A fine wire drawing machine with drawing cones, which was state of the art in the 1950s.

Photo: Leoni Draht

Modern tin plating with annual capacity for more than 3,500 tons.

Rolling mill in the 1960s for making wire rod from wire bars.

Milestones were continuous annealing, electroplating, continuous casting and multi-wire drawing.

Via simplification to specialisation

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The end of the Second World War saw the first decisive revolution in copper wire drawing involving conductive, continuous annealing. The novelty involved the installation of electric anneals for fine drawing after the conventional cone machines. This did away with the stationary annealing process in a furnace, which previously ran separately. The shortened process chain thereby involved approximately 15 percent less throughput time.
At this time, Leoni employed fewer than 1,000 people in the Nuremberg region and processed about 4,000 tons of copper per year.

Copper conductors have always been coated with tin or silver to improve solderability and the high-frequency behaviour of signal cables. In the past, this was done with the help of molten baths such as hot-dip tinning. In the nineteen sixties, the newly developed continuous coating in an electroplating process then began to prevail. This involved the wires and strands to be coated being dipped, for example, in a tin electrolyte so that a fine tin coating would deposit itself on their surface as soon as electric voltage was applied. This process from then on made it possible, in contrast to the conventional smelting method, to apply more even and also very much thinner coatings in the region of a few My (µm) – which meant more precision and simultaneously less consumption of material.
Nearly 1,800 employees at the Leoni plants in Mühlhof and Roth, northern Bavaria, made about 6,500 tons of copper wire products annually at the time. The product range encompassed enamelled wires, insulated cables, bare wires and strands as well as, for the first time, assembled cables and still the classic Lyonese wares.

Companies processing copper wire experienced a quantum leap in the nineteen seventies with the invention of wire rod, which was made using either the Southwire, Contirod or Properzi processes. The conventional wire bars weighing 90kg, which, having been preheated, had to be elaborately reshaped in a cold rolling mill into more or less round drawing stock and, prior to further processing, first had to be stained and welded apart in their dozens, were soon a thing of the past. The new, large wire rod coils with a better surface quality and fewer inclusions facilitated further speeding up of the drawing process with fewer wire ruptures – and therefore substantially improved fine-drawing ability.
Whereas, in 1950, it was still a proud achievement to be producing 4,000 tons of drawing stock per year in one cold rolling mill, the new machines raised output many times over. Present-day, high-performance wire rod plants produce up to sixty times more, with the coils consisting of about 13.4 kilometres of drawing stock with an 8 mm diameter and a total weight of six tons.
At the beginning of the 1970s the amount of copper processed at Leoni rose to about 8,000 tons a year.

Together with the improved input material there was also a radical change in subsequent processing – especially in fine wire production. Whereas it was previously normal to draw a single wire per machine, multi-wire technology made it possible at the beginning of the 1980s to draw up to eight wires at a time. The new machines took over around the world because simultaneous drawing, annealing and coiling of several wires had major advantages: not only was the space required for fine drawing reduced by about one third – there was also a drop by up to 85 percent in the subsequent stranding process of the labour-intensive set-up times.
LEONI decided in this period to abandon enamelled wire production because of the worldwide overcapacity. Our qualified staff was instead to be deployed in expanding the more promising wire and strand production, especially so for data cables. Leoni consequently set up further wire drawing capacity involving multi-wire drawing machines. The number of our employees globally in 1980 remained at about 1,800.

The realignment to production of small, surface-refined strands for the booming datacoms sector was to prove worthwhile in the final decade of the past millennium. Along with growth in the automotive cables sector, this focus was one of the most significant success factors for Leoni in this period. By way of both organic growth and targeted acquisitions, the Company increased its copper processing many times over between 1990 and 2000. The number of employees rose from 4,800 to 15,800.

In the new millennium, Leoni engaged in optimising multi-wire drawing technology and deployed state-of-the-art machinery on three continents, setting the highest requirements in terms of productivity and quality. The biggest lines can manage 56 wires at the same time. Leoni now processes more than 100,000 tons of copper annually in wire drawing. Group-wide, the workforce comprises about 50,000 people, of whom the majority work in the labour-intensive production of assembled wiring systems for the automotive industry.
700 staff in our Business Group Conductors & Copper Solutions are engaged in developing and producing increasingly customer-specific wire solutions – all of them copper-based conductors for transmitting electric currents and signals. In addition to the Group’s own cable production, the wires and strands are destined for outside customers such as cable plants, carbon brush manufacturers and solar panel producers. Off-the-shelf products are meanwhile becoming rarer – specialisation is the key to success.
Some examples: In order, for instance, to banish the harmful cadmium from conductor materials our developers came up with Leoni Histral®; for marine applications we launched a longitudinally waterproof strand and to save weight in motor vehicles we developed signal cables made of low-alloy copper materials. Cable manufacturers who use extremely high-grade insulation materials are increasingly investing in smooth-bunch strands to save on materials with thin-walled jacketing. For the renewable energy market Leoni’s wire segment offers lightning protection solutions for the blades of wind turbines as well as flat wires for connecting the silicon wafers in solar panels.

From a production-technology perspective, today’s challenges involve more frugal and efficient use of resources. Wire drawing nowadays uses only about 10 percent of the energy for the actual working operations. Overcoming friction and discharging the frictional heat devours the lion’s share.
In terms of product technology, the trends include electromobility, the area of renewable energy and medical equipment. New application possibilities will entail new requirements and will ensure that the copper industry remains on the ball in the future, too.

by Dr Wolfgang Steuff, Head of Development at Leoni Draht GmbH, Weißenburg/Germany.