Design and Development of Thresher for Onion Umbels (Allium Cepa Variety Aggregatum L.)

Threshing of freshly harvested, sun dried onion umbels was carried out in a farm level thresher to overcome the drudgery in the conventional threshing method which resulted in more seed damage and affected the germination and vigor index. High quality seeds can be produced through effective threshing and separation process. The thresher essentially consists of a pre thresher, thresher and blower. Peg tooth type pre thresher separates the florets from the hard umbel heads further florets are conveyed to the thresher for separation of seeds from the florets. The rasp bar type thresher separates seeds from the florets and the blower separates good seeds from dust and chaffy materials. The performance of the threshing unit was evaluated in terms of florets threshing efficiency, percent good seeds collected, percentage seed loss and seed damage at different feed rate, peripheral speed and cleaning air velocity. It was concluded from the evaluation that 100 +/- 5 kg/h feed rate, 7 m/s peripheral speed, 6 mm concave clearance with 4.5 m/s cleaning air velocity gave good results. The thresher recorded the maximum threshing efficiency, percentage of good seeds collected, seed damage and cleaning efficiency as 99.85, 97.70, 1.75 and 96.46%, respectively.