A copper wire has always a residual oxide film at ambient temperature. This is derived during the hot rod rolling stage in making the material, caused by the hot and continuous-cast bar. Depending on the required characteristics of the finished product, say a copper mesh or a plain wire, the thickness of such residual surface oxide film is being measured through a coulometric reduction testing. This process becomes a standard practice since the oxide film can cause undesirable effects in processing copper. It can result to inadequate solderability of the material, defects during the drawing process, and eventually poor adhesion between the bare copper and the enamel coating.
The major defects in copper rods are usually caused by the continuous casting and rolling process. These range from formation of oxide particles into the rod surface, slag and copper oxide inclusions, insufficient removal of the scale, slivers, hot-cracks, and so on. When it comes to the specific copper products, the most critical ones to make considering those defects are the fine magnet wire and shaped wire. Manufacturing copper mesh or just a plain copper wire can also be quite challenging to do if such defects are present.
Thanks to the modern technological advancements that prevent the root cause of surface damages, such as misalignment of the moving wire within the drawing machine. Modern processes are now geared toward avoiding production errors, improving the desirable qualities of copper products with numerous benefits and applications.