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F Diagram of a horizontal polisher which leather strips were nailed. The second was that the cone rotated at a speed that was 25 percent slower than the vertical cone design. The process began with the rice entering the space between the cone and the wire screen, it was then gripped by the leather strips that rolled the grains over each other and against the leather and wire screen. Then, with the application of a small amount of pressure, the remaining bran particles were removed and the rice became shinier or more transparent. Unfortunately, this method caused breakages, particularly in long grain rice, thus reducing its value. Furthermore, the leather strap needed to be replaced periodically, increasing maintenance costs. Performance matters These issues drove further innovations, including the creation Modern day polishing machines now offer a significant of the horizontal polisher, which consisted of three principal improvement in efficiency and wastage reduction. However, there parts: a feed screw, a cam roll and screen. are a number of factors that impact performance. Rice is fed into the machine by gravity, while both the feed Broken grains of rice can very much impair the polishing screw and cam rolls rotate. The feed screw pushes the rice into process because surface fractioning cannot be achieved if the the working chamber where a retainer plate, with an adjustable grains are sandwiched between broken kernels. The polishing counterweight, creates a controlled pressure on the rice kernels. effects are improved if ‘brokens’ are sifted out beforehand. The fractioning effect is achieved by rolling or rubbing the rice Polishing time is a deciding factor for both silkiness and and through displacement. A screen basket covers the cam rolls, breakage. A shorter polishing time results in less silkiness. allowing a pre-determined distance between them. Air suction A longer time improves silkiness but increases the risk of enhances the compactness and cools the rice while sucking away breakages. the residue. Screen basket and cam distance influences the degree of

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Mar 2016 - Milling and Grain magazine