Niehoff Technology: Flat Wire Drawing and Annealing

Efficient Production of Flat Copper Wire for Cable Shielding

The copper shielding surrounding the insulation layer is a crucial component of HV and EHV cables. It serves as a protective shield against electromagnetic radiation and is typically made of round wires. However, flat wires offer several advantages. The cross-section of flat wires can be used more effectively than that of round wires, cavities between wires would be smaller, the number of wires—and therefore the amount of material required—would be reduced, and the gaps between individual wires would be narrower, thereby increasing the shielding effect. 

However, these advantages were overshadowed by the widespread belief that flat wires could only be produced through flat rolling—a process significantly more time-consuming and, therefore, more costly than drawing round wires. 

This limitation has now been overcome through a process developed by Maschinenfabrik Niehoff in collaboration with a renowned cable manufacturer. In this process, wire rod is drawn into flat wire and annealed in a single operation. The manufacturing process can be implemented on any existing Niehoff rod breakdown (RBD) machine with appropriate modifications; in addition, a spooler equipped with a specially designed flat wire laying device is required. 

In this application, wire rod with a diameter of 8 mm is drawn and annealed on an existing MSM 88 + R 503 type RBD line in eleven drafts, nine of which pass through shaped dies, resulting in flat wire with a cross-section of 4.852 mm × 0.677 mm (= 3.192 mm²) at a production speed of 20 m/s. This flat wire meets all required specifications.

This proven process operates more efficiently than rolling techniques and enables the reliable and cost-effective production of high-quality flat copper wire for cable shielding. 

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