DEVELOPMENT OF A DOMESTIC RICE DE-STONING MACHINE USING WATER MEDIUM

Abstract

The quality of local rice is a major concern for the future of the Nigerian rice sector. The major problem being the appearance and cleanliness of the rice delivered to the market. Prior to the conception of rice destone machine, farmers make use of the traditional or manual method to separate impurities from rice. The manual method includes handpicking, sieving and separation using water in a bowl or calabash which allows separation of stones from rice. But is time consuming, tedious and contaminants such as stones, sticks, chaff and sand are not completely removed. In this research, a mechanically operated rice de-stoning machine using water as a medium of separation with a de-stoning and washing chamber facility of low cost and high efficiency was developed. A geared motor was chosen to evaluate the performance of the developed machine. Effect of varying machine speed (from 1400 rpm to 10 rpm) on the de-stoning efficiency of the machine with 2 kg of rice and 20 pieces of stones of different sizes at a constant operating time of 10 minutes was evaluated. The number of recovered stones in each trial were recorded with mass of remaining quantity of rice in the de-stoning chamber. The performance tests conducted on the machine showed that for the stone removal at a speed of 1400 rpm both the rice and the stone flow together as a result of high torque and there was no separation of stone from the rice. At the speeds of 1200 rpm, 1000 rpm, 800 rpm, 600 rpm, and 400 rpm gives 15%, 25%, 50%, 80% and 100% stone removal. At a speed of 200 rpm and 100 rpm gives 5% and 10% stone removal while at 50 rpm, 30 rpm, 20 rpm and 10 rpm gives 0% as there was no de-stoning of stone as a result of very low torque. For the clean rice at a speed of 1400 rpm, there was no rice destoning as both the rice and stone flow together to the washing chamber as a result of high torque. At 1200 rpm, 1000 rpm, 800 rpm and 600 rpm which gives 97.5%, 97%, 96.75% and 96.5% of the rice that flow to the washing chamber but still contains stones which make it not favorable but at 400 rpm gives 96.4% of the clean rice separated without a stone. At a speed of 200 rpm and 100 rpm gives 90%, 75% of clean rice but contain some pieces of stone, at a speed of 50 rpm and 30 rpm gives 37.5% and 15% only small quantity of rice without stones was separated while at 20 rpm and 10 rpm there was no de-stoning of rice and stone as a result of very low torque both the rice and stone settled at the bottom of the de-stoning chamber. It was observed that 2 kg per 10 minutes and 20.04 kg per hour were destoned at the de-stoning speed of 400 rpm without stones completely.