Abstract
Rice is one of the most important cereal crop in the world. This paper present the design and performance evaluation of a rice hulling machine fabricated for removing chaffs from paddy rice as the consumer’s demand for rice requires the most hygienic, easy and less time consuming process. The design was segmented into the hopper and housing (processing) unit, the frame support and the power transmission unit. The housing unit consists of the upper and lower body where the sieve, hulling blade and cylinder is enclosed. The machine is powered by a 3.0 H.P. 950 rpm electric motor via a V-belt mechanism which deliverers the power requirement to the shaft on which the hulling cylinder is mounted. The hulling cylinder presses the paddy rice against the hulling blade to remove the chaff. The paddy rice is fed into the housing unit for processing through the machine hopper. The probability failure of the machine during loading has been minimized by proper material selection and using a factor of safety of 4 in the design process. The machine was designed to process about 8 kg of rice for small scale production. Performance evaluation of the machine shows that its efficiency is within the range of 83 to 88%, the hulling capacity is within the range of 22 to 25 kg/h and the maximum efficiency is at 5 kg paddy rice hopper loading which is about 60% of the hoppers’ volume. Key words: Rice, hulling, dehusking machine, paddy, fabrication.  
Highlights
Rice (Oryza) is one of the most important cereal crop in the world
The hulling efficiency drops to 75.75% while the broken grains percentage rises to 5% as the mass of paddy rice loaded increases from 5 to 8 kg.The hulling efficiency is maximum while the percentage of broken rice grains is minimum at 5 kg paddy rice.This implies that the increase in quantity of the paddy rice up to 8 kg tends to subject the hulling cylinder mounted on the shaft to such a loading which the slows down the hulling mechanism and is responsible for the little additional quantity of paddy rice which breaks and that which escapes the dehusking process between the hulling cylinders and hulling blades
The machine is powered by a 3.0HP 950 rpm electric motor via a V-belt mechanism which delivers the power requirement to the shaft on which the hulling cylinder is mounted
Summary
Rice (Oryza) is one of the most important cereal crop in the world. Rice grains were recorded to have sustained 2.5 billion people of the world’s population in Cristina and Cristina (2008). Oryza sativa and Oryza glaberrima are the two common species of rice grown. O. sativa commonly known as Asian rice originated in the wet tropics of Asia while O. glaberrima commonly known as African rice originate from Niger river delta and extended to Senegal Maddox, (2006). Rice is normally grown as an annual plant, in tropical areas it can survive as a perennial crop. In Nigeria, rice can be grown in almost all states, a grain of paddy is oval in shape with 1.5 mm long and 0.9 mm wide.
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