The fine wire drawing process is sometimes referred to as hot cold working, which means that the wire temperature is still below the recrystallization range.
Wire drawing is not a simple operation. There are many factors to be considered in selecting the correct drawing condition to secure a proper control of splitting, diameter variations and ductility. In general the major parameters for wire drawing are:
- Wire temperature
- Drawing speed
- Drawing lubricant
- Drawing dies
- Reduction per pass
In order to prevent the wire from being over worked and the strength from being too high the wire must be annealed. The final size of the wire determines the location of annealing points. As a general rule, the more work after an anneal the better the recrystallized structure. However, the coilability of the wire can be adversely affected by too much work as well as by too little. Depending on the final size of the wire, a combination of anneals is used which will optimise the properties of the wire. The entire sequence of diameter reductions alternating with anneals serves to maintain stress levels in the wire that keep the wire ductile.
After completed drawing, the wire will for most applications be cleaned. The purpose of this process is to remove the graphite that has been used as lubrication in the drawing process. To reach the finest wire dimensions the wire is etched. Both etching and cleaning is made by using an electrolytic process.
Plating with gold and nickel
High quality plating is important for many of the more demanding applications. Luma Metall has developed an advanced plating technology to secure a well adhesive and densely coating. The process control is fully computerized and allows full traceability of all important process parameters.
Standard gold coat thickness for wires < 50 microns is 3-5% by weight. For wire dimensions > 50 microns the coat thickness is 0,5 micron. Upon request we also manufacture wire with non standard coat thickness