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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.
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Grain (agricultural products) industry
Color sorters are mostly used in sorting grain (agricultural products). The rice sorting industry is the first big market, the rice sorting technology is according to the color differences of rice (husked paddy) materials, using a high-resolution CCD optical sensor to separate different stones, black rice, etc. It is the final step after polishing rice with a rice polisher. The second sorting market is in use for coarse cereals, such as wheat, corn, peanut, different kinds of beans, sesame seeds, etc. Sorting machines improve product quality and add social benefits.
Food industry
Colour sorters are used for food processing industry, such as coffee, nuts, and oil crops. 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.. Compared with manual sorting: machines saving labor and time, with higher high efficiency, and lower processing costs. Throughputs have increased with the use of new CCD technologies and are now up to 100 t/h.
Diamond industry
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.
Recycling
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. Plastic colour separators are used to separate mixed-colour plastic flakes or granules. Plastic type separators are used to separate plastics with same colours but different materials (www.focusee-global.com)
Types
Sorters can be chute-type or belt-type. Belt-type machines break a smaller percentage of material (important for nuts) 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 ratio of broken material. The belt structure makes the transmission smooth and stable without bouncing of material.
Chute type is more common especially for food, as prices are lower, capacities are higher and products can be seen more easily from both sides, which is important when a dehulled grain has hull only at one side. Chute sorters are usually applicable to specific products as the chute is designed with special channels for this kind of material based on sizes and shapes of the material, for example 5 mm chutes are used for rice, grain and plastic granules. Flat chutes are right for plastic flakes, such as PET, or milk bottle flakes.