Improvement of Screw&Barrel of Injection Molding Machine

1: Improve production efficiency

Improving production efficiency is one of the important goals of the development of a new co-rotating twin screw extruder. It can be achieved by increasing screw speed, enhancing plasticization and mixing ability. At the same screw speed, increasing the depth of the groove can greatly increase the conveying capacity.

 

Correspondingly, the plasticizing and mixing ability of the screw is also required to increase, which requires the screw to withstand greater torque. At high screw speed, the residence time of material in the extruder decreases, which may lead to insufficient plasticization, melting and mixing of material. Therefore, it is necessary to increase the length of the screw properly, which will inevitably lead to the increase of the actual load-bearing torque and power of the twin-screw extruder. Increasing the free volume of the groove is also an important factor. It is necessary for screw element to have large free volume in feeding section and devolatilization section. For loose density material, increasing free volume in feeding section and filling degree of material in screw groove can greatly improve the production capacity of extruder.

 

In order to improve the torque and speed, it is necessary to design the deceleration distribution box carefully. To greatly improve the torque index of the equipment, higher requirements will be put forward for the design and manufacturing level of the gearbox. The higher the torque, the higher the design, manufacturing accuracy, material strength and heat treatment requirements of gears, output shafts, bearings and other parts in the transmission box. At the same time, the design and manufacturing accuracy requirements of the core shaft, threaded components and kneading discs of the screw are also higher. In order to increase the free volume of threaded components, the center distance between the two screw rods will decrease when the outer diameter of the screw rod remains unchanged, which will make the problem of insufficient installation space of the matched gear and thrust bearing more prominent.

 

2: Improving product quality

In order to obtain high quality products, the design of plasticizing system, the core component of extruder, is of great importance.

 

Plasticizing system mainly includes screw and barrel. In order to meet various processing requirements, screw and barrel are usually designed as building blocks combined structure. 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 and structures in the extrusion process, and the corresponding geometric parameters of screw elements are also different. Therefore, how to determine the geometric parameters of screw elements becomes the key to the design of plasticizing system. For co-rotating twin screw, there is a certain relationship between the pitch ratio (that is, the ratio of the center distance of two screw to the radius of the screw), the number of screw heads and the top angle of the screw. It is not optional to design, otherwise the interference between the two screw will occur.

 

Because of the increase of screw speed, the residence time of material in extruder is shortened. In order to make the material more fully plasticized and mixed, and to make the process of material temperature rise more gentle, high quality products can be obtained. In addition to the need to optimize the combination of screw components, the length-diameter ratio of screw needs to be increased. However, with the increase of L/D, the requirements for manufacturing accuracy and driving power of the machine, as well as the bearing torque of the screw mandrel are improved, and the requirements for manufacturing technology and structural design are higher.

 

In addition, optimizing the combination of threaded components in exhaust section, setting up pressure building elements in front of exhaust port and adopting large lead threaded elements can improve the devolatilization efficiency. In addition, using melt gear pump to build pressure between the head and extruder can reduce the pressure at the end of metering section of extruder, shorten the effective filling length of screw and lengthen the effective exhaust length, which can also improve to a certain extent. Exhaust effect.

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