Twin-Screw Extruders in Industries

Extrusion stands as a sophisticated and meticulously controlled process, wielding the ability to transform a diverse array of viscous substances into precisely structured products. This technique has permeated various industries, proving indispensable in plastics, food and pet food, chemicals, pharmaceuticals, minerals, and nonwovens. Its versatility is underscored by the accommodation of a wide spectrum of raw materials, ranging from solids such as powders, granulates, and flours, to liquids, slurries, and even gases. The outcomes of the extrusion process are as diverse as the industries it serves, yielding plastics compounds, chemically modified polymers, textured food and feed products, cellulose pulps, and an array of other high-quality products.

Among the types of extruders, the single-screw and twin-screw variants stand out as the most prevalent. Operating in a similar fashion, these extruders execute a series of critical processes, including transport, compression, mixing, cooking, shearing, heating, cooling, and shaping, ultimately transforming raw materials into finalized products. The twin-screw extruders, featuring two intermeshing screws, distinguish themselves by showcasing superior mixing and forming capabilities. This design proves particularly valuable in the processing of powder blends that demand meticulous mixing and transformation into molten, well-shaped products.

A noteworthy application of the twin-screw extruder is found in the realm of food production, specifically in the creation of puffed food. Originating from the single-screw extruder, the twin-screw food extruder is a specialized machine crafted for this purpose. Comprising two intermeshing, co-rotating screws within a closed barrel, this apparatus ensures a tight fit and self-wiping mechanism, preventing the formation of stagnant zones along the process section. In a co-rotating system, the screws efficiently transport material until intermeshing occurs, facilitating seamless material transfer between the screws.

The versatility of the twin-screw extruder is further highlighted by its multifunctional capabilities, including transport, friction, extrusion, and heating. This results in not only high efficiency but also impeccable self-cleaning and precise control over residence time distribution. The broad applicability of the twin-screw design across industries owes itself to its high capacity, robust tolerance to thermal and mechanical stress, and effective mixing of ingredients like additives, fillers, and liquids. In contrast to single-screw extruders, the twin-screw counterparts distinctly excel in delivering homogeneous mixing, solidifying their status as the preferred choice in the production of extruded products across diverse sectors.
Twin-Screw Extruders in Industries

Food Extrusion Efficiency Technology

Food extrusion entails the mixing and molding of low moisture food materials, and more recently, high moisture food materials, by passing them through a specifically designed opening or die. Subsequently, the resultant extruded material undergoes precision cutting using blades.

Extrusion cooking stands out as an exceptionally versatile and efficient technology in the field of food processing. Employing a high-temperature short-time (HTST) process, it deactivates enzymes and minimizes microbial contamination, gaining popularity for its heightened productivity and significant retention of nutrients compared to traditional cooking methods.

Throughout the extrusion process, as the food progresses through the extruder, thermomechanical cooking occurs at elevated temperatures (typically ranging from 100°C to 180°C), subjecting the food mix to pressure and shear stress generated in the screw-barrel assembly.

The laminar flow within the channels of the extrusion screw and die aligns the molecules in the direction of flow, resulting in the creation of a crunchy or chewy texture in the fabricated food.

Upon exiting the die, the extruded material undergoes a transition from high pressure to atmospheric pressure in the extrusion-cooked melts. Generally, minimal additional processing is required for the extrudates, often limited to slight drying.

The entire extrusion process is continuous and can be completed in under a minute. In the food industry, single-screw and twin-screw systems are the most commonly employed extruders, with twin-screw systems being more prevalent due to their versatility.

Extrusion induces various processes such as the gelatinization of starch, protein denaturation, and reduction of lipid oxidation and anti-nutritional factors. Furthermore, it is acknowledged as a versatile, cost-effective, and highly efficient technology in the realm of food processing.
Food Extrusion Efficiency Technology

Pasta extrusion process

Extruded food products such as pasta, snacks and ready to eat cereals differ from bakery products in the way their texture is formed.

In order to give the pasta its desired shape, the dough in its plastic state must be forced through an appropriate die relatively high pressure.

In the case of continuous extrusion presses, this pressure is generated by a screw. The ingredient are fed into a continuous high capacity extruder that is equipped with a variety of dies to produce having different shapes and appearance.

The shape of the holes in the die governs the shape of the pasta. For spaghetti, the die has round holes; for macaroni wheels, the die pushes the pasta. Leaving a large hole in the middle and gaps left by the spokes. 

When the extruded pasta reaches the right length, it is cut with sharp blades that rotate beneath the die.

Pasta extruder barrel are equipped with a water cooling jacket to dissipate the heat generated during the extrusion process and to help maintain a constant extrusion temperature around 35-50 °C to avoid gluten damage.

Most pasta shapes can be classified into two groups: long goods and short goods. The most familiar type of long goods is spaghetti which may have diameter ranging from 1.5 to 2.5 mm. Hollow extruded goods commonly referred to as macaroni, come in various lengths an forms.
Pasta extrusion process

Cereal extrusion

Breakfast cereal manufacturing was one of the earliest commercial applications of extrusion cooking technology and remains one of the most widespread.

Extrusion technology was first applied to food materials in the mid 1800s, when chopped meat was stuffed into casing using a piston type extruder. In the 1930s, a single extruder as introduce to the pasta industry.

It is a continuous process by which food biopolymers and ingredients are mixed, plasticized, cooked, and formed by combination of moisture, temperature, pressure, and mechanical shear.

Extrusion cooking is very efficient technology used in the processing grains particularly in processing of breakfast cereals.

It is predominantly a thermomechanical processing operation that combines several unit operations, including mixing, kneading, shearing, conveying, heating, cooling, forming, partial drying, or puffing, depending on the material and equipment used.

During extrusion cooking, the processed materials undergo significant physical and chemical changes. By appropriate selection of process parameters such as temperature, moisture and processing time, the mass becomes entirely gelatinized and cooked.

Extrusion cooking is popular for ready to eat cereals, where which they are shaped, toasted, flavored, colored and sometimes enriched or fortified before being packaged and shipped to the consumer.

Cereal extrusion

Cereal Extrusion Processing

Breakfast cereal manufacturing was one of the earliest commercial applications of extrusion cooking and remains one of the most widespread.

The application of extrusion technology is one of the most economic processes, being used increasingly in the food industry for the development of new products such as breakfast cereals and modified starch from cereals.

Cereals flour and other starchy materials are widely used as raw materials in the production of many extruded product. The physical of cereals fluids developed within an extruder and their extrudates are predominantly due to the starch component present, which usually represents between 50% and 80% of the dry solids.

The extrusion-cooking unit thermo-mechanically cooks breakfast cereal mixes to generate the right functional properties of the resulting melt according to the quality profile of the final products.

Chemical and structural transformation in foods during extrusion cooking determine the quality of the extruded products.

A few studies have been reported in extrusion cooking increased the availability of protein and other nutrients in the grain.

Extrusions processes are typically high temperature and high pressure for short time durations. This results in products with limited heat treatments that have nearly all the nutritional attributes of the raw materials remaining in the final products.
Cereal Extrusion Processing

Ready to Eat Cereals

Ready to Eat Cereals
Ready to eat cereals are processed grain formulations suitable for human consumption without further cooking in the home. They are relatively shelf-stable, lightweight, and convenient to ship and store. There are made primarily from corn, wheat, oats or rice, in about that of order of the quantities produced, usually with added flavor ad fortifying ingredients.

Hot cereals, on the other hand, are made primarily from oats or wheat; those made from corn or rice are of minor importance, being produced in relatively small quantities. The original hot cereals required cooking in the home before they were ready for consumption, but now some varieties are preprocessed so that they are ready for consumption with the addition of either hot water or milk to the cereal in the bowl.

The processing of ready to eat cereals typically involves first cooking the grain with flavor material and sweeteners. Sometimes the more heat stable nutritional fortifying agents are added before cooking, Two general cooking methods are employed in the industry today – direct steam injection into the grain mass in rotating batch vessel, and continuous extrusion cooking , with the latter very much on the increase in recent decades.
Ready to Eat Cereals