by Professor A. S. Rana
Head of the Department of Agricultural Engineering and Land Planning, University of Dar-es-Salaam lit many developing countries, most of the ir-'r.c (corn) is produced by small subsistence fanners, and whatever little surplus is available is sold at the market. The subsistence farmers in many countries in Africa grow only a few hectares of maize, and tl ese are often intercropped. The yields in general are low, about 1,000 kilograms per hectare. Under these conditions all the shelling is done by hand, and the following methods are generally used:
1. With bare hands, holding the cob in the palm with four fingers, a person removes the grains one by one with the movement of the thumb. The shelled corn is consumed or sold as is without cleaning or grading,
2. Rubbing a shelled cob on a cob to be shelled is faster than ¡lie first method but is more tiring and requires skill and practice. It is not very suitable for maize with a high moisture content, as the grains are sometimes bruised and the shelling rate is low. The shelled grains are used as in the first method.
3. This method involves putting the husked cobs in a bag and beating them wit!? a stick while turning the bag. Later on, the cobs and grains are taken out of the bag and cobs are picked. Any grains remaining on the cobs are taken off by hand as in the first method.
i. There are some variations of this method, but basically, the cobs are spread on a raised platform made of sticks and bamboo poles, with small gaps between the adjoining pieces. The spread cobs are beaten with a stick; the shelled grains fall through the gaps; the remaining grains on the cob are removed by hand. * Abridged from Appropriate Technology, vol. 2, no. I, May 1975.
Maize shelling is not a labor bottleneck tor the small producer, especially if he is only growing lor home -ansumption. The family sits together in the evening and shells mai/c by hand, while talking for a few hours, Due evening of shelling is sufficient tor a week's supply ot corn. Most ol the mai/e being brought to the market by the peasant fanner is shelled by one of the four methods described above.
For larger producers, such as those who grow corn to feed their livestock as well as themselves, these simple shelling methods aren't sufficient. The following device has been found to be, on the average, about three times more efficient than the methods described above.
The shelling section consists of U-uails (also called staples) arranged on a wooden board in a way that will facilitate the smooth rubbing of the maize to be shelled. Various arrangements of fixing the U-uails on the wooden board were tried. The best results have been obtained by fixing the U-natls ¡11 two rows parallel to each other 1.9 to 2.0 centimeters apart, and 2.5 centimeters between the nails within the row.
A manual cranking handle, sometimes accompanied by a flywheel, powers this simple but effective corn shelter, A compression spring adjustment enables the sheller to ach.pt to the size of each cob as it enters the feed opening. Husked corncobs are forced by hand into a feeding device which delivers the cob between one stationary and one rotating, toothed, cast-iron shelling plate, and are held in place by spring-loaded stripping claws. The action of the rotating plates causes the cob to rotate in a spiral fashion against the teeth, with the kernels flying olf as it feeds through. After shelling is completed, the bare cob follows an ejection path automatically and makes way for the next cob to follow directly, as soon as the operator can feed it into the opening. The least expensive models clamp directly to a fence or tub side while the sturdier, generally faster models come inside a wooden or metal housing. Many come with an attachment for shelling walnuts.
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