Pressure Sensing-Based Optimization System and Method for Pulp Molding Hot Pressing and Shaping Process

Abstract

This invention discloses a pressure-sensing-based optimization system and method for pulp molding hot pressing and setting process, relating to the field of pulp molding product manufacturing technology. The method collects zoned pressure signals and thickness distribution labels during the pulp molding hot pressing and setting process, extracts the effective pressure signal for fiber dehydration through frequency domain filtering, and calculates the real-time moisture content. Based on the real-time moisture content, thickness labels, and cumulative effective pressure, a dynamic elastic coefficient and equivalent rebound driving force are constructed, thereby predicting the rebound moisture content caused by fiber elastic rebound after pressure release. A dual criterion of moisture content compliance and rebound safety is established, merging adjacent label zones of the same thickness into process control areas, implementing differentiated pressure holding and gradient pressure release. This invention can accurately identify the pulp fiber curing state during the pulp molding hot pressing and setting process, adaptively adapt to differences in zoned curing progress, effectively avoid rebound risks, prevent local over-drying defects, and significantly reduce hot pressing energy consumption.

Description

Technical Field

[0001] This invention relates to the field of pulp molding product manufacturing technology, and in particular to a system and method for optimizing the hot pressing and shaping process of pulp molding based on pressure sensing. Background Technology

[0002] Pulp molding hot pressing is a core energy-consuming process in product manufacturing. Pulp fibers are wet elastic materials that are compressed and dehydrated during hot pressing, and then bonded and shaped through hydrogen bonding. If the holding time is insufficient, the compressed fibers will elastically rebound after pressure is released, expanding in volume and loosening the fiber network. This allows the fibers to quickly absorb residual moisture or ambient humidity from the mold cavity, leading to a significant increase in moisture content. A second hot pressing is then necessary, significantly increasing energy consumption.

[0003] To avoid the risk of rebound, the industry generally adopts a fixed holding time that far exceeds the theoretical requirements. However, this leads to another common problem: the suction molding process naturally results in uneven thickness of the blank. The thin area completes dehydration and shaping first, but is forced to be hot-pressed simultaneously with the thick area, causing serious local over-drying. This not only wastes energy, but also causes quality problems such as product embrittlement and edge cracking.

[0004] Existing processes cannot accurately determine the degree of curing of hydrogen bonds in pulp fibers, nor can they identify differences in dewatering progress in different areas, resulting in a crude control method with fixed durations. Therefore, there is an urgent need to develop a dynamic hot-pressing and shaping control method that can accurately identify the curing state of pulp fibers and adapt to regional curing differences. This method would avoid the risk of springback while achieving precise control of hot-pressing energy consumption and stable improvement in product quality. Summary of the Invention

[0005] In order to overcome the defects and shortcomings of the existing technology, the present invention provides an optimization system and method for pulp molding hot pressing and shaping process based on pressure sensing.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an optimization method for the hot pressing and shaping process of pulp molding based on pressure sensing, comprising the following steps: S1. Collect the zone pressure signals and basic parameters of the pulp material during the hot pressing and shaping process of pulp molding, and generate thickness distribution labels corresponding to the zone pressure signals; S2. Perform frequency domain filtering on the zone pressure signals to extract the effective pressure signals characterizing fiber dehydration, calculate the real-time moisture content of the zone in combination with the thickness distribution label, and identify the incompletely cured zone according to the zone temperature conditions. S3. Based on the real-time moisture content, effective pressure signal, and thickness distribution label of each zone, a dynamic elastic coefficient is constructed by moisture content correction, thickness weighting, and effective pressure cumulative correction, and the equivalent rebound driving force of each zone is calculated. The critical solidification state is determined by monitoring the inflection point of pressure decay rate and the inflection point of equivalent rebound driving force. Then, combined with the equivalent rebound driving force and thickness distribution label, the rebound moisture content of each zone after pressure relief is calculated based on the physical characteristics of fiber rebound water absorption. S4. Using moisture content and rebound safety as dual criteria, combined with thickness distribution labels, critical curing state judgment results and incomplete curing area markings, a zoned dynamic optimization strategy for pulp molding hot pressing and shaping process is generated.

[0007] According to the above technical solution, the steps of collecting the zoned pressure signals and basic parameters of the pulp material during the pulp molding and hot pressing process, and generating thickness distribution labels corresponding to the zoned pressure signals, include: S110. Divide the pulp molding mold into zones according to the geometric thickness distribution of the target pulp molded product, and synchronously collect the pressure signal timing data and temperature signal timing data of each zone, specifically including: The pulp molding mold is pre-divided into zones according to the geometric thickness distribution of the target pulp molded product. Pressure sensing units and temperature sensing units are arranged according to the zones. Pressure signal timing data and temperature signal timing data of each zone in the pulp molding hot pressing and shaping process are collected synchronously at a fixed sampling frequency. The pressure signal and temperature signal of each zone are kept in time alignment. The output timing data includes a timestamp and the pressure value and temperature value corresponding to that zone.

[0008] S120. Obtain the basic material parameters of the pulp used for the target pulp molding product, including pulp type, freeness, initial moisture content, fiber aspect ratio, and reference elastic modulus, specifically including: The pulp type, beating degree, initial moisture content, and fiber aspect ratio are provided by the pulp supplier of the pulp used in the target pulp molded product. The benchmark elastic modulus is used to reflect the basic elastic stiffness of the pulp fiber under typical hot-pressed curing moisture content (8%±1%), and is determined by uniaxial compression test of pulp fiber. The above parameters are stored in the form of structured data and used for subsequent calculations.

[0009] S130. Based on the degree of deviation of the thickness of each zone of the target pulp molded product from the thickness reference of the target pulp molded product, the zones are marked as thick or thin zones, forming a thickness distribution label, specifically including: Based on the CAD file of the pulp molding die or the pre-calibration results of the molding process, the geometric thickness data of each zone of the target pulp molding product is obtained. The thickness value of each zone corresponds one-to-one with the preset zone position in S110. All zones are traversed to obtain the average thickness array of the zones. The median value of the average thickness array of the zones is used as the product thickness reference value. A thickness deviation rate threshold is set based on the statistical results of qualified batches in the same process. Zones whose thickness deviation rate relative to the product thickness reference value is greater than the thickness deviation rate threshold are marked as thick zones, and all other zones are uniformly marked as thin zones, forming a thickness distribution label.

[0010] S140. A humidity sensing unit is installed on the outer side of the parting surface of the pulp molding mold to synchronously collect the relative humidity time-series data of the contact area of ​​the target pulp molded product during the hot pressing and shaping process, specifically including: Humidity sensing units are equidistantly arranged around the outer side of the parting surface of the pulp molding mold. The humidity sensing units maintain a heat insulation distance from the heating body of the pulp molding mold, and the sensing surface faces the product discharge side after the mold is opened. The relative humidity time series data of the contact area of ​​the target pulp molding product during the hot pressing and shaping process are collected simultaneously for humidity correction in subsequent rebound moisture content prediction.

[0011] According to the above technical solution, the steps of performing frequency domain filtering on the zoned pressure signals, extracting the effective pressure signals characterizing fiber dehydration, calculating the real-time moisture content of the zones in conjunction with thickness distribution labels, and identifying incompletely cured areas based on zoned temperature conditions include: S210. Based on the freeness and fiber aspect ratio of the target pulp molding product, determine the typical response frequency range characterizing fiber dewatering. Extract the effective pressure signal within the typical response frequency range through spectral analysis, and obtain the pressure decay rate by calculating the time derivative of the effective pressure signal. Specifically, this includes: The typical response frequency range of pulp fibers during compression and dewatering is determined based on the beating degree and fiber aspect ratio of the target pulp molded product. The higher the beating degree, the higher the degree of fiber fibrillation, and the pressure response frequency shifts to lower frequencies. The larger the fiber aspect ratio, the easier it is for the fiber network structure to transmit high-frequency fluctuations, and the response frequency range expands to higher frequencies. The spectral distribution of the pressure signal time series data of each zone of the target pulp molded product is obtained by spectral transformation. The fluctuation components in the spectrum within the typical response frequency range are retained, while the mold thermal expansion drift components below the lower limit of the typical response frequency range and the mechanical vibration noise components above the upper limit of the typical response frequency range are removed. The retained fluctuation components are taken as the effective pressure signal directly related to fiber dewatering. At the same time, the pressure decay rate is calculated based on the first derivative of the effective pressure signal with respect to time. The effective pressure signal time series data and pressure decay rate time series data of each zone are output.

[0012] S220. Based on the thickness distribution label differentiation, the instantaneous drying rate of each zone is calculated. For thick zones, the instantaneous drying rate is calculated by multiplying the pressure fluctuation amplitude by the steam discharge resistance coefficient, where the pressure fluctuation amplitude reflects the degree of steam discharge obstruction, and the steam discharge resistance coefficient compensates for dehydration lag. For thin zones, the instantaneous drying rate is calculated by multiplying the pressure decay rate by the fiber shrinkage coefficient, where the pressure decay rate directly characterizes the dehydration speed, and the fiber shrinkage coefficient enables unit conversion. The real-time moisture content of each zone is then obtained by integrating the initial moisture content, specifically including: Based on the thickness distribution label, a differentiated moisture content calculation method is adopted for each zone of the target pulp molded product: For the zone marked as the thick zone, the difference between the peak and valley values ​​of the effective pressure signal output by S210 in a single sampling period is extracted as the pressure fluctuation amplitude. The pressure fluctuation amplitude is multiplied by the steam discharge resistance coefficient to obtain the instantaneous drying rate of the thick zone. The steam discharge resistance coefficient is determined based on the statistical results of qualified batches in the same process, combined with the degree of freeness and the fiber length-to-diameter ratio. The higher the degree of freeness or the larger the fiber length-to-diameter ratio, the larger the value of the steam discharge resistance coefficient. For the zone marked as thin, the instantaneous drying rate of the thin zone is obtained by directly multiplying the pressure decay rate output by S210 by the fiber shrinkage coefficient. The fiber shrinkage coefficient is determined based on the statistical results of qualified batches in the same process and in combination with the reference elastic modulus. The larger the reference elastic modulus, the smaller the value of the fiber shrinkage coefficient. The instantaneous drying rate of the thick zone and the instantaneous drying rate of the thin zone are linearly mapped to the initial moisture content. That is, the real-time moisture content is equal to the initial moisture content minus the integral of the instantaneous drying rate over time, and the real-time moisture content time series data of each zone is output.

[0013] S230. Set the critical moisture content threshold for curing of each zone based on the thickness distribution label. The critical moisture content threshold for curing of thicker zones is higher than that for thinner zones. Set the curing temperature threshold based on the glass transition temperature of the pulp fiber. When the real-time moisture content of a zone is greater than or equal to the critical moisture content threshold for curing of the corresponding zone, or when the real-time temperature is less than or equal to the curing temperature threshold for the corresponding zone, the corresponding zone is marked as an incompletely cured zone. Specifically, this includes: The real-time moisture content time series data of each zone is aligned with the temperature signal time series data. Based on the statistical results of qualified batches in the same process and combined with the thickness distribution label, the critical moisture content threshold for curing of each zone is set. The critical moisture content threshold for curing of the thick zone is higher than that of the thin zone. The curing temperature threshold is set in combination with the glass transition temperature of the fiber corresponding to the pulp type. The glass transition temperature of the fiber is obtained from the pulp type supplier. For each zone, if the real-time moisture content is greater than or equal to the critical moisture content threshold for curing, or the temperature signal is less than or equal to the curing temperature threshold, the zone is marked as an incompletely cured zone; otherwise, the zone is marked as a normally cured zone. According to the above technical solution, the steps of constructing a dynamic elastic coefficient and calculating the equivalent rebound driving force of each zone based on the real-time moisture content of the zone, the effective pressure signal, and the thickness distribution label, through moisture content correction, thickness weighting, and cumulative effective pressure correction; determining the critical solidification state by monitoring the inflection point of pressure decay rate and the inflection point of equivalent rebound driving force; and then, combining the equivalent rebound driving force and the thickness distribution label, calculating the rebound moisture content of each zone after pressure relief based on the physical characteristics of fiber rebound water absorption, include: S310. Moisture content correction: The reference elastic modulus is linearly reduced by the ratio of the real-time moisture content of the zone to the fiber saturated moisture content; the higher the real-time moisture content, the greater the reduction. Thickness weighting: The weighting factor is determined by the ratio of the zone thickness to the reference thickness; the elastic modulus is amplified in thick zones and reduced in thin zones. The cumulative effective pressure is obtained by integrating the effective pressure signal of the zone, and a process correction factor is constructed using a saturated growth model to correct the elastic modulus over time. The three correction results are coupled to obtain the dynamic elastic coefficient and calculate the equivalent rebound driving force of each zone, specifically including: Using real-time moisture content time series data, effective pressure signal time series data, thickness distribution labels, and benchmark elastic modulus as inputs, dynamic elastic coefficients for each zone are constructed. Based on the benchmark elastic modulus, the benchmark elastic modulus is dynamically reduced according to the real-time moisture content: the higher the moisture content, the more dominant the fiber plastic deformation, and the greater the reduction in elastic modulus; the lower the moisture content, the stronger the dry elasticity of the fiber, and the elastic modulus approaches the benchmark value. Thickness-based weighted correction: In thick regions, due to the large fiber compression ratio and large effective energy storage fiber volume, the elastic modulus is weighted by amplification; in thin regions, due to the small compression and thin fiber layer, the elastic modulus is weighted by reduction. The effective pressure signal is integrated over time to obtain the cumulative effective pressure value. The elastic modulus is then corrected based on the cumulative effective pressure value: the more complete the cumulative dehydration, the more stable the fiber hydrogen bonding, the higher the proportion of irreversible elastic energy storage, and the further the elastic modulus increases. The corrected elastic modulus is defined as the dynamic elastic coefficient, and the product of the dynamic elastic coefficient and the current mold closing pressure is defined as the equivalent rebound driving force. The time series data of the equivalent rebound driving force for each zone is output.

[0014] S320: Real-time monitoring of the inflection point of the pressure decay rate from negative to positive and the inflection point of the equivalent rebound driving force from rising to stabilizing in each zone; combined with the critical moisture content threshold for curing, determining the critical curing state and recording the critical curing time, specifically including: Real-time monitoring of the time-series data of pressure decay rate and equivalent rebound driving force for each zone identifies two physical inflection points: the first inflection point is the moment when the pressure decay rate changes from negative to positive, indicating that the dehydration of free water inside the fiber is complete, the vapor pressure drop disappears, and the fiber shrinkage stress begins to dominate the pressure change; the second inflection point is the moment when the equivalent rebound driving force changes from continuous increase to stability, that is, within a consecutive preset number of sampling periods, the absolute value of the first derivative of the equivalent rebound driving force with respect to time is less than a preset fluctuation threshold, which is determined by the statistical results of qualified batches in the same process, indicating that the fiber hydrogen bonding is basically completed and the elastic energy storage no longer increases. Based on the critical moisture content threshold for partition curing set in S230, when a partition simultaneously meets three conditions—the pressure decay rate has reached a turning point from negative to positive, the equivalent rebound driving force has reached a turning point from rising to stabilizing, and the real-time moisture content is lower than the critical moisture content threshold for curing corresponding to that partition—it is determined that the partition has entered the critical curing state. This moment is recorded as the critical curing moment, and the critical curing state determination result and the corresponding critical curing moment for each partition are output.

[0015] S330: The pore moisture absorption space after fiber rebound is quantified by the peak value of the equivalent rebound driving force, the moisture absorption driving conditions are quantified by the relative humidity of the environment during depressurization, and the fiber stacking moisture absorption capacity is quantified by the partition thickness. Combining the saturated moisture absorption characteristics of pulp fibers, and based on the positive correlation between the peak value of the equivalent rebound driving force, the relative humidity of the environment, the partition thickness, and the saturated moisture absorption characteristics of pulp fibers, the rebound moisture content after partition depressurization is calculated, specifically including: Using the real-time moisture content data at the peak moment of the equivalent rebound driving force time series data of each zone, the ambient relative humidity data, the thickness distribution label, and the pulp type as input, the rebound moisture content after pressure relief is calculated based on the physical correlation law of fiber rebound water absorption. The rebound moisture content after pressure relief is positively correlated with the peak value of the equivalent rebound driving force. The larger the peak value of the equivalent rebound driving force, the greater the fiber rebound deformation and the larger the internal micropore water absorption space. It is also positively correlated with the relative humidity of the environment. The higher the environmental humidity, the more environmental moisture the fiber can absorb after pressure relief. Furthermore, it is positively correlated with the thickness of the zone. After rebound, the internal pore volume of the thick zone is larger and the water absorption capacity is higher than that of the thin zone. Based on the above positive correlation and the inherent water absorption characteristics of the material determined by the pulp type parameters, the rebound moisture content after depressurization of each zone is calculated, and the rebound moisture content after depressurization is output as the core input for subsequent rebound safety criteria.

[0016] According to the above technical solution, the steps of generating a zoned dynamic optimization strategy for the pulp molding hot pressing process, which uses moisture content and rebound safety as dual criteria, combined with thickness distribution labels, critical curing state determination results, and incomplete curing area markings, include: S410. Merge adjacent zones with consistent thickness distribution labels into a process control area. Use the arithmetic mean of the real-time moisture content of each zone constituting the process control area as the average moisture content of the process control area. Use the maximum value of the rebound moisture content after depressurization of each zone constituting the process control area as the maximum rebound moisture content after depressurization of the process control area. Use the average moisture content of the process control area being lower than the curing safety threshold and the maximum rebound moisture content after depressurization of the process control area being lower than the allowable upper limit as dual criteria. Force pressure holding is applied to the incompletely cured area. For process control areas that meet the dual criteria, pressure is reduced to maintain shape. Specifically, this includes: Partitions with adjacent locations and consistent thickness distribution labels are merged into a process control area, which serves as the smallest operational unit for subsequent adjustments. The arithmetic mean of the real-time moisture content of each zone within the process control area is lower than the corresponding critical moisture content threshold for curing, which is used as the criterion for moisture compliance. The maximum value of the rebound moisture content after depressurization of each zone within the process control area is lower than the upper limit of the allowable moisture content increase of products in the same historical batches, which is used as the criterion for rebound safety. If any zone within the process control area is marked as an incompletely cured zone, the entire area is considered an incompletely cured zone. If any zone enters the critical curing state, the entire area is considered to have entered the critical curing state. Differentiated pressure holding exit rules are implemented based on thickness distribution labels: Thin areas are prone to situations where the moisture content meets the standard but curing is insufficient. Both the moisture content standard criterion and the rebound safety criterion must be met simultaneously before full pressure holding can be exited. For thick areas, moisture content meets the standard as the core control objective. The moisture content standard criterion is met first, and the rebound safety criterion is checked simultaneously. Full pressure holding is forcibly maintained in incompletely cured areas (if the standard is not met, curing must continue). For areas where both criteria are met, pressure reduction and shape preservation are implemented (if the area is already cured, excessive pressure holding is not required).

[0017] S420. Based on the earliest critical curing time of each process control region, a pressure relief priority queue is generated. After all process control regions meet the dual criteria, a dynamic optimization strategy for labels with different thickness distributions is executed, specifically including: Based on the earliest critical curing time in each process control area, a region pressure relief priority queue is generated. The earlier the critical curing time of the process control area, the higher the pressure relief priority. After all process control areas meet the dual criteria, differentiated gradient pressure relief is initiated by matching the thickness distribution labels: the thick process control area adopts a smaller pressure relief step size and a longer interstage holding time, while the thin process control area adopts a larger pressure relief step size and a shorter interstage holding time. After complete pressure relief, the mold closing position is locked synchronously to complete the dynamic optimization of the hot pressing and shaping process.

[0018] Secondly, this application provides a pressure-sensing-based pulp molding hot pressing and setting process optimization system, including: The data acquisition module is used to collect the zone pressure signals and basic parameters of the pulp material during the hot pressing and shaping process of pulp molding, and to generate thickness distribution labels corresponding to the zone pressure signals. The signal processing module is used to perform frequency domain filtering on the zone pressure signal, extract the effective pressure signal characterizing fiber dehydration, calculate the real-time moisture content of the zone in combination with the thickness distribution label, and identify the incompletely cured zone according to the zone temperature conditions. The curing analysis module is used to construct dynamic elastic coefficients and calculate the equivalent rebound driving force of each zone based on the real-time moisture content of each zone, the effective pressure signal, and the thickness distribution label. It also uses moisture content correction, thickness weighting, and effective pressure cumulative correction to determine the critical curing state by monitoring the inflection point of the pressure decay rate and the inflection point of the equivalent rebound driving force. Then, based on the physical characteristics of fiber rebound water absorption, it calculates the rebound moisture content of each zone after pressure relief, combining the equivalent rebound driving force and the thickness distribution label. The optimized control module is used to generate a zoned dynamic optimization strategy for the pulp molding hot pressing process, based on the dual criteria of moisture content compliance and rebound safety, combined with thickness distribution labels, critical curing state judgment results, and incomplete curing zone identification.

[0019] Thirdly, this application provides an electronic device, including: a processor and a memory, wherein the memory stores a computer program that can be called by the processor, and the processor executes a pressure-sensing-based method for optimizing the hot pressing and shaping process of pulp molding by calling the computer program stored in the memory.

[0020] Fourthly, this application provides a computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform a pressure-sensing-based method for optimizing the hot-pressing process of pulp molding.

[0021] Compared with the prior art, this application has the following advantages and beneficial effects: This application achieves real-time sensing of the drying process of pulp molding hot pressing based on pressure sensing, overcoming the problems of local over-drying and rebound secondary hot pressing caused by the inability to judge the fiber curing state in traditional fixed-time processes. It constructs a critical curing state identification mechanism based on dual physical criteria of the inflection point of pressure decay rate and the inflection point of equivalent rebound driving force, improving the accuracy and reliability of predicting the risk of fiber elastic rebound during the hot pressing process. Through zoned differentiated moisture content calculation, incomplete curing zone identification, and rebound moisture content prediction, it significantly reduces ineffective pressure holding energy consumption and secondary hot pressing energy consumption while ensuring the quality of pulp molding products. These three aspects together constitute a closed-loop energy-saving optimization system for pulp molding hot pressing, from drying process sensing and rebound risk prediction to zoned differentiated control. Attached Figure Description

[0022] Figure 1This is a schematic diagram of the overall process of the pressure-sensing-based pulp molding hot pressing and shaping process optimization method provided in the embodiments of this application; Figure 2 This is a schematic diagram of the process for calculating real-time moisture content and identifying incompletely cured areas provided in an embodiment of this application; Figure 3 This is a schematic diagram of the process for calculating the rebound moisture content after pressure relief, provided in an embodiment of this application. Figure 4 This is a schematic diagram of the structure of the pressure-sensing-based pulp molding hot pressing and shaping process optimization system provided in the embodiments of this application. Detailed Implementation

[0023] The technical solution of this application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments and specific features in the embodiments are detailed descriptions of the technical solution of this application, rather than limitations thereof. In the absence of conflict, the embodiments and technical features in the embodiments can be combined with each other.

[0024] Please see Figure 1 , Figure 1 This is a schematic diagram of the overall process of the pressure-sensing-based pulp molding hot pressing and shaping process optimization method provided in the embodiments of this application, which specifically includes the following steps: S1. Collect the zone pressure signals and basic parameters of the pulp material during the hot pressing and shaping process of pulp molding, and generate thickness distribution labels corresponding to the zone pressure signals.

[0025] In this embodiment, step S1 includes the following specific contents: S110. Divide the pulp molding mold into zones according to the geometric thickness distribution of the target pulp molded product, and simultaneously collect the pressure signal timing data and temperature signal timing data of each zone.

[0026] Based on the 3D geometric model of the target pulp molded product (derived from the mold CAD file), the thickness distribution of the target pulp molded product on the horizontal projection plane is extracted. Thickness is defined as the vertical distance from the bottom surface of the product cavity to the core surface. The entire product surface is discretized into 1mm×1mm grid cells, and the thickness value of each grid cell is calculated to generate a thickness distribution cloud map.

[0027] Based on the thickness distribution cloud map, the following rules are used to divide the area into zones: identify areas where the thickness value changes continuously and the gradient of change is less than 0.5 mm / cm, and divide these areas into zones; identify areas where the thickness difference between adjacent grid cells is greater than 1.5 mm, and use the abrupt change line as the zone boundary, establishing zones on both sides of the abrupt change line, with a 2 mm transition interval reserved at the abrupt change boundary to avoid signal distortion caused by placing sensors in stress concentration areas; the area of ​​each zone is not less than 10 cm² and not more than 50 cm², the maximum difference in grid thickness within a single zone does not exceed 2 mm, and the number of zones is determined according to the actual geometric complexity of the product, usually 6 to 12.

[0028] For each zone, a pressure sensing unit and a temperature sensing unit are installed on the back of the cavity at the corresponding location in the mold (5mm from the cavity surface). The pressure sensing unit uses a miniature piezoresistive sensor with a range of 0~5MPa and an accuracy of ±0.5%FS; the temperature sensing unit uses a PT100 platinum resistance sensor with an accuracy of ±0.2℃. The sensing units are led out of the pulp molding mold via high-temperature shielded wires and connected to a multi-channel data acquisition device. The pressure and temperature signals of all zones are synchronously acquired at a sampling rate of no less than 100Hz, and the acquisition time covers the entire process from mold closing to complete pressure release. The timing data of the pressure and temperature signals of each zone are stored in a time-aligned manner.

[0029] S120. Obtain the basic material parameters of the pulp used for the target pulp molding product, including pulp type, beating degree, initial moisture content, fiber aspect ratio and reference elastic modulus.

[0030] Obtain the basic material parameters of the pulp used for the target pulp molded products: the pulp type is specified by the production formula; the freeness, initial moisture content, and fiber aspect ratio are provided by the pulp supplier or obtained by testing according to industry standard methods (such as GB / T3332, GB / T462, GB / T10336); The baseline elastic modulus was determined as follows: Pulp from the same batch of target molded pulp was used to prepare circular fiber mats with a diameter of 50 mm and a thickness of 5 mm using vacuum filtration molding. After pressing at 0.5 MPa for 5 minutes, the mats were dried at 105°C to a moisture content of 8% ± 1%. The fiber mats were placed on a universal testing machine and compressed at a rate of 1 mm / min to 0.5 MPa. The slope of the initial linear segment of the stress-strain curve (engineering strain of 0–0.1) was recorded. Five parallel samples were tested, and the arithmetic mean of the slopes of all samples was taken as the baseline elastic modulus, in MPa. This reflects the basic elastic stiffness of the pulp fibers under typical hot-pressed curing moisture content (8% ± 1%). In this embodiment, the baseline elastic modulus is assumed to be based on hardwood chemical pulp, consistent with the process baseline of this embodiment. The above parameters are stored in structured data format for subsequent steps.

[0031] S130. Based on the degree of deviation of the thickness of each zone of the target pulp molded product from the thickness reference of the target pulp molded product, the zones are marked as thick zones or thin zones, forming thickness distribution labels.

[0032] Based on the corresponding position of each partition in S110 on the three-dimensional geometric model of the target pulp molded product, the thickness values ​​of all 1mm×1mm grid units in the partition are extracted, and the average thickness of the partition is calculated. All partitions of the target pulp molded product are traversed to generate an array of average thicknesses of the partitions, and the median value of the average thickness array of the partitions is taken as the reference value of the product thickness. A thickness deviation rate threshold is set, where the thickness deviation rate is defined as (average thickness of the zone - product thickness benchmark value) / product thickness benchmark value; thickness data of all zones in historical qualified batches of the same process are collected, and the sample standard deviation of the thickness deviation rate of each zone is calculated. Take 2 As the benchmark for threshold calculation; to ensure the rationality of partitioning, upper and lower limits of 10% to 20% are set for the absolute value of the threshold calculation benchmark: when 2 When the absolute value of the calculated value is less than 10%, the final thickness deviation rate threshold is taken as ±10%; when 2 When the absolute value of the calculated value is greater than 20%, the final thickness deviation rate threshold is taken as ±20%; otherwise, it is taken as ±2%. The calculated value is used as the thickness deviation rate threshold; if there is no corresponding historical qualified batch data of the same process, the thickness deviation rate threshold is set to ±15% by default.

[0033] For each zone, if the deviation rate of the average thickness of the zone from the product thickness reference value is greater than the positive threshold, it is marked as a thick zone; all other zones are uniformly marked as thin zones.

[0034] Output the thickness distribution label corresponding to each partition, which corresponds one-to-one with the partition position where the sensing unit is deployed in S110.

[0035] S140. A humidity sensing unit is installed on the outside of the parting surface of the pulp molding mold to synchronously collect the relative humidity time sequence data of the contact area of ​​the target pulp molding product during the hot pressing and shaping process.

[0036] Four to eight humidity sensing units are evenly spaced along the circumference of the pulp molding hot pressing mold, outside the parting surface. Each humidity sensing unit uses a digital humidity sensor (such as SHT30 or equivalent), with a humidity measurement range of 0–100%RH and an accuracy of ±3%RH. The sensing units are mounted on a heat-insulating bracket outside the mold heating element, with the sensing surface facing the direction of the product ejection after mold opening, and 50mm to 100mm away from the edge of the mold parting surface to avoid direct contact with the mold heat source and condensation.

[0037] All sensing units are connected to the data acquisition device via shielded cables, and are synchronously acquired with the pressure and temperature signals in S110. During the hot pressing and shaping process, from the start of mold closing to the end of complete pressure release, ambient relative humidity data is continuously recorded at a sampling frequency of not less than 1Hz, and a timestamp is recorded at each sampling point. The output ambient relative humidity time-series data is stored in a time-aligned manner.

[0038] S2. Perform frequency domain filtering on the zone pressure signals to extract the effective pressure signals characterizing fiber dehydration, calculate the real-time moisture content of the zones in combination with the thickness distribution labels, and identify the incompletely cured zones based on the zone temperature conditions.

[0039] In this embodiment, as Figure 2 As shown, step S2 includes the following specific steps: S210. Based on the beating degree and fiber aspect ratio of the target pulp molding product, determine the typical response frequency range characterizing fiber dewatering, extract the effective pressure signal within the typical response frequency range through spectrum analysis, and obtain the pressure decay rate by calculating the time derivative of the effective pressure signal.

[0040] The typical response frequency range of pulp fibers during compression and dewatering is determined based on the freeness and fiber aspect ratio obtained from S120. The core principle is: the higher the freeness, the higher the degree of fiber fibrillation, and the lower the response frequency of the fiber network under pressure; the larger the fiber aspect ratio, the easier it is for the fiber network structure to transmit high-frequency fluctuations, and the response frequency range expands to higher frequencies.

[0041] This embodiment sets the basic response frequency range based on the following criteria: During the hot pressing process of pulp molding, the typical timescale for the vaporization and discharge of free water inside the fibers is 0.1 seconds to 2 seconds, corresponding to a frequency of 0.5Hz to 10Hz; the typical timescale for fiber network stress relaxation is 0.5 seconds to 5 seconds, corresponding to a frequency of 0.2Hz to 2Hz; the frequencies of interference signals such as mechanical vibration and hydraulic pulsation are higher than 30Hz, and the ultra-low frequency drift caused by mold thermal expansion is lower than 0.2Hz. Based on these physical characteristics, the basic range of the typical response frequency range is set to 0.5Hz to 30Hz, where the lower limit of 0.5Hz covers the fiber stress relaxation and dehydration process, and the upper limit of 30Hz effectively eliminates high-frequency mechanical noise.

[0042] Using general-purpose hardwood chemical pulp (25°SR, fiber aspect ratio 60) for industrial pulp molding as a benchmark, this benchmark corresponds to a typical industrial pulp with moderate fibrillation and medium fiber length. When the freeness is higher than the benchmark, the low-frequency range is adjusted by decreasing by 0.1 Hz for every 5°SR increase, with a minimum of 0.2 Hz; when the freeness is lower than the benchmark, the low-frequency range is adjusted by increasing by 0.2 Hz for every 5°SR decrease, with a maximum of 2 Hz. When the fiber aspect ratio is higher than the benchmark, the high-frequency range is adjusted by increasing by 2 Hz for every 10 Hz increase, with a maximum of 50 Hz; when the fiber aspect ratio is lower than the benchmark, the high-frequency range is adjusted by decreasing by 2 Hz for every 10 Hz decrease, with a minimum of 10 Hz. This ultimately yields the typical response frequency range of the target pulp molded product.

[0043] For the time-series data of pressure signals from each zone collected by S110, a fast Fourier transform was used for spectral analysis. Spectral components with frequencies within the typical response frequency range were retained, while mold thermal expansion drift components below the lower limit of the typical response frequency range and mechanical vibration noise components above the upper limit of the typical response frequency range were removed. Inverse Fourier transform was then performed on the retained spectral components to reconstruct the time-domain signal, thus obtaining the effective pressure signal time-series data directly related to fiber dewatering.

[0044] Simultaneously, the pressure decay rate is calculated based on the effective pressure signal. The pressure decay rate is defined. The first derivative of effective pressure with respect to time is discretized using the central difference method: ; in: The pressure decay rate at the i-th sampling point is expressed in MPa / s. and They are the (i+1)th and the i-th respectively The effective pressure value at one sampling point, in MPa; Δt is the sampling time interval, in seconds; for the first sampling point, forward differencing is used. For the last sampling point, backward difference is used: Output the effective pressure signal timing data and pressure decay rate timing data for each partition.

[0045] S220. Based on the thickness distribution label differentiation, the instantaneous drying rate of the zone is calculated. The instantaneous drying rate of the thick zone is calculated by multiplying the pressure fluctuation amplitude by the steam discharge resistance coefficient. The pressure fluctuation amplitude reflects the degree of steam discharge obstruction, and the steam discharge resistance coefficient compensates for the dehydration lag. The instantaneous drying rate of the thin zone is calculated by multiplying the pressure decay rate by the fiber shrinkage coefficient. The pressure decay rate directly characterizes the dehydration speed, and the fiber shrinkage coefficient realizes unit conversion. Then, the real-time moisture content of each zone is obtained by integrating the initial moisture content.

[0046] For thick regions: Extract the effective pressure signal time-series data output by S210, and calculate the peak-to-valley difference of pressure fluctuation within a unit time window (1 second in this embodiment, with a window sliding step of 0.5 seconds), that is, the difference between the maximum and minimum pressure values ​​within the unit time window, denoted as . Unit: MPa. Defines the instantaneous drying rate of the thick zone. for: ; in: The instantaneous drying rate of the thick zone is expressed in % / s (percentage change in moisture content per second). This is the steam discharge resistance coefficient, expressed in %·s. ¹·MPa ¹, reflects the dehydration rate caused by the unit pressure fluctuation amplitude due to the dense fiber accumulation and obstructed steam discharge in the thick area. This embodiment assumes... =0.35. The calibration method for this steam discharge resistance coefficient is as follows: take production data of at least 30 batches of qualified historical batches with the same process and the same slurry formula, take the pressure fluctuation amplitude within a unit time window of the thick area as the independent variable, and take the measured change in moisture content of the thick area after depressurization of the corresponding batch as the dependent variable, and perform univariate linear regression fitting; the typical industrial application range of this steam discharge resistance coefficient is 0.25 to 0.50, and it can be adjusted within this range according to the changes in slurry formula and process parameters.

[0047] For thin regions: directly use the pressure decay rate timing data output from S210. Define the instantaneous drying rate of the thin area. for: ; Where: represents the instantaneous drying rate of the thin area, in % / s; The pressure decay rate is expressed in MPa / s, and the absolute value is taken to ensure that the drying rate is positive. The unit is the fiber shrinkage coefficient, expressed as %·MPa. ¹ (i.e., the percentage decrease in moisture content corresponding to each megapascal of pressure decay). The fiber shrinkage coefficient reflects the proportional relationship between the rate of pressure decay and the rapid dehydration and significant fiber shrinkage in the thin zone. This embodiment assumes the fiber shrinkage coefficient. =12.5; The calibration method for this fiber shrinkage coefficient is as follows: Take at least 30 batches of historical qualified production data with the same process and the same slurry formula, take the average absolute value of the pressure decay rate of the thin area of ​​the batch during the holding pressure period as the independent variable, and take the average drying rate of the thin area of ​​the batch (i.e., the total change in moisture content before and after pressure release divided by the total holding pressure time) as the dependent variable, and perform univariate linear regression fitting; The typical industrial application range of this fiber shrinkage coefficient is 8.0 to 18.0, which can be adjusted within this range according to the changes in slurry formula and hot pressing process parameters.

[0048] After obtaining the instantaneous drying rates of the thick and thin regions, the initial moisture content obtained from S120 is then used as a basis. (Unit: %), real-time moisture content is calculated by integration. : ; in: The instantaneous drying rate of the corresponding zone (for thicker zones) (For thin areas), the integration uses a discrete accumulation method, accumulating once for each sampling time step Δt: Output real-time moisture content time-series data for each partition. The unit is %, and one decimal place is retained for subsequent use by S230 and S310.

[0049] S230. Set the critical moisture content threshold for curing of the zone according to the thickness distribution label. The critical moisture content threshold for curing of the thick zone is higher than that for the thin zone. Set the curing temperature threshold according to the glass transition temperature of the pulp fiber. When the real-time moisture content of the zone is greater than or equal to the critical moisture content threshold for curing of the corresponding zone or the real-time temperature is less than or equal to the curing temperature threshold for the corresponding zone, mark the corresponding zone as an incompletely cured zone.

[0050] Align the real-time moisture content time-series data of each zone output by S220 with the real-time temperature time-series data of each zone collected by S110 by timestamp. Set the critical moisture content threshold and curing temperature threshold for each zone.

[0051] The critical moisture content threshold for curing is set differently for different zones based on thickness distribution labels. It is used to determine the curing process of the fiber network and the risk of rebound during pressure relief during hot pressing. The critical moisture content threshold for curing is calibrated as follows: at least 30 historical qualified production batches with the same process and slurry formulation are taken. Harmful rebound is first defined as the rebound rate of the critical dimension of the product after pressure relief exceeding the allowable tolerance specified in the design drawings. Then, valid batches without harmful rebound are screened out. The moisture content data of the corresponding zone before pressure relief is extracted. The 95th percentile value of this set of data is taken as the calibrated lower limit of moisture content for that zone. Because the thicker fiber area has a higher compression ratio and bulk density, the full formation and stable shaping of inter-fiber hydrogen bonds require more thorough dehydration. Therefore, the critical moisture content threshold for curing in the thicker area is higher than that in the thinner area. In this embodiment, the critical moisture content threshold for curing in the thicker area is set to 15% by default, and the critical moisture content threshold for curing in the thinner area is set to 10% by default; if there is no corresponding historical production data for the same process, the above default values ​​are used directly.

[0052] The curing temperature threshold is determined based on the type of pulp used in the target molded pulp product, taking the glass transition temperature of the fiber in that pulp type. For a single pulp type, the typical reference value for the glass transition temperature is 80℃ for bamboo pulp fiber, 75℃ for wood pulp fiber, 70℃ for bagasse pulp fiber, and 65℃ for straw pulp fiber; for mixed pulp types, the glass transition temperature is calculated by weighting the percentage of each pulp type by its oven-dry mass. Alternatively, the specific value of the glass transition temperature can be provided by the pulp supplier or obtained by actual measurement using the differential scanning calorimetry (DSC) method specified in GB / T19466.2; the threshold value for hardwood chemical pulp fiber is 75℃; this embodiment defaults to 75℃, corresponding to the benchmark hardwood chemical pulp.

[0053] For each zone, when the real-time moisture content is greater than or equal to the critical moisture content threshold for curing, or the temperature signal is less than or equal to the curing temperature threshold, the zone is marked as an incompletely cured zone; otherwise, the zone is marked as a normally cured zone. The physical meaning of an incompletely cured zone is that the moisture content of the target pulp molded product in this area has not dropped to the threshold, or the temperature has not reached the glass transition temperature of the fiber, the fiber hydrogen bonding has not been initiated, the curing is insufficient, and there is a risk of springback after pressure relief.

[0054] Output the real-time moisture content time series data of each zone and the corresponding zone curing status marker (incompletely cured zone or normally cured zone) for subsequent S410 differentiated pressure holding strategy.

[0055] S3. Based on the real-time moisture content, effective pressure signal, and thickness distribution label of each zone, a dynamic elastic coefficient is constructed by moisture content correction, thickness weighting, and effective pressure cumulative correction, and the equivalent rebound driving force of each zone is calculated. The critical solidification state is determined by monitoring the inflection point of pressure decay rate and the inflection point of equivalent rebound driving force. Then, combined with the equivalent rebound driving force and thickness distribution label, the rebound moisture content of each zone after pressure relief is calculated based on the physical characteristics of fiber rebound water absorption.

[0056] In this embodiment, as Figure 3 As shown, step S3 includes the following specific steps: S310. Moisture content correction: The reference elastic modulus is linearly reduced by the ratio of the real-time moisture content of the zone to the fiber saturated moisture content. The higher the real-time moisture content, the greater the reduction. Thickness weighting: The weighting factor is determined by the ratio of the zone thickness to the reference thickness. The elastic modulus is amplified in thick zones and reduced in thin zones. The cumulative effective pressure is obtained by integrating the effective pressure signal of the zone. A process correction factor is constructed using a saturated growth model to correct the elastic modulus. The three correction results are coupled to obtain the dynamic elastic coefficient and calculate the equivalent rebound driving force of each zone.

[0057] Using real-time moisture content time-series data of each zone, effective pressure signal time-series data of each zone, and benchmark elastic modulus and thickness distribution labels as inputs, the dynamic elastic coefficient of each zone is constructed.

[0058] The calculation of the dynamic elasticity coefficient involves three correction steps, all based on physical logic derivation. The first step is a basic correction based on the real-time moisture content of the zone: defining the moisture content correction factor. This reflects the reduction effect of moisture on the fiber's elastic modulus. Higher moisture content leads to predominantly plastic deformation of the fiber and a greater reduction in elastic modulus; lower moisture content enhances the fiber's dry elastic properties, and the elastic modulus approaches the baseline value. This embodiment uses a linear reduction model: ; in: It is a dimensionless moisture content correction factor. Its core function is to quantify the reduction effect of real-time moisture content on the elastic stiffness of fiber network and correct the difference between fiber elastic properties and the benchmark elastic modulus test state under different moisture contents. Current real-time moisture content, in % (%) The fiber saturated moisture content (i.e., the moisture content when the fiber cell walls are completely saturated) is taken as 300% in this embodiment (corresponding to 3 times the moisture content of the oven-dry fiber). This fiber saturated moisture content is based on industry-standard data on the saturation point of pulp fibers. In addition, this 300% value corresponds to hardwood chemical pulp. For other pulp types, the fiber saturated moisture content should be replaced by the measured value according to GB / T 2677.4 standard. The moisture content correction factor adopts a linear reduction model. Because the fiber elastic modulus is strongly linearly correlated with the moisture content within the conventional moisture content range of pulp molding hot pressing, and the linear model is simple to calculate, adaptable to real-time online control, and its accuracy fully meets industrial requirements. Additionally, set boundary conditions when... ≥ hour, Take 0; when When ≤0, Take 1.

[0059] Then, a weighted correction is applied based on thickness partitioning. A thickness weighting factor is defined to reflect the difference in elastic energy storage capacity between thick and thin regions. Thick regions, due to their higher fiber compression ratio and greater effective energy storage fiber volume, receive amplified weighting for the elastic modulus; thin regions, due to their lower compression and thinner fiber layer, receive reduced weighting. In this embodiment: ; in: It is a thickness-weighted factor, dimensionless, used to quantify the equivalent elastic stiffness deviation caused by differences in fiber compression ratio and bulk density in different thickness zones. The average thickness of the corresponding zone, in mm; For reference thickness, 2mm is used in this embodiment, which is the general reference thickness for conventional products in the pulp molding industry;

[0060] The thick area magnification factor is set to 0.3 by default in this embodiment. The basis for this setting is that the thick area fiber has a larger mold compression ratio, denser fiber packing, and more fiber overlap points. The overall load-bearing capacity and elastic energy storage capacity of the three-dimensional fiber network are significantly higher than those of the benchmark test state. It is necessary to restore its true equivalent elastic stiffness through the magnification factor. The thick area magnification factor can be calibrated based on the linear regression fitting of the partition thickness and the measured equivalent rebound driving force of the qualified batches of the same process. The typical applicable range is 0.2~0.5. The thin area reduction factor is set to 0.2 by default in this embodiment. The basis for this setting is that the thin area has a small mold compression amount, a thin fiber layer, poor fiber network continuity, and few overlap points. The overall equivalent elastic stiffness is lower than the benchmark test state, and its true elastic characteristics need to be restored by the reduction factor. The thin area reduction factor can be calibrated based on the linear regression fitting of the partition thickness and the measured equivalent rebound driving force of the qualified batches of the same process. The typical applicable range is 0.1~0.3. Additionally, set boundary conditions when the calculation is... When less than 0.5, Take 0.5; When it is greater than 2.0, Set to 2.0. The boundary conditions are set based on the equivalent elastic stiffness of the pulp fiber network. The maximum value will not exceed twice the reference value, and the minimum value will not be lower than 50% of the reference value. This boundary constraint can prevent extreme thicknesses (such as ultra-thick ribs and ultra-thin planes) from causing the correction factor to deviate excessively from the reasonable physical range, avoid distortion in the calculation of the equivalent springback driving force, and ensure the stability of real-time control in the industrial field.

[0061] Finally, based on the process correction of the cumulative effective pressure value, the cumulative effective pressure value is defined as the definite integral of the effective pressure signal over the holding time dimension, and the expression is: ; in, for The cumulative effective pressure value at any given time, in MPa·s; for The effective pressure signal corresponding to the monitoring zone at any given time, in MPa; The time variable is the integral time variable, in seconds (s). The total duration from the start of mold closing and pressure holding to the current moment, in seconds; This cumulative effective pressure value reflects the real-time progress of fiber dehydration and hydrogen bonding throughout the entire process. The more thorough the cumulative dehydration, the more stable the hydrogen bonding between fibers, and the higher the proportion of stable energy stored in the elastic network that cannot be released due to hydrogen bonding. Consequently, the equivalent elastic modulus of the fiber network also increases. Based on the saturation growth characteristics of this curing process, a process correction factor is used. Using a saturated growth model: ; in: It is a dimensionless process correction factor used to quantify the positive amplification effect of the hydrogen bond curing process of the entire fiber process on the equivalent elastic stiffness. The maximum increase coefficient is 0.2 by default in this embodiment, which corresponds to the maximum increase limit of the elastic modulus of the fiber after complete curing relative to the reference state. It can be calibrated by the curing test data of qualified batches in the same process. The growth rate coefficient is 0.05 MPa by default in this embodiment. ¹·s ¹, used to characterize the growth rate of the fiber hydrogen bond curing process, matching the dehydration and curing rhythm of a conventional hot-pressing holding cycle. When the cumulative effective pressure... When large enough, Approaching This corresponds to the fiber curing process approaching saturation, and the increase in elastic modulus reaching its upper limit.

[0062] Based on the above corrections, the dynamic elasticity coefficient The calculation expression is as follows ,in The baseline elastic modulus obtained for S120 is expressed in MPa; other factors are dimensionless. Output the time-series data of the dynamic elastic coefficients for each partition. .

[0063] The equivalent rebound driving force is achieved by adjusting the dynamic elastic coefficient. With current mold closing pressure (The equivalent springback driving force is defined by the product of the pressure readings collected in real time by a high-precision pressure sensor that is matched with the main hydraulic cylinder of the pulp molding hot press corresponding to the mold, which is the mold closing and holding pressure control pressure at the current moment, and is completely matched with the holding pressure condition of the entire hot pressing process. The unit is MPa.) : ; in: The equivalent rebound driving force is expressed in MPa² (or MPa·MPa, dimensionless pressure square). This equivalent rebound driving force increases continuously with the degree of fiber curing, directly characterizing the driving force of fiber rebound. Output the time-series data of the equivalent rebound driving force for each partition. .

[0064] S320: Real-time monitoring of the inflection point of the pressure decay rate of each zone from negative to positive and the inflection point of the equivalent rebound driving force from rising to stabilizing. Combined with the critical moisture content threshold for curing, the critical curing state is determined and the critical curing time is recorded.

[0065] Real-time monitoring of the pressure decay rate and equivalent rebound driving force time-series data for each zone identifies two physical inflection points. The first inflection point is when the pressure decay rate changes from negative to positive, indicating that the dehydration of free water inside the fiber is basically complete, the vapor pressure drop disappears, and fiber shrinkage stress begins to dominate pressure changes. The second inflection point is when the equivalent rebound driving force changes from a continuous increase to a stable level, indicating that the fiber hydrogen bonding is basically complete, elastic energy storage no longer increases, and the curing process reaches a critical value.

[0066] To determine the peak inflection point of the equivalent rebound driving force from rising to stabilizing, the sliding window method is adopted: taking the target time to be determined as the node, the average value of the equivalent rebound driving force in the 2 seconds before the node (the average value of the preceding rising window) and the average value of the equivalent rebound driving force in the 2 seconds after the node (the average value of the subsequent stabilizing window) are calculated; when the relative deviation of the two sets of averages is less than 2%, and the equivalent rebound driving force in the 5 seconds before the node shows a continuous upward trend, the node is determined to be the peak inflection point of the equivalent rebound driving force.

[0067] When determining the critical curing state, three conditions must be met simultaneously: the pressure decay rate of the partition has reached an inflection point from negative to positive; the equivalent rebound driving force of the partition has reached an inflection point from rising to stabilizing; and the real-time moisture content of the partition is lower than the critical curing moisture content threshold set according to the thickness distribution label (specific values ​​are set in S230). When all three conditions are met, the partition is determined to have entered the critical curing state, and this moment is recorded as the critical curing moment.

[0068] S330: The pore moisture absorption space after fiber rebound is quantified by the peak value of the equivalent rebound driving force, the moisture absorption driving conditions are quantified by the relative humidity of the environment during depressurization, and the moisture absorption capacity of fiber stacking is quantified by the partition thickness. Combined with the saturated moisture absorption characteristics of pulp fiber, and based on the positive correlation between the peak value of the equivalent rebound driving force, the relative humidity of the environment, the partition thickness and the saturated moisture absorption characteristics of pulp fiber, the rebound moisture content after partition depressurization is calculated.

[0069] Define the moisture content of the rebound after depressurization. The calculation expression is: ; in: The moisture content of the rebound after depressurization is expressed as % (%). The basic water absorption coefficient of the pulp type is dimensionless and is a core correction coefficient characterizing the inherent moisture absorption capacity of different plant fibers under hot-pressing and rebound conditions. Its core essence is that the moisture absorption capacity of fibers is determined by their own chemical composition and microstructure. The higher the hemicellulose content, the lower the cellulose crystallinity, and the greater the cell wall porosity, the larger the basic water absorption coefficient of the pulp type. It directly corresponds to the hydroxyl hydrogen bond adsorption and microporous capillary condensation moisture absorption characteristics of the fibers after rebound. This basic water absorption coefficient of the pulp type is determined using the industry typical value method, preferentially based on the equilibrium moisture absorption rate test and fitting calibration according to GB / T 461.3 and GB / T 22899 standards. When no actual measurement conditions are available, the industry-standard values ​​commonly used in this embodiment are adopted: bamboo pulp 3.5, hardwood chemical pulp 4.0, bagasse pulp 4.5, and straw pulp 5.0. The mixed pulp types are calculated by linear weighted average based on the oven-dry mass ratio of each pulp type.

[0070] The peak value of the equivalent rebound driving force, in MPa², is extracted from the time series data of the equivalent rebound driving force in this partition. For reference to the equivalent rebound driving force, this embodiment defaults to 100MPa², which is the industry benchmark value for pulp molding under normal hot pressing conditions without harmful rebound, and is used for dimensionless processing. The relative humidity is expressed as a percentage. It is the average value of the relative humidity time series data in the last 10 seconds of the hot-pressing process, which represents the stable environmental humidity state at the end of the hot-pressing process and avoids interference from instantaneous fluctuations. For reference humidity, this embodiment defaults to 50%, which is a common standard reference relative humidity for industrial environments and is used for dimensionless processing; The average thickness of the zone, in mm, is derived from the thickness data of S130. For reference thickness, this embodiment uses 2mm by default, which is the general reference thickness for pulp molding industrial products and is used for dimensionless processing.

[0071] For thick and thin regions, the thickness value By directly substituting the actual measured value, the thickness factor in the formula for calculating the rebound moisture content after pressure relief automatically reflects the physical law that the water absorption capacity of the thicker area is higher than that of the thinner area. The calculated value is... If it exceeds 12%, then 12% is taken as the upper limit to conform to the actual physical limit of pulp fiber rebound water absorption. Output the rebound moisture content of each zone after pressure relief, in %, as the core input for subsequent S410 rebound safety criteria.

[0072] S4. Using moisture content and rebound safety as dual criteria, combined with thickness distribution labels, critical curing state judgment results and incomplete curing area markings, a zoned dynamic optimization strategy for pulp molding hot pressing and shaping process is generated.

[0073] In this embodiment, step S4 includes the following specific contents: S410. Merge adjacent partitions with consistent thickness distribution labels into a process control area. Use the arithmetic mean of the real-time moisture content of each partition constituting the process control area as the average moisture content of the process control area. Use the maximum value of the rebound moisture content after depressurization of each partition constituting the process control area as the maximum rebound moisture content after depressurization of the process control area. Use the average moisture content of the process control area being lower than the curing safety threshold and the maximum rebound moisture content after depressurization of the process control area being lower than the allowable upper limit as dual criteria. Force pressure maintenance is applied to the incompletely cured area. For the process control area that meets the dual criteria, pressure is reduced to maintain shape.

[0074] Adjacent zones with the same thickness distribution labels are merged to obtain several process control zones. Each process control zone contains only thick or only thin zones and serves as the smallest operational unit for subsequent regulation. For each process control zone, the arithmetic mean of the real-time moisture content of all zones within the process control zone is calculated as the average real-time moisture content of that process control zone; the maximum value of the rebound moisture content after depressurization of all zones within the process control zone is taken as the maximum rebound moisture content after depressurization of that process control zone.

[0075] The moisture content threshold is defined as follows: the average real-time moisture content of the process control area is lower than the corresponding critical moisture content threshold for curing in that process control area. The critical moisture content threshold for curing in the thick process control area is 15%, and the critical moisture content threshold for curing in the thin process control area is 10%. The specific settings are based on the critical moisture content threshold settings for curing in S230.

[0076] The rebound safety criterion is defined as follows: the rebound moisture content after maximum pressure relief in the process control area is lower than the upper limit of moisture content rise allowed for the target pulp molded product. In this embodiment, the upper limit of moisture content rise is defaulted to 5%, which is the safety control threshold within the 12% physical limit of fiber rebound moisture absorption, and is determined based on the statistical critical value of no dimensional deviations in qualified batches of the same process.

[0077] For each process control area, if any zone within the upper limit of moisture content recovery is marked as an incompletely cured zone in S230, then the entire process control area is considered as an incompletely cured zone; if any zone within the process control area is determined to have entered the critical curing state in S320, then the entire process control area is considered to have entered the critical curing state.

[0078] Differentiated pressure holding exit rules are implemented based on the thickness distribution label: thin areas are prone to situations where the moisture content meets the standard but the curing is insufficient, and both the moisture content standard criterion and the rebound safety criterion must be met simultaneously before the full pressure holding can be exited; for thick areas, the moisture content standard is the core control target, and the moisture content standard criterion is met first, while the rebound safety criterion is checked simultaneously; full pressure holding is forcibly maintained in areas that are not fully cured, and pressure reduction and shape preservation operations are performed in areas where both criteria are met.

[0079] S420: Generate a pressure relief priority queue based on the earliest critical curing time of each process control area. After all process control areas meet the dual criteria, execute a partitioned dynamic optimization strategy for labels with different thickness distributions.

[0080] Based on the critical curing time of each partition within each process control area, the earliest critical curing time reached within the process control area is taken as the representative critical curing time of that process control area; all process control areas are sorted in order of their representative critical curing times to generate a pressure relief priority queue, with the area whose representative critical curing time is earlier having a higher pressure relief priority.

[0081] During the hot pressing and setting process, the dual criteria status of each process control area is continuously monitored. When all process control areas meet the moisture content standard and rebound safety criteria, the global gradient depressurization process is initiated. The depressurization process is executed in the order of the depressurization priority queue.

[0082] The pressure relief parameters are set differently based on the thickness distribution labels of the process control areas: the thick process control areas use a smaller pressure relief step size and a longer interstage holding time. In this embodiment, the pressure relief step size is 20% of the current mold closing pressure and the interstage holding time is 2 seconds; the thin process control areas use a larger pressure relief step size and a shorter interstage holding time. In this embodiment, the pressure relief step size is 40% of the current mold closing pressure and the interstage holding time is 1 second.

[0083] After the pressure in the entire area is released until the mold closing pressure drops to zero, the mold closing position is immediately locked and locked for 3-5 seconds to freeze the fiber shape and suppress residual springback. After the lock is released, the mold is opened and the part is taken out, completing the dynamic optimization of the hot pressing and shaping process. The pressure release completion signal and the product qualification mark are output for subsequent batch process self-learning.

[0084] Please see Figure 4 , Figure 4 This is a schematic diagram of a pressure-sensing-based pulp molding hot pressing and setting process optimization system. This embodiment illustrates the composition and functional division of the system's four core modules, including: The data acquisition module is used to collect the zone pressure signals and basic parameters of the pulp material during the hot pressing and shaping process of pulp molding, and to generate thickness distribution labels corresponding to the zone pressure signals. The signal processing module is used to perform frequency domain filtering on the zone pressure signal, extract the effective pressure signal characterizing fiber dehydration, calculate the real-time moisture content of the zone in combination with the thickness distribution label, and identify the incompletely cured zone according to the zone temperature conditions. The curing analysis module is used to construct dynamic elastic coefficients and calculate the equivalent rebound driving force of each zone based on the real-time moisture content of each zone, the effective pressure signal, and the thickness distribution label. It also uses moisture content correction, thickness weighting, and effective pressure cumulative correction to determine the critical curing state by monitoring the inflection point of the pressure decay rate and the inflection point of the equivalent rebound driving force. Then, based on the physical characteristics of fiber rebound water absorption, it calculates the rebound moisture content of each zone after pressure relief, combining the equivalent rebound driving force and the thickness distribution label. The optimized control module is used to generate a zoned dynamic optimization strategy for the pulp molding hot pressing process, based on the dual criteria of moisture content compliance and rebound safety, combined with thickness distribution labels, critical curing state judgment results, and incomplete curing zone identification.

[0085] Embodiments of the present invention also provide an electronic device, including a memory, a processor, and a communication bus; the memory and the processor are connected via the communication bus. The memory stores a method for optimizing the pressure-sensing hot-pressing process of pulp molding, as provided in the above embodiments, which can be loaded and executed by the processor.

[0086] The memory can be used to store instructions, programs, code, code sets, or instruction sets. The memory may include a program storage area and a data storage area. The program storage area may store instructions for implementing an operating system, instructions for at least one function, and instructions for implementing the pressure-sensing-based pulp molding hot-pressing process optimization method provided in the above embodiments. The data storage area may store data involved in the pressure-sensing-based pulp molding hot-pressing process optimization method provided in the above embodiments.

[0087] A processor may include one or more processing cores. The processor executes instructions, programs, code sets, or instruction sets stored in memory, and calls data stored in memory to perform various functions and process data as described in this application. The processor may be at least one of a specific application-specific integrated circuit, a digital signal processor, a digital signal processing device, a programmable logic device, a field-programmable gate array, a central processing unit, a controller, a microcontroller, and a microprocessor. It is understood that, for different devices, the electronic devices used to implement the above-described processor functions may also be other types, and the embodiments of this application do not specifically limit the specific implementation.

[0088] A communication bus may include a pathway for transmitting information between the aforementioned components. The communication bus can be a PCI bus or an EISA bus, etc. Communication buses can be categorized into address buses, data buses, control buses, etc.

[0089] This application provides a computer-readable storage medium storing a computer program that can be loaded by a processor and executed as described in the above embodiments for optimizing the pressure-sensing-based hot-pressing process of pulp molding.

[0090] In this embodiment, a computer-readable storage medium can be a tangible device that holds and stores instructions used by an instruction execution device. A computer-readable storage medium can be, but is not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination thereof. Specifically, a computer-readable storage medium can be a portable computer disk, a hard disk, a USB flash drive, a random access memory, a read-only memory, an erasable programmable read-only memory, a static random access memory, a portable compressed disk read-only memory, a digital multifunction disk, a memory stick, a floppy disk, an optical disk, a magnetic disk, a mechanical encoding device, or any combination thereof.

[0091] The terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0092] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the foregoing application concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions claimed in this application.

Claims

1. An optimization method for pulp molding hot pressing and setting process based on pressure sensing, characterized in that, Includes the following steps: S1. Collect the zone pressure signals and basic parameters of the pulp material during the hot pressing and shaping process of pulp molding, and generate thickness distribution labels corresponding to the zone pressure signals; S2. Perform frequency domain filtering on the zone pressure signals to extract the effective pressure signals characterizing fiber dehydration, calculate the real-time moisture content of the zone in combination with the thickness distribution label, and identify the incompletely cured zone according to the zone temperature conditions. S3. Based on the real-time moisture content, effective pressure signal, and thickness distribution label of each zone, a dynamic elastic coefficient is constructed by moisture content correction, thickness weighting, and effective pressure cumulative correction, and the equivalent rebound driving force of each zone is calculated. The critical solidification state is determined by monitoring the inflection point of pressure decay rate and the inflection point of equivalent rebound driving force. Then, combined with the equivalent rebound driving force and thickness distribution label, the rebound moisture content of each zone after pressure relief is calculated based on the physical characteristics of fiber rebound water absorption. S4. Using moisture content and rebound safety as dual criteria, combined with thickness distribution labels, critical curing state judgment results and incomplete curing area markings, a zoned dynamic optimization strategy for pulp molding hot pressing and shaping process is generated.

2. The method for optimizing the hot pressing and shaping process of pulp molding based on pressure sensing according to claim 1, characterized in that, The process of collecting zoned pressure signals and basic pulp material parameters during the hot pressing and shaping process of pulp molding, and generating thickness distribution labels corresponding to the zoned pressure signals, includes the following steps: The pulp molding mold is divided into zones according to the geometric thickness distribution of the target pulp molded product, and the pressure signal timing data and temperature signal timing data of each zone are collected simultaneously. Obtain the basic material parameters of the pulp used for the target pulp molding product, including pulp type, freeness, initial moisture content, fiber aspect ratio, and reference elastic modulus; Based on the degree of deviation of the thickness of each zone of the target pulp molded product from the thickness reference of the target pulp molded product, the zones are marked as thick zones or thin zones, forming thickness distribution labels; A humidity sensing unit is installed on the outer side of the parting surface of the pulp molding mold to synchronously collect the relative humidity time sequence data of the contact area of ​​the target pulp molding product during the hot pressing and shaping process.

3. The method for optimizing the hot pressing and shaping process of pulp molding based on pressure sensing according to claim 2, characterized in that, Frequency domain filtering is performed on the zoned pressure signals to extract the effective pressure signals characterizing fiber dehydration. Combined with thickness distribution labels, the real-time moisture content of each zone is calculated, including the following steps: Based on the beating degree and fiber aspect ratio of the target pulp molding product, the typical response frequency range characterizing fiber dewatering is determined. The effective pressure signal within the typical response frequency range is extracted by spectrum analysis, and the time derivative of the effective pressure signal is obtained to get the pressure decay rate. The instantaneous drying rate of each zone is calculated based on the thickness distribution label differentiation. For thick zones, the instantaneous drying rate is calculated by multiplying the pressure fluctuation amplitude by the steam discharge resistance coefficient, where the pressure fluctuation amplitude reflects the degree of steam discharge obstruction and the steam discharge resistance coefficient compensates for the dehydration lag. For thin zones, the instantaneous drying rate is calculated by multiplying the pressure decay rate by the fiber shrinkage coefficient, where the pressure decay rate directly characterizes the dehydration speed and the fiber shrinkage coefficient achieves unit conversion. The real-time moisture content of each zone is then obtained by integrating the initial moisture content.

4. The method for optimizing the hot pressing and shaping process of pulp molding based on pressure sensing according to claim 3, characterized in that, And identify the incompletely cured areas according to the zone temperature conditions, including the following steps: The critical moisture content threshold for curing of each zone is set according to the thickness distribution label. The critical moisture content threshold for curing of the thick zone is higher than that for the thin zone. The curing temperature threshold is set according to the glass transition temperature of the pulp fiber. When the real-time moisture content of a zone is greater than or equal to the critical moisture content threshold for curing of the corresponding zone or the real-time temperature is less than or equal to the curing temperature threshold for the corresponding zone, the corresponding zone is marked as an incompletely cured zone.

5. The method for optimizing the hot pressing and shaping process of pulp molding based on pressure sensing according to claim 4, characterized in that, Based on real-time moisture content, effective pressure signals, and thickness distribution labels of each zone, dynamic elasticity coefficients are constructed through moisture content correction, thickness weighting, and cumulative effective pressure correction, and the equivalent rebound driving force of each zone is calculated, including the following steps: Moisture content correction linearly reduces the reference elastic modulus by the ratio of real-time moisture content of the zone to the fiber saturated moisture content, with higher real-time moisture content resulting in greater reduction. Thickness weighting determines the weighting factor by the ratio of zone thickness to reference thickness, amplifying the elastic modulus in thick zones and reducing it in thin zones. The cumulative effective pressure is obtained by integrating the effective pressure signal of the zone, and a process correction factor is constructed using a saturated growth model to correct the elastic modulus over time. The three correction results are coupled to obtain the dynamic elastic coefficient and calculate the equivalent rebound driving force for each zone.

6. The method for optimizing the hot pressing and shaping process of pulp molding based on pressure sensing according to claim 5, characterized in that, The critical solidification state is determined by monitoring the inflection point of the pressure decay rate and the inflection point of the equivalent rebound driving force, including the following steps: Real-time monitoring of the inflection point when the pressure decay rate of each zone changes from negative to positive and the inflection point when the equivalent rebound driving force changes from rising to stabilizing, combined with the critical moisture content threshold for curing, determines the critical curing state and records the critical curing time.

7. The method for optimizing the hot pressing and shaping process of pulp molding based on pressure sensing according to claim 6, characterized in that, Then, combining the equivalent rebound driving force and thickness distribution label, and based on the physical characteristics of fiber rebound water absorption, the rebound moisture content of each zone after pressure relief is calculated, including the following steps: The moisture absorption space of the pores after fiber rebound is quantified by the peak value of the equivalent rebound driving force, the moisture absorption driving conditions are quantified by the relative humidity of the environment during depressurization, and the moisture absorption capacity of fiber stacking is quantified by the partition thickness. Combined with the saturated moisture absorption characteristics of pulp fiber, and based on the positive correlation between the peak value of the equivalent rebound driving force, the relative humidity of the environment, the partition thickness and the saturated moisture absorption characteristics of pulp fiber, the rebound moisture content after partition depressurization is calculated.

8. The method for optimizing the hot pressing and shaping process of pulp molding based on pressure sensing according to claim 7, characterized in that, Using moisture content compliance and rebound safety as dual criteria, and combining thickness distribution labels, critical curing state determination results, and incomplete curing zone identification, a zoned dynamic optimization strategy for pulp molding hot pressing and setting process is generated, including the following steps: Adjacent zones with consistent thickness distribution labels are merged into a process control zone. The arithmetic mean of the real-time moisture content of each zone constituting the process control zone is used as the average moisture content of the process control zone. The maximum rebound moisture content after depressurization of each zone constituting the process control zone is used as the maximum rebound moisture content after depressurization of the process control zone. The average moisture content of the process control zone is lower than the curing safety threshold, and the maximum rebound moisture content after depressurization of the process control zone is lower than the allowable upper limit, which are used as dual criteria. The incompletely cured zone is forced to maintain pressure, and the process control zone that meets the dual criteria is depressurized to maintain shape. A pressure relief priority queue is generated based on the earliest critical curing time of each process control area. After all process control areas meet the dual criteria, a partitioned dynamic optimization strategy for labels with different thickness distributions is executed.

9. A pressure-sensing-based pulp molding hot pressing and setting process optimization system, implemented based on the pressure-sensing-based pulp molding hot pressing and setting process optimization method as described in any one of claims 1-8, characterized in that, The system includes: The data acquisition module is used to collect the zone pressure signals and basic parameters of the pulp material during the hot pressing and shaping process of pulp molding, and to generate thickness distribution labels corresponding to the zone pressure signals. The signal processing module is used to perform frequency domain filtering on the zone pressure signal, extract the effective pressure signal characterizing fiber dehydration, calculate the real-time moisture content of the zone in combination with the thickness distribution label, and identify the incompletely cured zone according to the zone temperature conditions. The curing analysis module is used to construct dynamic elastic coefficients and calculate the equivalent rebound driving force of each zone based on the real-time moisture content of each zone, the effective pressure signal, and the thickness distribution label. It also uses moisture content correction, thickness weighting, and effective pressure cumulative correction to determine the critical curing state by monitoring the inflection point of the pressure decay rate and the inflection point of the equivalent rebound driving force. Then, based on the physical characteristics of fiber rebound water absorption, it calculates the rebound moisture content of each zone after pressure relief, combining the equivalent rebound driving force and the thickness distribution label. The optimized control module is used to generate a zoned dynamic optimization strategy for the pulp molding hot pressing process, based on the dual criteria of moisture content compliance and rebound safety, combined with thickness distribution labels, critical curing state judgment results, and incomplete curing zone identification.

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