A novel PET foaming process

Abstract

The application relates to the technical field of PET foaming processes, and particularly discloses a novel PET foaming process, which realizes real-time monitoring of product quality by measuring the density of a PET foam product in different zones, calculating the overall density score and comparing the overall density score with a preset threshold value; when detecting that the density is uneven, the system can automatically analyze the cause and judge whether the cause is that the temperature of a cooling system is unstable; if yes, the system automatically adjusts the opening degree of a cooling water valve, adjusts the temperature by changing the flow of the cooling water, and improves the consistency of the density of the product; in addition, the system also has the functions of continuously monitoring the temperature and repeatedly adjusting the temperature when necessary, so that the temperature is stabilized, and the product quality and production efficiency are improved; the application has the advantages that problems caused by temperature fluctuation can be automatically identified and solved, and the production automation level and the finished product rate are improved.

Description

Technical Field

[0001] This invention relates to the field of PET foaming technology, and specifically to a novel PET foaming process. Background Technology

[0002] In the PET (polyethylene terephthalate) foaming process, the density uniformity of the product directly affects its performance and application range. Traditional quality control methods mainly rely on manual inspection, which is inefficient and easily affected by subjective factors. In recent years, with the development of automation technology, it has become possible to use sensors and control systems to monitor and adjust the production process. However, how to effectively achieve stable temperature control remains a challenge.

[0003] Existing PET foaming processes typically use a fixed cooling water flow rate, which cannot adapt to temperature fluctuations caused by different product specifications and environmental changes. This fixed setting may lead to unstable product quality, especially for products that require high density uniformity. In addition, although some advanced systems can monitor temperature changes through sensors, they often lack effective feedback mechanisms and are difficult to automatically adjust cooling conditions to maintain an ideal temperature range, thus affecting the consistency and reliability of the finished product.

[0004] To address these issues, this invention proposes an improved PET foaming process, aiming to achieve stable temperature control through intelligent means, thereby improving product quality and production efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a novel PET foaming process to solve the problems mentioned above.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A novel PET foaming process includes:

[0008] The finished PET foam products are divided into several sub-regions;

[0009] Measure the density of different sub-regions to obtain the density score of the PET foam product;

[0010] The density score of PET foam products is compared with the density score threshold to generate abnormal density signals and normal density signals of PET foam products.

[0011] Based on the density anomaly signal of PET foam products, the actual temperature of the equipment cooling system is obtained, and the error value between the actual temperature and the target temperature is obtained.

[0012] Based on the error between the actual temperature and the target temperature, generate temperature non-compliance signals and temperature compliance signals;

[0013] Based on the temperature non-compliance signal, the output control quantity is obtained to determine when the actual temperature reaches the target temperature;

[0014] Based on the output control quantity, the voltage value of the corresponding valve actuator is obtained.

[0015] As a further aspect of the present invention, the process for obtaining the density score of PET foam products is as follows:

[0016] Density data at the center of each sub-region within the PET foam product is collected to obtain the sub-region density MD;

[0017] The sub-region located at the center of the PET foam product is defined as the central sub-region;

[0018] Obtain the distance between the center position of each sub-region and the center position of the central sub-region, and obtain the edge sub-regions with the largest distance from the center position of the central sub-region.

[0019] The sub-region densities of all edge sub-regions are integrated, and the mean density of the edge sub-regions (MDbian) is obtained through the mean calculation formula.

[0020] The density of all sub-regions of the PET foam product is integrated to obtain the average density of the sub-regions, MDJ.

[0021] The sub-region density standard deviation (MDB) is obtained based on the sub-region density mean.

[0022] The ratio of the subregion density mean to the subregion density standard deviation is used to calculate the subregion density variation coefficient MDCV.

[0023] The density score (MDF) of the PET foam product was calculated.

[0024] Where k is a preset coefficient, and MDzhong is the density of the central sub-region.

[0025] As a further aspect of the present invention: the generation process of the PET foam product density abnormality signal and the PET foam product density normal signal is as follows:

[0026] Based on the density score of PET foam products, the density score of PET foam products is compared with the density score threshold;

[0027] If the density score of a PET foam product is greater than or equal to the density score threshold, an abnormal density signal for the PET foam product is generated.

[0028] If the density score of a PET foam product is less than the density score threshold, a normal density signal for the PET foam product is generated.

[0029] As a further solution of the present invention: The process of obtaining the error value between the actual temperature and the target temperature is as follows:

[0030] Based on the abnormal density signal of the PET foam product, collect the real-time temperature of the cooling system during equipment operation to obtain the actual temperature value of the cooling system;

[0031] Calculate the difference between the actual temperature value of the cooling system and the target temperature value of the cooling system to obtain the error value WCZ between the actual temperature and the target temperature.

[0032] As a further solution of the present invention: The process of generating the temperature unqualified signal and the temperature qualified signal is as follows:

[0033] Compare the error value between the actual temperature and the target temperature with the error value threshold;

[0034] If the error value between the actual temperature and the target temperature is greater than or equal to the error value threshold, generate a temperature unqualified signal;

[0035] If the error value between the actual temperature and the target temperature is less than the error value threshold, generate a temperature qualified signal.

[0036] As a further solution of the present invention: The process of calculating the output control quantity when the actual temperature reaches the target temperature is as follows:

[0037] Based on the temperature unqualified signal, obtain the output control quantity U(t) from the actual temperature to the target temperature;

[0038] As a further solution of the present invention: The process of obtaining the proportionality coefficients b1, b2, and b3 is as follows:

[0039] Calculate the coefficient b1;

[0040] Calculate the coefficient b2;

[0041] Calculate the coefficient b3;

[0042] Among them, bc is the proportionality coefficient value when the adjusted actual temperature starts to fluctuate continuously, that is, the critical gain, and Ts is the time required for the adjusted actual temperature to reach the final stable value for the first time from the initial value, that is, the rise time.

[0043] As a further solution of the present invention: The process of obtaining the proportionality coefficient value bc and the time Ts is as follows: [[ID=​​​​​​​​​​​​​​​30 To obtain the initial output control quantity;

[0046] Based on the initial output control quantity, the opening degree of the cooling water valve is adjusted, and the actual temperature of the cooling system after adjustment is monitored in real time.

[0047] While maintaining the initial coefficient b 20 and b 30 With the initial coefficient b remaining constant, gradually increase it. 10 The value of b1 is recorded when the actual temperature begins to fluctuate continuously, and is denoted as the critical gain bc.

[0048] The temperature change of the cooling system is monitored when the valve opening is adjusted based on the initial output control quantity. The temperature change over time is obtained and a temperature response curve is plotted to obtain the rise time Ts.

[0049] As a further aspect of the present invention, the process of obtaining the corresponding valve actuator voltage value is as follows:

[0050] Based on the output control quantity U(t), obtain the maximum DC voltage V of the equipment cooling water valve control unit. max ;

[0051] The DC voltage V corresponding to the output control quantity U(t) is calculated.

[0052] As a further aspect of the present invention: after controlling the cooling water valves of the cooling system, the actual temperature of the cooling system is re-acquired and analyzed. The specific process is as follows:

[0053] Collect the actual temperature of the cooling system to obtain a new error value between the actual temperature and the target temperature;

[0054] Compare the new error value with the error value threshold;

[0055] If the new error value is less than the error threshold, a temperature compliance signal is generated.

[0056] If the new error value is greater than or equal to the error threshold, a temperature non-compliance signal is generated.

[0057] Based on the temperature non-compliance signal, the output control quantity is obtained again to show that the actual temperature has reached the target temperature.

[0058] The beneficial effects of this invention are:

[0059] (1) This invention uses a unique temperature control system to monitor and automatically adjust the cooling water flow rate in real time to ensure the stability of the temperature during the foaming process. This improvement significantly improves the density uniformity of the product. The traditional fixed cooling water flow rate method cannot adapt to the temperature fluctuations in production, resulting in inconsistent product density. However, this invention uses precise sensors and controllers to dynamically adjust the cooling conditions according to actual needs, so that the entire foaming process is within the optimal temperature range. This not only reduces quality problems caused by temperature changes, but also greatly improves the performance of the final product, meeting the strict requirements of the high-end market for the density uniformity of PET foam materials.

[0060] (2) This invention achieves automated temperature control in the foaming process, greatly reducing the need for manual monitoring. In traditional methods, operators need to frequently check and manually adjust the equipment, which is not only labor-intensive but also prone to misjudgment. In contrast, the intelligent control system used in this invention can autonomously complete temperature monitoring and adjustment, significantly reducing the risk of human error. In addition, the automated production process can shorten the processing cycle of individual products, accelerate the turnover speed of the production line, and thus improve overall production efficiency. This is especially important for large-scale industrial production, helping enterprises reduce costs, increase output, and enhance market competitiveness.

[0061] (3) With the help of the temperature control technology proposed in this invention, the quality of PET foam products has been significantly improved, and the adaptability of the system has also been enhanced. By optimizing the dynamic adjustment strategy of cooling water flow, the technology can better cope with different specifications of products and changes in environmental conditions. This provides manufacturers with greater flexibility, enabling them to produce high-quality foam materials in a wider temperature range. Therefore, this invention is not only applicable to the conventional packaging industry, but also to aerospace, automobile manufacturing and other fields, which have higher requirements for material performance. Thus, this invention opens up new possibilities for the application of PET foam materials and promotes the popularization and development of this technology in more high-end markets. Attached Figure Description

[0062] The invention will now be further described with reference to the accompanying drawings.

[0063] Figure 1 This is a flowchart of a novel PET foaming process according to the present invention;

[0064] Figure 2 This is a flowchart illustrating the generation of abnormal and normal density signals for PET foam products in a novel PET foaming process according to the present invention.

[0065] Figure 3 This is a flowchart illustrating the generation of temperature non-compliance signals and temperature compliance signals in a novel PET foaming process according to the present invention. Detailed Implementation

[0066] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0067] Example 1

[0068] Please see Figure 1 As shown, this invention is a novel PET foaming process, comprising the following steps:

[0069] Step 1: Pour the PET raw material into the extruder and heat it to about 270 degrees Celsius.

[0070] It should be explained that PET is a thermoplastic widely used in packaging, fibers, and engineering plastics. Due to its excellent physical and chemical properties, PET is an ideal material for making foamed sheets.

[0071] Extruder: An extruder is a device used to heat and plasticize plastic raw materials into a molten state, and then extrude them through a die to form a shape.

[0072] Heat to approximately 270 degrees Celsius: This temperature is one of the melting temperature ranges for PET raw materials. At this temperature, the PET raw material softens and melts, facilitating subsequent processing and molding. Precise temperature control is required to ensure the PET melts completely without overheating and decomposing.

[0073] Step 2: Inject butane or carbon dioxide gas to induce foaming.

[0074] It needs to be explained that the foaming agent, either butane or carbon dioxide, is used here. It is injected into the molten PET to form tiny bubbles.

[0075] Foaming process: When foaming agents are injected into molten PET, they expand and generate bubbles. These bubbles diffuse and stabilize within the PET, forming a foamed structure. The foaming process can increase the volume of the material, reduce its density, and improve its thermal insulation, sound insulation, and cushioning properties.

[0076] Step 3: Cool the foamed sheet through the die head shaping sleeve.

[0077] It's important to explain: Die head: The die head is a key component of the extruder, determining the shape and size of the extrudate. In the production of foamed sheets, the die head is designed to form sheets of the required width and thickness.

[0078] Shaping sleeve: The shaping sleeve is usually located after the die head and is used to cool and shape the extruded foam sheet. Through cooling, the foam sheet will quickly solidify and maintain its shape and size.

[0079] Cooling process: As the foamed sheet passes through the shaping sleeve, it comes into contact with a cooling medium (such as water or air) and cools down. This process helps stabilize the foam structure and prevents the sheet from deforming during subsequent processing;

[0080] The process also includes the following steps to test the prepared PET foam product:

[0081] The finished PET foam products are divided into several sub-regions;

[0082] Measure the density of different sub-regions to obtain the density score of the PET foam product;

[0083] The density score of PET foam products is compared with the density score threshold to generate abnormal density signals and normal density signals of PET foam products.

[0084] Based on the density anomaly signal of PET foam products, the actual temperature of the equipment cooling system is obtained;

[0085] The difference between the actual temperature of the cooling system and the target temperature of the cooling system is calculated to obtain the error value between the actual temperature and the target temperature.

[0086] Based on the error between the actual temperature and the target temperature, generate temperature non-compliance signals and temperature compliance signals;

[0087] Based on the temperature non-compliance signal, the output control quantity is obtained to determine when the actual temperature reaches the target temperature;

[0088] Based on the output control quantity, the voltage value of the corresponding valve actuator is obtained.

[0089] Example 2

[0090] The PET foam product is divided into several sub-regions using a grid distribution.

[0091] Collect density data at the center of each sub-region, and denote it as the sub-region density MD;

[0092] Based on the sub-regional location distribution of PET foam products, the area located at the center of the PET foam product is defined as the central sub-region.

[0093] Obtain the distance between the center of each sub-region and the center of the central sub-region. By comparing the distances, identify the regions with the largest distances to the center of the central sub-region, and denote them as edge sub-regions.

[0094] By integrating the sub-region densities of all edge sub-regions, the mean sub-region density of the edge sub-regions is obtained using the mean calculation formula, and is denoted as the mean density of the edge sub-region MD. bian ;

[0095] By integrating the densities of all sub-regions of the PET foam product, a sub-region density group is obtained;

[0096] The sub-region density groups are processed according to the mean calculation formula to obtain the sub-region density mean MDJ;

[0097] Based on the sub-region density mean, the sub-region density group is processed according to the standard deviation calculation formula to obtain the sub-region density standard deviation MDB;

[0098] The ratio of the subregion density mean MDJ to the subregion density standard deviation MDB is calculated to obtain the subregion density variation coefficient MDCV.

[0099] The formula MDF = w1(MDJ - k × MDB) - w2(1 - MDCV) + w3(MD) is used to calculate the MDF value. bian -MD zhong The density score (MDF) of the PET foam product is calculated, where k is a preset coefficient, and MDF is the density score. zhong The density of the central sub-region;

[0100] Compare the density score of PET foam products with the density score threshold;

[0101] If the density score of a PET foam product is greater than or equal to the density score threshold, an abnormal density signal for the PET foam product is generated.

[0102] If the density score of the PET foam product is less than the density score threshold, a normal density signal for the PET foam product is generated.

[0103] It should be noted that the abnormal density signal of PET foam products indicates that the density difference between different locations of the PET foam product is significant, exceeding the upper limit of acceptable density difference. Inconsistent density of PET foam products can lead to a series of problems. These problems not only affect the appearance of the product, such as uneven surface, uneven color, and inconsistent structure, but also its mechanical properties, such as inconsistent strength, decreased impact resistance, and reduced bending performance. In addition, density inconsistency may also lead to poor thermal insulation and sound insulation performance, as well as uneven weight. These problems are particularly important for applications that require precise weight control. From a manufacturing perspective, products with inconsistent density may lead to increased scrap rates, increased processing difficulty, and increased costs. Therefore, solving the problem of inconsistent PET foam density is crucial to ensuring product quality and improving production efficiency.

[0104] Example 3

[0105] Based on the aforementioned abnormal density signal of PET foam products, since abnormal temperatures in the equipment cooling system can cause inconsistent density in PET foam products during molding, it is necessary to analyze and determine whether the abnormal density of PET foam products is related to abnormal temperatures in the equipment cooling system. If a relationship exists, adjustments to the equipment cooling system can be made promptly during subsequent processing to reduce the impact of the cooling system temperature on the density of PET foam products, effectively maintaining the stability of PET foam product density, and thus improving the yield of PET foam products. Specifically:

[0106] The real-time temperature of the cooling system during equipment operation is collected to obtain the actual temperature value of the cooling system;

[0107] The difference between the actual temperature value and the target temperature value of the cooling system is calculated to obtain the error value WCZ between the actual temperature and the target temperature.

[0108] The error between the actual temperature and the target temperature is compared with the error threshold. If the error between the actual temperature and the target temperature is greater than or equal to the error threshold, it indicates that the temperature of the cooling system is abnormal and a temperature failure signal is generated.

[0109] If the error between the actual temperature and the target temperature is less than the error threshold, it indicates that the cooling system is operating normally and a temperature compliance signal is generated.

[0110] Example 4

[0111] Based on the above-mentioned temperature non-compliance signals, since the design and control methods of the cooling system are different in the PET foaming process, if the power of the cooling system can be adjusted, then the power of the cooling elements (such as fans or pumps) in the cooler can be adjusted by directly controlling the power of the cooling system. If the power of the cooling system cannot be adjusted, the flow rate of the cooling medium (such as cooling water) can be controlled, that is, the flow rate of the cooling water can be changed by adjusting the opening of the cooling water valve, thereby controlling the cooling intensity. If the cooling medium of the cooling system contains refrigerant, then the temperature of the cooling medium can be adjusted by controlling the circulation rate of the refrigerant or the working state of the refrigeration unit.

[0112] In a specific real-time example, the cooling temperature is maintained near the target value by controlling the flow rate of the cooling water. In this case, this can be achieved by controlling the opening of the cooling water valve.

[0113] Based on the temperature non-compliance signal, using the formula The output control quantity U(t) is obtained from the actual temperature to the target temperature;

[0114] Where b1, b2, and b3 are the coefficients of the formula. It is an integral term calculated based on the cumulative error value WCZ over time. WCZ(τ) is the error value between the actual temperature and the target temperature at time τ, dτ is the small increment of the time variable τ, and t is the current time. It is the differential term calculated based on the rate of change of the error value WCZ. It is the rate of change of the error value WCZ with time t, that is, the rate of change of the error;

[0115] It should be noted that if the error value WCZ < 0, it means that the actual temperature is higher than the target temperature. The output control quantity U(t) will increase, the valve opening will increase, and the cooling water flow will increase, thereby accelerating the cooling. If the error value WCZ > 0, it means that the actual temperature is lower than the target temperature. The output control quantity U(t) will decrease, the valve opening will decrease, and the cooling water flow will decrease, thereby slowing down the cooling speed.

[0116] The process of obtaining coefficients b1, b2, and b3 is as follows:

[0117] Through formula The coefficient b1 is calculated, where bc is the proportional coefficient value when the adjusted actual temperature begins to fluctuate continuously, i.e., the critical gain, and Ts is the time required for the adjusted actual temperature to reach the final stable value from the initial value for the first time, i.e. the rise time.

[0118] It should be noted that the critical gain bc refers to the proportional coefficient value at which the actual temperature fluctuates continuously after adjustment under the control ratio. When the proportional coefficient exceeds this value, the actual temperature becomes unstable and exhibits continuous fluctuation behavior.

[0119] The process of obtaining the critical gain bc is as follows:

[0120] Preset an initial coefficient b 10 b 20 and b 30 ;

[0121] Based on the initial coefficient b 10 b 20 and b 30 To obtain the initial output control quantity;

[0122] Based on the initial output control quantity, the valve opening is adjusted, and the actual temperature of the cooling system after adjustment is monitored in real time.

[0123] Based on the adjusted actual temperature, while maintaining the initial coefficient b 20 and b 30 With the initial coefficient b remaining constant, gradually increase it. 10The value of b1 is recorded when the actual temperature begins to fluctuate continuously, and is denoted as the critical gain bc.

[0124] The process of obtaining the rise time Ts is as follows:

[0125] Monitor the temperature change when the valve opening is adjusted based on the initial output control value, obtain the temperature change over time, and plot the temperature response curve.

[0126] Based on the temperature response curve, the time required for the temperature to rise from the initial value to the final stable value is obtained, i.e., the rise time Ts.

[0127] Through formula The coefficient b2 is calculated.

[0128] The coefficient b3 is obtained by calculating using the formula b3 = bc * Ts;

[0129] It should be noted that the obtained output control quantity U(t) is a value in the range of 0 to 100%, representing the degree to which the valve should be opened, i.e., the valve opening degree. The control quantity is calculated based on the deviation between the actual temperature and the target temperature, and then the valve opening degree is adjusted to control the flow rate of cooling water, thereby maintaining the cooling water temperature near the target value.

[0130] Example 5

[0131] Based on the output control quantity U(t) from the actual temperature to the target temperature, the maximum DC voltage V of the equipment valve control unit is obtained. max ;

[0132] Through mapping formula Obtain the DC voltage V corresponding to the output control quantity U(t);

[0133] Based on the DC voltage V corresponding to the output control quantity U(t), a voltage signal is generated to drive the valve.

[0134] It should be noted that the output control quantity is a value within a range and needs to be converted into a signal format that the valve actuator can recognize. For example, if the output control quantity is 50%, the corresponding voltage signal range is 0V to 10V. Then, the output control quantity of 50% is converted into the corresponding voltage of 5V through a mapping formula. Based on the voltage of 5V, a voltage signal is generated to control the valve actuator. After receiving the 5V signal, the valve actuator outputs a 5V voltage, causing the valve to open to the 50% position. In this way, the output control quantity can be effectively converted into the action of the valve actuator, thereby controlling the opening of the cooling water valve and achieving precise control of the cooling temperature.

[0135] After the valve status of the cooling system changes for a certain period of time, the actual temperature of the cooling system is re-acquired to obtain a new error value WCZx between the actual temperature and the target temperature.

[0136] Compare the new error value WCZx with the error value threshold;

[0137] If the new error value WCZx is greater than or equal to the error value threshold, then the temperature is not qualified, and the steps of Examples 4 to 5 are repeated.

[0138] If the new error value WCZx is less than the error threshold, it means that the actual temperature has stabilized near the target temperature, which is a qualified temperature signal, and the valve control should be stopped.

[0139] It should be noted that as the valve status changes, the actual temperature will also change accordingly. As the temperature changes, the output control quantity is adjusted accordingly, thereby adjusting the opening of the cooling water valve. This continuous adjustment process helps to prevent excessive temperature fluctuations and ensures that the cooling water temperature can quickly respond to changes in the target temperature.

[0140] The working principle of this invention: This invention uses a unique temperature control system to monitor and automatically adjust the cooling water flow rate in real time, ensuring temperature stability during the foaming process. This improvement significantly enhances the density uniformity of the product. Traditional fixed cooling water flow rate methods cannot adapt to temperature fluctuations during production, resulting in inconsistent product density. However, this invention utilizes precise sensors and controllers to dynamically adjust cooling conditions according to actual needs, keeping the entire foaming process within the optimal temperature range. This not only reduces quality problems caused by temperature changes but also greatly improves the performance of the final product, meeting the stringent requirements of the high-end market for the density uniformity of PET foam materials.

[0141] This invention achieves automated temperature control in the foaming process, significantly reducing the need for manual monitoring. Traditional methods require operators to frequently check and manually adjust the equipment, which is not only labor-intensive but also prone to misjudgment. In contrast, the intelligent control system employed in this invention can autonomously monitor and adjust the temperature, significantly reducing the risk of human error. Furthermore, the automated production process can shorten the processing cycle of individual products, accelerate production line turnover, and thus improve overall production efficiency. This is particularly important for large-scale industrial production, helping companies reduce costs, increase output, and enhance market competitiveness.

[0142] The temperature control technology proposed in this invention significantly improves the quality of PET foam products and enhances the system's adaptability. By optimizing the dynamic adjustment strategy of cooling water flow, the technology can better cope with different product specifications and environmental conditions. This provides manufacturers with greater flexibility, enabling them to produce high-quality foam materials over a wider temperature range. Therefore, this invention is not only applicable to the conventional packaging industry but also to aerospace, automotive manufacturing, and other fields with higher material performance requirements. Thus, this invention opens up new possibilities for the application of PET foam materials and promotes the popularization and development of this technology in more high-end markets.

[0143] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A PET foaming process, characterized in that, Including: Dividing the finished PET foam product into several sub-regions; Measuring the density of different sub-regions to obtain the density score of the PET foam product; Comparing the density score of the PET foam product with the density score threshold to generate a density anomaly signal and a normal density signal for the PET foam product; Based on the density anomaly signal of the PET foam product, obtaining the actual temperature of the equipment cooling system to get the error value between the actual temperature and the target temperature; Based on the error value between the actual temperature and the target temperature, generating a temperature non-conformance signal and a temperature conformance signal; Based on the temperature non-conformance signal, obtaining the output control quantity for the actual temperature to reach the target temperature; Based on the output control quantity, obtaining the voltage value of the corresponding valve execution unit; The process of obtaining the density score of the PET foam product is as follows: Collecting the density data at the center position of each sub-region within the PET foam product to obtain the sub-region density MD; Designating the sub-region at the center position of the PET foam product as the central sub-region; Obtaining the distance between the center position of each sub-region and the center position of the central sub-region to get several edge sub-regions with the largest distance from the center position of the central sub-region; By integrating the sub-region densities of all edge sub-regions, the mean density (MD) of the edge sub-regions is obtained using the mean calculation formula. bian ; Integrating the density of all sub-regions of the PET foam product to obtain the sub-region density mean MDJ; Based on the sub-region density mean, obtaining the sub-region density standard deviation MDB; Calculating the ratio of the sub-region density mean to the sub-region density standard deviation to obtain the sub-region density variation coefficient MDCV; Through the formula The density score (MDF) of the PET foam product was calculated. Where k is a preset coefficient, MD zhong The density of the central sub-region.

2. The PET foaming process according to claim 1, characterized in that, The generation process of the density anomaly signal and the normal density signal for the PET foam product is as follows: Based on the density score of the PET foam product, comparing the density score of the PET foam product with the density score threshold; If the density score of the PET foam product is greater than or equal to the density score threshold, generating a density anomaly signal for the PET foam product; If the density score of the PET foam product is less than the density score threshold, generating a normal density signal for the PET foam product.

3. The PET foaming process according to claim 1, characterized in that, The process of obtaining the error value between the actual temperature and the target temperature is as follows: Based on the density anomaly signal of the PET foam product, collecting the real-time temperature of the cooling system during equipment operation to obtain the actual temperature value of the cooling system; Calculating the difference between the actual temperature value of the cooling system and the target temperature value of the cooling system to obtain the error value WCZ between the actual temperature and the target temperature.

4. The PET foaming process according to claim 3, characterized in that, The generation process of the temperature non-conformance signal and the temperature conformance signal is as follows: Comparing the error value between the actual temperature and the target temperature with the error value threshold; If the error value between the actual temperature and the target temperature is greater than or equal to the error value threshold, producing a temperature non-conformance signal; If the error value between the actual temperature and the target temperature is less than the error value threshold, producing a temperature conformance signal.

5. The PET foaming process according to claim 4, characterized in that, proportionality coefficient , and The process of obtaining it is as follows: Through formula Calculated coefficients ; Through formula Calculated coefficients ; Through formula Calculated coefficients ; Where bc is the proportionality coefficient value when the adjusted actual temperature starts to fluctuate continuously, i.e., the critical gain, and Ts is the time required for the adjusted actual temperature to reach the final stable value from the initial value for the first time, i.e., the rise time.

6. The PET foaming process according to claim 5, characterized in that, The process of obtaining the proportionality coefficient value bc and the time Ts is as follows: Preset an initial coefficient , and ; Based on initial coefficients , and To obtain the initial output control quantity; Based on the initial output control quantity, adjusting the opening degree of the cooling water valve and real-time monitoring the actual temperature of the adjusted cooling system; While maintaining the initial coefficients and With the initial coefficients remaining unchanged, gradually increase them. The value is recorded, and the process stops when the actual temperature begins to fluctuate continuously. The coefficient at the point when the actual temperature begins to fluctuate continuously is also recorded. The value is denoted as the critical gain bc; The temperature change of the cooling system is monitored when the valve opening is adjusted based on the initial output control quantity. The temperature change over time is obtained and a temperature response curve is plotted to obtain the rise time Ts.

7. The PET foaming process according to claim 6, characterized in that, The process of obtaining the corresponding valve actuator voltage value is as follows: Based on the output control quantity U(t), obtain the maximum DC voltage V of the equipment cooling water valve control unit. max ; The DC voltage V corresponding to the output control quantity U(t) is calculated.

8. The PET foaming process according to claim 7, characterized in that, After controlling the cooling water valves of the cooling system, the actual temperature of the cooling system is re-acquired and analyzed. The specific process is as follows: Collect the actual temperature of the cooling system to obtain a new error value between the actual temperature and the target temperature; Compare the new error value with the error value threshold; If the new error value is less than the error threshold, a temperature compliance signal is generated. If the new error value is greater than or equal to the error threshold, a temperature non-compliance signal is generated. Based on the temperature non-compliance signal, the output control quantity is obtained again to show that the actual temperature has reached the target temperature.

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