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Int.J.Curr.Microbiol.App.Sci (2018) 7(11): 1819-1830 International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 7 Number 11 (2018) Journal homepage: http://www.ijcmas.com Original Research Article https://doi.org/10.20546/ijcmas.2018.711.206 Development and Evaluation of Cleaner cum Pearler for Finger Millet V.V. Tejaswini*, D. Bhaskara Rao, R. Lakshmipathy and Sivala Kumar Processing and Food Engineering, ANGRAU, Bapatla, India *Corresponding author ABSTRACT Keywords Finger millet (Eleusine coracona), Ragi Article Info Accepted: 15 October 2018 Available Online: 10 November 2018 Finger millet (Eleusine coracona), popularly known as Ragi, has high yield potential of greater than 10 t/ha under optimum irrigated conditions. Usually millet seeds have four layers namely hull, bran, germ and endosperm. Among these, endosperm is only the edible part of millet. Bran and germ are rich in oil and hence affect the storage quality of millets. So dehulling / pearling of finger millet is necessary to remove the hull, bran and germ to increase the shelf life of the pearled grain and flour. In traditional dehulling, the grain is mixed with water, allowed to stand for 5 minutes and pounded with a wooden pestle for 10-15 minutes. Then grains are subjected to drying and then winnowing operation to remove the bran and other fine material. The pounding and winnowing processes are repeated several times till the good quality millet is obtained. The most rustic equipment for cleaning is the winnower fan, air blowers etc., this operation is time consuming, laborious and uneconomical to the farmers. Therefore, there is a need to develop a suitable small scale cleaner cum pearling unit for finger millet so that the pearling losses can be reduced and it can be useful for farmers with small land holdings. The developed cleaner cum pearler for finger millet machine consisted of cleaning unit, hopper, and outer cylinder, inner cylinder with 12 cotton felts (10 x 10 x 1 cm) with one end of them bolted on its surface, main frame, aspirator (0.5hp) and electric motor (2.5hp). The cleaning unit consisted of stainless steel plate with circular perforations of 2 mm diameter which works on the principle of vibration through which the cleaned grains goes into pearling unit which consists of inner and outer cylinders. The clearance between cylinders was 2 cm and 1 cm at cotton felts for maximum compression and shearing of grains so that the grains get pearled. Pearled grain enter into closed outlet at the middle of which a pipe from the aspirator was fixed so that the husk and other lighter particles were collected by suction and cleaned, pearled grains were collected at the other end of the outlet. The cleaning efficiency of the machine was 88.2%. The performance of the machine was tested for its pearling efficiency, percentage of broken grain at speeds 1400, 900, 500, 300 rpm; moisture contents 10, 13, 16 % (w.b) and at feed rates 90, 120, 150 kg/h for two passes. The pearling efficiency decreased with increase in moisture content and increased with the increase of cylinder speed and feed rate. The percentage of broken grain decreased with the increase in moisture content and feed rate and increased with increase in cylinder speed. The highest percentage of broken grain was found to be 9.5 % at 10 % w.b moisture content, 1400 rpm at 90kg/h (II pass). The optimum value of pearling efficiency was 80.1 %, 4.3 % of broken grain at 10% w.b moisture content, 900 rpm at 150 kg/h feed rate (II pass). 1819 Int.J.Curr.Microbiol.App.Sci (2018) 7(11): 1819-1830 Introduction Finger Millet (Eleusine coracona) popularly known as Ragi, is originally native to the Ethiopian highlands. It was introduced into India approximately 4000 years ago. It is highly adaptable to higher elevations and is grown in the Himalayas up to an altitude of 2300 m. It is the most important small millet in the tropics (12% of global millet area) and is cultivated in more than 25 countries in Africa (eastern and southern) and Asia (from Near East to Far East), predominantly as a staple food grain. The major producers are Uganda, India, Nepal, and China. Finger millet has high yield potential (>10 t/ha under optimum irrigated conditions). India contributes 55% of total world production. Finger millet is especially valuable as it contains the amino acid methionine, which is lacking in the diets of hundreds of millions of the poor who live on starchy staples such as cassava, plantain, polished rice, or maize meal. Finger millet can be ground and cooked into cakes, puddings or porridge. The grain is made into a fermented drink (or beer) in Nepal and in many parts of Africa. The straw from finger millet is used as animal fodder. Finger millet is nutritionally superior to rice and wheat. These are rich in protein, mineral, vitamins and contain higher proportion of dietary fiber than rice or wheat. Usually millet seeds have four layers namely hull, bran, germ and endosperm. Among these, endosperm is only the edible part of millet. The hull contains mainly indigestible fibers. Due to the presence of outer layer in finger millet the flour colour is black and taste is also not good due to presence of bitterness. Bran and germ are rich in oil and hence affect the storage quality of millets. So dehulling / pearling of finger millet are necessary to remove its outer layer to improve its flour quality. Finger millet is variable in shape, size and colour. It may be elliptical, oblanceolate, hexagonal or globular in shape. Finger millet grains are smaller in size with 1.2 - 1.7 mm diameter. The colour of seed coat of the millet varies from dark red to purple, but brick red is the most common colour. The endosperm and seed coat accounting for about 85% and13% of seed mass, respectively whereas the embryo forms only 1-2% of it. Pearling of finger millet is usually done at a moisture content of 10%. In the process of pearling, it is necessary to remove the hull, bran and germ to increase the shelf life of the pearled grain and flour. In traditional dehulling, the grain is mixed with water, allowed to stand for 5 minutes and pounded with a wooden pestle for 10-15 minutes. Then grains are subjected to drying and then winnowing to remove the bran and other fine material. The pounding and winnowing processes are repeated several times till the good quality millet is obtained. This operation is time consuming, laborious and uneconomical to the farmers. Keeping this in view a suitable small scale cleaner cum pearling unit for finger millet (Eleusine coracana) was developed and evaluated for its performance so that the pearling losses can be reduced and it can be useful for farmers with small land holdings. Materials and Methods Description of various parts of the machine Cleaning unit The hexagon shaped frame consisted of a perforated stainless steel sheet at the top and plane sheet fixed to a frame so that the grains that pass through the perforations fell on the bottom plate and then into the hopper. The circular perforations were of 2 mm. The particles greater than the grain size remains on the top and the grains along with some fine dust and foreign particles fell into the hopper. 1820 Int.J.Curr.Microbiol.App.Sci (2018) 7(11): 1819-1830 Later those fine dust and foreign particles were removed by aspiration. This whole frame was mounted with help of springs on a frame which was welded on the outer cylinder at an angle of 27˚. A cam like arrangement was made between the shaft and sieve so that it is vibrated along with the rotation of the shaft. felt was left free so that it can increase the shearing on the grains by carrying round the rotation and increases the percentage of pearling. It was mounted on a power shaft at its centre. Hopper The solid power shaft was made of mild steel of 3.8 cm diameter and 140 cm length. It was supported at the end on the main frame by UCP208 pillow block bearings. It is powered by motor by means of V-belt pulley arrangement. The hopper was fabricated in trapezoidal shape, using mild steel of 18 gauge thickness and dimensions of 20 cm length, 12.5 cm width and 22 cm height. It is placed on the outer cylinder at one end. Shaft Outlet and aspirator Outer cylinder The outer cylinder was made of 16 gauge mild steel sheet of 40 cm diameter and 80 cm length. One side of the cylinder is open and fixed with a circular plate of 48 cm diameter so that inner cylinder and shaft assembly can be easily accommodated. The pearled grain moved towards the outlet at the end of outer cylinder which had a circular perforations of 1cm diameter so that the grain get discharged slowly through them and fell on the closed outlet. The outer cylinder was welded to the main frame of the machine. Inner cylinder The inner cylinder was made of high carbon steel of 34 cm diameter and 60 cm length having cotton felts (12 Nos.) which were made of several layers of tough cotton fibres similar to material of cotton belts used for conveying with 10 cm length, 10cm width and 1cm thick on it. They were bolted to the drum such that 2 felts and 1 felt alternatively with a distance of 5cm alternatively. Hence there was a clearance of 2 cm between the cylinders and 1 cm where the cotton felts are present. One end of the cotton The outlet was a closed arrangement and made of mild steel at the middle of which a pipe from the aspirator was fixed so that the husk and other lighter particles are collected by suction. An aspirator of 0.5hp power was used for suction of husk and other foreign material from the pearled grains. The area of cross section of the pipe of the aspirator at the suction end was 113.09 cm2 and at the outlet pipe was 50.26 cm2. The velocity of air through the pipe was about 2 m/s hence the air flow rate was 0.025m3/s. The air flow rate was controlled by adjustable gate at the air flow according to the feed rate for better performance. This was concluded based the terminal velocity of the grains. Main frame The metal frame which made of (L) angle iron was fabricated in a trapezoidal shape of 82.5 cm front top width, 76 cm bottom width, 25 cm side top width, 27 cm side bottom width and 75 cm high were welded to the sides of the outer cylinder so that the weight of the whole assembly was balanced and vibrations were minimized. The motor and the electric aspirator motor were also mounted at the bottom of the main frame. 1821 Int.J.Curr.Microbiol.App.Sci (2018) 7(11): 1819-1830 Lb is pitch length of belt (cm) d1 is diameter of pulley mounted at motor (cm) Power Transmission A 3 phase, 2.5 hp motor was used for giving motion to shaft and inner cylinder through belt drive. The belt drive consists of V belt and pulley. The driver pulley of 12.7cm (5 in) was mounted on the motor and the driven pulley of required diameter (13, 20.3, 36.5. 60.9 cm) as per the required speed (1400, 900, 500, 300 rpm) was mounted on the shaft. The variation in the speeds was taken to know the results at low speeds also. As the motor was switched on the driver pulley rotates this motion is transferred to the driven pulley which in turn rotates the shaft and the inner cylinder and the grains get pearled. A 0.5 hp aspirator was used for aspiration of husk, dust and other lighter foreign materials. d2 is diameter of pulley mounted at shaft (cm) x is distance between centres of pulleys (cm) Power required driving the pulley P1 = 2 NT1 (3) Torque T1 = m x g x D/2 m = mass of smaller pulley attached to the belt drive D = Diameter of smaller pulley attached to the belt drive N= Speed of pulley Design of pulley size Power required for driving the shaft and cylinder of pearler unit The size of the pulley can be specified by the diameter of the pulley. It can be determined by the following formula P2 = 2 NT2 (4) T2 = Total weight on the shaft x Radius of the driven pulley (1) N1 = Speed of the driver pulley (rpm) (motor pulley); D1 = Diameter of the driver pulley (rpm) (motor pulley) N2 = Speed of the driven pulley (rpm) (shaft pulley); D2 = Diameter of the driven pulley (rpm) (shaft pulley) Length of the belt Length of the V- belt for different sizes of the pulleys was obtained from the following formula Lb   2 d 1 T2 = Torque to drive the shaft  d  2 2x  d 2  d1 4x  2 (2) = (wt of the cylinder + wt of the pulley) x Radius of the driven pulley Design of shaft diameter Based on the design of the machine horizontal mild steel solid shaft was used. The shaft was subjected to combined twisting and bending moment. Considering the load of cylinder acts at the centre of the shaft. Loads on shaft may be represented by following diagram: Force acting at point C by the weight of the pulley (weight of 60.9 cm pulley was taken). The bending load comprises of horizontal and vertical components. The resultants of the 1822 Int.J.Curr.Microbiol.App.Sci (2018) 7(11): 1819-1830 bending moments at point C and point D were calculated by horizontal and vertical load diagrams. The maximum value was taken as bending moment at that point Mb. Torque transferred by the shaft Mt = F = Fraction of clean seed in feed G = Fraction of clean seed at foreign matter outlet (aspirator outlet + sieve outlet) (5) Pearling efficiency Therefore the diameter of the shaft given by d3 = E = Fraction of clean seed at clean seed outlet The pearling efficiency was given by the following formula (IS: 9555 - 1980). (6) Pearling Ss = allowable combined shear stress for bending and torsion for steel shaft without keyway efficiency (%) ˟ 100 (8) = Percentage of broken grain = 55 MPa Kb = combined shock and fatigue factor applied to bending moment = 1.5 - 2.0 for minor shock. Kt = combined shock and fatigue factor applied to torsional moment = 1.0 - 1.5 for minor shock. The percentage of broken grain was given by the following formula. Percentage of broken grain (%) = ˟ 100 (9) Results and Discussion Performance evaluation of cleaner cum pearler for finger millet Design of pulley size The developed cleaner cum pearler for finger millet was evaluated for combination of different moisture contents i.e., 10, 13, 16 % at different feed rates i.e., 90, 120, 150 kg/h and at different cylinder speeds i.e., 300, 500, 900, 1400 rpm. The performance of the machine was evaluated based on its cleaning efficiency, pearling efficiency and percentage of broken grain. The motor of 1440 rpm (N1) was used and the diameter of the motor pulley was 12.7 cm (D1).The required speeds for testing the machine were 1400, 900, 500, 300 rpm. Hence by using above equation (1) the required diameter of the pulleys for 1400, 900, 500, 300 rpm speeds were obtained as 13 cm (5.1 in), 20.3 cm (8 in), 36.5 cm (14 in), 60.9 cm (24 in) respectively (Fig. 1–6). Cleaning efficiency Length of the belt The cleaning efficiency is given by the following formula. Length of the V- belt for different sizes of the pulleys was obtained from the equation (2) Cleaning efficiency (%) = d1 is diameter of pulley mounted at motor (cm) = 12.7 (7) 1823 Int.J.Curr.Microbiol.App.Sci (2018) 7(11): 1819-1830 d2 is diameter of pulley mounted at shaft (cm) = 13, 20.3, 36.5 and 60.9 P2 = 2 x 1.25 hp x is distance between centers of pulleys (cm) = 44.1 Total power required = 0.18 + 1.2 = 1.43 hp By using the equation (2) pitch length of the belts were obtained as 128.56 cm, 140.36 cm, 168.69 cm, 216.98 cm. x 1400 x 6.37/60 = 933.89 W = Factor of safety 1.5 was considered as different loads are used then, Power = 1.5 x 1.43 = 2.14 hp Hence the belts of B45, B52, B62, B80 available in the market were used. The available motor in market is 1.5 hp, 2 hp, 2.5 hp etc. Power required driving the pulley Hence, a motor of 2.5hp was selected to drive the machine P1 = 2 NT1 Design of shaft diameter Torque T1 = m x g x D/2 m = mass of smaller pulley attached to the belt drive = 1.5 kg From the figure 1, the bending moments at different points on the shafts are calculated as follows D = Diameter of smaller pulley attached to the belt drive = 0.13m Resultant bending moment at point C = 9.920 N-m N= Speed of pulley Resultant bending moment at point D = 35.250 N-m T1 = 1.5 x 9.81 x 0.065 = 0.956 N-m P1 = 2 x 0.18 hp x 1400 x 0.956/60 = 140.2 W = Therefore the maximum bending moment is at point D, Mb = 35.250 N-m Torque transferred by the shaft was given by Power required for driving the shaft and cylinder of pearler unit P2 = 2 NT2 the Equation (5) Mt = P = power of the motor = 2.5 hp = 1.865 kW, N = 1400 rpm T2 = Torque to drive the shaft Hence Mt = 12.72 N-m T2 = Total weight on the shaft x Radius of the driven pulley Therefore the diameter of the shaft was given by Equation (6) = (wt of the cylinder + wt of the pulley) x Radius of the driven pulley = (78.48N + 19.62N) x 0.065m= 6.37 N-m d3 = 1824 Int.J.Curr.Microbiol.App.Sci (2018) 7(11): 1819-1830 Fig.1 Schematic representation of load acting on the shaft 78.48N 58.86N C D RA RB Fig.2 Front view of power operated cleaner cum pearler for finger millet Fig.3 Top and Side view of power operated cleaner cum pearler for finger millet 1825 Int.J.Curr.Microbiol.App.Sci (2018) 7(11): 1819-1830 Fig.4 Variation of pearling efficiency with moisture content and speed of cylinder at feed rate of 90 kg/h Fig.5 Variation of pearling efficiency with moisture content and speed of cylinder at feed rate of 120kg/h Fig.6 Variation of pearling efficiency with moisture content and speed of cylinder at feed rate of 150kg/h 1826 Int.J.Curr.Microbiol.App.Sci (2018) 7(11): 1819-1830 Fig.7 Variation of percentage of broken grain with moisture content and speed of cylinder at feed rate of 90 kg/h Fig.8 Variation of percentage of broken grain with moisture content and speed of cylinder at feed rate of 120 kg/h Fig.9 Variation of percentage of broken grain with moisture content and speed of cylinder at feed rate of 150 kg/h 1827 Int.J.Curr.Microbiol.App.Sci (2018) 7(11): 1819-1830 Power operated small scale cleaner cum pearler for finger millet Hence the diameter of the shaft can be obtained as 17.14 mm. cleaning efficiency can be calculated using the Equation (7). As the shaft is subjected to other speeds also factor of safety 2 can be considered. E = 0.98 F = 0.852 G = 0.0122+0.002 = 0.0142 Diameter of the shaft d= 17.14 X 2 = 34.28mm Cleaning efficiency (%) = Hence shaft of diameter 38mm was adopted. Therefore cleaning efficiency obtained was 88.2%. Cleaning efficiency The average fraction of clean seed at clean seed outlet, fraction of clean seed in feed, fraction of clean seed at aspirator and sieve outlets for all the moisture contents were 0.98, 0.852, 0.0122, 0.002 respectively. Therefore Pearling efficiency Pearling efficiency of the machine was tested for 1400, 900, 500, 300 rpm speeds, at 10, 13, 16 % (w.b) moisture contents and in two 1828