WCA January 2015

❍ ❍ Foreign objects, foreign pellets or other organic contamination (Optical) The combination of these two technologies is unrivalled on the market. The specially developed X-ray technology is able to inspect transparent and coloured (eg black) pellets as well as semi-conductive XLPE material for impurities. The new technology from Sikora inspects the material for purity to 100 per cent. The system combines X-ray tech- nology with an optical system. This allows the detection of metallic and organic impurities of 50 μ m in the pellet itself and on its surface. It is for that reason that the Chinese Standard for high voltage cables, for example, demands the exclusion of contamination from 75 μ m in the processed materials. Accordingly, it is necessary to inspect the material to 100 per cent before it enters the end product. Sample tests are a first step but not sufficient to exclude all contamination reliably. Today, cable manufacturers use screens to catch impurities in the XLPE compound before they get into the cable. The screens are positioned directly in the melt flow after the extruder, before the crosshead. However, these screens can get clogged by scorches or excessive amounts of contaminants after a certain run time. Then the melt pressure in the extruder may increase significantly. Finally, the production has to be stopped in order to change the screens, which in turn means that later a joint is required at that position. Joints where the cables are welded together are always critical, in particular when talking about power cables for offshore applications. That is why cable manufacturers aim at delivering large cable lengths with only a minimum of joints as they contain a potential risk for breakdowns. This can be achieved by using highly pure raw material. As the integration of screens reduces the productivity of the line, an approach is to omit the screens. This requires, however, reliable alternative methods to detect and sort out contamination in the XLPE pellets at an early stage. Scorches can be avoided by temperature supervision and control of the melt flow by an ultrasonic- based temperature measurement. Green technology solution for clean material

1 Transport system 2 X-ray inspection 3 Optical inspection

4 Sorting unit 5 Bad stream 6 Good stream

❍ ❍ System for pellet inspection and sorting inside

Temperature measurement CCV line System for inspecting and sorting

VCV line

❍ ❍ Installation of the system for pellet inspection and sorting Contamination that is detected by the X-ray or optical technologies is identified by image processing soft- ware, characterised as contamination and automatically separated. The basic principle of the X-ray technology is the different attenuation of the material. XLPE mainly comprises two carbon and four hydrogen atoms. The carbon atom has six protons in its core while hydrogen has only one. A typical contamination would be steel particles from the extruder or granulator, which is mainly iron (FE). Iron has 26 protons in its core. Because these 26 protons have a much higher X-ray attenuation than the six protons from the carbon it is possible to generate a contrast between the two materials in the X-ray image. Regarding the optical inspection, the illumination plays an essential role. By using a special diffuse light construction technique, the smallest contamination is detected, among others, foreign objects, foreign pellets or organic impurities. In order to allow an industrial throughput up to 2,000kg/h, modern camera technologies are used. They allow precise images of the pellets to detect contamination down to a size of 50 μ m. In order to avoid contamination from the outside, the feeding of the pellets is carried out via a hermetically vibrating ramp. This at first avoids contamination that might occur by conveyor belts, and secondly an over-pressure avoids contamination from dust of the ambient air.

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Wire & Cable ASIA – January/February 2015