ABSTRACT
This project is on the design, construction and testing of a cassava pelletizing machine. The machine processes cassava mash by extrusion into cylindrical form of about 2-3cm length and 9mm diameter called pellets. The machine is made of these major components: hopper, barrel, auger conveyor and a circular die plate. The hopper is made of a stainless steel 1mm thick cut from a flat metal sheet. The sides if the hopper is joined by electric arc welding while the barrel is a cylindrical hollow shaft. This barrel is welded to the already fabricated hopper at its base, with the base of the hopper coinciding with an opening in one end of the barrel and the other end welded to an already perforated die plate. The auger conveyor is an intricate part of the machine made of a shaft wound round with a 20mm rod joined by arc welding with honcon electrode. A helical auger is mounted on a shaft which is supported on bearings so that the shaft rotates freely in the stationary cylindrical barrel. Cassava mash is introduced into auger through the inlet gate of the barrel. The auger conveys the mash to the die and builds up pressure for its extrusion. Pressure resulting from rotating auger forces the mash through the perforations in the die, compressing and forming it into pellets. Experiments were conducted to compare the moisture content of the pellets and that of the unpelletized cassava mash using the oven method and also to determine the production rate and efficiency of the machine.
Experimental results revealed that the pellets had a moisture content of 16.49% (d.b) and cassava mash 75.20% (d.b). The results also indicated that the pellets have more durability than the cassava mash since high moisture content have been found to decay mash faster hence the need for pelletizing. Furthermore, the production rate and efficiency of the machine were found to be 63.86g/min and 81.27% respectively. Though the performance of the machine is satisfactory, I recommend that a force feed mechanism be introduced to avoid caking of the mash especially while operating on large quantity and also the noice level minimized.
CHAPTER ONE
1.0 INTRODUCTION
Cassava is a perennial crop and is widely grown in Africa and South America. It has an estimated height of 2metres when fully grown and has great potentials to germinate in not very fertile soils which could be impossible for other cops to grow. The roots of a fully grown cassava plant are rich in starch and the percentage of carbohydrate present in its dried state is higher than other staple crops. However, it possesses very low percentage of protein (Food and Agriculture Organization FOA, 2004a). A substance called cyanogen glycosides is present in cassava in its raw form making it poisonous. Also present, is an enzyme called linamarase which is responsible for changing the poisonous glycosides to hydrogen cyanide (HCN), this occurs when the plant cell bursts open when processed or eaten. Cassava is of two categorise, sweet and bitter. The latter has greater cyanide content than the former; though it is not in all cases the former (sweet) have low cyanide content present in it. The range of cyanide is between 10 to 450 mg/kg of fresh root and is greatly reduced in its processing hence making it safe for consumption when transformed into a variety of food and non food products (FAO, 2004b).
1.1 Problem Statement
Cassava is very perishable, therefore the need for its processing immediately after harvest to minimize wastage. The limitations in its processing are high cost of transportation, inadequate supply of tubers annually, low output in small-scale processing and inadequate and inefficient processing equipment amongst others. Over the years, there have been some locally produced pelletizing machines for processing cassava by compaction process but this work is focussing on the use of extrusion process in order to achieve greater efficiency, minimize waste and improve on the ease of operation of the machine.
1.2 Justification of the machine
Over the years the existing machines used for various processing of cassava are very expensive and as such difficult for peasant farmers to afford, thus is one of the focus here is its construction at reduced cost. The products produced by the machine such as cassava chips, pellets have considerable export potentials hence the need for its manufacture to boost the nation’s revenue. More so, for export purposes, cassava tubers are processed into raw cassava chips, but because of environmental concerns, over 90% of cassava chips that are exported to the European Union (EU) enter as pellets (Ugoamadi, 2012a).
The operation of giving a plastic material a structure by forcing it through a die via an extrusion process is called Pelletizing. When raw cassava chips is compressed putting in mind relevant operational parameters, it results in the formation of an unfermented dried cassava products called cassava pellet. This product is estimated to be 3cm long and is used greatly in feeding farm animals. The product is now greatly accepted because of its durability and portability when packaged. This makes handling, storage and transporting convenient hence exporting is achieved Ugoamadi, (2012b).
Furthermore, this project emphasizes on the use of available resources (cassava) which is in line with the national policy and forecast on industrialization. It supports the long term forecast of the Federal Institute of Industrial Research Oshodi (FIIRO) to investigate the actualization of commercializing cassava processing.
Consequently, it agrees with the goal of the Raw Materials Research and Development Council (RMRDC) to encourage and enhance the use of local raw materials and technology for industrial development. The design will bring down the cost of production to a minimum in order to make it available to the end users, mostly rural farmers at a reduced price. This is achieved through reduction of the complexity of the design while at the same time maintaining high design efficiency and aesthetics.
1.3 Aim and objectives
The aim of this project is to design, fabricate and test cassava pelletizing machine based on extrusion process.
The specific objectives are to:
1. Develop cassava pelletizing machine at a reduced cost.
2. Determine the efficiency and rate of production of the machine.
3. Compare the moisture content of the extruded material (pellets) and that of cassava mash.
1.4 Scope of the Research
The project covers the Design, Fabrication and Testing of a Cassava Pelletizing Machine. The test is limited to:
1. Testing the efficiency and production rate of the machine.
2. Comparing the moisture content of the extruded material (pellets) and that of the cassava mash.
This material content is developed to serve as a GUIDE for students to conduct academic research
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