Maize Sheller For Every Household

Senior Lecturer. Dept. of Mtthiinic.il Engineering, University of Nairobi, Keny;i

One type of hand sheller currently sold in parts of Africa is made from a metal tube, with internal ribs set in the direction of the cylinder axis. The sheller is held in one hand while the other hand pushes the maize cob tnt-j the tube with a twisting action. The internal ribs strip the kernels from the cobs, and the kernels fail out the bottom of the tube. This sheller, which is now being made from an aluminum casting, has been found to have two disadvantages. First, the ribs are too numerous and tend to become clogged witfi grain. Second, the sheller is really only suited to one diameter of cob. Where both traditional and hybrid varieties are grown, therefore, it is not capable of stripping all cobs satisfactorily.

I have overcome these difficulties by redesigning the tube sheller and incorporating two novel features. At the same time, the cost has been lowered by a change of material.

The tube of the new sheller is constructed from a short length of 2-inch diameter rigid, polyvinyl chloride water pipe. This is a readily available material in industrial centers in most countries. The ribs are made from the same pipe, cut into thin ┬╗trips and glued together in stacks of three or four. For glue, a polyvinyl chloride solvent is used which is supplied for tise with polyvinyl chloride water pipe by all distributors. Four such ribs are then glued to the inside of the tube at i)0-degrcc intervals. This placement allows the ribs to reach the core of the maize cob, and still leaves enough space between them to allow the grain to drop through. The two novel features I introduced are as follows:

1. A slit is made along the tube to allow it to expand when very large cobs are being stripped. This is made possible by the elasticity of the material. Residual stresses in the material, as a result of the pipe extrusion process, ensure that the tube normally remains well closed.

2. One of the four internal ribs is positioned higher up the tube than the other three and this is the rib which does most of the stripping. It is found that this feature results in an easier stripping action than when four ribs strip off the grain simultaneously.

The performance of the new maize sheller is quite impressive and a dry cob can be stripped in about 5 to 7 seconds. This compares very favorably with the performance of other designs, though

* Reprinted with permission from Appropriate Technology, August 1976.

it is accepted that the vigorous wrist action involved could not be maintained for prolonged periods. The tools required for manufacturing this shelter are minimal; they consist of a hacksaw, smalt clamp or vice, and sandpaper. The cement used is a standard polyvinyl chloride solvent which produces a very powerful bond, provided the surfaces are free of grease.

The material cost including normal waste is low, and each shcller takes around 1 10 hours to assemble by hand. The product is beginning to sell in a few areas ou a trial basis and indications are that demand will t-e considerable when the product is given a little promotion.

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