Development And Performance Evaluation Of Rice Destoning Machine

The Hopper
The hopper was made of 1.5mm thick galvanized metal sheet, it is in pyramid shape.
The galvanized metal sheet was cut into approximate accommodating length, breadth of 350mm×180mm on the grinding disc machine, the hopper shape was then mark out with steel rule and sharp scriber. This marked out shaped is then cut on the grinding disc cutting machine; the feed regulator is located at the base of the hopper. The curves are formed on the anvil to the design shape and are welded fully.
The Blower
The blower is a centrifugal fan made of mild steel plate, it is measured and marked out with a sharpened scriber of diameter 170mm×180mm width, and the length of 250mm. This was cut by a grinding disc cutting machine and folded to designshape on an anvil, it is located at the lower part of the machine.
The Eccentric shaft
This eccentric shaft is a slid circular mild steel shaft of 16mm diameter and 472mm length; this was measured and cut to size on the lathe machine. The eccentric shaft is integrated to the machine to enhance the movement of the vibrating sieve in order toacquire low speed for the stoning machine. The 16mm shaft allow for the mounting ofthe bore bearings to both ends.   
Lower vibrating sieve
This has only one mechanical sieve, it was constructed from 2mm galvanized metal sheet, the length, breadth, and height (243mm×210mm×100mm) were measured and marked out with a sharp scriber. This was cut with a grinding disc and fold to     design shape on anvil, an opening is made in order to collect the clean rice from thisunit.
An eccentric shaft was welded at the center of the vibrating sieve to enhance the     oscillatory movement of the vibrating sieve.
3.6    Principle of Operation of the Machine
The machine requires only one operator since it is easy and simple to operate. Before the operation of the machine it must be ensured that all the parts are properly set and fixed or bolted together. The machine is switched on and a charge of mixture of rice and sand is fed into the machine through the hopper. As the motor operates it vibrates the sieves and the grain mixture flows from the upper vibrating sieve through the hopper to the last de-stoning section. In this section, the blower (blast fan) supplies air stream across the flowing grains. The air stream gives the mixture grains and stones velocity that changes their directions and causes them to experience different projectile motions. The range of projectile motion is greater than that of stones due to higher density of stones; therefore, pure rice grains are collected in a tray that is farther than that of stones.
3.8    Performance Evaluation
3.8.1    Sourcing of Experimental Materials
    Three different varieties of rice were purchased at Lafiagi in Kwara state, west central Nigeria.Lafiagi is now the headquarters of the Edun local Government council.
3.8.2    Sample Preparation
    The local rice (Orizaglaberrima) of three varieties was separated and the physical properties of each variety were measured using vernier caliper. Each variety of the rice were weighed into 500g in three replicate using a digital weighing scale machine and stones of 30g was also measured and mixed with each sample of the rice.
3.8.3    Experimental Design and Layout
    The factors considered in this study were:
    Design layout
    Federate (500g/min) (3 level)
    Varieties (Bokola, Kodoqiche, AlhajiA’aba (Orizaglaberrima) (3 levels each)
    Machine speed ( 1,500rpm  ) (constant)
3.8.4    Experimental Procedure
    The de-stoning machine was allowed to run at no load to ascertain that the machine is in perfect conditions. The samples prepared was transferred in to the hopper of the de-stoning machine and stop watch was used to take the time taken for the de-stoning machine to separate the stones from the rice, the clean rice was collected for the rice outlet while the stones were collected from the stones outlet. Tachometer was used to obtain the operating speed.