The development and evaluation op small scale threshing and cleaning mechanisms for grain legumes

Abstract

ne®^ was felt to develop locally small scale threshing and cleaning machinery especially in view of the recent orientation towards commercialization of the small scale farming in Bast Africa, i'.oreorer, the recent drive to increase the cultivation of grain legumes in East Africa provided a stimulus to develop the required machinery for grain legumes. The study was, therefore, undertaken with a view to look for appropriate mechanisms and to establish operational parameters for the threshing and cleaning of grain legumes using soyabeans as a testing crop, A basic ob^eotive was that the equipment should be hand operated, v.'ork on threshing was divided into two phases. During the first phase, a novel mechanism oalled the Peristaltic* f was fabricated locally and then its performance was assessed in comparison with the rasp bar mechanism. Output potential, threshing efficiency and grain damage were assessed at varying revolving speeds of the mechanisms and crop m,c. Host of the second phase consisted of a series of observations on the toothpeg mechanism to ascertain its suit* akility and to work out ita optimum operational parameters for threshing soyabeans* The 'peristaltic’ mechanism did not prove to be a suitable mechanism for the purpose in view. Its main draw backs were its inability to thresh a crop above 23-25 per cent moisture content and overall high scutcher peripheral speeds required for efficient threshing and high output* Moreover, its construction requirements did not lend themselves very well for local manufacturing* Both versions of eylinder/concave mechanism, namely the rasp bar and the toothpeg, whioh were evaluated proved to be suitable for threshing grain legumes* However, the toothpeg appeared to have a marginal advantage over the rasp bar because of its ability to thresh high moisture content crop and to strip groundnut shells from their haulms - a process reputed to be labour demanding when done manually* As a result, the study on the toothpeg was extended to cover the collection of basic operational parameters for designing a toothpeg type of threshing machine The study also brought out into light that it may not be very convenient to hand operate these machanisms, largely because of the high amount of energy demanded for rotating them. This was in agreement with a similar type of work undertaken elsewhere. Thus, it is recommended that the machine be power motivated. This machine can then be economically and efficiently operated on hire basis either by a private contractor or a co-operative venture to spread its high initial cost over a large annual produce use. Its likely output can be envisaged within the range of 90- 120 kgs/hr. of grain. Work on cloaning and grading aspects received little attention apart from constructing locally the Universal Cleaner for collecting some basic operational parameters involved in cleaning and grading of the threshed material. This aspect of the study was not pursued in great depth as it was soon realised that a table or stationery screen attached to the thresher and relative simple operations of picking the haulms, would on the whole be adequate, provided that a suitable winnower like the fl.I.A.E. winnower could be made available. The conclusions drawn from the study are summarised in the final Chapter* Some tentative recommendations for fabricating a toothpeg type of machine are also suggested in the same chapter*