Quality online monitoring and regulating method and system for compression molding of semi-crystalline polymer and storage medium

Abstract

The invention discloses an on-line quality monitoring and regulating method and system for a semi-crystalline polymer compression molding product and a storage medium, and the method comprises the following steps: setting temperature measuring points in a mold cavity, and forming temperature field distribution in each stage of a material molding process so as to judge the real-time temperature change condition of materials in each position in the mold cavity; on-line monitoring is conducted on pressure borne by materials in a die cavity in the compression molding forming process, and the real-time stress change condition of the materials is obtained; and the product quality is obtained in real time according to the material crystallization behavior and characteristics through the temperature change condition and the stress change condition. The method has the advantages of rapidness, convenience, systematicness and the like in the aspect of quality regulation and control of the semi-crystalline polymer product, can greatly shorten the product manufacturing period in the aspects of product performance regulation, new product research and development, market reaction capability and the like of a semi-crystalline polymer product manufacturing enterprise according to market requirements, remarkably reduces the product cost, and improves the product quality. And the market competitiveness and sensitivity of enterprises are greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of intelligent manufacturing technology, and more specifically to an online quality monitoring and control method, system and storage medium for semi-crystalline polymer molded products. Background Art

[0002] Compression molding is one of the earliest and most mature molding methods in the field of polymer molding. It is still widely used in the molding of thermoplastics, thermosetting plastics, rubber and other materials. For thermoplastics with particularly low melt index, such as ultra-high molecular weight polyethylene, polytetrafluoroethylene and other semi-crystalline polymers with very high molecular weight, it is difficult to transport and plasticize, and it is impossible to use molding methods such as injection molding and extrusion. Usually, static molding, high-speed impact molding, ultrasonic molding, pulse vibration molding and other molding methods are selected.

[0003] For static or dynamic compression molding, the compression molding process of semi-crystalline polymers can be divided into placing materials into the preheated mold cavity, closing the mold and pressurizing and exhausting, melting and hot pressing, cooling and recrystallization, etc. The molding parameters involved include molding temperature, exhaust stage pressure, melting and hot pressing pressure, cooling and recrystallization pressure, cooling rate, molding cycle, etc. Moreover, in the compression molding process of semi-crystalline polymer products, phase change and energy transfer usually occur, there are a large number of uncertain and nonlinear factors, and they are often in a non-visible high-temperature, high-pressure closed environment. The complex characteristics of the molding process restrict the establishment of accurate mathematical models and process simulation. This also means that the quality analysis of semi-crystalline polymer molded products is more likely to be conducted through offline macro-performance testing and micro-structural characterization, while quality control requires adjustment of molding process parameters based on the offline quality analysis results, resulting in serious delays in product production time and high costs. This is especially true for common production situations such as market performance requirements (different usage scenarios have different requirements for product mechanical strength, toughness, wear resistance, etc.) or replacement of raw materials. It is necessary to repeat the tedious work of "molding test-offline test-structure performance correlation-molding parameter adjustment-molding test" based on engineering experience, resulting in slow market response and high product regulation costs for molded product manufacturers. Summary of the invention

[0004] In view of this, the present invention provides a method, system and storage medium for online monitoring and control of the quality of semi-crystalline polymer molded products to solve the problems existing in the background technology.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A method for online monitoring and controlling the quality of a semi-crystalline polymer molded product comprises the following steps:

[0007] Temperature measurement points are set inside the mold cavity to form the temperature field distribution at each stage of the material molding process, so as to determine the real-time temperature changes of the materials at various locations in the mold cavity;

[0008] Online monitoring of the pressure on the material in the mold cavity during the molding process to obtain the real-time force changes on the material;

[0009] Through temperature changes and stress changes, according to the crystallization behavior and characteristics of the material, the crystal phase and amorphous phase characteristics such as sample crystallinity and chip thickness are obtained, and the product quality is obtained in real time.

[0010] Optionally, the method also includes controlling the crystallization behavior by regulating the mold cavity pressure and temperature to adjust the product quality.

[0011] Optionally, the compression molding process includes a pre-pressing and venting stage, a melting and hot pressing stage, and a cooling and recrystallization stage, which are monitored by online temperature monitoring. Based on the monitoring data, the oil flow in the mold is adjusted to achieve temperature control during the compression molding process.

[0012] Optionally, monitoring is performed through online pressure monitoring, and based on the monitoring data, the pressure value of the upper mold on the lower mold is adjusted through a hydraulic valve to eliminate gaps at the interface of the semi-crystalline polymer particles or inside the particles.

[0013] Optionally, the temperature change and the force change are plotted into a first curve and a second curve, and different crystallization behaviors are determined based on the first curve and the second curve.

[0014] An online quality monitoring and control system for semi-crystalline polymer molded products, comprising:

[0015] Temperature change monitoring module: used to set temperature measurement points inside the mold cavity to form the temperature field distribution at each stage of the material molding process, so as to determine the real-time temperature change of the material at each location in the mold cavity;

[0016] The force change monitoring module is used to monitor the pressure of the cavity material during the compression molding process online and obtain the real-time force change of the material;

[0017] Product quality acquisition module: used to obtain product quality in real time based on temperature changes and force changes, and according to the crystallization behavior and characteristics of the material.

[0018] Optionally, it also includes a pressure and temperature control module: used to control the crystallization behavior by regulating the mold cavity pressure and temperature to control the product quality.

[0019] A computer storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the steps of any one of the methods for online monitoring and control of the quality of a semi-crystalline polymer molded product are implemented.

[0020] It can be seen from the above technical scheme that compared with the prior art, the present invention provides a method, system and storage medium for online monitoring and control of the quality of semi-crystalline polymer molded products, which has the advantages of being fast, convenient and systematic in quality control of semi-crystalline polymer products. It can greatly shorten the product manufacturing cycle, significantly reduce product costs, and greatly enhance the company's market competitiveness and sensitivity in terms of adjusting product performance, new product research and development, and market responsiveness of semi-crystalline polymer product manufacturers according to market demand. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0022] Figure 1 It is a schematic diagram of the method flow of the present invention;

[0023] Figure 2 It is the temperature and pressure curve change diagram of online monitoring of static compression molding process;

[0024] Figure 3 This is a temperature and pressure curve change diagram for online monitoring of the dynamic compression molding process. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The service performance of semi-crystalline polymer molded products, such as mechanical strength, toughness, and wear resistance, depends on the microstructure of the product, such as crystal phase arrangement, grain size, and amorphous phase structure. The microstructure is mainly affected by molding parameters such as molding temperature, molding pressure, and molding cycle. In particular, the change trend of the pressure and temperature of the material in the mold cavity can reflect the phase change inside the mold cavity in real time. Therefore, the online detection and collection of the molding pressure and temperature of the molded product is of great significance for improving the molding efficiency of the molded product, reducing costs, and developing new products. In view of the problems of long time and high cost in the existing quality analysis and control of semi-crystalline polymer molded products, the present invention proposes an online monitoring and control technology for the quality of semi-crystalline polymer molded products. By establishing an online detection mechanism for the molding pressure and molding temperature of semi-crystalline polymer products, using pressure, temperature sensors and monitoring systems to detect and collect cavity pressure and temperature data in the molding process in real time, and by real-time analysis of the cavity pressure and temperature data, the crystallization behavior and characteristics of the product are obtained, thereby obtaining the product quality in real time, and the crystallization behavior can be controlled by regulating the cavity pressure and temperature to control the product quality.

[0027] The embodiment of the present invention discloses a method for online monitoring and controlling the quality of a semi-crystalline polymer molded product. Figure 1 As shown, the following steps are included:

[0028] Step 1: Set temperature measurement points inside the mold cavity to form the temperature field distribution at each stage of the material molding process to determine the real-time temperature changes of the material at various locations in the mold cavity;

[0029] Step 2: Online monitoring of the pressure on the material in the mold cavity during the molding process to obtain the real-time force change of the material;

[0030] Step 3: Obtain product quality in real time based on temperature changes, force changes, and material crystallization behavior and characteristics.

[0031] The service performance of semi-crystalline polymer compression molded products depends on the microstructures of the products, such as the crystal phase arrangement, grain size, and amorphous phase structure. For the temperature changes in the compression molding process, in the pre-pressing and exhausting stage, the melting and hot pressing stage, and the cooling and recrystallization stage, online temperature monitoring can be used to monitor and control the temperature of the compression molding process; at the same time, multiple temperature measurement points can be used for monitoring to form the temperature field distribution of each stage of the material molding process, so as to judge the real-time heating conditions of the materials in various places in the mold cavity. Another focus of the present invention is to monitor the pressure of the mold cavity material in the compression molding process online. In the pre-pressing and exhausting stage, a sufficiently large pressure or dynamic pressure is usually applied, and monitoring through online pressure monitoring can eliminate the gaps at the interface of the semi-crystalline polymer particles or inside the particles; in the melting and hot pressing stage, if the compression pressure is too large, on the one hand, it will cause the melting point to increase, and on the other hand, the free volume between the molecular chains in the melt will be severely compressed, which is not conducive to the movement and diffusion of the molecular chain segments, while too small a pressure is not conducive to driving the diffusion of the molecular chains. These all affect the crystallization behaviors such as the regular arrangement of molecular chains into the crystal lattice during the subsequent cooling and recrystallization (reflected by the changing trends of temperature and pressure curves). Therefore, real-time pressure monitoring is required during the melt hot pressing stage. In the cooling and recrystallization stage, when cooling begins, some molecular chain segments are regularly arranged into the crystal lattice, while others are constrained by the physical entanglement of molecular chains or fail to enter the crystal lattice in time, forming an amorphous phase. Different crystallization behaviors can be judged and distinguished by the corresponding changing trends of temperature and pressure curves. Taking static molding and pulse molding as examples, the changing trends of temperature and pressure curves in the molding process are as follows: Figure 2 and Figure 3 As shown, especially in the cooling recrystallization stage, three inflection points appear, namely ①, ②, and ③, which correspond to the beginning of cooling, the beginning of crystallization, and the end of crystallization, respectively, and can be corroborated by offline DSC tests, SEM, AFM and other test characterization analyses.

[0032] Therefore, the present invention emphasizes that by online monitoring of the temperature and pressure curve changing trends of the cavity material obtained during the compression molding process, especially the position and shape of the pressure inflection point at the crystallization temperature during the cooling stage, the crystallization behavior of the semi-crystalline polymer can be judged online. Based on this, an "online temperature-pressure curve-crystallization behavior" correlation mechanism is formed, which is used to regulate the crystallization behavior of semi-crystalline polymers, so as to online regulate the macroscopic properties of the product and realize online monitoring and regulation of product quality.

[0033] In view of the problems that the quality control of the existing traditional static compression molding semi-crystalline polymer products has long relied on engineering experience and off-line test analysis, and that the new dynamic compression molding parameters are complex and highly coupled, and the product quality control also needs to go through a long-term engineering process of "compression molding test-offline test-structure performance correlation-molding parameter control-compression molding test", the present invention proposes an online monitoring and control technology for the quality of semi-crystalline polymer compression molded products. By online monitoring of the pressure and temperature of the material (discrete material particle state-melt state-solid-liquid two-phase state-solid state) in the mold cavity during the compression molding (including static and dynamic compression) process, the online pressure and temperature curve change trend is obtained, and an "online temperature and pressure curve-crystallization behavior" correlation mechanism is formed, which is used for the crystallization behavior control of the semi-crystalline polymer, and the macroscopic properties of the product can be controlled online, thereby realizing online monitoring and control of the product quality.

[0034] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0035] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for online monitoring and control of the quality of semi-crystalline polymer molded products, characterized in that: The following steps are involved: Temperature measurement points are set inside the mold cavity to form the temperature field distribution at each stage of the material molding process, so as to determine the real-time temperature changes of the materials at various locations in the mold cavity; Online monitoring of the pressure on the material in the mold cavity during the molding process to obtain the real-time force changes on the material; Through temperature changes and stress changes, according to the crystallization behavior and characteristics of the material, the crystal phase and amorphous phase characteristics such as sample crystallinity and chip thickness are obtained, and the product quality is obtained in real time.

2. The method for online monitoring and controlling the quality of a semi-crystalline polymer molded product according to claim 1, characterized in that: It also includes controlling the crystallization behavior by regulating the mold cavity pressure and temperature to control the product quality.

3. The method for online monitoring and controlling the quality of a semi-crystalline polymer molded product according to claim 1, characterized in that: The compression molding process includes the pre-pressing and venting stage, the melting and hot pressing stage, and the cooling and recrystallization stage. It is monitored through online temperature monitoring. Based on the monitoring data, the oil flow in the mold is adjusted to achieve temperature control during the compression molding process.

4. The method for online monitoring and controlling the quality of a semi-crystalline polymer compression molded product according to claim 1, characterized in that: The system is monitored through online pressure monitoring. Based on the monitoring data, the pressure value of the upper die on the lower die is adjusted through the hydraulic valve to eliminate the gaps at the interface of the semi-crystalline polymer particles or inside the particles.

5. The method for online monitoring and controlling the quality of a semi-crystalline polymer molded product according to claim 1, characterized in that: The temperature change and the stress change are plotted into a first curve and a second curve, and different crystallization behaviors are determined according to the first curve and the second curve.

6. An online quality monitoring and control system for semi-crystalline polymer molded products, characterized in that: include: Temperature change monitoring module: used to set temperature measurement points inside the mold cavity to form the temperature field distribution at each stage of the material molding process, so as to determine the real-time temperature change of the material at each location in the mold cavity; The force change monitoring module is used to monitor the pressure of the cavity material during the compression molding process online and obtain the real-time force change of the material; Product quality acquisition module: used to obtain product quality in real time based on temperature changes and force changes, and according to the crystallization behavior and characteristics of the material.

7. The online quality monitoring and control system for semi-crystalline polymer compression molded products according to claim 6, characterized in that: It also includes a pressure and temperature control module: it is used to control the crystallization behavior by adjusting the pressure and temperature of the mold cavity to control the quality of the product.

8. A computer storage medium, characterized in that The computer storage medium stores a computer program, which, when executed by a processor, implements the steps of a method for online monitoring and control of the quality of a semi-crystalline polymer molded product as described in any one of claims 1 to 5.

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