In addition to the different raw materials (From fibre to rope, part I), the type of processing and finishing also influences the properties of each rope. Background information on this can be found in the second part of our article on the making of a rope.
As it's not possible to run raw material fibres straight through a rope braiding machine, the yarns have to be prepared first. During this intermediate stage, the individual core and sheath yarns are prepared before the braiding process begins. There are different types of braiding processes that involve twisting, doubling, braiding and shrinking.
The core is the load-bearing part of the rope. It's made of very fine multifilaments that are made into core strands or core braids. We use two distinct multi-stage processes: twisting and braiding.
Twisting is the standard technique for making core yarns. It involves winding multifilaments together. Up to 135 ultra-fine nylon threads are twisted together to make a core yarn. This process is called twisting. A number of these basic core yarns are then twisted together. Depending on the construction, two, four or five other yarns are combined to make a core strand. These core strands are then combined to form the rope core. The twisting process gives the rope its dynamic elongation, i.e. the ability to act like a spring when shock loaded. The number of twists over a given length determine the mechanical elongation and strength of a rope. Static ropes have much less twist in the core than dynamic ropes, creating a rope with much less elongation. To prevent unwanted twisting and kinking in the rope, some of the core strands are twisted in one direction, while the others are twisted the opposite way. As a result, the torsional forces cancel each other out and the rope remains twist and kink free.
With braiding, up to three basic twisted core yarns are interlaced to make a braided core strand. A number of these braided core strands are then combined to produce the rope core. This gives a particularly compact structure. Ropes with braided core strands keep their shape significantly better and have greater edge resistance than ropes with twisted core strands. In addition, they are easy to splice and are very strong with stitched terminations.
The sheath protects the core from external influences, such as abrasion, UV radiation, etc. and prevents dirt from getting in. You can visually inspect a kernmantel rope by looking carefully at the sheath. If the sheath is damaged, and the inner core is visible then the rope should be retired. We use different types of sheath constructions depending on what a rope is to be used for:
During twisting, two, three, four, or five individual sheath yarns are twisted together with a pre-set tension and rotation speed. Twisting the yarns increases the surface area of the sheath, which makes it significantly more abrasion-resistant.
In this process the yarns are twisted and then additionally shrunk. This takes place in an autoclave, a kind of gigantic pressure cooker. The fibres are shrunk together using a particular combination of heat and pressure. Shrinking the sheath yarns in this way ensures that they remain pleasantly soft and easy to handle throughout the rope's lifespan. Furthermore, the sheath will not shrink, even with intensive use.
Doubling is different to twisting. The yarns are wound parallel to one another (without twisting) onto bobbins. Running the fibres in parallel, allows us to utilise them to their full length. We can achieve very high breaking strengths, depending on the technical specifications of the fibres used. The only drawback is that doubled sheaths are less robust than twisted sheaths.
This method combines the advantages of twisting and doubling. It is the most complex, high-quality and expensive technique available. First the sheath yarns are twisted, then wound parallel onto bobbins. We use this complex construction exclusively for our high-end ropes, where maximum breaking strength and abrasion resistance are required in equal measure.
Braiding is where the actual rope is produced. The sheath and the core are braided together. Braiding machines twist the sheath strands around the required number of twisted core strands or braided core strands, depending on the type of rope being produced. Bobbins with the sheath yarns dance around the core strands at high speed – rather like dancing around the maypole.
During braiding, it's important that the sheath yarn tension remains constant for the duration of the process. If it varies, then the rope will end up either stiff and inflexible or soft and spongy – and have a high degree of sheath slippage.
During the braiding process, an identification tape and tracer thread indicating the year of manufacture are woven into the rope core. The year of manufacture tracer thread is made from polyamide, and is in a particular colour. Its colour shows the year the rope was manufactured, although the same set of colours is repeated every ten years. The year of manufacture tracer thread means that this information is permanently marked for the lifespan of the rope. The identification tape is a thin strip of polypropylene. In accordance with the EN 1891 standard for static ropes, it has to display the following information:
Once a length of static rope has been braided, it's sent off to the finishing department. Here, every single metre of the rope is inspected by experts, by hand. They immediately feel if a fibre is loose, or if the rope is too rough, too smooth or not supple enough. EDELRID employees are so experienced they can detect even the slightest irregularities. Over the years, they've developed an extraordinary touch perception. This is an important additional quality control measure for our ropes as it is something machines just cannot do.
Once a batch has passed this final inspection, it's cut into the required lengths. A machine adds the middle marking and welds the sheath and core together at the rope ends.
The rope ends are given a label with the most important information about the rope:
The static rope is then coiled on drums (also known as reels) to be sold by the metre. Or they are coiled on a coiling machine and sold as finished lengths. Every finished rope drum or coiled rope is then weighed again. The specific weight of each rope is recorded and checked. If there is even a minimal deviation in weight, this is immediately detected, and the rope is withdrawn. Once the finished static rope has been packaged with a product label and the user manual, it's ready for distribution.