Colour sorters or Color Sorters (sometimes called optical sorters or digital sorters or electronic colour sorters) are machines that are used on the production lines in bulk food processing and other industries. They separate items by their colours, detecting the colours of things that pass before them, and using mechanical or pneumatic ejection devices to divert items whose colours do not fall within the acceptable range.
Colour sorters are used for colour sorting harvested foodstuffs, such as coffee, nuts, rice, other cereals such as wheat or rye and pulses. The goal is the separation of items that are discoloured, toxic (such as ergot), not as ripe as required, or still with hull after dehulling such as sunflower seed.. Throughputs have increased with the use of new technologies and now up to 40 t/h if wheat can be sorted. Stable types of colour sorters are used for the sorting of mineralsor stones, with up to 100 t/h.
They are also used in the diamond industry. The transparency of the diamond is measured by the colour sorter and used as a measurement of its purity, and the diamonds are mechanically sorted accordingly. This has an advantage over X-Ray fluorescence methods of robotically detecting purity, since purer diamonds are less likely to fluoresce.
In the recycling industry, colour sorters can distinguish between coloured and colourless PET and coloured and colourless HDPE flakes, as well as being able to separate flakes by colour before re-granulation.
Sorters can be chute-type or belt-type. Belt-type machines break a smaller percentage of material and the product stays relatively static during the transport process as it moves horizontally on the belt. Whereas in the chute type, material slides on the chute because of gravity, causing collision, friction, and larger vertical movements, thus worsening the broken ratio of the material. The belt structure makes the transmission smooth and stable without jumping of material. Chute sorters are usually applicable to specific products as the chute is designed for this kind of material based on sizes and shapes of the material.
- Somani 1989.
- Kumar 2008.
- Malhotra et al. 2009, p. 486.
- Scheirs 1998, p. 15.
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