Design and Development of an Engine Driven Onion Grading Machine

ABSTRACT


INTRODUCTION
Onion (Allium cepa L.) is a member of the Allium genus of the Alliaceae family. It is thought to have originated in southwestern Asia, which was the center of domestication and variability. It is from this place that it spread worldwide and has been cultivated annually for bulb production for over 4700 years (Brewster, 2008). The introduction to Africa in general, and Ethiopia specifi cally, was not well-known. However, it has been suggested that as introduced by foreigners in the early 1970s and by now produced widely in many parts of the country than the traditionally grown shallot (Adgo, 2008). In Ethiopia, onion is one of the most important vegetable crops grown on a small scale. It is also one of the most economically important vegetables in the country. The area under onion is gradually rising, owing to its high profi tability per unit area and ease of production, and the expansion of small-scale irrigation regions (Nigussie et al., 2015). It ranked second in the production of all vegetable crops next to Tomato, which has been concentrated in the central rift valley of the country, particularly in the upper Awash and Lake Batu areas (Bossie, 2009). In Ethiopia, the crop is used extensively in food fl avoring and everyday stews, as well as in various vegetable food preparation uses. Despite its year-round production settings, the crop's yield and productivity are much below (10.02 t/ha) the world average (19.7 t/ha) (FAO, 2012). Because of the lack of improved cultivars, the use of inappropriate agronomic practices such as pre-harvest and post-harvest management practices, and a lack of attention/awareness about the benefi ts of intensive production, the low yield results indicate that there is a huge gap in production and productivity in the country. In onion production, postharvest losses are widespread due to the perishable nature of the onion and the lack of proper postharvest practices and processing technology, which is a major production restriction that reduces productivity. The major causes, according to the fi ndings, are primarily related to technical limitations in harvesting techniques, handling, conveying, packing, storage, and cooling facilities in diffi cult climatic conditions, infrastructure, and marketing systems (Gebru, 2015). Similarly, several studies identifi ed the most common causes of postharvest losses as a lack of sorting and grading to eliminate defects before storage. Demand for onion has increased over the years and so is its quality. After the harvest of onions, their quality is important to the fi nal consumer. Damage-free post-harvest handling is regarded as a necessity for increasing the farmer's profi t margin in in-freshly eaten commodities like an onion.Grading is the process of classifying materials into various homogeneous groups based on specifi ed qualities such as size, shape, colour, and quality (Londhe et al., 2018). It lowers handling losses during transport and saves time and energy in various processing procedures. Grading also facilitates packing, marketing, and other post-harvest procedures. Grading agricultural products, particularly fruits and vegetables, according to their size is an important value-adding technique that increases the market value required for cross-border trade (Charles and Etiese, 2020). According to the World Trade Organization (WTO), new marketing trends need high-quality graded items. Uniformity in size makes the product more attractive to consumers and also improves its processing qualities. In a developing country, most fruit and vegetable growers grade their products by hand. Grading by hand is expensive and the operation is hampered by labour shortages during high seasons. Human operations can be ineffi cient, inconsistent, and time-consuming. Farmers are hoping for suitable agricultural product grading equipment to help ease labour shortages, save time, and improve the quality of graded products (Mostafa, 2004).

Keywords
https://journals.e-palli.com/home/index.php/ajfst Am. J. Food. Sci. Technol. 2(2) 1-13, 2023 In Ethiopia, onion growers are the major actors who perform most value chain functions from farm inputs preparation to post-harvest handling and marketing (Agidew, 2018). Farmers sell their onion produce without grading which leads to post-harvest losses during packing and transporting. Also, they receive a lower price for their produce. However, manual size grading of onion crops is practiced by whole-sellers and retailers thereby, they make a higher profi t than farmers. Manual grading is laborintensive, inconsistent, time-consuming, less effi cient, and not standardized. To achieve a uniform size of onion bulbs proper grading mechanism is required, and with the aid of a grading machine, that goal can be achieved (Aher et al., 2019). Different fruit and vegetable grading machines have been developed worldwide. Divergent roller type, expanding pitch type, inclined vibrating plate, and counter-rotating roller with inclination type graders are developed for grading fruit and vegetables depending on size basis (Charles and Etiese, 2020). In Ethiopia persons engaged in postharvest handling of crops have no chance to use imported high-cost size separation and grading techniques. Such high-grading equipment is not useful to small-scale farmers because of the high cost of the machine, high cost of operation, and more maintenance cost. Small-scale farmers and wholesalers are in crucial need of low-cost graders. Various types of onion grading machines suitable for small-scale farmers were developed using different design approaches. However, these machines are with some limitations related to functional requirements, safety aspects, portability, and ease of operation which affects the performance of the machine. Mainly, the problem observed with those machines were a high percentage of onion bulb damage, low capacity, the rigidity of the design, and also the power source they used is not suitable for the farmers in our country who mostly have no access to electricity. In order to solve this, the present study work was carried out to design and develop an onion grading machine while taking into account the needs of the local market and the lack of suitable low-cost onion grading equipment for small and medium-scale farmers.

MATERIALS AND METHODS Description of Experimental Site
To fulfi ll objectives, the designing and manufacturing of the onion grading machine prototype was conducted in the Asella Agricultural Engineering Research Center (AAERC) which is located in Oromia National Regional State, Ethiopia. It is located at 6° 59' to 8° 49' N latitudes and 38° 41' to 40° 44' E longitudes, having an elevation of 2430 meters above sea level.

Design Principles and Considerations
To design and fabricate a suitable machine, machine design parameters were considered before the design and fabrication of the machine. Therefore, designs parameters consider to be important were as follows (Khurmi & Gupta, 2005); The kinematics of the machine: The successful operation of any machine depends largely upon the simplest arrangement of the parts which give the motion required. Selection of materials: A designer must have a thorough knowledge of the properties of the materials and their behavior under working conditions. Some of the important characteristics of materials are strength, durability, fl exibility, smoothness, weight, resistance to heat and corrosion, ability to be casted, welded, or hardened, machinability, electrical conductivity, etc.

Design and Analysis of Machine Components
The machine was designed to grade onion bulbs into three distinct size ranges small (<40 mm), medium (40-60 mm), and large-sized (>60 mm) bulbs according to the size of onion bulbs with three rotating cylinders having parallel bars spacing of different dimensions. These categories of size were made based on international standards of the marketable size of onion bulbs suitable for commercial applications (Ashraf, 2007). The main components of the onion bulbs grader prototype designed and developed were: Feeding hopper, concentric cylindrical grading unit, pulleys and belts, bearings, power source, and supporting frame as shown below in Figure 1. 1-Feeding rate; 2-Top cover; 3-Rotating shaft; 4-Pulley; 5-Belt; 6-Engine; 8-Speed reduction pulley; 9-Ground wheel; 10-Collection outlets; 11-Grading unit; 12-Mainframe; 13-Handle  The designed volume of the hopper is 0.09 m 3 is greater than the theoretical volume (0.073 m 3 ) determined by equation 2. Therefore, the designed dimensions of the hopper are valid.

Main Frame
The frame is the skeletal structure of the grader which forms the platform on which other components are mounted. The total weights carried by the frame are; the weight of the feed hopper, weight of the grading unit, weight of the collection tray, weight of the shaft, the weight of bearings, pulleys, and the belt. The two design factors considered in determining the material required for the frame were weight and strength. The machine frame was constructed from steel angles and rectangular pipe of 50×30×3 mm. Two rubber wheels were provided on one end to simplify the transportation of the machine. The frame and other parts of the grading machine were connected using appropriate sizes of bolts and nuts and the welding process.

Design of Feeding Hopper
The hopper was designed using a mild steel sheet with a 1.5mm thickness. The size of the hopper was determined on the basis of mass and volumetric capacity of the maximum feeding rate and average bulk density of ungraded onion bulbs. The inclination of the hopper was designed based on the angle of repose of onion bulbs (Ukey & Unde, 2010). A trapezoidal shape of the hopper was used for the machine due to consideration of the free fl ow of onion bulbs. The bottom of the hopper is slightly tilted downwards to enhance the fl ow of onion bulbs directly to the center of the rotating cylinder. The hopper has a sliding gate to control the feed rate. The following parameters were considered for the design of the hopper; Angle of repose = 46.30, Bulk density of onion bulbs = 549.7 kg/m 3 . Then theoretically, it was assumed to hold at least 40 kg onion bulbs as the maximum feeding rate of the machine was 35 Kg/min and the volume of the hopper was calculated by the following formula according to Begum (2018).
(2) V h =1.1((40 kg)/(549.7 kg/m 3 ))=0.073 m 3 Where: V h = volume of hopper, (m 3 ) V o = volume of onion bulbs, (m 3 ) Wo= weight of onion bulbs, (kg) ρ_bulk= bulk density of onion bulbs, (kg) Therefore, the required volume of the hopper is 0.073 m 3 Figure 3 show the shape of the hopper was designed in a trapezoidal shape and we can get the practical dimensions by assumptions. Hence, here also it was assumed that the hopper has a square in size with base width

Grading Unit
The grading unit was designed using a mild steel rod, mild steel fl at bar and mild steel shaft consisting of three cylindrical sieves having parallel bars cells. The rotating cylinders are arranged one inside the other according to the size (the larger spacing being internal, while the smaller one being external) and shown below in Figure  4. The ungraded onion bulbs are directed to the internal cylinder and the larger size bulbs are graded directly and collected at the end of the internal cylinder, while the medium and smaller size bulbs are dropped down to the second cylinder for further grading and the medium bulb size onion bulbs are left on this second cylinder collected at the end. Finally, the bulbs with smaller sizes are going to the third sieve or cylinder and are collected at its end. The cylindrical sieves are fi xed on the driveshaft and fi xed with the machine frame. The volume of the rotating cylinders can be determined based on the fl ow of granular material through a circular shape. Many researchers suggested that the diameter of the rotating cylinder could be varied between 200 and 550 mm depending on the size range of the fruits and vegetables, volume, and desired capacity of the grading unit (Dereje, 2019;Charles and Etiese, 2020;Hegazy and Mady, 2018;Gunathilake et al., 2016). For this design, the dimensions of the internal cylinder were 850 mm long and 250 mm in diameter with a spacing of 60 mm. The middle cylinder has 650 mm long and 350 mm in diameter with a spacing size of 40 mm, and the external cylinder has 450 mm in length and 450 mm in diameter with a spacing size of 20 mm. The length of the rotating cylinders was decided by considering the previously developed rotating type graders and by assuming that the dimensions can provide enough path and time of retention for onion bulbs to be graded.

Weight of Grading Unit
The mass of the rotating cylindrical grading unit was determined from the volume and density of the mild steel rod and rolled mild steel fl at bar materials used to manufacture the grading cylinder (Charles and Etiese, 2020). Based on previous work recommendations related to material selection to minimize bulb damage the mild steel rod having a diameter of 10 mm was used for all cylinders and arranged with different spacing and lengths as mentioned above. Also, the rolled fl at bar with different diameters was welded with the steel rods and constitutes the overall mass of the rotating cylinders.

Theoretical Analysis of the Grading Unit
To determine the power required to move onion bulbs through the rotating grading unit it is important to consider the process by which ungraded onion bulbs are delivered from one end of the inclined rotating cylinder and try to reach the other end of the cylinder. During this process, onion bulbs at the lower portion of the cylinder are lifted upward by the screen surface, after which they are again lifted along with it and slide down. They gradually move toward the opposite end of the cylinder. The bulbs are in contact with only a part of the cylindrical surface with no relative movement with respect to it during their lifting. The nature of the motion of onion bulbs over the surface of the cylindrical sieve depends upon the coeffi cient of friction on the given surface. The kinematics operating condition is governed by centripetal acceleration (rω 2 ), the initial conditions of motion of the bulbs, the point at which they are delivered onto the grading surface (grading cylinder), and their initial velocity. Depending upon the relationship between the above factors, the bulbs in the cylinder may slide along with it, separated from its surface, and perform a free fl ight or may move with the surface being at rest relative to it. In the last case, the bulbs are not graded (Bosoi et al. 1991). Neglecting the sliding motion of the onion bulbs inside the cylinder, the release of onion bulbs through the cylindrical grader depends upon the relative velocity and the forces acting on each bulb. The weight of onion bulbs is directed downward and the centrifugal force is given below (Abd El-Tawwab et al., 2012).
W o =mg (9) Fc = m r ω 2 (10) Where: W o = weight of the onion bulbs (N), m = mass of the onion bulbs (kg), F c = the centrifugal force (N), g = acceleration due to gravity (9.81m/s 2 ), r = the radius of the internal cylinder to which ungraded onion bulbs were applied fi rst (0.125 m), ω = the angular speed of the rotating cylinder (s -1 ). The motion of the bulb on the cylinder surface is not determined by the tangential forces alone. But, if the resultant of the normal forces (N f ) is not directed towards the cylinder surface, the bulb will lose contact with the cylinder.
The number of rotations per minute (N c ) found above is the critical speed at which falling ends and onion bulb remains in constant grading cylinder contact, held there by centrifugal force. The rotating cylinders are set inclined to the horizontal plane, to improve the internal pressure forces during the rotation of the mass of the onion bulbs. In this study, the slope angle of the rotating cylinders on the horizontal plane (6°) was selected according to Charles & Etiese (2020).

Rotational Torque of the Rotating Cylinder
The torque developed by a rotational body was estimated by multiplying the Force (Fc) causing the motion by the radius of rotation (r) of the rotating cylinder (Hannah and Stephens, 2006). T=F c ×r (26) Where: F c = centrifugal force required to produce acceleration (N) and r = radius of rotation (radius of the rotating cylinder). But, F c =ma=mω 2 r (27) Where: m = mass of the rotating cylinder (kg), ω = angular speed (rad/sec), N c = rotational speed of the rotating cylinder (62.95 rpm) based on the value from equation (21), and r = radius of rotational cylinder = 0.125 m. ω=(2πN c )/60=2π×62.95/60=6.60 rad/sec So, F c =mω 2 r=43.41×(6.60) 2 ×0.125=235.80 N The torque on the rotating cylinder was; T=F c ×r=235.80×0.125 =29.48 N m The power required by the rotating cylinder was determined using the equation below as developed by Khurmi and Gupta, (2008). P C =(2πN c T)/60 (28) =(2π×62.95×29.48)/60=194.30 Watts The power required to overcome air resistance was determined by Eqn. (29) (Sale et al., 2016). P AR =K f ×F r ×V t 2 (29) Where: P AR = power required due to air resistance, (Watts), K f = constant which is equal to 0.06 (Sale et al., 2016), F r = feed rate, 35kg/min = 0.5833 kg/s, V t 2 = peripheral or tangential velocity of the grading mechanism (m/s) N c = rotational speed of the grading cylinder (62.95 rpm), and r = radius of cylinder (0.125mm). V t =N c ×π/30×r (30) V t =62.95×π/30×0.125 m V t = 0.83 m/s Then, the power requirement due to air resistance P AR will be; P AR =0.06×0.5833kg/s ×(0.83 m/s) 2 P AR = 0.0238 kW = 23.80 Watts

Power Transmission and Drive System Selection of Pulley and Speed Reduction
The pulleys used in the drive system were groovetype pulleys made of cast iron. Pulley diameters were selected based on the need to reduce the engine speed to the required one. The power transmission system was designed to reduce the engine output shaft speed from 1400 rpm to 87.5 rpm of the grading unit rotating shaft. During the test, the engine throttle valve was used to adjust the rotating speed to an optimum level. The power reduction was designed in 2 stages and fi nally, the pulleys shown in Figure 6 were selected. Two-speed reduction stages are given below: The speed ratio was calculated by using Eqn. (46) (Khurmi and Gupta, 2005). Speed ratio= N 1 /N 2 =D 2 /D 1 (31) Where: D 1 = diameter of the driving pulley on the engine shaft(m), D 2 = diameter of the driven pulley on the speed reduction shaft(m), N 1 = speed of the engine pulley (1400 rpm), and N 2 = speed of the driven pulley on the speed reduction shaft (rpm)

First Stage Speed Reduction
In the fi rst stage of reduction, the driving and driven pulley has been selected. Assume the diameter of the driving pulley with a speed ratio of 3.33: 1. From Eqn. (31) the diameter and speed of the driven pulley were computed as follows. D 2 /D 1 =3.33=D 2 /0.075= D 2 =0.249 m, an available pulley of 250 mm diameter was selected. So, the speed of the counter pulley on the speed reduction system was calculated using the following formula (Khurmi & Gupta, 2005). N 1 /N 2 =D 2 /D 1 =N 1 D 1 =N 2 D 2 , N 2 =N 1* D 1 /D 2 =(1400*0.075)/0.25= 420 rpm, hence, in the fi rst reduction stage engine speed was reduced from 1400 rpm to 420 rpm.

Second Stage Speed Reduction
In the second stage, speed was reduced by using a small size pulley mounted on the freely rotating shaft with a speed ratio of 4.8:1. Then, the diameter and speed of the pulley mounted on the rotating grading cylinder shaft were calculated as follows (Khurmi and Gupta, 2005). D 4 /D 3 =4.8 =D 4 /0.075= D 4 =0.36 m = 360 mm. Also, the speed of the driven pulley was calculated as follows. N 3 /N 4 =D 4 /D 3 =N 3 D 3 =N 4 D 4 ,N 4 =N 3* D 3 /D 4 =(420*0.075)/0.36= 87.5 rpm, In the second stage of speed reduction speed was reduced from 420 rpm to 87.5 https://journals.e-palli.com/home/index.php/ajfst Am. J. Food. Sci. Technol. 2(2) 1-13, 2023 rpm. Where: D 3 = diameter of the driving pulley on the speed reduction shaft (m), D 4 = diameter of the driven pulley on the grading unit rotating shaft (m), N 3 = speed of the driving pulley on the speed reduction shaft (420 rpm), and N 4 = speed of the driven pulley on the grading unit rotating shaft (rpm). Therefore, in power transmission, engine speed was reduced by two stages from 1400 rpm to 87.5 rpm for grading operation. Further material selection and design calculation related to the driving pulley on the speed reduction shaft and driven pulley mounted on the grading unit rotating shaft used for the grader power transmission system was computed as follows. The width of the pulley (face width) "B" is usually considered to be 25% greater than the width of belt (b) and Eqn. (32) (Richard and Nisbett, 2011) can be used to estimate the width of the pulley. According to IS:2494-1974 top width of an "A" type v-belt for a 75 mm pulley diameter is 13 mm. So, B=b+0.25b=1.25b =13+0.25×13=16.25 mm The thickness (t) of the driving and driven pulley rim for a single v-belt can be determined using Eqn. (33 or 34) (Richard and Nisbett, 2011). So, for a driving pulley; V=(πd 2 /4)×t=(π×0.075 2 )/4×0.00225=9.94×10 -6 m 3 m=ρ×V=7200×9.94×10^(-6)=0.0716 kg W p =m×g=0.0716 ×9.81=0.7021 N Also for the driven pulley, we have; V=(πd 2 /4)×t=(π×0.36 2 )/4×0.0048=4.88×10 -4 m 3 m=ρ×V=7200×4.88×10 (-4) =3.5 kg W p =m×g=3.5 ×9.81=34.5 N The velocity ratio between two pulleys transmitting torque is given as:

Selection of the Belt
Classical V-belt and groove-type pulley arrangements were used in this work to transmit the power required by the grading machine (Figure 7). The main reasons for using the v-belt drive are its fl exibility, simplicity, and low maintenance costs. Additionally, the v-belt can absorb shocks thereby mitigating the effect of vibratory forces (Khurmi and Gupta, 2005).

Determination of Belt Contact Angle
The belt contact angle(φ) is given by the following equation (Khurmi and Gupta, 2005). φ=sin -1 ((D 4 -D 3 )/2x) (39) Where: φ = belt contact angle (rad), D 3 = diameter of driving pulley on the speed reduction rotating shaft (m) = 0.075 m, D 4 = diameter of driven pulley on the grading unit rotating shaft (m) = 0.36 m, and x = distance between the pulleys from center to center. The distance between the pulleys from center to center was determined by using Eqn. (40) (Khurmi and Gupta, 2005).

Determination of Belt Tensions
The driving pulley was considered for the calculation of tensions in the V-belt because the pulley of a smaller diameter governs the design. According to IS: 2494-1974 dimensions of "A" type v-belt for 75 mm pulley diameter is; top width, b = 0.013 m, thickness, t = 0.008 m, bottom width, w = 0.011 m, length of the belt, L=1.331 m, the density of rubber belt, ρ=1140 kg/m 3 , coeffi cient of friction, μ = 0.25 and the allowable stress, σ a = 2.5 MPa (Khurmi and Gupta, 2005).
The peripheral velocity, V of the belt on the driving pulley is: V=r×ω 3 (44) V=0.0375×43.98 =1.65 m/s Where: V= the peripheral velocity of the belt on the driving pulley (m/s), r = radius of the driving pulley, and ω 3 = angular velocity of a belt on the speed reduction driving pulley (rad/s). The mass of the belt, m was given by; m=cross sectional area ×length×density (45) m=b×t×L×ρ (46) m=0.013 m×0.008 m×1.331 m×1140 kg/m 3 = 0.1578 kg Where; m is the mass of the belt. The centrifugal tension, T c between the contact pulley face and belt is given by; T c =mv 2 (47) =0.1578 kg×(1.65 m/s) 2 = 0.43 N The maximum allowable tension in the belt was determined as; T max =σ a ×A (48) =2.5 N/mm 2 ×104 mm 2 =260 N Therefore, the tension in the tight side of the belt, T 1 was computed as; T 1 =T max -T c (49) T 1 =(260-0.43)N=259.57 N Where: T 1 = tension in the tight side (N), T c and T max = the centrifugal and maximum tension of the belt (N) respectively, A = cross-sectional area of a belt (mm 2 ), m = mass per unit length of a belt (kg/m), and σ = maximum allowable stress of belt (MPa). Tension in the slack side of the belt, T 2 was calculated as follows (Khurmi and Gupta, 2005). ln(T 1 /T 2 )=μ×θ 1 ×Cosecβ (50) Where: T 1 = tension of the belt on the tight side (N), T 2 = tension of the belt on the slack side (N), μ = coeffi cient of friction between the belt and the pulley (0.25), θ 1 = lap angle on driving pulley (2.12 rad), and β = groove angle (18o). ln(T 1 /T 2 )=0.25×2.12×Cosec18 (259.57 N)/T 2 )=e 1.715 ((259.57 N)/T 2 )=5.557 5.557 T 2 =25 T 2 =46.77 N

Design of Grading unit Driving Shaft
The shaft transmitting power under various operating and loading conditions can be designed based on the strength or rigidity principle (Richard and Nisbett, 2011). The shaft would be subjected to fl uctuating torque and bending moments during operation under load conditions. Shock and fatigue factors were therefore taken into consideration. To determine the diameter of the grading cylinder shaft; all forces acting on the shaft (weight of grading cylinders, weight of maximum feeding rate of onion, tight side and slack side tensions of the belt, and weight of pulley) were considered. From Eqns. (8, 9, 35, 49, and 50), the weight of grading cylinders, the weight maximum feeding rate of onion bulbs, the weight of the pulley, and the tight side and slack side tensions of the belt were determined as 425. 85 N, 343.35 N, 259.57 N, 46.77 N, and 34.5 N, respectively. Shear force and bending moment diagrams on the vertical and horizontal planes were determined by considering the inclination of the rotating grading unit shaft to the horizontal plane. For rotating shafts, where the load is suddenly applied (minor shock) the combined shock and fatigue factor applied to the bending moment is given as 1.20 to 2.00 while the combined shock and fatigue factor applied to the torsional moment is given as 1.00 to 1.50 (ASME, 1995). The diameter of the rotating shaft was determined by computing the force acting on the shaft in a vertical and horizontal direction as shown below in Figure 8.

Forces Acting on Grading unit Driving shaft on Horizontal (XZ) Plane
Analysis of horizontal forces acting on the shaft as shown in Figure 11.  Based on the magnitude and location of all horizontal forces acting on the shaft of the rotating grading unit, the shear force and bending moment diagram on the horizontal plane (Figure 12 Khurmi and Gupta (2005), torque on a shaft can be calculated using Eqn. (52). T=(T 1 -T 2 )×D 4 /2 (52) =(259.57 N-46.77N)×0.36/2=38.30 Nm The power required to rotate the grading cylinder shaft will be determined from the equation below. P SH =2πNT/60 (53) P SH =(2π×62.5×38.30)/60=252.48 Watts Where: P SH = power required to rotate the grading unit shaft (Watts) T = torque on the shaft (Nm), T 1 = tight side tension of a belt (259.57 N), T 2 = slack side tension of a belt (46.77 N), D 4 = diameter of the driven pulley on the grading unit rotating shaft (0.36 m), and N= rotational speed of rotating shaft (62.95 rpm). For a solid shaft with little or no axial load, the diameter of the shaft that can withstand the applied loads can be determined using Eqn. (53) (ASME, 1995;Khurmi and Gupta, 2005).
(53) =16/(π×45) √((1.3×90.07×1000) 2 +(1.2×38.30×1000) 2 d 3 =14,236.29 mm 3 d=24.24 mm Therefore, the diameter of the driving shaft was taken as 25 mm. Where: d = diameter of the shaft (mm), M b = bending moment (90.07Nm), M t = torsional moment (38.30 Nm), and the values of combined shock and fatigue factor applied to bending moment(K b ) and combined shock and fatigue factors applied to the torsional moment(K t ) were taken as 1.3 and 1.2 respectively for the gradually applied load on the rotating shaft and the allowable shear stress of the shaft (τ) as 45 N/mm 2 based on the ASME code. The amount of twist permissible depends on the type of load application and varies between 2.5 to 3.00 degrees per meter for line shafting. Therefore, the angle of twist (for the solid shaft) can be determined using Eqn. (54) Khurmi and Gupta, (2005). θ=(T×L)/(J×G) (54) =(38.30×1.35)/(3.8×10 -8 ×80×10 9 )= 0.01685 rad or 0.96o The maximum twist on the shaft was found to be 0.96o/m. The calculated angle of twist was less than the permissible angle of twist (3˚/m). So, the shaft design based on the torsional rigidity is safe. 2.3.6. Bearing selection A bearing is a machine element that supports another moving machine element (known as a journal). It permits a relative motion between the contact surfaces of the members while carrying the load (Khurmi and Gupta, 2005). Bearing size can be selected by determining the maximum resultant force on it, bore size, and desire maximum lifespan. https://journals.e-palli.com/home/index.php/ajfst Am. J. Food. Sci. Technol. 2(2) 1-13, 2023 N = rotational speed of the rotating the shaft (rpm), L d = the number of design revolutions, H m = according to Robert, (2018), the desired maximum life span of the bearings for agricultural equipment was 6,000 hours, and K= 3 for ball bearings and 10/3 for roller bearings. Since the diameter of the shaft has been determined to be 25 mm, the bearing number 205 by the bore of 25 mm with a width of 15 mm was selected according to Khurmi & Gupta, (2005) (Figure 13). Consequently, the basic dynamic load rating of the bearing was estimated using Eqn. (57) and found to be 1.08 kN. Since the basic dynamic load rating of the bearing selected is less than the dynamic load rating by the manufacturers (i.e. 1,080N < 11000 N), the bearing selected was safe.

Estimation of Power Required to Operate the Grading Machine
The power required to operate the grading machine is the total sum of the power required to move the onion bulb inside the cylinder (P O ), the power required to drive the grading unit (rotating cylinder) (Pc), the power required to overcome air resistance (P AR ), and the power required to rotate the grading unit shaft (P SH ), based on equations (25), (28), (29), and (53). The total power (P TO ) required for grading and overcoming friction was determined using Eqn.58 (Nduka et al., 2012). P T =P O +P C +P AR +P SH (58) =446.35+194.30+23.08+252.48=916.21 Watts P TO =P T +0.10P T (10% is possible power loss due to friction drive) (59) =916.21+0.10(916.21 )= 1007.83 Watts = 1.35 hp Where: P T = power required by the machine (Watts), P TO = Total power required for grading machine and overcome loss due to friction, (watts) P C = power required to rotate grading cylinder (Watts), P SH = power required rotating the grading cylinder shaft (Watts) P O = power required to move the onion bulb inside the cylinder (Watts), and P AR = power required to over-come air resistance (Watts). Therefore, a 3 hp Honda diesel engine with the desired crank speed of 1400 rpm was selected to drive the grading machine during the performance evaluation of the prototype.

Manufacturing Process of the Machine Components Constructional Materials
The selection of a proper material for a machine part or structural member is one of the most important decisions the designer is called on. The main factors considered while selecting materials were the availability of the materials, suitability of the materials for the working conditions in service, and the cost of the materials. The important properties, which determine the utility of the material, are physical, chemical, and mechanical properties (Khurmi and Gupta, 2005). This chapter will cover a detailed description of the manufacturing process of each machine part of the grading machine Manufacturing can be defi ned in two ways; technologically and economically. Manufacturing from the technology point of view can be defi ned as the application of physical and/or chemical processes to alter the geometry, properties, and/or appearance of a given starting material to make parts or products. Then these multiple parts may be assembled to make fi nished products. Economically manufacturing is the transformation of materials into items of greater value by means of one or more processing and /or assembly operations, i.e. manufacturing adds value to a starting material by changing its shape or properties, or by combining it with other materials that have been similarly altered. The material has been made more valuable through the manufacturing operations performed on it (Groover, 2020). The step of the manufacturing process helps to produce the machine locally using available material. Required tools and machines are used as per necessity. The processes to accomplish manufacturing of the machine involve a combination of machinery, tools, power, and labor to give the fi nished part as summarized in Table 1below. Machines used in the manufacturing of the grader components are: 1. Lath machines 2. Welding machine 3. Bending machine 4. Manual rolling machine 5. Grinding machine 6. Hand drilling machines Measuring, cutting, holding and other tools used: 1.Turning tool and drill bits 2. Measuring tape and Caliper 3. Steel rule, try square, screwdrivers 4. Grinder discs and cutter discs 5. Metal sand paper, Scriber (pencil), and Center punch 6. Vice gripper, bench vice, and c-clamp 7. Hammer (plastic and metal), compass, and protractor 8. Paints and paint brushes. The above parts of an onion grading machine are those that can be manufactured with the tools and machines available at Asella Agricultural Engineering Research https://journals.e-palli.com/home/index.php/ajfst Am. J. Food. Sci. Technol. 2(2) 1-13, 2023 Center (AAERC) workshops and tools that can be purchased easily from local markets. However, bearings, belts, and pulleys are directly purchased from the market based on the design requirements and dimensions.

CONCLUSION AND RECOMMENDATION
By utilizing materials found on the local market, an onion grading machine's design and construction were completed. The machine, which has wheels for transporting it from one location to another, weights 125 kg. The developed grading device had a 1488.43 kg/ hr grading capacity and a 96.04% grading effectiveness. By adding additional feeding mechanisms and using manufacturing materials appropriate for grading other crop types, the design can still be enhanced to increase the capacity and effi ciency of a grading operation. In areas with access to electricity, using a variable speed motor for straightforward control of the grading unit cylinder speed is recommended. It is advised to investigate the possibility of enhancing the design and fabrication in order to put the product into mass production, which can also open up the possibility of income generation.