Current situation and development direction of pet

2022-08-09
  • Detail

Current situation and development direction of pet preform injection molding equipment in China Abstract: This paper analyzes the current situation and development trend of pet preform injection molding equipment in China, and puts forward the development direction of pet preform injection molding equipment in China

key words: pet preform injection molding equipment technology development direction

China's pet preform injection molding equipment has developed with the filling of carbonated beverages. With the expansion of the application range of PET bottles, higher performance requirements are put forward for pet preform injection molding equipment. Pet preform injection molding equipment with excellent performance in the world continues to enter China, which has promoted the development of PET bottles in China and the scientific and technological progress of pet preform injection molding equipment in China. However, we should be sober to see that domestic PET bottle blank plastic molding equipment can not enter large enterprises, just like scattered soldiers beating in the market piecemeal, can not become a climate. In this paper, the author puts forward some opinions for reference according to his own understanding of the above problems

pet preform injection molding equipment is mainly related to two aspects: preform injection molding machine and preform mold

1 several problems worthy of attention in the scientific and technological progress of pet preform injection molding machine

domestic pet preform injection molding machine mainly researches and develops the injection molding equipment of single-layer pet preform. Although a certain amount of pet injection molding equipment has been developed in China, its quality and technical level are at least 20 years behind the international advanced level. This problem is illustrated by the fact that none of the injection molding equipment for PET bottle blanks is domestic, which is the largest unit in domestic PET bottle production. The author believes that pet preform injection molding equipment is a high-end equipment, and the development idea is different from the development of ordinary injection molding equipment. Some domestic units take the research and development of PET bottle blank injection molding machine as an ordinary medium and low-end product, and change the screw barrel as a pet injection molding machine. In this way, the development has embarked on a wrong line at the beginning, so it always hovers at the low-end level. First of all, we should correct the development idea and develop the pet preform injection molding machine as a high-end product, so as to develop a high-performance pet preform injection molding machine that can adapt to the market

1.1 progress in the main performance of PET bottle blank injection molding machine

the main performance of pet injection molding machine continues to improve with the progress of science and technology, and it is convenient to meet new requirements by converting hardness to strength. In the mid-1980s, the application of PET bottles was in its infancy, and the hot runner technology was still in the development stage. In particular, the application of hot runner technology in PET bottle blank mold was not mature enough, and the group cavity PET bottle blank mold was still in the research and development stage. Therefore, there were no particularly high requirements for the performance of PET bottle blank injection molding machine, for example, In 1987, Italy xindiduo Plastic Machinery Co., Ltd. introduced the main features of its PET bottle blank injection molding machine in Shanghai, mainly introduced the research and development of screws and nozzles to adapt to PET bottle blank injection molding, and has not touched on other aspects. With the development of hot runner technology, the development of group cavity mold, especially the geometric growth of the application of PET bottles, higher and higher requirements are put forward for the performance of PET bottle blank injection molding machine. In order to adapt to the development of the market, the mechanism and structure control of PET bottle blank injection molding machine further reflect the performance characteristics of special injection molding machine, mainly in the aspects of high speed, high efficiency, precision and so on

1.2 progress in the main mechanism and structure of pet preform injection molding machine

1.2.1 clamping mechanism

before the group cavity mold of pet preform was applied, the research on the performance of the clamping mechanism of pet preform injection molding machine did not receive enough attention. For example, Italy xindeduo Plastic Machinery Co., Ltd. introduced its clamping mechanism of pet preform injection molding machine in Shanghai in 1987. The clamping mechanism of the company is an ordinary elbow bar clamping mechanism. With the application of multi cavity mold for PET bottle blank, new requirements are put forward for the clamping mechanism of PET bottle blank injection molding machine, that is, the clamping mechanism must be able to maintain the parallelism between templates and the stability of the accuracy of clamping force (clamping force) for a long time

pet preform group cavity mold has the inherent characteristics of high precision and low rigidity compared with the forming mold of ordinary plastic products. The price of a set of pet preform group cavity mold even exceeds the price of the host machine. Therefore, the clamping mechanism must play a good role in protecting the mold. To achieve this function, the clamping mechanism must have sufficient stiffness, optimal speed characteristics of mold locking and mold opening, uniform formwork deformation and good deformation repetition accuracy

which clamping mechanism is suitable to meet the above requirements? This is the key point that must be clear in the development. The clamping mechanism mainly includes elbow bar clamping mechanism and hydraulic clamping mechanism. The elbow bar clamping mechanism is divided into single fulcrum, four fulcrum and five fulcrum clamping mechanism. The hydraulic clamping mechanism also includes single cylinder and four cylinder synchronous clamping mechanism. Due to its inherent characteristics, the elbow bar clamping mechanism cannot meet high requirements for the distribution uniformity of its clamping force and the long-term stability of the mechanism accuracy, which is detrimental to the protection of high-precision group cavity molds. The imbalance of the accuracy of the clamping mechanism will damage the accuracy and service life of the mold. Although improving the processing accuracy can improve the accuracy of the clamping mechanism and make up for the lack of purchasing performance of the elbow bar clamping machine, But it cannot fundamentally overcome its inherent shortcomings. Due to the soft hydraulic rigidity of the four cylinder synchronous hydraulic clamping mechanism, the distribution uniformity of clamping force during high-pressure clamping has been improved, and the protection of mold performance has been improved. However, because the four cylinders cannot achieve the ideal synchronous high-pressure clamping of the mold. The inherent characteristics of the single cylinder hydraulic clamping mechanism can protect the accuracy of the mold to an ideal state. It has excellent performance in the uniformity of clamping force distribution, mold low-pressure protection, clamping force stability and so on. It is the preferred clamping mechanism for precision injection molding machines. According to the above brief analysis, it can be seen that in order to protect the performance of the pet preform group cavity mold, the clamping mechanism of the pet preform injection molding machine should be the single cylinder hydraulic clamping mechanism

at present, most domestic injection molding machine manufacturing companies use elbow bar clamping mechanism as the clamping mechanism of PET bottle blank injection molding machine. Users also have a full understanding of the injection molding equipment of PET bottle blank, so they will never put a set of imported expensive PET bottle blank group cavity mold on the ordinary elbow bar clamping mechanism injection molding machine. The form of clamping mechanism determines that the pet preform injection molding machine with elbow type clamping mechanism can only enter the low-end pet preform injection molding machine market, and cannot enter the high-end market of pet preform injection molding machine

1.2.1 progress of injection plasticizing mechanism

the injection plasticizing mechanism of PET bottle blank injection molding machine is in the process of continuous development, and scientific and technological progress towards high speed and efficiency. In the initial stage of PET bottle blank injection molding machine, the main research is how to reduce the production of acetaldehyde in the plasticizing injection process and improve the transparency. The application of group cavity mold of PET bottle blank reduces the manufacturing cost of PET bottle blank, and focuses on high-speed and efficient research and development. High speed and efficiency refers to high-quality and high-speed molding, not high injection speed. Pet's own characteristics do not allow high injection speed. During PET injection molding, if the material temperature is too high, the screw shear force is too large, or the rotation speed is too fast, acetaldehyde is easy to produce and lead to acidification. Usually, the acetaldehyde content of PET bottle after molding must be less than 3ppm. Higher requirements are put forward for the quality deviation of PET bottle billets. For example, the maximum negative deviation of tube billets with a mass of 50 grams is 0.5g, the maximum negative deviation of tube billets with a mass of 70 grams is 1.5g, and the maximum negative deviation of tube billets with a mass of 100 grams is 2.5G. Therefore, accurate measurement is also a research and development topic

high speed injection plasticization is an important feature of the scientific and technological progress of PET bottle blank injection molding machine. High speed and high yield can enable investors to obtain greater output and high returns with lower input. In order to realize high-speed injection plasticization, we should explore and innovate from the aspects of mechanism, structure and control

the common coaxial one-line injection plasticizing mechanism has its own structural characteristics, which limits the improvement of productivity and quality. There are only two ways to improve the plasticizing ability, that is, increasing the plasticizing speed or increasing the screw diameter; There are basically two ways to improve the plasticizing quality of pet, that is, reducing the plasticizing temperature or prolonging the residence time of melt in the barrel. Increasing the plasticizing speed can not be taken because increasing the shear rate will accelerate the production rate of acetaldehyde, so the plasticizing capacity can only be improved by increasing the screw diameter. Reducing the plasticizing temperature or prolonging the residence time of molten material in the barrel can improve the plasticizing quality, but at the same time reduce the plasticizing capacity. Therefore, in order to improve the plasticizing ability and quality at the same time, we must develop new injection plasticizing mechanisms to meet the requirements of high speed and efficiency. According to the characteristics of injection plasticization, the functions of injection and plasticization are divided from the conventional one-line type into two-line type, that is, the two functions of plasticization and injection are divided into two parts from a conventional part. Plasticization is divided into independent movement of screw and independent injection of plunger. Injection and plasticization do not interfere with each other, and plasticization does not occupy the forming cycle, so as to improve the plasticization quality and ability. By increasing the diameter of the plasticizing screw, the plasticizing capacity can be improved. At the same time, because the plasticization is independent of the cycle, the residence time of the molten material in the barrel can be prolonged and the uniformity of material mixing and plasticization can be improved; At the same time, because the plasticizing time can be appropriately extended, it can provide enough time to realize low-temperature plasticization, and reduce the probability of sudden temperature rise and thermal decomposition of materials due to excessive shear of materials

the design of plasticizing screw has a great influence on the melting, mixing uniformity and melt temperature of pet. The injection molding of PET bottle embryo should use screws with low shear and low compression ratio (about 2:1). The feeding section should be longer, and the transition section and metering section should be shorter

high speed injection plasticization is an important feature of PET bottle blank injection molding machine. High speed injection plasticization is not high-speed injection and high-speed plasticization, but an organic combination of injection and plasticization. It is innovative in terms of mechanism, structure and control, so as to minimize the total time of injection and plasticization. The so-called pet preform injection molding machines of most domestic units basically only increase the length diameter ratio of the screw and make some changes in other screw parameters, which simply cannot meet the high-speed performance requirements. [3] The special injection molding machine for PET bottle preforms, which was exhibited by Husky company of Canada at the 2006 Shanghai International Rubber and plastic exhibition, combined with the company's internationally leading hot runner mold, formed 96 bottle preforms in one mold, with a cycle of less than 7.5 seconds, and the qualification rate basically reached 100%. The main feature of the high-speed structure of the whole machine is the high plasticizing efficiency. The plasticizing injection mechanism divides the two functions of plasticizing and injection into two parts from a conventional part. The plasticizing is independent movement of the screw, independent injection of the plunger, completion of the screw plasticization, opening of the molten material flow path, injecting the molten material into the plunger storage cavity, measuring until the molten material flow path is closed, and then the plunger injection into the mold cavity. In this way, plasticizing does not occupy the forming cycle, Increased productivity. It is worth mentioning that the screw injection action is the screw injection action when injecting molten material. The screw injection is not a simple straight-line forward movement, but a rotating forward movement, and the direction of rotation is the same as the direction of plasticization rotation. The author believes that in order to adapt to the plasticization of pet, reduce the entry of air in the feeding process, and make the solid material fill the screw groove in the feeding process. In the process of extruding the molten material into the injection chamber, the plasticizing screw rotates and extrudes, which is conducive to discharging the air in the solid material entering the barrel. At the same time, it reduces the plasticizing time and shortens the production cycle. To reduce the axial direction of molten material

Copyright © 2011 JIN SHI