Development of a multi-purpose twin-screw extruder

Abstract

The extrusion market of South Africa has a smaller demand for products than most of the First World countries in which mainly single process twin-screw extruders are used. This leaves a void for the development for a multi-purpose twin-screw extruder. This will enable companies to manufacture a greater diversity of products with one machine, not only in South Africa, but in the rest of Africa as well. Africa has one of the biggest rates of poverty and famine in the world . The famine crisis in Africa is mainly due to the lack of food with a high nutritional value. The conventional cooking method currently used, that of preparing food over an open fire, causes the loss of most of the vitamins and essential nutritional values in the food . Extrusion is the process whereby high quality food is manufactured by using simple raw materials. The raw material goes through a process of heating, mixing and shearing to produce a high quality end product. The main disadvantage of extruders currently available on the market is their cost. Extruders are currently manufactured in the First World countries. This causes that the machines are too expensive and unaffordable for most of the African markets. This creates the opportunity for an affordable extruder to be manufactured and maintained in Africa. This study provides an introduction to extrusion. Chapter 2 contains a literature study on the various extruders and their respective available sub-components. It also discusses the differences between different extruders. In Chapter 3 a generic approach to the design and manufacturing of an extruder unit is formulated and discussed. Chapter 4 is dedicated to the explanation of basic screw geometry and designs. Chapter 5 contains case studies on two types of barrels designed and tested during this study. It also provides the best choices of designs for various components. In Chapter 6, a case study of a fully operational twin-screw food extruder is discussed. This extruder was manufactured in Africa, and maintained in Africa. Recommendations and conclusions of this study are summarized in Chapter 7.