Performance Evaluation of an Okra Thresher

Thesis Overview

<p> 1. INTRODUCTION&nbsp;</p><p>Okra (abelmoschus esculentus L. moench) of the family malvaceae is commonly called okra. It is an oblong edible pod, which is large at one end and slender at the other. Okra can be eaten grated raw or cooked. It possesses high nutritive value, which is higher than tomatoes, eggplant and most cur bit except bitter gourds (Nonneck 1989). The dried Okra pods are also consumed directly and it is also used as flavoring in preparing other food products. The fresh stem of okra serves as robes, while the dried ones serves as source of paper pulp or fuel (Kalra and Pruthi 1984). The seeds of okra have been used as coffee substitutes and edible oil also has been extracted from dried okra seeds. Vegetable curds prepared from the dried seed have been used as substitutes for cheese in recipes. The amino acid profile of the seed indicates that it could be used to complement other partially complete protein sources such as soybean (Bryant et. al.,1988). The economic value of the fresh okra pods, fresh stems, dry okra stem, pods and seed cannot be over emphasized, hence there is the need to produce large quantities of dried okra seeds for seedlings and for use in other processed forms. The traditional methods of threshing dry okra pods involve manual rupturing of the pods and the separation of the seed from the chaff. The process is tedious and time consuming; it also results in losses as well as low quality product. An okra thresher was designed and constructed to solve this problem. The machine had a threshing efficiency, cleaning efficiency and a percentage total loss of 88.1%, 46% and 15.3% respectively (Bolaji 2000). Design modifications were carried out on the initial design to further improve its performance. This paper reports the effect of machine and crop variables on the performance of the modified machine.&nbsp;</p><p><b>2. MATERIALS AND METHODS </b><br></p><p><b>&nbsp;Modified Machine&nbsp;</b></p><p>The thresher is consisted of a threshing unit, separating unit and the frame (Fig.1) <br></p><p> The threshing unit is consisted of a threshing head and concave (Fig.2). Threshing head is made up of a hollow pipe of 67mm diameter and 640mm long with ends closed. Spikes (20mm diameter) made of mild steel are welded alternatively in rows on the cylindrical pipe. This arrangement is to allow easy movement of crop in the concave. Also, a stretch of rod curled round the whole length of the main shaft is welded to form an auger (screw) to convey the materials out. The cylinder shaft is mounted on a bearing, which is attached to the frame by a set of bolts and nuts. The concave is made of steel sheets rolled into a cylinder of 330mm diameter and 640mm length. The lower part is punched with round holes of 10mm diameter which performs the function of a screen. The upper end consists of a 360mm by 140mm hopper from where the crop is fed into the concave. The concave sits on the frame with the aid of two flat steel bars joined on each side by bolts and nuts. The sprout of 100mm is located directly below the concave. The straw comes out of the concave at the other end of it, opposite to the position of the hopper. A cup shaped sheet is welded to channel the straw not to obstruct or come in contact with the end bearing. This is in such a way that the straw comes out after passing through the length of the concave. The separating unit comprises of a housing and a blower. The blower is made of mild steel sheet and enclosed in spiral shaped housing. An inlet for the sprout is provided at the top of the Housing along its length and attached directly to the sprout. The blower is made of 3 vanes of 140mm by 60mm and is attached to a 10mm diameter blower shaft mounted on two bearings on each side to allow free rotation. It is connected to the threshing pulley by a belt to its own pulley. The spiral section of 80mm diameter and 160mm long is provided to allow outflow of the chaff. The collector opening below the blower is tapered to convey the seed into the container or bag below. The machine is mounted on a 200 x 650 x 1000mm frame. The machine has a rigid platform attached to base of its main frame to seat the source of power. The following modifications were made on the initial design to further improve its performance.&nbsp;</p><p>i) Increase in the number of spikes in the threshing head from 27 to 36 in order to increase the force of impact by the spikes on the material; thus increasing the threshing efficiency.&nbsp;</p><p>ii) The length of the threshing head and the concave were increased from 620mm to 640mm so as to increase the dwell time; thus enhancing the threshing and cleaning efficiency.</p><p>&nbsp;iii) The diameter of concave was increased from 200mm to 220mm to increase capacity.&nbsp;</p><p>iv) The fan blades are under the concave and curved to about 65o to allow for more volume of air, which will increase the cleaning efficiency.</p><p>&nbsp;v) A cover is made for the hopper to prevent splashing of seeds during threshing. The thresher is dismantleble for easy transportation.&nbsp;</p><p>&nbsp;<b>Performance Evaluation</b>&nbsp;</p><p>The modified machine was installed on level and hard surface. Sufficient quantity of dried okra pods of the same variety was taken. The thresher was evaluated at three different levels of moisture content, three concave clearances, three level of cylinder speed and a feed rate. The thresher was powered by an electric motor (1hp) at a maximum speed of 1410rpm. The prototype thresher was evaluated as per test procedure of IS:6284 (1986). The codes prescribe method of testing power threshers to evaluate their performance and durability. The threshing efficiency, cleaning efficiency, percentage total loss and germination were evaluated at each combination of variables. <br></p>