The development status of blow molding technology
The PET plastic bottles are cheap, with good transparency, airtightness and compressive strength, and are easy to shape. More and more beverages, such as juice, non-carbonated beverages, iced tea, coffee, sports drinks, purified water, pasteurized milk, etc., must maintain good antibacterial properties during the filling process. In recent years, PET bottles have been increasingly used for these beverages. The total output of PEI bottles in the world is growing at an annual rate of 7%, and the growth rate of PET bottles in China is also very rapid.
As shown in Figure 1-1, from 2005 to 2010, my country’s PET production capacity increased from 20 million tons in 2005 to 24 million tons in 2010, with an average annual growth rate of 6.4%. The output increased from 13.3 million tons in 2005 to In 2010, the average annual growth rate of 19 million tons was 12.9%. The consumption increased from 14.3 million tons in 2005 to 20 million tons in 2010. The average annual growth rate was 88%, and the domestic self-sufficiency rate was over 95%. It is estimated that the market for aseptic filling of PET bottles will grow at twice the current rate in the next few years. With the growing market demand for PET bottles, economical and efficient production is becoming more and more important for PET bottle manufacturers. Many manufacturers of blow molding machines are actively developing and producing high-speed blow molding machines. To occupy the huge market of beverage packaging machinery industry.
“One-step” PET bottle stretch-blow molding equipment is commonly known as fully automatic PET bottle stretch-blow molding equipment. It combines heating preform and stretch blow molding on one piece of equipment, with high production efficiency and stable quality. Suitable for 0.2L~15L Mass production of containers.
“One-step” PET bottle stretch-blow molding equipment is divided into two types: rotary type and linear type. It is difficult to form a bottleneck, and it is difficult to exceed 6000 bottles/hour, while the rotary blow molding machine has a complex structure, high manufacturing precision, high control performance requirements, high production capacity, and the production capacity can reach 60,000 bottles/hour.
Rotary blowing technology, because of the full automation of the blowing process and high production speed, is representative of today’s blowing technology. The production capacity of a single cavity is a very important indicator to measure the level of blowing technology.
At present, the highest international blowing speed has been Reached 2000BPH. Foreign manufacturers of blow molding machines mainly include Cincinnati Company in the United States, Sidel Company in France, and SIG Kautex Co., Ltd. in Germany. Japan Aoki Zhou Research Institute, Italy’s Sipa SIPA), Germany’s Krones (KRONES) and other manufacturers. Sidel and the Philips Group have jointly developed a new infrared lamp for blow molding machine ovens that can save 15% of electricity consumption.
In foreign countries, due to the early research and development time of the blow molding machine and the high level of research and development. Before 2005, China’s injection-stretch-blow equipment for PET bottle production was basically the world of imported products, especially in the production of high-speed and large-volume products, domestic equipment could not compete. In recent years, with the efforts of the domestic packaging industry enterprises and researchers, the research and development and production of various equipment have made great progress, and the research and development and production of “rotary” blow molding machines have also achieved leaps in development.
At present, there are many domestic manufacturers engaged in “rotary” blowing equipment. China’s first fully automatic rotary high-speed blow molding machine was launched in Guangzhou Techlong Packaging Machinery Co., Ltd. in August 2003. In 2005, Dongguan Jiahong Machinery Co., Ltd. developed a hot-filling PET rotary blow molding machine: In addition, There are also a number of companies such as Guangdong Guozhu and Guangdong iBottling (Steplead PacTek) who have entered the research and development and production of “rotary-type” blow molding machines. China’s rotary-type blow molding machine is gradually replacing imported equipment and gradually going out. However, there are still many gaps between my country’s blow molding machines and foreign equipment. The quality gap is mainly manifested in poor stability and reliability, backward modelling, rough appearance, short life of basic parts and supporting parts, short trouble-free operation time, and short overhaul cycle. And the vast majority of products have not yet developed reliability standards.
In addition, as resources become less and less, the use of lightweight bottles has also attracted more and more attention from beverage companies. Coca-Cola China has developed the “Ice Dew” environmentally friendly lightweight bottle, which is called “environmentally friendly lightweight bottle” and weighs only 9.8 grams. carbon emission. The use of this “lightweight bottle” puts forward higher requirements on the design of the blow molding machine. Therefore, at present, some domestic enterprises and research units are actively developing models that can produce environmentally friendly PET bottles stably and efficiently.
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The overall structure of the PET rotary blow molding machine
Figure 1-3 is a schematic diagram of the structure of a 20-mode PET rotary blow molding machine. The preforms installed in the 1 preform hopper are lifted to the 3 preform unloader through the 2 preform lifting and conveying mechanism. The preforms in the single slide in the preform Rotate and arrange the preforms one by one. The straightened preforms enter into the 4 preform guide rails. The preforms are transported to the 16 preform star wheel through the preform guide rails. Then the preform mouth goes down into the 9 heating devices through the 14 flip cam. To heat the preforms, the 8 preform conveying chain components are driven by the 15 preform driving gear mechanism and the 6 preform driven gear transmission mechanism in the heating device to rotate and transport in the counterclockwise direction. Then the 14 preforms are turned over to make the bottles. Mouth up. Then, the heated preforms are sent to the 12 sealing stretch blow molding device through the 17 fingers and cam mechanism. During the rotation of the main machine, the preforms complete the stretch blow molding process in the sealing stretch blow molding device. Finally, the blown PET bottle is taken out from the mold of the bottle blowing device through the 19 bottle picking and feeding fingers and the cam structure. Then the 20 bottle docking finger mechanism picks up the formed bottle and enters the connected filling line.
Picture 1. Preform Hopper 2. Preform Lifting and Conveying Mechanism 3. Preform Arranger 4. Preform Guide Rail 5. Heating Control Cabinet 6. Preform Driven Mechanism 7. Heating Bed 8. Preform Conveying Chain Components 9. Heating device 10. Main transmission mechanism (main motor) 11. Braking device 12. Sealing and stretching bottle blowing device 13. Base and frame 14. Turning cam 15. Preform driving gear transmission mechanism 16. Preform feeding Star wheel 17. Finger and cam mechanism for taking and feeding embryos 18. Cam structure for opening and closing molds 19. Finger and cam structure for taking and feeding bottles 20. Finger mechanism for discharging bottle 21. Water supply system 22. Air supply system (high and low-pressure gas)
Cam System of PET Rotary Blow Molding Machine
The cam mechanism is a commonly used mechanical structure in mechanical transmission, enabling the follower to obtain a more complex motion law. In the rotary blow molding machine, multiple cam structures are used to ensure the whole blowing process, including heating and pressing the preform cam, turning the preform cam, unmolding and clamping cams for the stretch blow molding device, and the blowing process. The stretching cam, the mold opening and closing cam for opening and closing the mold, the finger plate cam for taking the preform and the finger plate cam for taking the bottle. The rotary blow molding machine’s cam system plays a critical role in the production speed and stability of the entire machine, especially the opening and closing cams and the two-finger cams. The rotary bottle blowing machine’s mold opening and closing cam guide rail system is one of the important components in the rotary bottle blowing machine. Its primary function is to make the mold installed on the high-speed rotating body complete the opening and closing actions within a specific rotation angle. To ensure that the blowing process can be successfully completed in the mold. The two cam mechanisms for picking up embryos and bottles are composite cams composed of two cam tracks, respectively. It consists of inner and outer track cams and mechanical fingers proposed by Krones in Germany in 2002. The inner cam track is used to control the deflection angle of the robot finger, and the outer cam contains the extension or shortening of the robot finger. These two cam track mechanisms cooperate with each other so that the robot finger can achieve the transfer function of grasping the preform or bottle . Figure 1-4 shows the schematic diagram of the mold opening and closing cam. Figure 1-5 shows the finger cam for taking the preform and taking the bottle.
Figure 1-4 Mould opening and closing cam
Figure 1-5 The cam for taking embryos (left) and taking bottles (right)
Research status of cam mechanism
Cam mechanism is one of the typical common mechanisms, widely used in automated machines, instruments and assembly lines. A general cam mechanism consists of a cam, a follower or follower system, a frame, etc. [10,11]. The cam transmits the predetermined motion to the follower through direct contact. Before designing the cam and the cam profile curve, it is necessary to establish the motion law of the follower according to the working performance requirements of the cam. Almost all monographs on cams have systematically introduced the laws of motion. The early literature on the motion law of the follower only introduced some basic motion laws suitable for low-speed mechanisms , such as the law of simple harmonic motion, the law of constant velocity motion, the law of continuous acceleration and deceleration, etc., which often cannot meet the requirements of medium and high-speed cams. Practical application requirements for institutional design. In the design of a modern cam mechanism, different types of basic motion laws can be connected to form a combined motion law to promote strengths and avoid weaknesses. The general principle is to splice the basic motion parameters of the motion law in each segment, including displacement, velocity, acceleration, acceleration-like, etc., to maintain continuity. Some also require that the jerk-like degree be continuous to avoid the occurrence of motion at the beginning, end position and connection point of the motion. Rigid shock and soft shock.
The steps usually experienced in the cam mechanism design are shown in Figure 1-4. First, according to the characteristics and performance indicators of the designed equipment or product, a feasible process is formulated. According to the process requirements, determine the actuator’s motion characteristics and main parameters. Using the knowledge of mechanism, select the type of mechanism that realizes the kinematic characteristics of the actuator and the transmission relationship between each mechanism to form the transmission scheme of the mechanism. Then, after the mechanism transmission scheme is determined, the motion distribution diagram is drawn according to the action requirements of the process for the executive components. Finally, it is the selection and size design of the cam mechanism. According to the original data determined by the mechanism motion distribution diagram, each independent actuator group is designed respectively.
When dimensioning a cam mechanism, the following tasks are usually required:
1. Selection of cam mechanism, including the geometry of the cam, the geometry of the follower, the movement mode of the follower, the way the follower and the cam profile maintain contact, etc.
2. Calculate the main motion parameters of the follower. The follower stroke of the cam mechanism, that is, the maximum displacement or the maximum swing angle, is calculated according to the motion requirements of the actuator.
3. Determine the motion law of the follower. The motion characteristics of the follower in the entire range of motion, such as displacement, velocity, acceleration and even jerk, are closely related to the operational aspects of the actuator. There are certain constraints between the type of cam mechanism selected.
4. Basic dimension design of cam mechanism.
5. Cam profile design of cam mechanism. Based on the basic size of the cam mechanism and the follower’s motion law, the cam’s contour curve coordinates can be obtained. When the moving speed of the cam mechanism is high, or the rigidity of the components in the tool is small, the elastic deformation of the components will have a significant impact on the actual motion characteristics of the follower. The designed cam mechanism must be analyzed and designed according to the characteristics of the high-speed cam mechanism.
6. Structural design and construction design of cam follower.
7. Calculation of tool centre path coordinates. To correctly realize the cam design scheme, it is necessary to process an accurate cam profile curve. After selecting a machining method, the relative position of the tool and the cam blank can be properly controlled to cut the cam profile that meets the design requirements. In general, designers always follow the sequence of “design-evaluation-modification” and repeat this process in the design until the design requirements or the optimal solution are met. In fact, this design problem can be transformed into an optimization problem, using the method of mathematical programming, with the help of the high-speed operation and logical judgment function of the computer, according to the predetermined goal, to complete the optimal plan. The high-speed cam mechanism mostly adopts the polynomial motion law, which is the most versatile. As long as there is a high enough power, the corresponding high-order derivative is always smooth, and the endpoints are continuous . In order to meet the needs of increasing the working speed of the machine, it is an important development direction to study and provide the motion law function and dynamic analysis and dynamic design theory and method of the follower under the condition of high-speed operation.
The equation of motion of the polynomial law of motion has more terms in it. As the number of acts increases, the determination of the coefficients in each item becomes more cumbersome. Ge Zhenghao  et al. gave the general equations and boundary conditions of the polynomial motion law of cam mechanisms under various conditions and gave the corresponding solution methods; Huang Minyi  et al. Starting from the requirements, the cubic interpolation spline function is used to determine the motion law of the follower of the cam mechanism to design the cam profile curve, and it is pointed out that when the cam speed is high, the shape and value of the acceleration curve are very important. The contact stress of the cam, the main factors affecting the vibration of the mechanism, and the smoothness and continuity of the acceleration curve can ensure that the mechanism obtains good high-speed characteristics. Tsay and Huey  proposed in 1988 to ensure that the speed and acceleration of the entire curve are continuous at the connection point, and the Spline function is used to synthesize the cam motion curve, which provides a systematic and simple method to synthesize the cam motion curve with the follower. Motion curves limited by displacement, velocity, acceleration, etc. K. Yoon, Vu-Thinh Nguyen et al. [17-18] also proposed the motion laws of various spline functions for the design of cam mechanisms. These motion laws are highly versatile, but the curve construction method is relatively complex.
The significance and content of the research paper
In recent years, the research, development and application of domestic fully automatic rotary PET blow molding machines have made great progress, but compared with foreign machines, the output of single mold blow molding is relatively low, and the running stability of the machine is poor. The mold opening and closing cams and finger discs in the rotary blow molding machine directly affect the single mold output and the stability of machine operation. Most of these two cams in China use the traditional graphic method and experience. The designed cam will make the overall vibration of the machine larger, and the stability is poor. During the working process of the mold opening and closing cam, there will be vibration and loud noise, which will affect the blowing speed and the mechanical stability of the entire blowing equipment. Finger disc manipulator cam When the blowing speed reaches a high level, if the contour line of the cam disc is not continuous and the mechanical properties are not good, the force between the two bearings of the manipulator and the cam will increase or the cam will be separated instantly, which will cause Finger shaking will affect the service life of the robot bearing, reduce the stability of the blowing process, and even cause problems when picking up preforms and bottles, and increase the noise of the entire machine. Guo Songwang  improved the drawing method by using the vector analysis method and establishing the dynamic model of the mold opening and closing cam guide rail system by using the uniform experimental design method and virtual prototype technology. . Wu Hongzhi  also used the vector analysis method to study the analytical method of the contour line of the cam plate of the automatic rotary blow molding machine, and introduced the spline curve into the design of the contour line of the transition part of the cam plate of the rotary bottle blow moulding machine. Three curve construction methods, including the Bézier curve, cubic spline and quintic spline, are used to design the contour line. The contour line of the cam plate is designed by MATLAB and VB language programming. However, the mold opening and closing cam of the rotary blow molding machine and the two-finger disk cams work together. The design of the mold opening and closing cam and the selection of various parameters have a great influence on the design of the finger disk cam. However, in this regard, Few studies have been conducted yet.
In this paper, the machine vibrates during the high-speed operation of the rotary bottle blowing machine, the embryo feeding is not in place, the bottle mouth is easily damaged when the bottle is taken, and the finger shakes when taking the bottle and taking the embryo during the operation. The cam is optimized to achieve the purpose of improving the blowing speed and stability. At the same time, a pioneering study is carried out on the relationship between the mold opening and closing cam design and the finger plate cam. Influence the results to carry out research,
The specific research contents of this paper are as follows:
1) Discuss and study the optimal design of the cam mechanism in high-speed situations;
2) Establish the mathematical model of the mold opening and closing cam mechanism, and establish and derive the mathematical relationship between the cam contour curve and the opening and closing angle, select the contour curve suitable for high-speed occasions, and use AutoCAD and Pro/Engineer to complete the generation of the curve;
3) The vector analysis method is used to analyze the cam profile of the finger plate pick-up and delivery working section, and the transition part is constructed by spline curve and Bézier curve, and the optimization idea and solution model of each curve are established. 4) Analyze the influence of various factors selected for opening and closing moulds on the design of the finger plate cam, and conduct optimization research on the mould opening and closing cam and finger plate cam as a whole, and obtain the overall optimal cam system;
5) Use the kinematics simulation module of Pro/Engineer to carry out kinematics simulation of the entire cam system and apply it to the research and development equipment to verify the design effect of the contour line.
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