1 The Design and Construction of Maize Threshing Machine Abdulkadir Baba Hassan, Matthew Sunday Abolarin, Olufemi Ayodeji Olugboji and Ikechukwu Celestine Ugwuoke Department of Mechanical Engineering, Federal University of Technology Minna, Niger State, Nigeria > Abstract Many farmers grow maize but could not afford the cost of acquiring some of the imported threshing machines because of their cost. Such people resort to manual means of threshing which results into low efficiency, high level of wastage and exerting of much labor. This machine was constructed to shell maize and separate the cob from the grains. It was constructed from locally available materials and its cost is very low and affordable. Its threshing efficiency is 99.2% and breakage is very insignificant, as well as losses. Keywords: Hopper, shutter, threshing chamber, breakage, collector, wastage. Introduction Grains, according to Okaka (1997) are fruits of cultivated grasses belonging to the monocotyledonous family, Gramineae. The principal cereal grains of the world include wheat, barely, rye, sorghum, rice and maize. The last has become a popular staple in West Africa. Maize is another world s most versatile seed crop. Its cultivation originated from Europe but was soon brought to Africa by explorers early in the sixteenth century. Within hundreds of years, it was well established as a staple food in areas around the north and south shores of Mediterranean Sea. In later years, maize cultivation spread widely into Africa down to Nigeria as well as many parts of Asia all at the same span of time. Its production in the southern states of the United States of America also expanded greatly just as it was in Africa and Asia (Adaokoma 2001). The use of sticks for threshing was predominant in the prehistoric era. In Egypt, livestock was earlier employed for threshing out grains after which it was winnowed. In Palestine, threshing sledge was used 3,000 years earlier. In Nigeria, maize was threshed originally by bare hands. Other popular method was the use of pestle and mortar. This method is still used in the rural areas today. The above methods became Technical Report 199 unsatisfactory because of their low output, tediousness and their requirement of extra strength. According to Kaul and Egbo (1985), the performance of a thresher depends upon its size, cylinder speed, cylinder concave clearance, fan speed and the sieve shaker speed. Oni and Ali (1986) reported that the factors influencing threshability of maize in Nigeria are field drying, maize varieties, ear size cylinder speed and feed rate. The properties of the crop that affect the thresher performance are crop variety, shape and size, hardness of the seed, the moisture content of the seed and the density. The Hopper Design Analysis The hopper (Fig. 1) is designed to be fed in a vertical position only. The material used for the construction is mild steel sheet metal, which is readily available in the market and relatively affordable. The hopper has the shape of a frustum of a pyramid truncated at the top, with top and bottom having rectangular forms. Calculation of the Overall Height Lengths AC and EG are calculated by
2 using the Pythagorean theorem, AC 2 = AB 2 + BC 2. Also, AC = (AB 2 + BC 2 ) 1/2, and OC = (AB 2 + BC 2 ) 1/2 /2, EG 2 = EH 2 + HG 2, EG = (EH 2 + HG 2 ) 1/2, and MG = [(EH 2 + HG 2 )/2] 1/2. A E F D P H B Fig. 1. Schematic diagram of the hopper. From the principle of similar triangles, for triangles PMG and POC: PM/MG = PO/OC, or PM = PO x MG/OC. Then the volume of the hopper is given by: V hopper = [(area of base) x height]/3 = [(AB x BC) x h (EH x HG) x x]/3, h = overall height; x = height of the truncated top. The Main Frame The main frame supports the entire weight of the machine. The total weights carried by the main frame are: - weight of the hopper and housing; - weight of the threshing chamber; - the collector and pot; and - the bearings and pulleys. The two design factors considered in determining the material required for the frame are weight and strength. In this work, angle steel bar of 1 1 / 2 by 1 1 / 2 and 2mm thickness is used to give the required rigidity. G C The Threshing Bars Weight, W, of threshing bar is given by: W = mg, m = mass of threshing bar; g = acceleration due to gravity. Mass, m, of threshing bar: m = ρ x V, ρ = density of mild steel; V = volume of threshing bar. Volume, V, of threshing bar: V = l x b x h, 1 = length; b = breadth; h = height. Shaft Design A shaft is a rotating or stationary member, usually of circular cross-section having such elements as gears, pulleys, flywheels, cranks, sprockets and other power transmission elements mounted on it Shigley (1986). The shaft of this machine has a threshing tool attached to it (by welding) at two opposing sides and a pulley mounted on it. It is supported on bearings. Shaft design consists primarily of the determination of the correct shaft diameter to ensure satisfactory strength and rigidity when the shaft is transmitting power under various operating and loading conditions. Shafts are either solid or hollow. The following presentation is based on shafts of ductile materials and circular cross-section. The length of the shaft has been pre-determined at 770mm. Power Delivered By Shaft Power, P = work done per second: P = (work done)/time = (force x distance)/time = force x velocity. Calculation of Reactions R B and R D From Fig. 2: X T = total length of shaft; X = distance along the shaft; W p = weight of the pulley; Technical Report 200
The Design And Construction Of Maize Threshing Machinepdf
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8 maximum centre distance of belt, X max = 102.5mm; length of belt, L = 537mm; reaction, R D = 647.9N; reaction, R B = , negative sign means one should reverse the direction of R B ; maximum bending moment M bmax = Nm; torsional moment, M t = Nm; maximum shear force = N, negative sign implies the direction of the force; shock and fatigue factor (bending moment), K b = 1.5. Performance Test The completed work was subjected to test and it was found to thresh maize very effectively. Losses and breakages were found to be very negligible. The efficiency of the machine was found from the equation below to be equal to 99.2%: Efficiency = [(W 1 W 2 )/W 1 ] x 100, W 1 = weight of unthreshed cobs; W 2 = weight of cobs not well threshed. Conclusion Self-reliance is the major drive of development and vibrant economy. This machine has been fabricated with the use of locally available materials. The machine is simple, less bulky and effective with its selfcleaning ability. Grains loss and mechanical visible damage have been very minimal. Performance test has revealed that the efficiency of the machine is 99.2%. The machine threshes 200kg of maize within an hour. The machine can either be powered by an electric motor or engine (diesel or petrol). The electric motor seat provides adjustment so that the V-belt can be fixed easily. There is no doubt that the machine will ease the long term scourge of youth unemployment in our land. References Adaokoma, A The design and fabrication of a multi-purpose grain dehauler. M. Eng. Thesis, Department of Mechanical Engineering, Federal University of Technology (FUT), Minna, Nigeria. ASME Design of Transmission Shafting. American Society of Mechanical Engineering, New York, NY, USA. Black, P.H.; and Adams, O.E., Jr Machine design. 3 rd ed. McGraw-Hill, New York, NY, USA. Hall, A.S.; Holowenko, A.R.; and Laughlin, H.G Theory and problems of machine design. Shaum s Outline Series, S.I. (metric) ed. McGraw-Hill, New York, NY, USA. pp Hannah, J.; and Stephens, R.C Mechanics of machines: elementary theory and examples. Edward Arnold, London, England. Kaul, R.N.; and Egbo, C.O Introduction to agricultural mechanization. Macmillan, London, England, UK. pp Ogunwede, O.I Design and construction of plastic crushing machine. PGD Thesis, Department of Mechanical Engineering, Federal University of Technology (FUT), Minna, Nigeria. Okaka, J.C Cereals and legumes: storage and processing technology. Nigeria Data and Microsystem Publishers, Enugu, Nigeria. pp Oni, K.C.; and Ali, M.A Factors influencing the threshability of maize in Nigeria. Agricultural Mechanization in Asia, Africa and Latin America (AMA) 17(4): PSG Tech Design data. Faculty of Mechanical Engineering, Poolamedu Sathankulam Govindsamy Naidu College of Technology (PSG Tech), DPV Printers, Coimbatore, India. Shigley, J.E Mechanical engineering design. S.I. (metric) ed. McGraw-Hill, New York, NY, USA. Spotts, M.F Design of machine elements. 6 th ed. Prentice Hall, Englewood Cliffs, NJ, USA. Williams, W.A Mechanical power transmission manual. Conover-Mast Publ., New York, NY, USA. Technical Report 206
The machines of Western designare known as 'through-flow' threshers because stalks and earspass through the machine. They consist of a threshing device withpegs, teeth or loops, and (in more complex models) acleaning-winnowing mechanism based upon shakers, sieves andcentrifugal fan (Figure 4.2. 'Through-flow' Thresher.). The capacities of the models fromEuropean manufacturers (eg, Alvan Blanch, Vicon, Borga) ortropical countries (Brazil, India, etc.) range from 500 to 2000kgper hour.
The 'hold-on' thresher ofJapanese design (Figure 4.4. 'Hold on' thresher - Japanesedesign.), is so-calledbecause the bundles are held by a chain conveyor which carriesthem and presents only the panicles to the threshing cylinder,keeping the straw out. According to the condition of the crop,work rates can range between 300kg and 700kg per hour (Isekimodel). The main disadvantage of these machines is theirfragility.
Specially designed for harvestingmaize as grain, the corn-sheller was initially a cornhusker inwhich the husking mechanism was replaced by a threshing one(usually of the axial type). Corn-shellers are self-propelledmachines of the 3 to 6-row type with capacities of 1 to 2 hoursper hectare (Figure 4.6. Maize sheller.). The surface areas harvested during a180-hour campaign range between 100ha (with a 3-row unit) and200ha (with a 6-row one). 2ff7e9595c
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