A yawning abyss of murky water, jagged cliffs, fast-flowing currents, a quaking sea bed, and a host of bizarre creatures –Ralf Egerer should be terrified by what might happen to the optical fibers that his machines are designed to protect! The ocean depths are a hostile environment, exerting a pressure in every pore equivalent to a needle weighing several tons. And the only thing that shields Egerer’s cable cores from those tremendous forces is a thin sheathing of copper or aluminum, held together by a continuous weld seam that stretches for kilometers.
“Everything depends on that seam,” says Egerer, sitting under a sun umbrella at a café in Hanover. Putting down his espresso, he cradles his left index finger in his right hand and explains the construction of the submarine cables that form the backbone of international communication. At the heart of the cable are the optical fibers that form the cable core. This is surrounded by a number of different layers, each of which has a specific function.
These functions include reducing signal losses, holding the optical fibers firmly in place, and ensuring the cable remains flexible. The outermost layer of the cable is made of thick rubber. This helps protect the cable against the water, although its primary purpose is to provide mechanical protection against abrasion and tearing.
Completely watertight for 80 years
Rubber is too porous to stay watertight when the average pressure of the surrounding water is between 300 and 400 bar. It takes just a few months for the far smaller water molecules to make their way through the rubber shell. “That’s no good because we need those cables to keep working perfectly for between 40 and 80 years.”
That’s why the real barrier against the ocean is to be found between the outer layer and the cable core: an endless tube made of copper or aluminum that cable manufacturers wrap tightly around the core and weld together. The metal atoms form a tightly packed lattice to keep the water molecules at bay. But the potential weak spot is the weld seam. If its thickness varies, if there are any pores or inclusions, then it will eventually fail. “If that happens, the water destroys the cable core completely. It can’t be repaired,” says Egerer.
The search for a low-maintenance process
Taking another sip of his espresso, Egerer tears open the little package of cookies on his saucer. The packet is actually thicker than the metal sheathing used in the undersea cables that his employer – the French cable maker Nexans – manufactures and lays across the world’s oceans.
Once the parameters have been set correctly, the tube welding machine can run for days on its own without having to constantly readjust them. Ralf Egerer
Ralf Egerer is the director of machine & cryogenic systems at Nexans Germany. He supervises the development of machines that apply protective sheathing to the cores of submarine cables, not only at Nexans, but also at other companies. And he explains how the Nexans machines recently made the switch from electrode welding to laser welding.
“Right now, the longest cables offering optimum signal transmission can be as long as 100 kilometers – and that means you need a weld seam the same length. Traditional methods of electrode welding can achieve that, but it requires a lot of supervision and maintenance,” Egerer explains, leaning back. “We thought it would be great to have a system that could weld seams reliably day after day without someone having to constantly keep an eye on it. So we went looking for a new solution.”
That was when the developers at Nexans hit upon on a diode laser. Once the parameters have been set correctly, a diode laser can, in principle, carry out welding for days without requiring any adjustments.
A diode laser gets the balance right
“If we were just dealing with copper, then we would choose the green light of a disk laser, which offers the best efficiency at that wavelength. But right from the start we knew that we wanted to be able to switch between copper and aluminum as necessary. The diode laser gets the perfect balance if you’re looking to weld both those metals,” says Egerer. “Depending on the material and the process we can achieve a solid 30 percent efficiency rate even in the worst-case scenario. And in the best case we get 80 percent efficiency.”
Egerer’s eyes light up when he mentions his machine, which pits a thin seam against the weight of the ocean depths, and he enthusiastically explains how it works. First, the Uniwema tube welding system unwinds aluminum or copper strips from a spool.
Next, the cable core and the metal strip are fed into the machine where high-precision tube forming rollers shape the flat metal strip into a perfect tube that now encapsulates the cable core, leaving a thin gap at the top. The shaping process is so accurate that the system can mechanically fix the gap in exactly the right place ready for welding.
The metal tube passes beneath the laser beam, which welds the seam together from above. At the same time, the system blows shielding gas around the cable core to protect it from any exposure to heat. Finally the machine shrinks the sheathing until it sits snugly around the cable core.
The energy applied by the diode laser can be metered so precisely that we can achieve pipe wall thicknesses of just 0.10 millimeters. Ralf Egerer
A laser that uses less shielding gas
Compared to conventional electrode welding methods, this laser process uses up to 90 percent less helium or argon as a shielding gas, because the gas can be applied directly to the welding point and is not required to shield electrodes or the significantly wider TIG seam. “Many of our customers see that as a key point in this system’s favor based on today’s high gas prices.”
Nexans also offers its Uniwema machines without a cable core feed, catering to customers who simply wish to produce empty tubeswith a diameter of between five and 200 millimeters, such as heating pipes.
Precise energy input enables thinner tube walls
Welding, brazing or heat conduction welding: The beam quality and laser power of the TruDiode offers the best and most reproducible application results – at low investment and low operating costs. Automotive, supplier, and tubes and profiles are typical industries for this laser.
Ralf Egerer takes a sip of water and then spreads his hands emphatically. “It’s already a pretty amazing system as it stands, but the diode laser makes it even better. Now, we can make the tube walls even thinner.”
The diode laser makes it possible to meter the energy input with sufficient precision to produce tubes from aluminum and copper strips with a wall thickness of just 0.1 millimeters. “Technical limitations meant that cables typically used to be at least 0.2 millimeters thick – for example the telecommunication cables for terrestrial signal transmission in mobile telephony. So with the Uniwema you’re using some 50 percent less material”, Egerer says, “and that means major savings for each kilometer of tubing.”
Ralf Egerer has reached the end of his break. He pays the check, shakes hands and heads back to the Nexans building. Those submarine cables may be exposed to the most punishing conditions imaginable – but still, you get the feeling they are in safe hands.
Nexans Deutschland GmbH
phone: + 49 (0) 511 676 – 3349