Puffed food extruder choose single screw or twin screw, first understand these contents

The extruder is mainly composed of a barrel and a rotating screw in the barrel. There are two categories: single screw extruder and twin screw extruder. In the extrusion process, the material is extruded, mixed, compressed and shear when it enters the die cavity from the feeding port and is pushed forward by the screw. Due to the action of driving force, friction and shear force and external heating, the material becomes hot under pressure, reaches the state of high temperature and high pressure, and matures into a modified paste. When the material is extruded from the front mold hole, due to the sudden drop of temperature and pressure to room temperature and room pressure, the water in the material is vaporized and evaporated rapidly, and the volume expands rapidly, becoming an expanded substance.

One, single screw extruder

The screw of the single screw extruder is composed of a shaft connecting the screw elements of various structures. The whole screw consists of three sections: feeding section, kneading section and melting and homogenizing section. After the material enters the barrel from the feeding port, it undergoes solid transportation, melting and homogenization process in the screw, so that the material changes from loose state to continuous plastic dough.

In the single screw extrusion cavity, the material is basically close around the screw, a spiral continuous strip, the screw rotation of the material along the screw like a nut moving forward, but when the friction between the material and the screw is greater than the friction between the material and the barrel, the material will be co-rotating with the screw, which can not realize the forward extrusion and delivery of the material. When the moisture and oil content of the material are higher, this trend is more obvious. In order to avoid these problems, most of the single screw extruder now adopts a segmented type, single and double screw, pressure ring and kneading ring staggered combination screw and inner wall grooving barrel, to adapt to the changes in the material in the machine cavity.

Two, double screw extruder

Twin-screw extruder is a kind of multi-screw extruder, which is developed on the basis of single-screw extruder. In the barrel of twin-screw extruder, two screws are placed side by side, so it is called twin-screw extruder. According to the relative position of the screw can be divided into meshing type and non-meshing type, meshing type can be divided into partial meshing type and full meshing type; According to the screw direction can be divided into the same rotation and reverse rotation of two types, reverse rotation can be divided into inward and outward two types.

The properties of the pressure zone of the co-rotating twin screw are different. The material is rotated by the screw in the inner cavity of the sleeve, resulting in high pressure zone and low pressure zone. Obviously, the material will flow from high pressure area to low pressure area in two directions: one is to form two C-shaped material flows along the inner wall of the sleeve with the rotation direction of the screw, which is the mainstream of the material; The other is the formation of countercurrent through the gap of the meshing part of the screw. The reason for the counterflow is that the left screw pulls the material into the meshing gap, and the right screw pulls the material out of the gap, so that the material is “∞” forward, changing the direction of the material flow. This not only contributes to the mixing and homogenization of materials, but also causes grinding (shear) and rolling between the cogs of the screw, resulting in calendering effect, which is much smaller than the calendering effect of the reverse screw. Of course, the calendering effect is small, the wear of the material on the screw will be reduced, the material is so through transportation, shearing, mixing and heating of the barrel shell, under the action of high temperature and high pressure to reach maturation, and finally be extruded out of the barrel.

Reverse rotating twin screw extruder generally adopts two screws with the same size but opposite thread direction. The difference between inward rotation and outward rotation is that the position of the pressure zone is different. The pressure generated by inward rotation of the twin screw is high and low. When the material passes through the twin screw, it will produce extremely high pressure at the entrance, causing difficulties in feeding. The pressure generated by the outward rotation of the twin screw is upper, lower and higher, which is conducive to feeding. However, compared with the same rotation, the C-shaped material flow formed by the material in the screw can not move from one screw to another, the mixing degree of the material is significantly reduced, and its self-cleaning ability is not as effective and stable as the same rotation twin screw.

Due to the pressure difference between the upper and lower parts of the reverse rotating twin screw, the separation force F that makes the screw shift to both sides is generated. The screw presses to the barrel under the action of F, which accelerates the wear of the barrel and the screw. The higher the speed is, the greater the F is, the more serious the wear is, thus limiting the speed of the screw. The same rotating twin screw does not have the force to separate the two screws, so the wear is small, can run at high speed, and can achieve high output, so the same rotating twin screw is widely used.

The heat source required by the material, in addition to the same part as the single screw, is mostly from the meshing gap; Heat is generated by shearing, extrusion and mixing of engaged threads, and the heat is homogenized. The size of the gap has a great influence on the quality of the expansion, the gap is small, the shear force is large, but the amount of material through the reduction; When the gap is large, the amount of material passing through increases, but the shear force decreases. Double screw forced conveying and self-cleaning characteristics, so that the material in the barrel residence time is short and uniform; The good mixing performance of the twin screw makes the heat of the material homogenized in time, speeds up the ripening degree of the material, reduces the fluctuation of the material temperature, and improves the output and quality of the expanded product.

Our company specializes in the production and manufacture of extruder screw barrel, with a strong self-cleaning function, screw groove can be self-purification, so change the formula and product varieties, no need to stop cleaning, screw has a strong pumping effect, material viscosity diffusion effect is strong, fast speed, product quality is relatively stable. It is made of special alloy material after heat treatment, with long service life, strong and durable, low failure rate and convenient operation and maintenance. Easy to use, smooth transmission, low noise. The screw nozzle can be designed by building block, easy to adjust. Please contact us Whatsapp:+13567672668 or Email:[email protected]