INSIGHT-Seattle, WA USA via Wedel, Germany-October 16, 2004- Jobwerx News-The sorting of PET flakes imposes high requirements on the technology employed in order to obtain optimum starting materials, for instance for the fibre and packaging industry. The detection and sorting system MikroSort AF0916 from Mogensen was specially developed for this purpose and can be integrated into existing plants. It sorts up to 1.6 tonnes of PET flakes per hour by colour and removes any remaining incorrect colours almost completely. According to the company, parts with a minimum size of 2 millimetres can be removed in the colour-sorting process. The main sales market for recycled PET is the fibre industry, but new sales markets for other high-value products, e.g. food packaging, are also opening up.

Sorting of Recycled PET

To allow the reuse of PET flakes in the fibre and foodstuffs industry, these must be freed of impurities such as
- other types of plastic (PVC, PP, PS, silicon)
- wood
- metals
- other coloured PET
- opque PET
by various processing methods.

For the effective removal of these impurities, different detection and processing methods are employed:

Distinction of other types of plastic in the PET with near infrared systems (NIR) by detection of the different material properties of PS, PP and PVC.
- Employed in the sorting of whole bottles and, within limits, flakes from 25 mm.
- Colour sorting of whole bottles in the range of visible light.
- Distinction of impurities and off-colours for flakes in the size range 3-12 mm by sorting in the range of visible light. Depending on the application, sorting with colour-line or black-and-white cameras is possible.
- Metal detection by induction coils, removal by compressed air, sometimes integrated in existing optical detection devices.
- Separation of polyolefins (bottle-tops and foil labels) by the classical sink and float method downstream of the shredder.

There is a comparison of the sorting methods revealing several important advantages and disadvantages, and you can learn more when visiting their website.

Optical sorting systems can be used to improve the quality of recycled PET or to maintain its quality at a consistently high level.

Accodring to Mogensen the sorter vibrates and loosens up the material in the feeder to form a single layer of particles and conveys it to a chute. The material is accelerated, and below the edge of the chute, during free fall, or on the chute it is scanned by a colour line camera and an industrial parallel computer evaluates the images. These scanned images are evaluated by a parallel computer. Depending on the individual program settings, the results are transmitted to one or more compressed air valves, which eject the unwanted components out of the material flow.

Metal detection can also be integrated as an option. This enables the reliable detection of metal particles from a size of 1 mm and their removal parallel to colour detection.

Besides the detection system, the separation system was adjusted to the particular requirements for sorting fine material.

In addition, the machine is equipped with a special extraction function in the separation zone. This is used to minimize any turbulence that may disturb the sorting process taking place with reject rates of up to 2.500 particles per second. Thanks to the successful adaption of the detection and separation system to the fine material, the machine operates at very high specific feed rates and with a very low oversorting rate.

To minimize the maintenance work, access to all relevant points in the machine is secured amongst other things by a tilting device for the components of the camera and the incident illumination unit. No special tools are required for the maintenance work. Sensitive parts such as the camera and reflector box are designed to be dust-tight and practically maintenance-free.

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