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How to Improve the Extruding Efficiency and Quality of Screw Extruder?

At present, plastic blending modification and granulation are mostly completed by extruders. There are three main types of machines: Single Screw Extruder, Co-Rotating Twin screw Extruder, and Triple Screw Extruder. Among them, the Co-rotating twin-screw extruder is the most widely used for filling, mixing, modification, chlorination of rubber, plastics, and engineering resins or processing of polypropylene and superabsorbent resins. Especially in the engineering plastics industry, the co-rotating twin screw extruder has become the main equipment for plastic modification, reinforcement, and mixing. For users, how to choose a suitable extruder, how to improve production efficiency and product quality are their important considerations.

The selection of equipment mainly considers the following factors:

1. product quality

Product quality is the life of an enterprise and is related to the development of an enterprise. Whether the consistency of each batch of products can be guaranteed for a long time is an important indicator for evaluating the quality of an extruder.

2. production efficiency

On the basis of ensuring quality, how to improve production efficiency and maximize production capacity within unit time is the goal pursued by every enterprise.

3. Cost Control

Cost is also an important factor for businesses to consider. To a certain extent, improving efficiency itself is also one of the ways to reduce costs.

4. Machine life

Under the premise of ensuring high efficiency, it cannot be at the expense of shortening the product life. Therefore, in the process of manufacturing and processing extruders, more durable materials should be selected.

5. Easy to operate

From the user’s point of view, the equipment is simple to operate and easy to maintain; stable operation of the equipment and low failure rate are also important indicators for them to consider.

According to customers’ demands, it is not difficult to find that “product quality” and “improvement of efficiency” are not only the ultimate pursuit of extruder manufacturers but also customers.

Tips for Improving Extrusion Efficiency

At present, the development trend of twin screw extruder in the world is to develop in the direction of high torque, high screw speed, and low energy consumption. By increasing the screw torque and increasing the screw speed, the plasticizing and mixing capacity can be enhanced. By increasing the screw speed, the conveying capacity of the screw can be increased to increase productivity.

Increase screw torque and speed

The coreThe core of increasing the torque of the screw is that there must be a reduction box with higher torque (abbr. gearbox); At present, gearboxes are mainly divided into domestic production and foreign brands. The design principles of high torque gearboxes are basically the same; the main differences are in gear (gear shaft) materials and material heat treatment;

At present, the domestic gearbox is below the torque level of 11. After nearly ten years of use, the At present, the domestic gearbox is below the torque level of 11. After nearly ten years of use, the performance and service life are basically the same as those of foreign brands; for the gearbox with a torque level greater than 11, it has not been widely used in China, and it is recommended to use foreign brands;

Schematic diagram of ordinary gearbox
Schematic diagram of ordinary gearbox
Schematic diagram of ordinary high torque gearbox
Schematic diagram of ordinary high torque gearbox

Under the same screw speed, increasing the depth of the screw groove can greatly increase the conveying capacity. However, it has been proved from theory and practice that the mixing effect is the best under a certain geometric relationship between the screw outer diameter and the screw bottom diameter (screw outer diameter/screw bottom diameter=~1.55). At high screw speed, the residence time of the material in the extruder is reduced, which may cause insufficient plasticization, melting, and mixing of the material. For this reason, it is necessary to appropriately increase the length of the screw, which will inevitably lead to an increase in the actual bearing torque and power of the twin screw extruder.

At the same time, increasing the torque and rotational speed requires higher requirements for the design, production, and manufacture of parts such as the mandrel, screw elements, and kneading elements of the screw.

At present, twin screw manufacturers pay more attention to the development of mandrels, barrel inner sleeves, and threaded elements, and are committed to developing higher-strength mandrels, more wear-resistant barrel inner sleeves, and threaded elements.

Mandrel material type:

MaterialFormsHRCFeatures
WR15ERound bar40±2High toughness, high strength
WR30Round bar40±2High toughness, high strength, high wear resistance and corrosion resistance
40CrNiMoARound bar40±2High toughness, high strength

Properties comparison between WR30, WR15E and 40CrNiMoA

PropertiesWR30WR15E40CrNiMoA
MpaTensile strength/Mpa13241300900
MpaYield strength/Mpa10751000800
Elongation at break/Mpa>14>12>12
Reduction of area/Mpa>47>40>55
Impact absorbing energy/Mpa>250>250>78

For high torque extruders, the mandrel is preferably made of imported WR30 and WR15E materials to reduce the distortion of the mandrel;

For high torque extruders, the overload protection of torque is very important. We strongly recommend torque-limiting couplings (BIBBY or R+W safety couplings) imported from Europe. During the production process, if the torque-limiting couplings are abnormally overloaded, the device can be disengaged instantly, which can protect the gearbox and screw more effectively;

(The following figure shows the safety coupling)

the safety coupling 1
the safety coupling 2

Enhanced plasticizing and mixing capabilities

Increasing the channel volume is also an important factor. In the feeding section and the devolatilization section, It is very necessary for the threaded element to have a large free volume. For bulk materials, Increase the free volume of the feeding section and the filling degree of the material in the screw groove, which can greatly improve the production capacity of the extruder.

Optimized screw combination

The plasticizing system mainly includes screws and barrels. In order to meet various types of production and processing requirements, the screws and barrels are generally designed as building blocks. According to the function of each section, the screw can be divided into feeding section, plasticizing section, mixing section, exhaust section, and extrusion section. These sections have different functions in the extrusion process, their structures are different, and the corresponding geometric parameters of the screw elements are also different. Therefore, how to determine the geometric parameters of the screw elements becomes the key to the design of the plasticizing system.

Appropriately increase the length to diameter ratio according to the material properties

Due to the increase of the screw speed, the residence time of the material in the extruder is shortened. In order to make the material more fully plasticized and mixed, and to make the material temperature rise slowly, high-quality products can be obtained. In addition to the optimized combination of screw elements, it is also necessary to increase the length diameter ratio of the screw. The increase of the aspect ratio increases the requirements for the manufacturing accuracy of the machine, the driving power, and the torque of the screw core bearing, and requires a higher level of manufacturing technology and structural design.

Enhance the feeding and conveying capacity of materials

Many processors need to produce very high filled materials, which tend to have very low bulk densities, and the volumetric feeding capacity depends on the free volume of the side feeder and main screw screws, and the rotational speed of these two screws. The main screw preferably has a long-pitch screw elements extending 2D-4D downstream of the side feeding port, so that the filler can be eaten by the main screw to the maximum extent. In addition, in order to prevent the material from “bridging”, agitation can also be added to the main feeding and side feeding hoppers; vertical forced feeding can be added to the first section of the barrel to enhance the conveying capacity of the material.

Improve exhaust devolatilization efficiency

Optimizing the combination of screw elements in the exhaust section, setting up pressure building elements in front of the exhaust port, and using large-lead screw elements can improve the devolatilization efficiency. It is also possible to design multiple exhausts (natural exhaust and vacuum exhaust) to discharge the exhaust gas during the mixing process, omitting the intermediate steps in the polymerization and mixing process, and improving production efficiency.

Strengthen the development of various systems

With the increasing use of twin-screw extruders, in addition to the general feeding, conveying, cWith the increasing use of twin screw extruder, in addition to the general feeding, conveying, compression, plasticization, mixing, exhaust, homogenization, and other processes, It is often necessary to complete various processes such as dehydration, drying, degradation, and reactive extrusion, and the extruder is required to have functions such as multi-channel feeding and multi-stage exhaust. In order to meet the process requirements of different customers, the development of each component should be strengthened in the design process of the plasticizing system to improve product performance.

InIn addition, strengthen the training of operators, strengthen the maintenance and maintenance of equipment, and correctly grasp the operation process of equipment. The more familiar with the equipment, the higher the production capacity of the machine.

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