Roped together

Ropes have been made of steel wire ever since 1831 when a mining engineer by the name of Wilhelm Albert, in the Harz Mountains in Germany, twisted four wires into a strand then twisted three of his strands around each other to make the first wire rope. Until then lifting ropes had been made of natural fibre such as hemp; or when those were inadequate – as they frequently were – chains were used instead. Chains at the time were brittle and inclined to snap suddenly, even when not overloaded. It was that same Wilhelm Albert who discovered the cause of this: he built a test rig which subjected chains to repeated small loadings and discovered a phenomenon he called metal fatigue.

The lifting industry clearly owes him a lot, and it is not remotely unfair that the wire ropes that he replaced his mining chains with were for many years called ‘Albert ropes’. They were clearly so much better that they gained almost immediate acceptance in the ever-deeper mining enterprises that were springing up worldwide. Today they are almost universal in the lifting industry.

Good as they are wire ropes are not perfect. They are heavy. They are vulnerable to corrosion and strand breakages – including in the inside strands which visual inspection cannot see.

Incorrect matching of groove width to rope diameter can lead to ‘birdcaging’ in which the rope appears to unravel; and they need lubrication, which is time consuming and labour intensive and, particularly in marine environments, potentially polluting.

Now we have ropes of synthetic fibres. The big advantage of synthetics is their low weight. It lies somewhere between one-fifth and one-tenth of that of steel. On a long lift – as in deep-shaft mining, and sub-sea operations – the self-weight of steel rope can become a major issue. Weight is also important in handling. A single rigger can carry a fibre sling on his shoulder; the same fitting in wire rope would need a fork-lift or crane. And fibre is much less abrasive, and more pleasant, to handle – and much less fatiguing, and therefore much less dangerous.

Add that they are more flexible, can take tighter bends and therefore smaller pulleys, and what is not to like about replacing a steel rope with a synthetic one?

There are still issues. Fibres can fray when they rub on sharp edges in a way that steel rope does not. So where synthetic rope meets, for example, the corner of a load protective sleeves must be fitted.

Wireco is one of the world’s largest rope producers; it has both wire and synthetic ropes in its portfolio and brands such as Casar and Lankhorst. Andreas Schmeiss is the company vice president. He points out some of the pros and cons.

“Synthetic is still considerably more expensive than wire,” he says, “sometimes by a factor of three or four. It does not corrode but it can degrade particularly under ultraviolet light which is a component of sunlight. High temperatures can also cause a condition known as ‘creep’ in which a rope becomes pliable and stretches to a point beyond its original length.”

Schmeiss believes that the best choice of rope will continue to depend on the application and that “there will remain a place for both types for some time yet”.

TURNING POINT?

Nevertheless synthetic fibre ropes offer such advantages over conventional wire ropes that we may now be at a changeover point similar to that of 1831: synthetics may supplant wire as the default choice in exactly the way that wire supplanted chain and hemp.

The advantages of synthetic fibre are scalable: both smallcapacity lifting machines and some of the largest can benefit from the switch to synthetic. At the lighter end of the scale French company Verlinde makes the overhead hoists more usually covered in our sister magazine Hoist; but this month (January 2023) it announced a new range of hoists specifically designed for synthetic rope and the timing and relevance is too good to ignore.

Its Eurobloc VF range handles loads up to 20,000kg and the rope they use is Dyneema, a polyethylene fibre up to 15 times stronger than steel and 85% lighter. It has high energy absorption capacity – so it effectively cushions a load on pick-up, very low elongation, and is extremely resistant to abrasion, humidity, UV rays and chemicals. It also offers a wide operating temperature range, from -10°C to +40°C.

The ropes are available in diameters of 7mm, 8.5mm and 12mm, with a 12-strand antirotation weave. And the rope has a longer service life than steel.

At the high-capacity end, MacGregor has a new 150t maritime crane, which we describe further down. And, in between, several manufacturers have recently announced cranes specifically designed to be used with synthetic rope.

Liebherr is an example. It has two new synthetic-rope cranes. At Bauma in October (2022) it announced what it says is the first luffing jib crane specifically designed around high-tensile fibre rope. Its 258 HC-L 10/18 Fibre luffing jib crane achieves hook heights comparable to its 230 HC-L 8/16 steel rope model but has greater load capacity. The wire rope model manages up to 1,900kg at the jib head; its synthetic-rope sister gives 2,500kg, which is 43 percent more. Maximum lifting capacity goes up as well, by 25%, to 10 tonnes in one-line operation; that, says Liebherr, meets today’s market demands for this size class.

The increased performance of this crane, says Liebherr, is largely due to the rope fibre being significantly lighter than steel of comparable diameter meaning that a similar crane design is able to offer greater load capacities and a faster working speed.

“When using our Fibre cranes the greater the hook height is the more substantial the possible increases in load capacity are,” says Markus Kinateder, product manager, Liebherr-Werk Biberach. “Reduced wear on sheaves, pulleys and materials and exceptional durability contribute to the machine’s long service life and, therefore, its cost-efficiency”.

Liebherr has been ten years developing the synthetic rope it is using. It has been working with the rope manufacturer Teufelberger and it claims it as ground-breaking technology.

As well as higher crane performance Liebherr echos the other advantages we described above: the fibre rope is more durable, easier to handle when reeving due to its lighter weight, and maintenance is less complicated as lubrication is not required.

Operational safety is also increased: Liebherr’s rope has a cover layer, with a red layer just below it. When the red layer shows through the operator is able to see it at a glance and knows that the rope has reached the end of its service life and should be replaced. The 258 HC-L 10/18 Fibre luffer is now available for order worldwide.

Liebherr’s second offering is also a tower crane, but a hightop – what other manufacturers call a flat-head. The 1188 EC-H 40 Fibre is Liebherr’s most powerful standard crane and is an upward expansion of its portfolio. It is intended for heavy-lift tasks: its jib head load capacity is up to 13,100kg at 80-metre radius and maximum load capacity is 40t. Bridge, power station and plant construction are applications suggested by Liebherr; such projects often involve prefabricated parts weighing several tonnes that need to be moved and positioned with millimetre precision. The crane has smart assistance systems for handling such lifts.

Again, the use of synthetic rope has increased capacity: the Fibre model surpasses the already powerful 1000 EC-H steel rope crane by up to 2.1 tonnes in jib head load.

The maximum reach is long as well, at 90 metres; freestanding hook heights of up to 81.3 metres can be achieved in a cost-effective way in combination with Liebherr’s 24 HC 1000 tower system.

“The 1188 EC-H 40 is our first high-top crane with fibre rope technology,” says Kinateder. “We’ve increased the performance capacity of our EC-H series even further with this crane and can now offer our customers even greater support for the implementation of large and custom projects.”

Fellow tower crane maker Wolffkran is not being left behind in the transition from steel. It also presented its latest offering at Bauma 2022. Its work has been with rope specialist Trowis, of Chemnitz, eastern Germany.

MODIFICATION-FREE

As well as all the positives of synthetics already outlined its ChaRope fibre rope has another advantage that Wolffkran says will be decisive: it can be substituted for a steel rope 1:1 without any modification of the crane. The ‘cha’ stands for ‘change’.

The reason for the 1:1 substitution is that the Trowis rope has a cover of a special composite design that gives it the same diameter as the steel rope that it replaces. “ChaRope is thus significantly thinner than comparable products from competitors,” says Thomas Heidrich, CTO and member of Group Management Board at Wolffkran.

“The rope design is a multilayered, twisted core made of high-tensile high-tech fibres and an abrasion-resistant, thin-walled fibre composite cover,” says Dr. Thorsten Heinze, managing director of Trowis. “Thanks to this structure, we can offer 12 and 16mm diameter crane ropes at market entry.

“All Wolff cranes with 12 or 16mm steel wire rope can be equipped with the new ChaRope fibre rope,” adds Heidrich. “The ropes are fully compatible with the crane series, and no adjustments to the rope sheaves, hoisting gear, or load capacities have to be made. In our current portfolio this applies to all models in the Wolff Clear series, the new Wolff 21 FX cranes and the Wolff 8033.16 Cross.”

As well as the small diameter the fibre-composite design of the rope cover claims another advantage over conventional, braided, covers: it is monolithic – that is, it is seamlessly impermeable. As a result, moisture can't penetrate through to the inside of the rope, nor can lubricants or fibre abrasions leak through to the outside.

“The rope does not run dry, even after many years, and the environment is not polluted with microscopic plastic,” says Peter Streubel, managing director of Trowis. The rope cover also gives 100% UV protection for the interior core and serves as an indicator of when the rope needs to be discarded. The rope must be replaced if it shows damage such as material degradation, cracks, or twists.

The ChaRope fibre rope is roughly 80 percent lighter than its steel equivalent, a large saving in weight that translates to benefits in lifting power and reduced wear on sheaves. “Rope sheaves hardly experience wear,” says Heidrich. “It has a lifespan claimed to be at least four times greater than a conventional steel wire rope.”

The ChaRope made its first appearance on the new Wolff 6021 FX at Bauma in October. It has been undergoing extensive testing on a spooling test bench and is due to undergo field testing in Wolffkran’s UK rental fleet.

“The test phase will be completed in June 2023 and the rope will be available on the market in August 2023,” explains Heidrich. “As of that time, we will supply all Wolff models with 12 or 16mm rope optionally with the steel or fibre version. We will also successively fit cranes in our rental fleet with the new fibre rope. In the medium term, we plan to develop further ropes with other typical diameters with Trowis, to offer the entire Wolff crane range with the innovative rope.”

NEUTRAL BUOYANCY

Sub-sea lifts in the offshore industry can vary from deep to very deep indeed; and here synthetics have an added, gamechanging, advantage. On a deep lift the weight of a steel rope fully paid out becomes not just significant but very significant, possibly greater than the load itself. The weight of the wire steadily robs the crane of its lifting capacity as more wire is paid out.

Synthetic rope can be made either to float or, preferably, with neutral buoyancy so that it neither floats nor sinks. No matter how much of it is paid out the weight of the rope is exactly balanced by the upthrust from the water so there is no loss at all of lifting capacity with increasing depth.

Offshore equipment manufacturer MacGregor, part of Cargotec, has therefore produced a dedicated fibre-rope offshore crane, called FibreTrac, using neutral-buoyancy rope. It allows operators to use the full lifting capacity of the crane at practically any depth; this means that a smaller crane and vessel can be used for more assignments and owners are able to bid on a wider range of contracts.

At the end of last year (2022) it delivered just such a crane to marine transporter Otto Candies. It is a 150t active heave compensated FibreTrac offshore crane, the first of its type, and the supply contract includes full delivery of the crane together with Lankhorst Lanko Deep Dyneema DM20 fibre rope for 3400m operational depth.

Due to the rope’s neutrally buoyancy it allows full payload at all depths. The crane itself is highly innovative. The FibreTrac concept was developed in close collaboration with Parkburn Precision Handling Systems, who will deliver the fibre rope Deepwater Capstan that detensions the rope between the hightension operational side and the low-tension storage side. Parkburn also developed the crane’s Lift Line management system which manages rope health monitoring and feedback using a combination of sensing technologies and a lifetime usage algorithm developed by the maker of Dyneema, based on its DM20 material.

The crane will have the world’s first DNV-DRS class notation based on the DNV-ST-E407 standard. This new standard governs how such a crane and its fibre rope system can remain continually certified based on real-time measurements of rope health; it represents a significant departure from earlier certifications based on prescriptive rules and periodic inspections. It means, says MacGregor, that owners and operators can now have an up-to-date health status of every portion of the lift-line and use it confidently and to its fullest potential, instead of guessing based on work hours since the last inspection and cutting back or replacing it.

Steel ropes reigned supreme for close on two hundred years. If synthetic fibres are the new steel, any guesses as to whether they will still be around in 2223?

SYNTHETIC ROPES UNRAVEL SECRETS OF THE UNIVERSE

Neutrinos are the most elusive and pervasive of the known elementary particles. Originating from sources far distant in space such as supernovae or colliding stars they travel with high energy at or near the speed of light and, lacking electrical charge, they interact only weakly with other matter. The vast majority of neutrinos reaching Earth pass straight though it leaving no trace. Instruments to detect them are placed at the bottom of mines or deep underwater so that the neutrinos will encounter a lot of dense matter before reaching them, increasing the chances of a detectable collision which releases a faint flash of light.

The KM3NeT or Cubic Kilometre Neutrino Telescope is situated at a depth of 3500m in the Mediterranean Sea about 80 km from Sicily. It is an array of more than 200 detection units. Each one is 700m tall and must be moored in place accurately and without allowing movement. They are secured by synthetic ‘LankoScience’ ropes made by Lankhorst in Portugal.

Fernando Eblagon, R&D manager, explains: “The combined requirements of deep sea mooring and the KM3NeT telescope meant that the rope needed to achieve the necessary minimum breaking load whilst meeting the diameter specifi ed to work with the clamping system. The mooring systems must also guarantee a very accurate positioning for each sensor; hence a high stiffness and minimum construction elongation was specified. A robust HDPE braided core provides the right diameter for the clamping system while a Dyneema DM20 jacket bears the load and provides the stiffness needed for the precise positioning of the sensor array. To minimise deformation during installation and service, the rope was thermal stabilised under tension and a protective coating applied. As Lankhorst’s signature yellow could cause a refl ection affecting the sensors, the protective coating also contained a black pigment.”

“Although particle physics isn’t an everyday application for Lankhorst, we welcome the challenge. Hopefully our ropes can contribute in a small way to our understanding of astrophysical phenomena,” said Elles Munstra of Lankhorst Ropes.