Prior to the use of electrostatic separation, cables must be ground until the copper falls away from the insulation. Thin wires in particular require fine granulation to loosen the mechanical bond between the copper wire and the plastic insulation.
After granulation, copper and plastic are separated by gravity using setting tables. The setting tables are adjusted to produce copper that is as much as 100 percent pure. This is especially important because even the smallest impurities in the copper fraction lead to significant revenue reduction. Copper smelters pay the highest prices for No. 1 copper, so the aim is to produce copper of maximum purity.
For technical reasons, however, it is difficult to produce copper with 100 percent purity while also producing a “copper-free” plastic fraction using a gravity separation table. Particularly when processing mixed cables (namely cables containing course and fine wires and strands) or thin telephone cables, a recycler can expect to lose a small amount of fine copper wire and dust to the insulation. Typical copper losses can—depending on cable type—range from 2 percent to 12 percent, a proportion that implies significant financial losses as processing volumes increase.
Dry electrostatic separators can provide economical separation of even the smallest and finest residual copper particles from cable scrap.
Wet separation methods, such as so-called “water tables,” require further processing of wet plastics, which may not be economical in light of the additional drying time required. In addition, problems can arise with this method if ambient temperatures are low.
Dry electrostatic metal separators use conductivity differences between metal and plastic to achieve separation. After electrostatically charging the fractions with high voltage, the metal and plastic fractions subsequently discharge on a fixed roll surface. While metal particles discharge immediately and fall off the roll surface, the plastic particles discharge slowly and adhere to the roll surface.
Purity of the individual separated products is adjusted to an optimal level using splitters. The separated plastic fractions are extracted from the equipment with integrated conveying screws, causing the metal fraction to fall to the bottom of a container located underneath the equipment.
Electrostatic separators are available in different sizes and with throughput levels. Typical production machines separate at a rate of 1,760 to 2,200 pounds per hour. Throughput rates of several tons per hour can be achieved by using high-performance equipment and installing several separators parallel to one another.
