Steel wire ropes are mission-critical assets in mining hoists, ship repair, draglines and bulk materials handling. They run under constant tension, bending fatigue and abrasion and are often in corrosive atmospheres. When a rope fails prematurely, the cost is measured in downtime, safety risk and unplanned replacement, says zinc products advocacy organisation International Zinc Association (IZA) Africa director Simon Norton.

Material selection at the wire level is therefore a frontline engineering decision.

“Steel wire rope is quite literally the lifeline that holds operations together. Whether hauling thousands of tonnes of ore from the depths of a South African gold mine or suspending a multimillion-rand vessel on a Syncrolift ship-lifting platform, the integrity of these ropes is non-negotiable,” he adds.

IZA advises design, mining and mechanical engineers on zinc use and recommends that zinc coatings remain one of the most practical ways to extend wire rope life in aggressive service, but only when specified and maintained as part of a layered protection system.

“When wire ropes are manufactured, they can be made from Galfan coated wires or continuously galvanised wires. The zinc coating should be overcoated with a top-class wire rope grease or rope dressing,” says Norton.

He notes that the science behind zinc’s protective capability lies in electrochemistry. When moisture and oxygen meet steel, oxidation begins. Zinc halts this process in two ways; by acting as a barrier layer, physically preventing moisture and chlorides from reaching the steel, and by bonding metallurgically to the steel, ensuring fallback protection even if lubrication fails.

“By contrast, ungalvanised or ‘bright’ wire rope relies solely on grease for protection. Once grease is washed away by rain or high-pressure cleaning, corrosion can begin unseen within the rope’s internal structure.”

While zinc is vulnerable to acidic environments and high chloride concentrations, such as acidic mine water or sea spray at coastal plants, the wire rope dressing acts as the first barrier to corrosion. The zinc layer is next and only after both are depleted is bare steel exposed. This results in the zinc acting as a life extender for the rope, he adds.

Norton notes that persistent humidity and rain exposure can affect the integrity of the steel rope by washing off its grease or dressing – leaving it exposed to the elements, often leading to corrosion and turning it into brittle iron oxide.

With Galfan or galvanised wires, the zinc coating remains as a barrier even if the dressing fails. “Should the wire rope dressing be of inferior capability or get removed from the wire ropes, the zinc coating acts as a barrier to the environment.”

IZA Africa’s recommendation to engineers and specifiers is simple: to design industrial wire rope systems using Galfan or galvanised wire rope and ensure a tough, suitable wire rope dressing is applied over the zinc-coated wires and strands.

Norton adds that there is sometimes confusion around whether zinc-coated cores influence the choice of rope construction in high-friction duties and clarifies by saying that corrosion protection and mechanical construction are separate decisions.

“While zinc coated wire rope adds extra protection against corrosion, the choice of wire rope construction is tightly dictated by application.”

Lang Lay construction is one example that is highly favoured in specific, tightly controlled setups as the wires in each strand are laid in the same direction as the strands in the rope. “[The] full locked coil ropes use interlocking outer wires to create a smooth, watertight layer that shields the internal lubricant and zinc-coated core from corrosive ingress.”

Lang Lay construction is used for Koepe or friction winders in mining hoists where rope ends are securely anchored and bending fatigue resistance is paramount. It is further applied to earthmoving scrapers and draglines where the rope constantly drags through abrasive grit and haulage ropes and funiculars are under constant tension.

“Great care has to be taken to ensure that the correct rope type is ordered, and this is independent of whether the rope wires are zinc coated.”