Double screw extruder by divya IIFPT

Presentation about extruder

1. DOUBLE SCREW EXTRUDERS & ITS APPLICATIONS BY DIVYA .P (2017694706 )

2. Extrusion-technology is gaining increasing popularity in the global agro-food processing Extrusion cooking technologies are used for cereal and protein processing in food. Now a day’s consumers do choice for nutritionally rich, therapeutic benefits and for attractiveness especially in case of baby foods. Thus to obtain above mentioned designer food, Food Extrusion technology is used . INTRODUCTION

3. Extrusion cooking is a high-temperature short-time ( HTST ) process. R educes microbial contamination and inactivates enzymes. Extrusion brings gelatinization of starch, denaturation of proteins Modification of lipids inactivation of enzymes and many anti nutritional factors. The main method of preservation of both hot- and cold-extruded foods is by the low water activity of the product (0.1–0.4) and for semi-moist products in particular, by the packaging materials that are used. EXTRUSION

4. Extrusion cooking is a modern (HTST) cooking process (thermo-mechanical process) in which heat transfer, mass transfer, pressure changes and shear are combined to produce effects such as, Cooking, Sterilization, Drying, Melting, Cooling , Texturizing, Conveying, Puffing, Mixing, Kneading, Forming, etc. It is important food process in the manufacture of pasta, ready ‐ to ‐ eat cereals, snacks, pet foods

5. PRINCIPLE OF EXTRUSION COOKING The raw materials are allowed into the extruder barrel and the screw(s) then convey the food along it. Further down the barrel, smaller flights restrict the volume and increase the resistance to movement of the food . As a result, it fills the barrel and the spaces between the screw flights and becomes compressed. As it moves further along the barrel, the screw kneads the material into a semi-solid, plasticized mass. If the food is heated above 100˚C the process is known as extrusion cooking (or hot extrusion).

6. Here, frictional heat and any additional heating that is used cause the temperature to rise rapidly. High temperature of operation in presence of water promotes gelatinization of starch components and stretching of expandable components . The food is then passed to the section of the barrel having the smallest flights, where pressure and shearing is further increased. Finally, it is forced through one or more restricted openings (dies) at the discharge end of the barrel as the food emerges under pressure from the die, it expands to the final shape and cools rapidly as moisture is flashed off as steam.

7. CLASSIFICATION OF EXTRUDERS EXTRUDERS (Based on Construction) EXTRUDERS (Based on Operation) Hot extruders Single screw extruders Cold extruders Double/Twin screw extruders

8. The term ‘twin-screw’ applies to extruders with two screws of equal length placed inside the same barrel. It consists of two parallel screws in a barrel. It is more complicated than single screw extruders . It provides much more flexibility and better control. Twin screws produce a more uniform flow of the product through the barrel due to the positive pumping action of the screw flights Twin-screw extruders

9. TWIN-SCREW EXTRUDERS

10. Twin-screw extruders are mainly of two types as follows : Counter- rotating twin- screw extruder Non-intermeshed, counter rotating Intermeshed, counter rotating Co-rotating twin-screw extruders Non-intermeshed, co-rotating Intermeshed, co-rotating

11. TWIN SCREW EXTRUDER PARTS & COMPONENTS Extrusion Drive: The Power supply in food extruder is done by Electric motors. The size of the motor depends on the capacity o f the extruder and may be as large as 300 KW. The screw speed on extruder is a valuable control parameter. The speed on food extruders is normally less than 500 rpm. Thrust bearing must be able to sustain the load produced under normal extrusion conditions giving an expected life of 20,000 to 50,000 hr.

12. 2. Pre-conditioning Pre-conditioning with steam or water has always been an important part of the extrusion process. Pre-conditioning is not applied to all extrusion processes. In general, this step is applied when moisture contents around 20 to 30% and long residence times of the material are used. Pre-conditioning favors uniform particle hydration, reduces retention times within the extruder and increases throughput, increasing the life of the equipment, due to a reduction in the wearing of barrel and screw components, also reducing the costs of energy involved in the process.

13. 3 . Feeder : A device providing a uniform delivery of food ingredients which are often sticky, non-free- flowing substances. It will regulate rate/pressure of flow. Some types of feeders commonly used are vibratory feeders, variable speed auger and weigh belts . 4 . Barrel or sleeves The barrel is divided into feeding, kneading an the sleeves surrounding the screw can be solid. They are often jacketed to permit circulating of steam or superheated oil for heating and water or air for cooling.

14. 5. Screw The screw of the extruder is certainly its most important component The screw which conveys the materials. Diameter of the screw of a single screw extruder normally varies between 2-15 cm Length to diameter ratio varies between 8-20 and helix angle between 20-30 ˚.

15. 6 . Die or nozzle: The die presents two main functions: give shape to the final product and promote resistance. It increase in internal pressure. The die can present various designs an d number of orifices . Dies may be designed to be highly restrictive, giving increased barrel fill, residence time and energy input. Die design and its effects on functional properties and quality of a final product.

16. 7 . Cutting mechanism The cutting mechanism must permit obtaining final products with uniform size. Product size is determined by the rotation speed of the cutting blades. This mechanism can be horizontal or vertical

17. FACTORS AFFECTING EXTRUSION COOKING Rheological properties of the food The properties of the feed material have an important influence on the texture and color of the product; the most important factors are: The type of feed materials M oisture content P hysical state of the materials Their chemical composition, particularly the amounts and types of starches, proteins, fats and sugars pH of the moistened material. Feed rate Screw speed Barrel temperature Die characteristics Screw design

18. Characteristics of Extruded Products Degree of Expansion on Exit from the Extruder. For many products, the sudden release of pressure when exiting the die of the extruder causes water to flash off and the product to expand. The extent of expansion depends on the composition of the product, its internal microstructure as it exits the die, and the conditions (pressure and temperature) in the ex truder. Degree of expansion may be calculated as either the ratio of the diameters or areas of the extruded product to the die 2. Bulk Density. The density of the final product depends on the nature of the solid material as well as on the amount of air space within the product. A highly expanded product, with plenty of air spaces, has significantly lower bulk density than a product with little air inclusion.

19. 3. Mechanical Properties. Physical and rheological properties determine the characteristics of the extruded product. These may be expressed as fundamental parameters, like elastic modulus, or may be characterized by Empirical measures, such as hardness or crispness. Instruments that measure fundamental properties ( rheometers ) or empirical techniques ( Instron or penetrometer ) may be used to quantify characteristics of extruded products . 4. Protein Quality. The nature of extruded proteins depends on the Extruder operating conditions, especially temperature profile as the extruded product is formed. High-heat treatment causes denaturation of many proteins, which influences physical characteristics such as viscosity.

20. 5. Starch Characteristics . Properties of starch in an extruded product that influence quality characteristics include such measures as water absorption index, water solubility index, and enzyme susceptibility. These depend on the operating parameters within the extruder as well as the type of raw materials used for extrusion . 6. Internal Microstructure. The arrangement of the components of the extruded product leads to the physical properties described above. The state of starch, whether partially or completely gelatinized, in the final product strongly influences physical characteristics. Typically, internal microstructure is evaluated using microscopy (scanning electron microscopy).

21. Advantages of Twin Screw Extruders Handle viscous, oily, sticky or very wet material and some other products which will slip in single screw extruder, (it is possible to add up to 25% fat in a twin screw extruder) Less wear in smaller part of the machine than in single screw extruder. Wide range of particle size (from fine powder to grains) may be used, whereas single screw is limited to a specific range of particle size

22. The main limitations of twin-screw extruders are the relatively high capital and maintenance costs (up to twice the cost of single-screw equipment ). G reater constraints on operating ranges (Harper, 1987 ). The complex gearbox that is needed to drive the twin screws results in limitations on the maximum torque, pressure and thrust that can be achieved. Disadvantages of Twin Screw Extruders

23. Co-extruded Products Food gums Reformed fruit bits and sheets Soup and gravy mixes Precooked pasta Noodles, Spaghetti and Macaroni Texturized vegetable protein from partially defatted soy flour Cereals and Corn flakes Applications of Twin-screw extruders

24. REFERENCES HARPER, J. M. (1979) Food extrusion. CRC Crit. Rev. Food. Sci. Nur . February 155–215. HARPER, J. M. (1981) Extrusion of Foods, Vol II. CRC Press, Boca Raton, FL. CHESSARI, C.J & SELLEHEWA, J.N. (2001). Effective control processing. In: extrusion cooking : technologies & application, R. GAY, (Ed.), pp. 83-107, CRC press, ISBN 978-084-9312-076 , Boca Reton , United states of America. Richardson P. Thermal Technologies in Food Processing. Wood head Publishers, Cambridge Guy R. Extrusion Cooking, Technologies and Applications. Wood head Publishing Limited, Abington , Cambridge. P J Fellows Food Processing Technology, Second edition 2000, Woodhead Publishing Limited and CRC Press LLC

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