PROCESSING EQUIPMENTS

Friction cleaning

The air-screen combinations cannot remove debris that has a size and density similar to the seeds. However, if the debris has a different surface texture, it may be possible to remove by friction cleaning. Any object rolling or sliding over a sloping surface encounters a certain friction depending on the texture of itself and that of the sloping surface. Separation is made on a velvet cloth or rubber belt with variable inclination, which ensures that the slope necessary for the run off of the seed is different from the slope necessary for run -off of the debris. The belt continuously moves upwards and removes the debris while the seeds roll down the slope.

Spiral separator

The separator, which classifies seed according to its shape and rolling ability, consists of sheet metal strips fitted around a central axis in the form of a spiral. The unit resembles an open screw conveyor standing in a vertical position. The seed is introduced at the top of the inner spiral. Round seeds roll faster down the incline than flat or irregularly shaped seeds, which tend to slide or tumble. The orbit of round seed increases with speed on its flight around the axis, until it rolls over the edge of the inner flight into the outer flight where it is collected separately. The slower moving seed does not build up enough speed to escape form the inner flight. Most spirals have multiple inner flights arranged one above the other to increase the capacity.

Liquid flotation

Cleaning by flotation relies on the principle that the density of the seed of a given species is specific both for filled and ill filled seed. In this method, liquids with a density or specific gravity between that of the full and empty seed are used. The specific gravity of the liquids used is such that the full seed sinks and the empty seed and light debris float.