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Paddy separator

The output from the husker is a mixture of paddy rice, brown rice, husk, broken paddy, and sometimes bran. The husker aspirator removes the lighter material such as husk, bran and very small brokens. The remainder passes onto the paddy separator where the unhusked paddy rice is separated from the brown rice.  The amount of paddy present depends on the efficiency of the husker, and should not be more 10%.  Paddy separators work by making use of the differences in specific gravity, buoyancy and size between paddy and brown rice. Paddy rice has a lower specific gravity, higher buoyancy, and is physically bigger, longer and wider than brown rice

The capacity of the separator should be at around 80% of the husker capacity (example: a 3 ton/hr husker requires a 2.4 ton/hr paddy separator).

Tray separator

The tray separator uses the differences in specific gravity, grain length and the co-efficient of friction to separate paddy and brown rice. The oscillation and slope of the tray forces the brown rice to move up the slope and the paddy to slide down. The separation performance of this type of paddy separator is very good.  This machine is very compact, easy to adjust, and consumes less power than the compartment type separator.

The capacity differs with the shape and size of the paddy: a separator with a 0.75 kW motor has a capacity of approx. 3 t/hr for short-grain varieties and 2.2 t/hr for long-grain varieties.

Compartment separator

The compartment type of paddy separator uses the difference in specific gravity and the buoyancy to separate paddy and brown rice.  When paddy and brown rice move over an inclined plane, they move at different speeds depending on their specific gravity, their shape and contact area, smoothness of inclined surface and the co-efficient of sliding friction.  Brown grains are smaller, heavier, rounder and smoother and will slide faster than paddy grains. The processing capacity of the compartment separator is dependent on the compartment area. For a 2-ton/hr capacity rice mill, a 45-compartment separator made up of 15 compartments on each of three decks is used

Screen separator

A very simple separator with no moving parts is the screen separator, which can be seen in smaller commercials mills located near rural markets. Brown rice/paddy will move through a number of screens that are at 31-35º angle.  The rough rice moves down the top screen, a mixture of rough rice and brown rice moves down the middle screen and finishing screen, and brown rice will pass through the finishing screen.

In operation, the mixture of brown rice and paddy are introduced in the upper end, and as the plate oscillates the paddy grain and brown rice mixture separates as it moves down. The grain layer on the deck should be maintained at 7 mm to 9 mm thick, which can be controlled by the rate of feed and the inclination of the deck. Too thick a layer will result in too much mixture, while too thin a layer will decrease separating capacity.