leather dressings and many others. However, the concern of this paper is the processing of groundnut into groundnut oil and Figure1 shows a typical processing flow chart. Processing or extracting or expressing oil from groundnut involves a wide range of traditional, mechanical, chemical and mechano-chemical methods (Ewaoda et al, 2008). The traditional method involves roasting and crushing the groundnuts into fine particles, after which the crushed mass is mixed with water and boiled so as to allow the oil to float. The oil is then skimmed off and dried by heating (Ajao et al, 2010). This method is time consuming, labour intensive, low output and low efficiency with lots of drudgery. The mechanical methods involve the use of screw and hydraulic presses (Asiedu, 1984). The screw press is more reliable than the hydraulic press, but is slower and produces less pressure. The hydraulic press is more expensive, needs more maintenance and risk contaminating the oil with poisonous hydraulic fluid. Generally, the mechanical methods have relatively higher operating cost than the traditional methods; however, they have higher efficiencies and are usually more adaptable for small and medium scale producers (Abubakar and Yiljeb, 1996;Adgidzi, et al 2006;Olayanju et al, 2004;NCRI, 1995). The chemical method or solvent method is done either by continuous solvent extraction or aqueous extraction. This method is more appropriate for largescale processing than small-or medium-scale processing because of higher capital and operating costs. However, there is the risk of fire and explosions from the solvents coupled with the complexity of the process (Davie and Vincent, 1980;Jaswant and Shukla, 1991). The mechano-chemical extraction involves using the cake from the mechanical extraction as a solute to which solvent is introduced to further release the oil held in the cells. Though this method is the most efficient, it is very expensive and time consuming. The various modern methods of processing are predominant in developed countries while the manual processing is still the norm in many developing countries despite the drudgery and low output (Maduako et al, 2006). In Nigeria, some imported large-scale plants are replacing the small groundnut processing units, but due to high foreign exchange rate, the cost of such imported machines is clearly out of reach of the poor farmers. Therefore, the mechanical processing method using the screw press has been selected for this study and this paper reports the performance evaluation of a locally built oil screw expelling machine. Fig. 1: Flow chart for processing of groundnut into groundnut oil. (Source: NCDEX 2010) a) Machine Description The machine consists of the feeding chute (hopper), expelling unit, discharge units, frame and prime mover. The feeding chute is pyramidal in shape and made of 5mm gauge galvanized iron sheet. The expelling unit consists of a screw shaft with a perforated barrel outer casing. The screw is divided into three sections; the feeding, milling and discharge sections as it tapers. The friction and pressure produced by the screw on the barrel causes the mass to heat up, thus facilitating oil extraction as the screw grinds and presses the fine mass against the expelling chamber. The oil flows through the perforation in the casing and is collected beneath the expeller chamber while the residue (cake) is extruded from the unit through the cake discharge outlet. The frame supports the machine and is firmly fastened together with bolts and nuts to allow easy dismantling for transportation. The prime mover is a two (2hp) electric motor of 1400rpm speed with belt and pulley arrangement. Fig. 1 shows a pictorial view of the oil screw expelling machine. Fifty kilograms (50kg) of groundnut was purchased in the market and prepared for the test. The preparation involves cleaning the groundnut by removing dirty and other particles and washing. The cleaned groundnut was milled to form paste. Three kilogram (3kg) was prepared for each experiment and each experiment was carried out in five replicates. The speeds of the machine were varied by varying the diameter of the pulleys. The diameters of the pulleys used for the experiment were 525mm, 600mm, 675mm, 750mm and 825mm corresponding to 730, 675, 600, 525 and 450rpm respectively. At the end of each operation, the weight of oil expelled and mass of cake were recorded in order to evaluate the effect of machine speed on the machine feed rate, output capacity, efficiency, percentage of oil recovery and the mass of cake produced. The machine performance parameters were determined by using the following equations: The performance of the locally developed oil screw expeller was evaluated at the various machine performance parameters. Figure 2 through 6 shows the results obtained from the test carried out on the machine. Generally, from Figure 2, the feed rate of the oil expeller increased with increase in the speed of the machine. The highest feed rate for the expeller was at 87kg/h at machine speed of 690rpm. Also, from Figure 3, the output capacity of the machine increased with increase in the machine speed. The highest value of output capacity of 68kg/h was achieved at machine speed of 780rpm. Figure 4 showed that the mass of cake expelled from the machine also increased with increase in the speed of the machine. At machine speed of 750rpm, 2.5kg of groundnut mash was recovered. The efficiency of the machine increased with increase in the machine speed (Figure 5). The high efficiency of the machine at high machine speed may be attributed to the high rate of movement of the screw press against the expeller wall. The highest value of 67% and 65% for actual efficiency and predicted efficiency of were observed at machine speed of 600rpm. Figure 6 showed that at machine speed of 600rpm, the maximum oil of 1.8kg was obtained from the groundnut mash and further increase in speed of machine resulted in decrease in amount of oil expelled Performance test was carried out on a locally fabricated oil screw press. It was tested and found to be efficient in the expelling of groundnut oil. Generally, the performance parameters of the machine increased with increase in the machine speed. The machine is cheap, easy to operate and maintained because the parts can be locally sourced. It is recommended for small-scale farmers to process their nuts into oil which are hitherto sold as raw material at very cheap price. Feed Rate = FR = ----------1 Output Capacity = Q c = --------1![Fig.1: Pictorial view of the Oil Screw Expelling Machine](image-2.png "Fig. 1 :") ![oil content in kg per 100kg of groundnut (Wiemer and Korthalds, 1989) Efficiency= x 100% = x 100% -----------4 Oil yield = Mass of paste -Mass of cake = ? ----------5](image-3.png "") 2![Figure 2: Effect of machine speed on machine feed rate](image-4.png "Figure 2 :") 34![Figure 3: Effect of machine speed on the output capacity](image-5.png "Figure 3 :Figure 4 :") 5![Figure 5: Effect of machine speed on machine effeciency](image-6.png "Figure 5 :") 6![Figure 6: Effect of machine speed on the oil yield.](image-7.png "Figure 6 :") December December * Design and development of a groundnut Kneader SZAbubakar YDYiljep Proceeding of the Nigerian Society of Agricultural Engineers (NSAE) eeding of the Nigerian Society of Agricultural Engineers (NSAE) 1996 * Development of an oil expeller DAdgidzi SMDauda OOEmeruwa Proceedings of the Nigerian Institution of Agricultural Engineers the Nigerian Institution of Agricultural Engineers 2006 28 * KRAjao HAAjimotokan JOlaomi H * Design and development of a groundnut oil expelling machine Akande Journal of Agricultural Technology 6 4 2010 * Some physical properties of groundnut (Arachis hypogeal. 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