As the wire is drawn, the material is strain-hardened and the material loses its ductility. Thus, prior to final wire drawing, the intermediate wire is soft-annealed to improve the wire’s ductility to minimize breaks during the final wire drawing processes.
Annealing is the heat treatment process for increasing the metal’s ductility and reducing its hardness. At IWM, both annealing ovens and furnaces are utilized to stabilize, partially anneal, and fully (soft) anneal our wire. The annealing process requires precision control of temperature (heat & cooling), time, and atmosphere to ensure the desired mechanical properties of the wire. IWM process quality control and monitoring ensures consistent annealing processes to eliminate issues found during the annealing process such as microstructural inclusions, decarburization, and carbon sooting.
Tempering is the heat treatment process to increase the metal’s hardness, which is performed by heating the metal just below its recrystallization value and sustaining it at that temperature for a duration of time. For harder materials, this relieves internal stresses providing improved ductility. This process is common for wire springs and other tensioned products.
Galvanizing is the process of applying zinc to a ferrous metal to inhibit surface corrosion. For wire, this is performed either via Hot Dipped Galvanizing (HDG) or via Electroplating. The HDG processing of wire can be performed via a batch process (vat dipped) or via a continuous process. For both the batch or continuous processes the wire is cleaned, then processed to remove any surface oxidation (pickling, fluxing), and then submerged into heated molten zinc where through a diffusion process the zinc reacts with the iron to form a protective coating of the wire. The coating thickness of wire through the HDG process can be as much as 300g/m². Galvanizing through electroplating is performed through electro-deposition process where the wire, which acts as a cathode, attracts the zinc (anode) which is ionized through a zinc sulfate solution. Electro-plating can deposit as much as 915g/m² and can be drawn or reduced up to 95% of its origin area while maintaining adequate coating for surface corrosion for intermediate and fine wire size diameters.
Copper Coating
IWM typically copper coats its low carbon steel wire where the copper acts as both a surface lubricant for the fine wire drawing process as well as a corrosion inhibitor and/or conductor for the fine wire’s use or application. Copper coating can be applied through a chemical coating (immersion coating) of the wire through an acidic copper solution after the wire has been properly cleaned and surface treated (pickled).
