Ropes have been used for lifting and moving loads for many centuries. Even during the construction of the Egyptian pyramids, strong ropes were used to transport stone blocks. Since then, several thousand years have passed, not only the lifting mechanisms have changed, but also the ropes themselves. At first, ropes were woven from fibers of plant or animal origin, but now steel ropes are usually used in construction cranes. However, in the West, a number of companies are conducting research on the creation of fiber ropes for cranes, and they have achieved some success.
The rope is called the "heart of the tower crane". The development of synthetic fiber ropes around the world is mainly in the cargo rope sector, and mainly for ship and mooring cranes, because steel ropes suffer greatly from corrosion under the influence of sea water, in addition, lighter fiber ropes can increase the load capacity of ship cranes, for which their own weight is especially critical.
Only a few companies in the world have produced fiber ropes for cranes, and for construction tower cranes has developed a new type of synthetic fiber rope with high tensile strength, only one company – manufacturer of lifting equipment-Liebherr in cooperation with the Austrian rope manufacturer Teufelberger. We can say that Liebherr tower cranes have received a "synthetic heart".
At the Bauma exhibition in March 2019 in Munich, Liebherr presented new models of headless tower cranes of the EC-B series, some of which are equipped with synthetic fiber ropes.
Advantages of Liebherr fiber ropes
First of all, we will answer the question: why do you need to replace a steel rope with a fiber one in a tower crane?
The Liebherr rope made of reinforced synthetic fibers weighs five times less than its steel counterpart and has high tensile and tear strength. Due to the use of a lighter and stronger fiber rope and hook suspension, the crane's load capacity increases significantly throughout the working diagram (from 8%, but the maximum load capacity does not increase! The increase occurs near the end of the boom), and at the maximum reach of the boom increases by up to 20% compared to cranes with steel ropes. Also, there is no loss of load capacity due to the weight of the rope at high altitude. The productivity of the crane increases accordingly.
A special shell and coating protects fiber ropes from the negative effects of climate, pollution and various chemicals, increasing their service life. The core of the Liebherr fiber rope is made of non-corroding synthetic fibers and has a design that prevents water penetration. This eliminates the possibility of corrosion inside the rope, which is usually very difficult to detect. The stocking scheme of a new fiber rope is similar to that of a steel rope. However, in situations where the lower layers of the rope are subjected to less tensile stress than the upper ones, the new fiber rope is able to withstand higher stresses than steel. Liebherr fiber rope has high wear resistance and fatigue strength, able to withstand a lot of cuts and breaks the fibers, while maintaining their performance, as well as assists in 13 times more cycles of bending, and due to this (and other factors), according to test results, the service life of synthetic rope (with proper use) is 4 times longer than similar steel, or about 10 years. This means that the rope on the tower crane will have to be replaced 4 times less often with the corresponding savings in money and working time.
Thanks to the properties of the material from which it is made and its unique design, the Liebherr fiber rope provides a higher level of safety compared to steel rope. The rope sheath does not perform a protective function, but a function of indicating wear. It consists of fibers that wear out at different speeds. Due to this, as the rope wears out, its shell becomes more and more saturated red color, clearly visible from a distance and clearly indicating the need for replacement. 40% wear – clearly visible wear of the upper indicator fibers of the rope sheath. 60% wear – in addition to the colored indicator fibers, the gray and white protective fibers begin to wear out. Wear of about 90% – all the shell fibers have signs of wear. On some sections of the rope, at most two adjacent strands, the core is exposed. It is necessary to start preparing for the replacement of the rope. Wear of about 95% – all the shell fibers have obvious signs of wear. In some areas (the rope), a maximum of three adjacent strands have a core visible. The rope must be replaced. The wear rate is about 100% – on large sections of the rope, its core is clearly visible, not protected by anything. This rope cannot be used.
Since both the core and the rope sheath are made of synthetic fibers, workers will not be able to injure themselves with wires sticking out of the rope.
It is much easier to work with fiber rope for specialists who service cranes. Light and elastic fiber rope is much easier to replace, such work can be performed without the use of special equipment, with fewer people, faster and safer. It is also much easier to assemble the crane after transportation to a new location. This means significant savings in maintenance costs and time. Synthetic fibers, which suites the ropes, no need lubrication, so the details of the crane in contact with the rope bridges on the crane with fibre rope are not slippery from grease, dirty hands and clothing of service personnel and maintenance costs decreased. And the rope itself will have to be cleaned much less.
The fiber rope is wound evenly on the winch drum, like a steel rope. In the process of operation, steel ropes damage the pulleys and blocks on the crane, fiber rope is softer, friction is much less, and therefore it does not damage the pulleys and blocks, and they do not need to be replaced with appropriate savings of money and working time.
Bench tests of Liebherr ropes
The development of the Liebherr fiber rope lasted for many years. During the development process, 87,000 hours of testing were performed on more than 100 different prototypes of the new rope, with a total length of about 85,000 m. Initially, the samples were tested on a conventional stand for testing ropes for endurance by bending at 90° and extending. Then a special test stand with a lifting height of 42 m was developed. It allowed testing ropes up to 31 mm thick with a load of up to 45 t on the drum for multi-layer coiling of the rope. Liebherr also built a climate chamber in which prototype ropes were exposed to a variety of climatic factors and temperatures from + 80 to -25 °C. Sand and dust were added to the air to artificially recreate operating conditions in a dusty atmosphere. As a result, a synthetic fiber was created, whose characteristics correspond to the difficult working conditions on modern construction sites.
Operational testing of Liebherr ropes
After bench laboratory tests, a number of tests of prototypes of the new rope were carried out in real operation. Ropes made of artificial synthetic fiber of various diameters with a total length of 2035 m were used on 15 construction sites on 11 tower cranes operating in five European countries. Operational tests began in 2016, lasted a total of 318 weeks, and have now been completed.
According to representatives of Liebherr, the test results showed that the critical length (the length at which the suspended rope breaks only under its own weight) of the new fiber rope is 4 times larger than that of a conventional steel one, and it is much easier to work with. Experts emphasize that the advantages of a lighter fiber rope are particularly evident during the Assembly and disassembly of cranes, since the fiber rope can be installed and refueled manually, without the use of auxiliary filling winches. Installing the rope in the hook blocks is also faster and easier.
Maintenance of Liebherr fiber ropes
Liebherr has an after-sales service Department for tower cranes, Tower Crane Customer Service, which offers customers service contracts for the maintenance of cranes with fiber ropes.the service package also includes a number of services for the maintenance of fiber ropes.
It should be noted that Liebherr fiber ropes can only appear on the Russian market as part of new tower cranes
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