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CHAPTER 3 DESIGN OF BEATER WHEAT THRESHER COMPONENTS

In view of nonscientific design, use of extra materials for various components, more power requirements, unsafe feeding mechanism, grain losses/damage and high initial purchase cost of conventional wheat threshers, present study had been planned to
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  38 CHAPTER 3 DESIGN OF BEATER WHEAT THRESHER COMPONENTS   In view of nonscientific design, use of extra materials for various components, more power requirements, unsafe feeding mechanism, grain losses/damage and high initial purchase cost of conventional wheat threshers, present study had been planned to investigate problems and find out the appropriate justifiable solutions. The succeeding sections provide detailed  procedures for redesigning and fabricating the faulty components and testing them under the field conditions. 3.1 Operating principle of the conventional beater wheat thresher   Tractor operating at rated engine speed powered the thresher through tractor PTO revolving at 540 RPM. The PTO shaft transmitted power through belts and pulleys for crop feeding, threshing, separating and cleaning units. Wheat crop manually fed into the hopper of conventional thresher was threshed by revolving beaters of threshing drum at 815 RPM using impact and rubbing action in the clearance between beaters and concave. Both, the separated grains and chopped straw passed through the concave grates and fall onto the sieves. The tossing action of oscillating sieves separated grain from larger straw chaff and allowed them to fall onto small hole-mesh sieve underneath. The straw chaff was sucked vertically upward  by radial centrifugal fan blower and thrown out of the thresher through the exit outlet installed at the rear side of thresher. The grains were further cleaned from small straw pieces and debris by air coming horizontally from a small blower across the bouncing mixture of grain and material other than grains (MOG). A conventional thresher manufactured by Noorani Industries Samundari Road, Faisalabad (Model 2010) was procured and coupled with MF-375 Massey Ferguson Tractor (PTO Power 75 horse power ‘hp’ at 540 RPM)) for the present study at Postgraduate Agricultural Research Station(PARS) research area, University of Agriculture, Faisalabad Pakistan during threshing season 2011 & 2012. The specifications of conventional beater wheat thresher have  been given in Table 3.1.  39 Table 3.1Comparison of design parameters specifications between conventional and redesigned wheat thresher General Make Noorani Thresher Model 2010(Conventional) Thresher model 2012 (Redesigned) Type Cross flow – double blower Vertical Cross flow – double  blower Application Wheat threshing Wheat and Rice Power requirement 50 hp or above 30 hp and above Transport wheels 02 Nos. 6-16, 8 ply 02. 6-16, 8 ply Sieves 03. MS sheet 1.25 mm thick, Upper: 6.5 mm round hole Middle: 5.8 mm round hole, Lower: 2.4 mm round hole 03. MS sheet 1.25 mm thick, Upper: 6.5 mm round hole Middle: 5.8 mm round hole, Lower: 2.4 mm round hole Power source PTO shaft driven PTO shaft driven Overall dimensions Length (mm) 3700 3700 Width (mm) 1600 1600 Height (mm) 1900 1900 Weight (kg) 1600 1300 Material specifications Threshing drum width,  RPM, Rings, Beater bars,  No. of beaters 1375 mm, 815 RPM, 05. 08 No, equally spaced at 45 O , and 1375 mm long each 100 1375 mm 822 RPM, 05, 8+8, equally spaced at 45 O and 687.5 mm long each at alternate  positions for feed distribution 100 (Design changed) Feeding hopper/chute width 1275 mm 1345 Feeder star shaft 47 mm MS round, hot rolled 45 mm ,cast carbon steel Feeding star wheels 8 Nos. cast steel 8 Nos. cast steel Flywheels (03 No.) flat belt pulley 02 Nos. cast iron (80 kg each), 1  No. (60 kg),1No.(50kg) 01 cast iron 100 kg (instead of two) flat belt pulley 50 kg pulley removed in new thresher Threshing shaft diameter 80 mm MS round, cold drawn 63 mm MS round, cold drawn 3.2 Non-scientifically conventional wheat thresher components to be redesigned The evaluation of thresher components had revealed that following components had been developed non-scientifically.  40 3.2.1 Flywheel The conventional thresher had three flywheels for controlling the vibrational fluctuations. The main function of flywheels was to store energy and dissipate when required, to absorb the vibration and to provide the steady motion to the system. The two flywheels (each of diameter 0.736 m and weight 80 kg) attached at both ends of the main shaft of threshing cylinder rotated at 815RPM speed to absorb excessive vibrational impacts resulting from variations during non-uniform manual feeding (Figure3.1).The third flywheel (0.493 m diameter and 60 kg weight) placed on the tractor PTO, rotated at 540 RPM for presumably damping the vibrational effects received from the tractor (Figure3.2) and fourth one is the flat  belt pulley (0.300 m diameter and 50 kg)placed on the opposite to tractor PTO side on main shaft. The available flywheels were considered too heavy, utilizing extra energy, out of place, more in number, and therefore they demanded redesigning. In order to reduce their weights as well as number for optimum requirement, available literature relating mechanical design  provided elaborative information for determining energy stored in flywheel, mass and dimensions of flywheel (Khurmi and Gupta, 2009; Shigley and Mische, 2007 and Kepner et al., 2005). Figure 3.1 Top view of conventional wheat thresher  41 Figure 3.2 Side view of conventional wheat thresher 3.2.2 Centrifugal radial fan blower  A fan blower (975 mm pedal diameter with 1000 mm casing diameter) was employed in the conventional thresher (Figure 3.3, part no 8, 12). During field test 1-2% wheat grain loss was observed in the outgoing straw from the exhaust chute of thresher. Since the wheat was a high value food crop, this grain loss was unacceptable. This high amount of loss quantity suggested the redesigning of the conventional thresher exhaust chute / blower.  42 Figure 3.3 Exploded view of various components of conventional thresher  Parts Description 1 Star blade 2 Star shaft 3 Star shaft pulley 4 Idler pulley 5 PTO Pulley 6 Flywheel 7 Conventional beaters 8 Pedal fan blower 9 Flywheel 10 Main cylinder beater shaft 11 Feeding chute 12 Casing of fan blower 13 Pulley 14 Concave sheave 15 Frame for sheave 16Feeding frame 17 Cam for vibrating motion of mesh 18 Small cleaning chaff  blower 19 Vibrating mesh 20   Main frame of thresher
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