extrusion ku

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Extrusion Chee 490

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Extrusion is the process of squeezing metal in a closed cavity through a tool, known as a die using either a mechanical or hydraulic press. Extrude  “to push or force out through an opening (Die)” e.g. tooth paste Dies The extrusion die is a steel disk with an opening, the size and shape of the intended cross-section of the final extruded product.

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Food extrusion was born from the Plastic Industry in 1935 when the process was first applied for the continuous extrusion of pasta . It is indisputably the most important unit operation in the Polymer Industry today. It is a process of great and ever increasing importance in the food industry

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Extrusion cooking is a modern high-temperature short-time (HTST) processing technology. It offers several advantages over other types of cooking processes, faster processing times significant reduction in energy consumed which consequently results in lower prices The products of extrusion are of major importance in the food and feed industries today. Extruders can be used for a wide range traditional (conventional) food products New products

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Extruders are generally classified according to how pressure is developed in the unit or thermodynamically. Thermodynamic Classification Autogeneous Extruder : (Nearly Adiabatic) generate own heat by conversion of mechanical energy in the flow process itself. No external heating or cooling, e.g. puffed snack extruders. Isothermal Extruder : Constant temperature maintained throughout the extruder by cooling to remove heat by conversion of mechanical energy. Polytropic Extruder : (between Autogeneous and Isothermal) All food extruders are polytropic

The Single Screw Extruder: 

The Single Screw Extruder Food materials are drawn by gravity from a hopper to the gap between a rotating screw and a heated barrel. They are transported forward, compacted, melted and pumped through a die where the melt is shaped prior to solidification by cooling

Solids Conveying (Feed) Zone: 

Solids Conveying (Feed) Zone Most hoppers have a cylindrical top section, and a conical lower element that, preferably, provides mass flow at discharge rates that exceed the extruder demand. The hopper angle should be sufficiently steep to maintain solids flow at the wall – this is dictated by the nature of the feed particles. Particles may take the form of pellets or powders, but must be free flowing and have low compressibility to avoid bridging. Materials that do not contain particles smaller than 0.2 mm are typically free flowing.

The Metering Zone: 

The Metering Zone Conventional single-screw extruders (without grooved feed sections) rely on the metering zone to develop the pressure needed to force the melt through the shaping die. Flow in the metering zone can be estimated by solving the equations of motion, making this section quite amenable to design calculations.

TWIN SCREW EXTRUDER: 

TWIN SCREW EXTRUDER

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High Pressure Forming Extruder For compressing and shaping pre-gelatinized dough feed into products, which normally require further processing, e.g. deep-fat frying (snacks) and gun puffing (cereals). Similar to the pasta extruder but with a grooved barrel.

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Collet Extruder Cools, puffs and forms dry granular feeds such as corn meal to produce puffed snack products like corn curls. Very high shear. • Short Residence Time. Very difficult extruder to model because of : * High  T * Large changes in rheological properties 12

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High-Shear Cooking Extruder (Sometimes referred to as HTST, High Shear Short Time Extruder) Used for making a wide range of products such as puffed cereals and snacks, textured plant protein and dry pet foods. Similar to Collet Extruder except that it has • Greater Residence Time and • Excess heat is removed by cooling.

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Low-Shear Cooking Extruder Used for cooking continuous of high-moisture dough/feeds. Due to low  (high moisture) external heat application is required. Has deeply grooved barrels and compression screw (variable D/h, pitch) to enhance heat transfer. Chee 490 23. 14

FORMING EXTRUDER: 

FORMING EXTRUDER Specially designed - various viscous masses Fruit gum, Fruit snack, Sugar paste etc. These twin screw, co-rotating extruders have a strong and versatile design, to adjust to various masses to be processed. The intermeshing screws are self-wiping, making cleaning an easy job. The infeed section is a twinscrew , counter-rotating design, offering a stable, deareated infeed , resulting in a constant massflow from the extruder. Extrusion 23. 15

Food Extrusion – Overview: 

Food Extrusion – Overview Use of extruder has become very extensive in the food industry especially in those processes that require cooking or gelatinization at some stage such as : Pasta products; • Snacks and Noodles Cereals; • Confectionery Sausage products; • Protein supplements Meat analogs; • Pet foods Other animal feeds.