs lubricant protection.  According to the Roebling Wire Rope Handbook1, fatigue tests were conducted with two sections of 9/16" diameter 6 x 19 wire rope.  One was lubricated and one was dry.  The lubricated rope lasted 2.4 times longer on the 10" tread diameter sheave, and 5.2 times longer on the 24" tread diameter sheave.
 
 

But when users and manufacturers begin to discuss specifics, such as types of lubricants, additives, environmental issues and application methods, opinions diverge.

 For instance, here are some basic lubricant compounds used for manufacturing or re-dressing:

• asphaltic
• petrolatum based
• combination (asphaltic and petrolatum)
• soap (stearate) thickened
• inorganic thickened
• greases (pumpable)
• amorphous polypropylene
• resin based
• linseed/castor oil

• corrosion inhibitors
• anti-wear additives
• water displacing additives
• polymers (tack and adherence)
• plasticizers (low temp)
• anti-oxidants
• polar additives (wetting)

Hostile environments
Key to choosing the correct lubricant is knowing the rope's application and in what environment it will be used.

For instance, with applications like the dragline discussed above, the lubricant must have additives that cause it to remain pliable as the rope is used.  As the strands inside the rope move against each other, the lubrication can wear off in spots.  "A good lubricant will re-distribute itself evenly between the strands — a characteristic known as ‘self healing'," says Bill McAlaine.

The marine environment is one of the most hostile for wire rope.  At sea, the wire is subjected to high corrosion from wind-blown salt air, as well as from short immersions in salt water during lowerings.  The zinc corrodes first, and how quickly it corrodes depends on a number of factors:
the depth of water in which the rope is used.  Oxidation is a kind of corrosion.  The closer the rope is to the surface of the water, the higher the temperature, and the more reactive the oxygen is.  So, the rope will corrode faster when it is closer to the surface of the water.

The temperature and chemical content of the water.  In a 1969 study, with the assistance of the Woods Hole Oceanographic Institution, Oregon State University, the Halan Company and U.S. Steel, an experiment was performed where specimens of bright steel wire, galvanized wire and electromechanical cable were submerged for three months in three different locations.  The results showed "accelerated rates of corrosion...ultimately traced to a combined effect of chemical levels in the water and the temperature of the sea water."3
 
 

How thick, how hot?
 In many applications, the lubricant's tolerance to fluctuations in temperature is a major concern.  In hot desert climates, for instance, the wrong lubricant will literally drip off the wire.  At low temperatures, it may flake or crack.
 Lubricants very in viscosity, and viscosity always varies with temperature.

"There are many different standards for measuring lubricant viscosity,", explains Bob Kirkpatrick, President of The Kirkpatrick Group, Inc.  Most commonly used are: "NLGI" (National Lubricating Grease Institute), "Saybolt" (Sus), and "Centistoke" (Cst). Laymen and experts alike have difficulty making conclusive comparisons between the standards.  There are few, if any, complete comparison charts that provide accurate cross reference between the standards.  Most lubricant manufacturers use only one or two measurement specifications when preparing technical data.  To avoid confusion...we...use the terms "Pourable" for low viscosity and "Nonpourable" for high viscosity when referencing given wire rope dressing ranges.  Pourable (Low Viscosity) wire rope dressings range from SAE 90 weight oil density upwards to NLGI #0 a near equal to molasses.  Nonpourable (High Viscosity) wire rope dressings range from NLGI #1 (consistency of soft butter) to NLGI#3 (consistency of thick peanut butter).
 

"Ambient temperature must be considered when measuring dressing viscosity..As an example: NLGI pourable dressing grade #0 at 85 degrees may easily become #1 or #2 nonpourable at 40 degrees.  Prior to operation, check you viscosity...In extremely cold temperatures, it may be necessary to pre-heat wire rope dressing to assure it is easily pumped and applied to the wire rope."

Where ropes are being stored, Nonpourable lubricant may protect the rope with a heavier film.  Relatively recent advancements in pressure lubricators manufactured by companies like The Kirkpatrick Group make it possible to force heavier oils into the inner parts of the wires.  When this is possible, it is sometimes preferable, since more highly viscous lubricant affords greater strand-to-strand protection.

But, for certain applications, and where a pressure lubricator is not available, thinner oils are preferred.  They can be applied by spraying or simply pouring, and drip into the inside of the rope readily.  Lower viscosity lubricants must be re-applied frequently.
In confined spaces, or where motors might produce sparks, avoid using inexpensive petroleum solvents.  They have a low flash point, which can present a serious fire hazard.

From the first drawing
 Before considering field dressing (relubricating), a user may need to start where lubrication begins: with the wire rope manufacturer (OEM).  At intervals while the rope is manufactured, the OEM applies lubricant.  This lubricant differs from the type used to re-dress the rope.  But it is important to be aware of the OEM lubricant applied, since the re-dressing lubricant may interact with it, causing unforeseen problems.
 The type of lubricant and the amount added is determined by the manufacturer based on his information about the future use of the rope.
 "A wire rope may be lubricated at three intervals during its manufacture," explains Bill McAlaine, Vice President and Business Manager of Allied Kelite, "once at ‘stranding' (when the wires are joined to form strands), once at ‘closing' (when the strands are formed to make rope) and sometimes after the rope is made, to provide an added level of protection."
 "As the wire is drawn, it passes through a ‘soap', Bill adds, "which is designed to facilitate lubrication between the wire and draw dies.
"However, it is not designed to protect the wire in use.  If anything, it actually causes us problems, because the soap left on the wire often absorbs water. (Many drawing soaps contain borax, which is highly hydrophilic).  Applying a lubricant at stranding over a moisture laden soap/borax film can cause moisture encapsulation and result in premature corrosion.  We build water displacing properties into our stranding lubricants, which helps address this problem.  However, the best practice is to take the last wire reduction without lubricant to help minimize the amount of water-absorbing residual film left on the wire surface."

If a termination is added, lubrication should be re-applied.  It is important that the juncture of the strand and socket be inspected periodically, because of torsional twisting, which subjects it to corrosion.

The core of the problem
 Once the customer receives new rope, he should store it inside a building and away from direct sunlight, or at least cover it with a tarp if it has to be left outside.  Turn the storage reel periodically to prevent the lubricant from seeping to the bottom, especially where temperatures are high or the lubricant is very fluid.

When the rope is put to use, field dress it immediately.  Like devious enemies, moisture and pollutants can invade the wire quickly, corroding the core of the rope. (Note that we are referring to a wire, rather than fiber, core.)

"Corrosion damage is impossible to estimate and must be avoided in order to maintain necessary strength and safety.  A corroded rope is reduced in strength for various reasons.  First, metallic area is lost by chemical or electro-chemical action.  Second, corrosion mars the smooth finished wire surfaces, resulting in erratic contours which form stress raisers.  These stress concentrations are very susceptible to failure by crack propagation as the rope bends and stretches during operation.  Third, corrosion hinders normal movement between wires, creating a binding condition which increases stresses to an indeterminable extent and speeds corrosion-fatigue fracture growth."1
 A major concern in re-dressing should be the compatibility of the lubricant with the OEM lubricant.  Incompatible materials can cause dangerous results: the re-dressing lubricant may not penetrate the wire sufficiently; components of the OEM lubricant may leach out; or the re-applied dressing may flake away.

If in doubt, consult the OEM.  According to law, the wire rope manufacturer should tell the customer how to field dress the rope.

And, cautions Al Lucht, President of Wire Rope and Metallurgical Engineering Services, "a basic requirement for all lubricants is that it must stick to the rope and not fall off.  Strange as it may seem, this is not always an easy problem to resolve.  One can read all the advertisements and listen to the vendor, but the only way to find out is to use the wire rope and try it in the intended application. If the lubricant does not stick (adhere), it will do absolutely no good at all."

Here are some lubricant related field problems:2
 

• adherence
  • Film is too heavy for the rope speed.
  • Field dressing or rig wash is softening the film.
  • Stranding lubricant is wrong.

• corrosion
  • Lubricant is poorly matched to the environment.
  • Film thickness is wrong.
  • Adhesion and film integrity are poor.

• low temperature flaking
  • Lubricant is wrong for the application.
  • Lubricant was overheated during application.
  • Film thickness is wrong.
•  dry rope
  • Field dressing is inadequate.
  • Penetration at the "point of twist"during the manufacturing process is poor.
• dry core
  • Field dressing is wrong.

• melt-off/throw-off
  • Melting point is low or viscosity is above the melting point.
  • Film thickness is wrong for application or temperature at which it is being used.

• internal wear
  • Rope is dry.
  • Contaminants are infiltrating rope.

• wash-off
  • Field dressing or OEM lubricant is wrong.

Re-lubricating: how often?
Testing is key to finding out how well the lubricant is protecting the rope, and establishing a re-lubricating schedule.

Since each rope application varies, it is impossible to specify a uniform re-dressing time interval.  It depends on many factors, including the type of load, frequency of use, and kinds of environmental exposures.

For certain ropes used consistently in the same environment and under the same conditions, rope re-dressing can be performed at reasonably predictable intervals.  For instance, when using a hoist dragline, frequent lubrication is a must.

"As a general rule, the entire length of the rope should be lubricated every eight hours on a machine operating continuously.  This procedure will vary depending on temperature.  And lubricant temperature depends on ambient temperature, which can be affected by wind, heat sources and humidity...An average dragline uses about 55 gallons of wire rope lubricant per month."4
 But in many cases, the rope needs to be visually checked frequently for broken wires and corrosion.  Even stationary wire rope like guy wires and suspension cable should be inspected periodically because of damage caused by atmospheric contaminants.  It is vital that the lubricant is soft so that it can be easily wiped from the rope surface.  Lubricants that harden cover defects, presenting a hazard.  They can indirectly cause serious injury or death.
 Here is a sample visual inspection for galvanized rope:

Periodically the wire rope should be visually inspected to determine the condition of the strand, and if there is a question on the coating, the following procedure should be followed:

• Remove the residue that is present with a pencil eraser or fine steel wool, but don't use too much pressure that will remove the coating.
• Make a concentrated solution of copper sulfate with water (dark blue) and apply it to the test area with a saturated cotton ball or cloth.  Wear rubber gloves.
• If there is no chemical reaction, the coating of lubrication is present.  If the test area turns black, the coating is not present, but zinc is.  If it turns copper color, then there is no zinc or coating present."

"A better method of evaluating lubricant effectiveness is to test a rope by the NDT procedure at periodic intervals throughout its service life.  The rope is passed through a sensor head that determines the rope's loss of metallic area (LMA) and local faults (LF) such as broken or missing wires.  The NDT method, while not eliminating the visual rope inspection, provides advantages in that it allows determination of the structural integrity of the internal rope parts and requires less downtime for testing.  Researchers at the Bureau of Mines Spokane Research Center evaluated NDT date on various ropes by comparing the LMA and LF and noting the trends."5

And...how?
 Once the wire rope is in use, a major concern when re-dressing should be first removing the water and dirt that has become trapped in the rope.  If the rope is lubricated without first being cleaned, the existing moisture and pollutants will still cause corrosion and abrasion.  And, they will prevent the lubricant from adhering to the rope uniformly.  As a result, the rope will deteriorate faster.

There are many cleaning methods.  Any good method should remove dirt and liquids not only on the surface, but in the "valleys" between the strands, where it can become embedded, and work its way inside the rope.

As mentioned before, a primary concern in preparing a rope or cable to receive a field dressing compound is that it is free from entrained water.  Re-lubricating rope without first removing internal moisture will, rather than inhibiting corrosion, accelerate it.  Some wire rope dressing compounds now contain additives that will combine with water to prevent corrosion.

Here is a sample cleaning and re-dressing procedure:

• Strands must be examined for any build-up of residue in the valleys between the wires.  If, upon examination, there is a build-up of residue in the valleys between the wires, the valleys must be cleaned with a cable cleaner to allow the lubricant to penetrate the outer wires into the core of the cable and to combine with entrained water.
• If the residue of old lubricants and coating is just present on the crowns of the wires, then a wire brush may serve the purpose.
• After the valleys are free of any residue that would restrict the flow of lubricant, they should be dressed.
• If there is a large salt deposit in the valleys of the wires, a fresh water wash forced air dry procedure should be used.

Cleaning systems are available to remove old lubricant and grit while the rope is in use.  Most scrape the rope clean as it passes through the system.

Lubricating can be done many ways, including wiping and spraying but a lubricating system is usually preferred.  A good lubricating system re-dresses the rope uniformly with less lubricant waste.  With pressure, it forces the lubricant into the core, where it is needed most.  And the higher the pressure, the deeper the lubricant penetrates, especially if the strand is under tension.  Like a cleaning system, it can also be used while the rope is in use, cutting down time dramatically.

Imperfect pitch
Concern about lubricating wire ropes began only in fairly recent history, according to Al Lucht.  As Chief Wire Rope Engineer of American Steel and Wire (U.S. Steel) in 1963, he first became aware of extensive problems with wire rope corrosion and oxidation.  Back then, lubricants applied while manufacturing wire rope were basically asphaltic.
 "AS&W had extensive files which dated back to the late 1800's.  In a random perusal one day, I read a report dated around 1913.  Wire ropes were used extensively with sailing vessels (windjammers) used to carry freight across the oceans.  At that time, AS&W had a wire rope mill in Worcester, Massachusetts where it was the practice not to coat wire ropes.  They were furnished dry without any lubrication.  Naturally, these ropes, when used on sailing vessels traveling the salt water seas, corroded rapidly."

The report stated that hemp ropes, which were coated with pitch, lasted much longer, AS&W began coating their wire ropes with pitch obtained from Jamaica.  Life of the wire ropes remarkably improved.

Years later, the pitch was replaced by asphalt, which was a bi-product of oil refining.  Asphalt, the dregs of the refining process, didn't resist corrosion well, was a poor lubricant, and differed from shipment to shipment--but it was cheap.

"When I entered the scene," Al Lucht says, "[research and development] was mixing different types of lubricants such as petrolatum (petroleum jelly) and asphaltic and adding anti- oxidants, etc., to try to improve various characteristics."  But there was a problem in that the mix varied with the person mixing.

"To help resolve our problems, our Monroeville, Pennsylvania Research Laboratory developed a specification for a petrolatum-based general purpose lubricant which was then used for 90% of our products.  It was very successful.  Our rusting and corrosion problems and oxidation problems disappeared as if by magic."

Various compounds were added to the mixture, including corrosion inhibitors, anti- oxidants, water displacing additives and compounds designed to withstand very high pressures.

Lubricants for the ‘90's
In recent years, the spotlight has turned to environmental issues.  In marine use particularly, regulations require that the lubricant does not leave a sheen on the water surface.  Also, disposal of lubricant containers, and even the lubricated wire rope itself, is now an environmental consideration.
 "The use of additives is like going to the drug store and taking pills to counteract whatever ailment you have or do not want to get," Al Lucht says. "This era has seen a big change in the quality of lubricants used for wire rope.  The lubricants cost more but they are good and present a savings in wire rope use."
 

1. Roebling Wire Rope Handbook, The Colorado Fuel and Iron Corporation, 1966.
2. Provided by Allied-Kelite, A Witco Company.
3. Handbook of Oceanographic Winch, Wire and Cable Technology, Second Edition, Alan H. Driscoll, ed. 1989.
4. "Making Wire Rope Last Longer," by K. L. Barden and F.J. Klaus, Coal Age, March 1972.
5. "Evaluation of Lubricants to Increase Wire Rope Life," by Jack E. Fraley and Grant L. Anderson, Spokane Research Center, Bureau of Mines, U.S. Department of the Interior, Spokane, Washington.

Robert Kirkpatrick, President of The Kirkpatrick Group, Inc., Texas, which designs and sells lubrication systems.

Wilbert A. (Al) Lucht, President of Wire Rope and Metallurgical Engineering Services, California; and retired Chief Wire Rope Engineer of American Steel and Wire (U.S. Steel).

William McAlaine, V.P. and Business Manager of Allied Kelite, A Witco Company; and formerly General Manager of The Hodson Corporation, specializing in formulating and marketing wire rope lubricants.