Fabrication Of Yam Pounding Machine

CHAPTER TWO
2.0    LITERATURE REVIEW
Pounding has been an integral part of majority of the African people particularly Nigeria where virtually all the ethnic groups have one or more items to pound before use. The ancient and traditional methods of pounding is carried out with the use of the wooden mortar and pestle. The wooden mortar has a concave base with a cup-like hole in it for housing the items to be pounded, the pestle also, in a wooden long single or double edge smooth cylindrical base (dumb bell shaped) used for the pounding.
At present, there exists different makes of yam pounding machines. One type cooks and pounds while another pounds only. The problem associated with them is that they are expensive to operate and acquire.
Herbert and Kenwood mixing machines were in 1975 introduced into the market for use, this however, gave rise to the conception and development of the yam pounding machine. The Herbert and Kenwood mixers were not originally designed for yam but gradually faded away due to its inefficiency in operation such as longer time in meshing operation and overheating of the machine which had to be stopped intermittently for cooling and the non-homogeneity in bond formation after meshing. Hence, the above argument ascertains that both the Herbert and Kenwood mixers were not originally designed for yam pounding, but potatoes meshing as their mode of operation is similar. Also, these mixers have the following deficiencies on the pounded yam.
•    Hardness of the yam after pounding,
•    Presence of much un-pounded yam seedlings and they are not compatible enough
In 1980, some final year students of Obafemi Awolowo University took up the challenge to research and developed a yam pounding machine having studied the problems of the being accomplished with the machine but the problem of overheating continues and even higher than those of Herbert and Kenwood mixer irrespective of the number of vents introduced for cooling. However, this machine gives a better quality product at a higher speed but the cost of production or manufacturing was high hence its high cost of purchase. Also, a particular species of yam was known to pound well with this machine that is the water yam. Likewise the bulky nature of the machine makes its portability a mirage. Hence, in this design, the above mentioned challenges were been eliminated by eliminating the cooking chamber thereby overcoming the issue of overheating, operating the machine at a moderate speed and as a result increases the lifespan or durability of the machine. Also, improvement in the quantity and quality of yam pounded in less time which was one of the major problems of the Herbert and Kenwood mixers. Hence, these improvements make the machine suitable for commercial and domestic use. Also, to put a machine usage, the protective electric motor device (fuse) considering the fluctuating and inconsistent power supply thereby increasing its reliability finally, the simplicity in its manufacturability is an added advantage as it tends to provide job for the young and unemployed mechanical engineers/technologists as the raw materials are readily and locally available. This will to a great extent reduce unemployment.
2.1.1 AGRONOMIC CHARACTERISTICS OF YAM
The tuber shape and size can vary greatly due to genetic and environmental factors. However, cultivated forms of yam generally produce tubers that are more or less cylindrical in shape and 3-5kg in weight. The yam tuber grows from a corm-like structure located at the base of the vine. Occasionally this corm remains attached to the tuber after harvest and sprouts will develop from it. When the corm separates from the tuber sprouting occurs from the tuber near to the point at which the corm was attached.
A transverse section of a mature yam tuber shows it to be composed of four concentric layers:
•    Corky periderm: The outer portion of the yam tuber, it is a thick layer of cork cells, often cracked, but which provides an effective barrier against water loss and invasion by pathogens.
•    Cortex: A layer located immediately beneath the cork, comprising thin-walled cells with very little store starch.
•    Meristematic layer: Elongated thin walled cells under the cortex, sprouts are initiated from this layer.
•    Ground tissue: The central portion of the tuber, composed of thick-walled starchy cells, with vascular bundles ramifying throughout the mass. Most yams are essentially composed of water, starch, small quantities of protein and other minor constituents.