|Polymet utilizes both traditional methods of wire manufacturing – rolling and drawing. In both processes, alloyed rod stock as large as .500″ diameter is reduced down to as small as .020″ diameter.
Rolling is a process in which metal stock is passed through a set of mechanically driven rolls. The process is deemed hot rolling if the metal stock is above its re-crystallization temperature and cold rolling if it is below its re-crystallization temperature. During hot rolling, the metal stock remains in a ductile and workable state, allowing for a greater amount of alteration. Because of high temperatures during rolling, the cooling process typically involves surface oxidation.
Cold rolling increases the yield strength of the metal stock, producing a denser, more compact end product. Also, the hardness is increased and the surface finish is smoother compared to hot rolling. Because of the change in the crystalline structure of the metal, ductility is affected and the metal stock must be annealed (heated) every so often to allow for workability.
Drawing is a process in which wire is pulled through either a single drawing die or series of dies. As the wire passes through the die(s), two things occur: the diameter decreases while the length increases. The volume remains constant. Drawing is classified as a cold working process because the wire is typically drawn at room temperature. Lubrication is frequently used during this process to extend die life as well as to maintain the integrity of the surface finish of the wire. Polymet, however, can implement lube-free techniques for an exceptionally cleaner wire using distilled water.