Clevertex - Grado Zero Espace Srl

2.1.2.1 Electro-conductive fibres
Electro conductive fibres have already been used for years in various industrial applications for the
purpose of controlling static and electromagnetic interference shielding. Today, conductive fibres find
new applications in the development of electronics and smart textiles. They can be classified into two
general categories, namely intrinsically conductive fibres and fibres that are specially treated to gain
conductivity. Different production methods are used to produce electro conductive fibres, among them
are wire drawing, bundled wire drawing, cutting production method, melt spinning and melt extraction.
Intrinsically conductive fibres
These fibres are pure metals, such as nickel, stainless steel, titanium, aluminium and copper, a metal
alloy or carbon. Recently, also the development of intrinsically conductive polymer fibres has been
reported, which is described at the end of this paragraph. In general, intrinsically conductive fibres
conductors without adding a conductive substance.
The conventional process to produce metal fibres is wire drawing, a mechanical production process.
This process is characterised by its various drawing steps, called coarse, medium, fine and carding
train. The drawing die, used to draw the fibre, consists of a steel mount with a core out of ceramics,
carbide or diamond. The initial diameter of the metal wire varies depending on the material. For
copper, for instance, it is usually is 8mm, while for iron it is 5mm. After drawing, the wire is annealed in
steel at temperatures ranging between 600 and 900°C. Subsequently, they are quenched. The fine
metal wire is then wrapped onto a revolving wire drawing cylinder.
The wires produced in this way are used today in metal spun yarns which are produced by wrapping
the wire around a core yarn or are used to be processed further, e.g. by the bundling drawing process
that is briefly described below [12].
Another mechanical metal fibre production process is the bundle drawing procedure. In this process
1000 to 2000 conventional drawn wires are bundled to one strand and are wrapped by a thin metal
cylinder. The method is illustrated in Fig.1.
7