Wire drawing machines
From cast copper wire rod to fine wire
In last November, the NE Drahtforum (NF Wire Forum – non-ferrous wire forum) took place for the first time in Bad Sassendorf, Germany. The German Copper Institute (DKI), the copper manufacturer Aurubis, the lubricant manufacturer CARL BECHEM and Maschinenfabrik NIEHOFF organized an interdisciplinary lecture event on the production and processing of fine wires and super-fine wires made of copper.
Continuous cast rod, wire rod, drawn wire
Cornel Abratis, Aurubis AG, described the factors which have an effect on the production of cast wire rod. The selection of the copper cathodes as the starting materials already determines whether a continuous cast rod can be processed into super-fine wire or not. The chemical composition has an impact on the continuous cast rod as well as all further processes, from smelting the copper via casting and solidifying to rolling the wire.
Michael Sander from DKI explained what needs to be considered when further processing the cast wire rod. According to him, fine drawing ability is the suitability of a primary wire and/or a drawing process for producing wire below a certain diameter in a quality-appropriate manner and with sufficient process reliability. This is a demanding task, since starting material with a diameter of 8 mm has to be drawn to a final diameter of 0.50 – 0.10 mm (by fine drawing) or even 0.15 – 0.05 mm (by super-fine drawing). Simply said, the influencing factors are the primary wire, the drawing dies, the cooling lubricant and the drawing machine as well as their interaction. In addition, there is also the interlinking of drawing processes as well as upstream and downstream processes. And last but not least, the persons involved in the wire production also have a significant influence on the drawing result.
Further conference contributions dealt with wire breaks, the fatigue strength of copper wires and material-related process developments in the production of flat wire.
Drawing machines and drawing process
Wire drawing is carried out in two steps, drawing to a diameter of > 4.5 – 1.0 mm (by rod breakdown or intermediate drawing) and the subsequent drawing to a diameter of 0.15 – 0.05 mm (by super-fine wire drawing). Stephan Gorgels, Maschinenfabrik NIEHOFF, emphasized the importance of the selection of drawing machines and annealers, their settings, the graduation (wire elongation) and the production speed. Of course, attention must be paid also on the condition of the operating materials. The drawing of super-fine wire on multiwire drawing machines gets difficult from a diameter of 0.10 mm and is no longer possible from a diameter of 0.03 mm.
The various types of lines on which copper wire rod is produced create a characteristic microstructure in the wire which influences the later recrystallisation behaviour. Dr. Rainer Menge of metallurgy consultant Herborner Drahtbüro showed the possibilities to recrystallize the microstructure of a wire created during drawing by resistance annealing or inductive annealing, and also discussed the latest developments.
Operating materials
When selecting the drawing medium for copper fine wire, according to Christopher Folland of CARL BECHEM, a number of criteria must be considered. They include the final diameter to which the wire is to be drawn, a subsequent surface treatment or a further processing which requires a residual lubricating film. It is essential to note that a trouble-free wire production is only possible through a targeted maintenance and monitoring of the drawing emulsion.
Michael Biller of Balloffet described the properties of drawing dies with a PCD core or a natural diamond (ND) core, their structure and the analysis and quality monitoring of drawing dies. A sophisticated drawing die management enables a clear stock-keeping and helps to plan the production more effectively, to produce cost-efficiently, and facilitate the evaluation.
Summary
The NF Wire Forum provided insight into the current state of the art of all disciplines involved in the production of super-fine copper wire. As the development does not stop, the next NF Wire Forum event is already planned. It will take place in Hamburg, Germany, on November 8 and 9 in 2021 and will be opened with a plant tour at Aurubis AG.
More information: www.ne-drahtforum.de
