Design and Development of a Cost-Effective Semi-Mechanized Maize Thresher

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1 JAEET ISSN Journal of Agricultural and Environmental Engineering Technology Vol. 1, No., 004 Design and Development of a Cost-Effective Semi-echanized aize Thresher A. J. Akor, E. Ugwoha and D. D. Davis Department of Agricultural and Environmental Engineering Rivers State University of Science and Technology, PB 5080, Port Harcourt. Abstract This paper presents the design and fabrication of a semi-mechanized maize thresher. The machine employs the principle of scratch / abrasion to effect threshing and requires only one person to operate. The machine was designed using locally available materials, which makes it cheap and easy to maintain and repair. The test runs carried out showed that at a speed of 5rpm, the machine functions effectively, producing a high threshing efficiency of 96.7%, a low kernel breakage factor of and a throughput of 8.7kg/hr. In comparison with other threshing machines, particularly the Chinese version which is times heavier and 10 times more expensive, this machine was found to be effective, efficient, simple, portable, cheap, easy to operate and requires no special expertise. And because of its lower kernel breakage factor and less dust production, the machine stands a better chance of being selected than the Chinese thresher and other threshing machines, which have high kernel breakage factor and produce much dust during threshing. Key Word: Semi-mechanized, aize, Thresher. Introduction According to Okurowa (1995), maize (zea mays), a cereal crop of tropical exican origin, has a multitude of uses, and ranks second to wheat among the world s cereal crops in terms of total production. Also, because of its worldwide distribution, nutritive value and relative low cost compared to other cereals, maize has a wider range of uses than any other cereal. aize can be processed into different products for various uses at the smallmedium scale as well as industrial scale. At the local level, maize is processed into akamu, agidi, ericha and ogi. Industrially, it can be processed into brewer s grits, maize flour and maize meal. But for the maize grains to be processed to any usable form, threshing is an important preliminary unit operation since maize grains are naturally attached to the cob (Adegbulugbe, 1986). aize threshing is the removal of maize grains from the cob. Inglett (1970), stated that threshing is difficult at a moisture level content above twenty five percent (5%). At this moisture content, grain-stripping efficiency is very poor with high operational energy and high level of mechanical damage to grains. A more efficient threshing is achieved when the grain is dried to thirteen percent fourteen percent (1% - 14%) moisture content. Barkstorm (1964) stated that threshing kernels is comparatively easy to achieve by mere rubbing action or striking, at this range of moisture level. According to ILO (1984), maize threshing could be carried out at or close to its growing area either as part of the harvesting operation using combine harvesters or at a nearby production unit. The large difference in weight and volume between the un-threshed cobs and shelled grains is an added advantage of threshing at or near the growing area. aize threshing can be achieved by different methods. These include the traditional methods, the use of hand and hand-held shelling devices of various designs, and by the use of small to large power threshing machines most of which are complex, expensive and scarce and can only be operated by skilled manpower. This implies that they cannot be easily used by the 178

2 Akor et. al: Design and Development of a Cost Effective Semi-echanized aize Thresher JAEET vol. 1, No., 004 unskilled farmers. oreso, some of them are powered by electricity, which is not in most cases available at the village level where the farms are located. Traditionally, threshing of maize includes: using the fingers in scratching the grains to detach from the cobs or scratching the dried maize cob on rough surfaces. However, it was stated by the UNIDO (1986) that manual threshing and hand-held devices are time consuming and arduous, requiring large number of labor, which is becoming more expensive, even with the associated low output. A number of maize threshing machines have been developed by different individuals and organizations with a view to improve labour-productivity, reducing the tedium involved, minimizing hazard in the operation and cost of machine (FAO, 1979, ILO, 1984; UNIDO, 1986). However, the above threshers are not locally manufactured. They are imported and therefore too expensive for poor farmers. Because they are imported machines, their spare parts are not usually available or within the reach of the poor farmers. Thus, it is the objective of this paper: to develop a cost effective semi-mechanized maize thresher for the rural farmers, using locally available material; test the maize thresher in order to evaluate its performance and, recommend possible ways of improvement and marketing of the Sheller. aterials and ethods Description of achine The maize thresher consists of the following parts: Sleeve, Rotating cylinder, Spikes, Torque Arm, Support bar and G- Clamp. Sleeve The sleeve is a 10mm external diameter, 0mm long and 9mm thick medium carbon steel pipe which bears the rotating cylinder, and both are arranged such that a 1mm clearance exists in between them. This clearance and the smooth surfaces reduce friction in the operation. Rotating Cylinder Is an 8mm external diameter, 70mm long and 9mm thick mild steel pipe. It has two ring stoppers welded to it on the outer surface. The two ring stoppers help to keep the rotating cylinder in position with respect to the sleev. Inside the rotating cylinder are arranged the spikes that shell the maize grains. Spikes These are four (4), 5mm-diameter 6mm long metal rods, welded to the rotating sleeve, responsible for the rub-off of grain from cob, in the process of shelling. Torque Arm The torque arm is made from a 10mm long mild steel rod fixed to the rotating cylinder. Its handle is also 10mm length, covered with a floating pipe to prevent hand injury. The torque arm is of uniform thickness 9mm, but tapers uniformly from the boss at both sides, to the handle, where it is 7.5mm. Support Bar This is made of mild steel of length 170mm, fixed to the sleeve at one end and to the G-clamp at t he other end. The support is a mild steel bar of uniform width and breadth of 0mm. G-Claming This comprises of mild steel plate, 5mm thick, formed into a C-shape. A screw of nominal diameter 11mm is attached to the C-shape to form the G-clamp. The screw is turned by its handle, which is 40mm long, and 11mm diameter. Design Consideration In the design of this machine, considerations were given to the physical properties of maize-fruit such as moisture content, shape, size, friction and texture, as far as they affect the threshing process, (functionality and efficiency). aterial selection was made based on cost, 179

3 Akor et. al: Design and Development of a Cost Effective Semi-echanized aize Thresher JAEET vol. 1, No., 004 availability, durability, simplicity, effectiveness and safety. The shape of the maize-fruit, which can be approximated to a mild cone, was considered in the determination of the cross-section of the annulus bearing the spikes. In dimensioning the spaces between the spikes, consideration was given to the size of maize-fruit, and energy minimization. Design of the machine component parts i. Roundness Factor A mean roundness factor was obtained for maize cob, using methods in Odigboh, (1976) and checked, according to the ohsenin (1970) as follows: Roundness () = A A Ap = Actual projected area of object in natural rest position Ac= Area of smallest circumscribing circle and = roundness factor. ii. Spike Spacing Spike spacing was determined using the formula as given by Harrington (1970): A = (abc) 1/ A = Size of the maize cob a = major diameter of maize cob b = intermediate diameter of maize cob and C = minor diameter. iii. Diameter of the Handle (d) The main components of the machine are shown in figure 1. The handle is a rotating cantilever at the connecting rod, and is therefore designed using cantilever and tensile principles. The maximum applied load on the handle acts at of its length from the rod end (Khurmi and Gupta, 1997). Therefore, the maximum bending moment is: max FL p c 1 (max) = ax. bending moment F = bending force, and L = length aximum bending stress is given by Khurmi and Gupta (1997) as follows: (max), b(max) = 4 Z Z sectional mod ulus d 5 Substituting for equations () and (5) in (4), and noting that b(max) b(perm) (permissible stress) 64FL d max perm Therefore diameter of handle, d: d 64FL b max 1/ iv. Torque Arm The arm is subjected to constant twisting moment, T, and an alternating bending moment,, which is maximum at the boss (welded joint). If L is the length of the torque arm, then: T FL 8 Since, at present, there is insufficient information on the subject of combined bending and twisting of rectangular sections to obtained equivalent bending or twisting moment with sufficient accuracy, an indirect approach is adapted with a torque factor of 0.5 (Khurmi and Gupta, 1997). Hence: (max) = 1.5FL 9 The sectional modulus of the torque arm given by (Khurmi and Gupta, 1997) as follows:

4 Akor et. al: Design and Development of a Cost Effective Semi-echanized aize Thresher JAEET vol. 1, No., 004 Z = tb 6 10 t = thickness of the torque arm, and B = width of the torque near the welded joint Substituting equations (9) and (10) in (4): b(max) = (max) = Z 7.5FL tb For B = t (Khurmi and Gupta, 1997) b(max) = t = 7.5PL 4t 7.5FL 4 b perm 1/ The shear stress, (s) induced by the twisting moment, T in the section of the torque arm near the boss is obtained by (Khurmi and Gupta, 1997): (max) = where: FL tb 14 (max) = maximum shear stress. The cross-section of the torque arm is checked for principal shear and bending stresses using the following equations (Khurmi and Gupta, 1997): b(prin) = 1 max max 4 max b 15 (prin) = ½ 1 max 4 b max 16 (prin) and b(prin) are principal shear and bending stresses respectively. v. Thickness of Rotting Cylinder In operation, the maize cob is fed into the rotating cylinder and the torque arm is rotated to effect threshing, the cylinder wall is subjected to combined twisting and bending moments. The thickness of the rotating cylinder is therefore designed for static strength, using the combine twisting and bending moment criterion. Figures and shows the free body diagram of the rotating cylinder under vertical and horizontal loading respectively. The resulting bending moment at points D, A and B are respectively as follows: D B A D A B ( ) DV DH ( ) AV AH ( ) BV BH = Resultant bending moment at point D. = Resultant bending moment at point A. = Resultant bending moment at point B. DV = ax. bending moment at point D, for vertical loading DH = ax. bending moment at point D, for horizontal loading AV = ax. bending moment at point A, for vertical loading AH = ax. bending moment at point A, for horizontal loading BV = ax. bending moment at point B, for vertical loading BH = ax. bending moment at point B, for horizontal loading The highest value, computed, among equation (17), (18) and (19) was chosen as the maximum bending moment. The equivalent bending moment is giving as ((Khurmi and Gupta, 1997):

5 Akor et. al: Design and Development of a Cost Effective Semi-echanized aize Thresher JAEET vol. 1, No., 004 T e T 0 Again, the equivalent twisting moment moment for hollow shaft is given as ((Khurmi and Gupta, 1997): T e But 16 D c permd c dc c c 1 d t t c = Thickness of the rotating cylinder Equating equations (0) to (1) yields: t c 16 T perm vi. Support Bar The support bar of machine was designed according to Euler s critical load equation: W a EI L W a = buckling load; E = young s modulus and I = moment of Inertia For equal strength of material in both X and Y plains: EI L xx EI L yy 4 Ixx = Iyy 5 xx and yy represent directions. There is also a bending stress: b(max) = (max) max 6 Z = W al Wa L bh 6 Z = bh 6 h Depth of rectangular section and b Breadth of rectangular section For b(max) b(perm) and b = h: b 6 W L a b perm 1 / 7 vii. G Clamp Stand The G clamp stand of machine design configuration is shown in figure 4. Power required to turn the handle is given by (Liljedahl et al, 1979): P = Where T x N 9,550 T Fl P = l h = h 8 Fl h N 9 9, P FN P = Power, kw; F = Force, N; N = Number of revolution (rpm) and l = Length of G-clamp screw h handle The handle is subjected to only bending moment. Therefore, its cross-section is determined considering bending stress. (max) = F l h 1 And Z = 0 dh 18

6 Akor et. al: Design and Development of a Cost Effective Semi-echanized aize Thresher JAEET vol. 1, No., 004 b(max) = max Fl h d h Z For b(max) b(perm) d h Fl h b perm 1/ Where d h = Diameter of handle 4 achine Performance Analysis i. Threshing Efficiency () This was Obtained from the relationship (Adegblugbe, 1986): = ns ns n u ns = number of shelled grains nu = number of unshelled grains 5 ii. Kernel breakage factor The kernel breakage factor is given as (Adegblugbe, 1986) n b = 6 nb nw n b = number of broken kernels and n w = number of whole kernels. iii. Throughput (Q) Q = t w w = Weight of threshed maize t = time 7 Design, Fabrication, Testing and Analysis Using the appropriate equations from design of machine component parts, the following dimensions were obtained: Torque arm: Diameter of handle, d = 1mm Length of handle, 1 = 10mm Thickness of torque arm, t = 9mm Length of torque arm, B = 18mm Length of torque arm, L = 10mm - Rotating Cylinder Thickness of the rotating cylinder, tc = 9mm Length of the cylinder = 70mm Internal diameter = 64mm External diameter = 8mm Length of spikes = 10mm Annulus = 44mm A pipe of 84mm internal diameter was chosen as the sleev to ensure a smooth and uniform rotation of the rotating cylinder during shelling. Support Breadth, b = 11mm Width, h = 11mm Length, 1b = 170mm G - Clamp Length of handle, 1h = 40mm Diameter of handle, dh = 11mm Screw diameter, dc = 11mm C Bracket = 60mm x 60mm Sleeve Thickness = 9mm Length = 0mm Internal diameter = 84mm External diameter = 10mm Fabrication The fabrication of the thresher was achieved following a sequence of work. A mild steel pipe of 9mm thick, 70mm long and 8mm external diameter was cut to form the rotating cylinder, while medium carbon steel of 9mm thick, 0mm long and 84mm internal diameter was cut to form the sleeve, and both were filed to shape. Two mild steel rods of 148mm long and 1mm diameter were cut and welded to form the stoppers. The rotating cylinder was then located inside the sleeve and held in position by the two stoppers, one on each side such that a clearance of 1mm exists between each stopper and the respective side of sleeve. 18

7 Akor et. al: Design and Development of a Cost Effective Semi-echanized aize Thresher JAEET vol. 1, No., 004 A mild steel bar of 170mm long, 0mm width and 0mm breadth was cut, shaped and used as the supporting bar. A 150mm long, 5mm width and 40mm breadth C shaped bar welded to nut and bolt to form the G-clamp. A washer was cut from a mild steel plate, filed to shaped and attached to the upper part of the screw. The support bar was then welded to the sleev at one end and to the G clamp at the other end. A mild steel bar of 9mm width, 6mm breadth and 10mm long was cut to form the rod and fitted to the free handle. Four mild steel rods of 0.5mm diameter and 10mm long were cut, and welded to the inside of the rotating cylinder as t he spikes. Finally rough ends of the fabricated maize Sheller was filed and sand papered to a good finish and the machine coated with an anti-rust paint. Results and Discussion Results The fabricated maize thresher (Plates 1 and ) was tested by threshing thirty-six (6) maize cobs. Results obtained from the test were used to determine the Shelling efficiency, kernel breakage factor and the throughput of the machine. The results are shown in tables 1 and. From the table 1: a. The largest diameter measured was 4.mm. Therefore, the annulus was chosen as 44mm. b. The least size of maize cob calculated was 1.5mm. Therefore, the spikes spacing was chosen as 1.5mm. i. Shelling Efficiency (s) The s of the machine was determined from equation.8. Using table 1.1, column and 4: in the equation shelling efficiency (s) was computed as 96%. ii. Kernel Breakage Factor () Using the values form table 1. column 5 and 6, in equation of kernel breakage factor was obtained as iii. Throughput The throughput of machine was obtained using equation 7, for a threshing time of 966 sec, as 8.7kg/hr. iv. Comparative Test The fabricated thresher was compared to a Chinese thresher (Plate ) of similar capacity and the result is shown in tables and 4. Discussion Test result shows that the semimechanized maize thresher has threshing efficiency (s) of 96.7%, kernel breakage factor (KBF) of 0.006, and a throughput of 8.7kg/hr. The result of a comparative test between the thresher and equivalent Chinese version (tables and 4) shows that the thresher gives a better overall performance than the Chinese version. The Chinese version is about 7 times more expensive (N, 59 : N5,000), produces 1 times more broken grains, times more energy required (waste more energy); produces 45% dust load per unit volume of air and is not available locally. The 100% threshing efficiency of the Chinese version is offset by thresher low breakage factor; its higher throughput; dustless operation and low cost. Threshing efficiency can be improved by increasing the number of spikes with slight increase in energy consumption. Conclusion The lower kernel breakage factor of the thresher places the machine in a better position than the Chinese Sheller, especially where the viability of the threshed grains is important. The test shows that the thresher is simpler and easier to use than the Chinese version. This is because the thresher is small in size with a weight of.5kg. Thus, the thresher is more portable than the Chinese version whose weight is 6.8kg (about times heavier). A simple, cost effective, semimechanized maize threshing machine has been designed and developed for the rural 184

8 Akor et. al: Design and Development of a Cost Effective Semi-echanized aize Thresher JAEET vol. 1, No., 004 farmers using available materials. With maize cobs dried to moisture content of (1 14)%wb, a high threshing efficiency of 96.7%, a low kernel breakage factor of , a throughput of 8.7kg/hr was obtained using the machine, and a lightweight of.5kg. This machine is ready for the market (national and international). Since the machine does not require electricity during its operation, the problem of incessant power outage (where available) is solved. The machine can easily be motorized for higher throughput. Recommendation The following recommendations are vital to maintain high efficiency and production capacity of the machine. i. the machine should be properly clamped and the maize to be threshed dried to a moisture content of 1% - 14%. ii. the shelling efficiency and throughput of the machine can be improved by increasing the length of sleeve, rotating cylinder and addition of a second ring of spikes. iii. Grain scattering during threshing can be controlled by incorporating a catchment around the machine. Table 1: Dimensions of the maize cobs used in the test. S/NO. Length of aize Cob, L (mm) ajor dia, a (mm) Intermediate dia. B (mm) inor dia. c (mm) Size of aize cob (A = (abc) 1/ )

9 Akor et. al: Design and Development of a Cost Effective Semi-echanized aize Thresher JAEET vol. 1, No., 004 Table : Data from threshing experiment aize Cobs Shelling Time(ts) (Seconds) No. of Shelled Grains No. of Unshelled Grains No. of Broken Grains No. of Whole Grains TOTAL 96 16, ,54 EAN Total Weight of Shelled Grains = 9.1kg. Table : Comparative test - Fabricated thresher aize Cobs Threshing Time, t (Seconds) No. of Threshed Grains N s No. of Unthreshed Grains N u No. of Broken Grains N b No. of Whole Grains N w ` TOTAL 1, ,717 EAN Total weight of threshed grains, W T = 0.6kg, N b/n w =

10 Akor et. al: Design and Development of a Cost Effective Semi-echanized aize Thresher JAEET vol. 1, No., 004 Table 4: Comparative test Chinese thresher aize Cobs Threshing Time, t (Seconds) No. of Threshed Grains (N s) No. of Unthreshed Grains (N s) No. of Broken Grains (N b) No. of Whole Grains (Nw) Total 4 1, ,65 ean Total weight of threshed grains, W T = 0.41kg, N b/n w = 0.06 Table 5: Comparison of the machine parameter between fabricated and Chinese maize thresher Fabricated achine (%) Chinese Version (%) Threshing Efficiency () % 100% Kernel Breakage Factor () Throughout (Q) 8.7kg/hr 61.5kg/hr Dust generation Nil 45% of air Cost N, N 5, Table 6: Cost estimate of the fabricated aize Thresher S/N. Name of Part Qty. Description Rate N Amount N 1. Sleeve 1 10, 0mm long and 9mm thick 50:00 50:00 medium carbon steel pipe. Rotating cylinder 1 8, 70mm long and 9mm thick mild steel pipe. Spikes 4 5, 10mm long mild steel Torque Arm 1 L-shaped 10mm long x 6mm x mm mild steel bar and 1, 10mm long mild steel rod 5. Support bar 1 17mm x 0mm x 0mm mild steel Clamp 1 D-shaped, consisting of 60mm C shaped miled steel bar and 1, 9mm long (vertical by 40mm long (horizontal T-shaped mild steel rod 7. Electrodes 1 4 PKS Welding Electrodes Paints 1 Tin Red Oxide Add 50% Labour and Contingencies. 1, Total N, X 1 X X D A B C FC + W T R A R B Figure : Free body diagram of the rotating cylinder under vertical loading Figure 1: Orthographic view of the component parts of the aize Threshing machine 187

rotating cylinder under horizontal loading Screw Nut Handle h du

11 Akor et. al: Design and Development of a Cost Effective Semi-echanized aize Thresher JAEET vol. 1, No., 004 X 1 X X D A B C F C R A R B Figure : Free body diagrm of the rotating cylinder under horizontal loading Screw Nut Handle h du Figure 4: G-Clamp Plate : Testing of the Fabricated aize Threshing Plate 1: A view of the Fabricated aize Threshing PLATE : comparison of the fabricated thresher with a Chinese thresher 188

12 Akor et. al: Design and Development of a Cost Effective Semi-echanized aize Thresher JAEET vol. 1, No., 004 References Adegbulugbe, T. A. (1986):Handbook on Construction of aize Sheller, Institute of Agricultural Research and Training oor Plantation, Ibadan. Barkstorm, K. (1964):Processing Tropical Crops, acmillan Press, Ltd. London, pp FAO (1979):Food and Agricultural Organization, Journal pp. 18. Harrington, R. E. (1970): Thresher Principles Confirmed with a ulti-crop Threshers, Journal of Agricultural Engineering, Vol. 7, No., pp ILO (1984):International Labour Organization, Small-Scale aize illing, Technical emorandum, Geneva, No. 7, pp. 15. Inglet, G. E. (1970):Corn: Culture, Processing, Products. ajor Feed and Food Crops in Agriculture and Food Series. AVI, Westport, Connecticut, U.S.A. Khurmi, R. S. and Gupta, J. K. (1997): A Textbook of achine Design Eurasia Ram Nagar, New Delhi Liljedahl, J. B., Cariton, W.., Turnquist, P. K. and Smith, D. W. (1979): Tractors and their Power Units. ( rd Ed.) John Wiley and Sons LUV, Canada. ohsenin, N. N. (1970): Physical Properties of Plant and Animal aterials (1 st Ed) Gordon and Breach Science Publication, New York, U.S.A Odigbo, E. U. (1976) A Cassava Peeling achine: Development, Design and Construction. Journal of Agricultural Engineering research. Vol. 1, No. pp61-69 Okoruwa, A. E. (1995):Utilization and Processing of aize. IITA Research Guide 5,pp UNIDO (1986): United Nations Industrial Development Organization. Small- Scale aize illing UNIDO. 189

Performance evaluation of a power operated maize sheller

RESEARCH PAPER International Journal of Agricultural Engineering Volume 5 Issue 2 October, 2012 172 177 Performance evaluation of a power operated maize sheller D.B. NAVEENKUMAR AND K.S. RAJSHEKARAPPA