DESIGN IMPROVEMENTS OF INDIGENOUS BEATER WHEAT THRESHER IN PAKISTAN

Abstract

Mechanical wheat threshing has gained a spectacular popularity in Pakistan over a short span of time and so is the population of beater-wheat threshers that are being manufactured and marketed by the roadside vendors with little scientific and engineering experience. In fact, the major problems on conventional threshers have been identified as bulky weight, poor machine performance, human accidents and a high fuel consumption rate. Therefore, there was a dire need of research in Pakistan for modification and improvements in the prevalent design of the conventional wheat thresher to bring about durability, reduction in weight of machine and grain losses in addition to an accident free and cost effective thresher. A review of the indigenous thresher suggests presence of three heavy flywheels with little scientific argument and similarly poorly designed beaters/spikes and five rings on the beater-drum appear injudicious and unscientific. A horizontal throw of straw from the exhaust-blower takes away a noticeable amount of grains with it. Indigenous threshers have witnessed terrifying accidents for the persons feeding the material. The local manufacturers least care about the fabrication drawings of the conventional machines and therefore their knowledge of manufacturing is restricted to the whims and wishes of “ustad-shagird” (seniors, juniors).In view of above mentioned problems, the present study hypothesizes engineering oriented solutions for the ill-designs of the conventional threshers. Modified designs and fabrication drawings of various components such as flywheel, beater, beater drum, blower and feeding conveyer were prepared. Both machines were operated during the wheat threshing seasons for two consecutive years at farmer’s field. During threshing seasons 2011-2012 farmers were interviewed about this new design. Their comments were commamorable. Major hindrance in purchasing conventional thresher is high cost. Total weight of redesigned wheat thresher was reduced from 1600 kg to 1300 kg by improving beaters in thresher drum and the grain damage in redesigned thresher reduced four times, thereby saving buying cost about Rs. 50,000 The mean threshing efficiency is increased from 98% to 99%.The replacement of the three flywheels by one wheel of required size saved 24.37 kN-m energy. The fluctuation in speed was reduced to 2.055 times and coefficient of energy two times than that of conventional thresher. By redesigning and redeveloping the direction of fan blower exhaust, the mean grain cleaning efficiency improved from 97.44 to 98.18% causing elimination of grain loss through straw blowing process. In improving the crop feeding system by designing, developing and fabricating a new conveyor, not only smooth uniform feed rate was achieved and saving of 1.3L/hr (15Kw) was assured. 40-66 % vibrations were eliminated on major components of redesigned thresher.