Gradient temperature vulcanization method for rubber sealing element

Abstract

The invention provides a gradient temperature vulcanization method for a rubber sealing element, and belongs to the technical field of rubber vulcanization chemical method.The gradient temperature vulcanization method comprises the steps that multiple phase-change material layers arranged according to phase-change temperature increasing are embedded into the inner wall of a mold cavity, and a phase-change temperature matching experiment is conducted on the multiple phase-change material layers to obtain phase-change temperature range parameters; judging whether a preset interval is met or not according to the phase-change temperature range parameter and deciding whether to perform a re-experiment or not, and constructing a sectional type pressure and temperature cooperative control curve according to the phase-change temperature range parameter and the optimal sound wave parameter, a multi-physical field simulation model is established to predict shrinkage distribution data, and reverse compensation design is performed on the size of a mold cavity, so that the technical problem that collaborative optimization of temperature gradient control in the thickness direction and vulcanization uniformity is difficult in the gradient temperature vulcanization process of the rubber sealing element is solved.

Description

Technical Field

[0001] This invention belongs to the technical field of rubber vulcanization chemical methods, and specifically relates to a method for gradient temperature vulcanization of rubber seals. Background Technology

[0002] The vulcanization process of rubber seals is a crucial manufacturing process that uses heating to cause the rubber molecular chains to cross-link and form a three-dimensional network structure. Traditional vulcanization methods employ constant-temperature heating, treating the entire seal at a single set temperature. This constant-temperature heating method is widely used in the production of automotive engine seals, hydraulic system seals, and aerospace rubber products. However, when processing thick-walled seals, the traditional constant-temperature vulcanization method suffers from several drawbacks. Due to the low thermal conductivity of rubber, the outer layer of the seal heats up rapidly while the inner layer lags behind. This results in over-vulcanization of the outer layer and under-vulcanization of the inner layer. Over-vulcanization makes the rubber material hard and brittle, while under-vulcanization leads to insufficient cross-linking and reduced strength. Ultimately, this results in uneven distribution of the seal's mechanical properties along its thickness, affecting sealing reliability and service life. In existing technologies, gradient temperature vulcanization methods, used to improve vulcanization uniformity, achieve a gradual transition from low to high temperature by adjusting the heating temperature in stages. However, the temperature jumps during the temperature transition process cause thermal stress concentration inside the seal. Simultaneously, the mismatch between the gas escape rate and the cross-linking curing rate inside the rubber material leads to the formation of bubble defects, which severely weaken the seal's tightness. In other words, existing technologies suffer from the technical problem of difficulty in coordinating and optimizing the thickness-direction temperature gradient control and vulcanization uniformity during the gradient temperature vulcanization process of rubber seals. Summary of the Invention

[0003] In view of this, the present invention provides a method for gradient temperature vulcanization of rubber seals, which can solve the technical problem in the prior art that it is difficult to coordinate and optimize the control of the temperature gradient in the thickness direction and the uniformity of vulcanization during the gradient temperature vulcanization process of rubber seals.

[0004] This invention is implemented as follows: A method for gradient temperature vulcanization of rubber seals is provided. A multi-layer phase change material (PCM) layer is embedded in the inner wall of a mold cavity. A PCM temperature matching experiment is conducted on the multi-layer PCM layer to record temperature distribution data. Gradient smoothness analysis is performed on the temperature distribution data to obtain the PCM temperature range parameters. Based on the PCM temperature range parameters, it is determined whether the sample meets a preset range and whether to repeat the experiment. An acoustic parameter optimization experiment is conducted to prepare vulcanization test samples. The crosslinking density is measured and bubble defects are detected on the vulcanization test samples. The crosslinking density uniformity coefficient and bubble defect rate are calculated. Based on the crosslinking density uniformity coefficient and bubble defect rate, the optimal acoustic parameters are selected. A segmented pressure-temperature co-control curve is constructed based on the PCM temperature range parameters and the optimal acoustic parameters. A seal size prediction and compensation model is established to obtain viscoelastic parameter data. Shrinkage distribution data is extracted through multiphysics simulation. The mold cavity size is then designed with reverse compensation based on the shrinkage distribution data.

[0005] Among them, the multilayer phase change material layers are, from the outside to the inside, a paraffin layer, a fatty acid layer, and an inorganic salt phase change layer.

[0006] The phase change temperature matching experiment involves placing a rubber seal sample into a test mold equipped with multiple layers of phase change material, and gradually increasing the temperature from the initial temperature to the final temperature. Each temperature point is held for a preset duration, and the temperature distribution data is recorded by an array of thermocouples embedded at different depths inside the rubber seal sample.

[0007] The gradient smoothness analysis specifically involves calculating the ratio of the temperature difference to the distance between adjacent measuring points along the thickness direction of the rubber seal sample as the local temperature gradient value, statistically analyzing the standard deviation of the local temperature gradient value under each temperature range, and selecting the temperature range that minimizes the standard deviation as the phase change temperature range parameter for each phase change material layer.

[0008] Specifically, determining whether the preset range is met involves checking whether the phase change temperature range parameters of the paraffin layer, the fatty acid layer, and the inorganic salt layer are within the first preset range, the second preset range, and the third preset range. If all three phase change temperature range parameters are within their respective ranges, an acoustic parameter optimization experiment is performed. If any one of the three phase change temperature range parameters is not within its respective range, the material ratio of the multilayer phase change material layer is adjusted, and the phase change temperature matching experiment is performed again.

[0009] Among them, the acoustic parameter optimization experiment specifically involves fixing the heating temperature to the median temperature of the inorganic salt phase change layer phase change temperature range parameters, applying ultrasonic combination parameters with different frequencies and sound intensities, and audible acoustic wave combination parameters with different frequencies and sound pressure levels, and setting the vulcanization time to a preset duration. A vulcanization test sample is prepared for each parameter combination.

[0010] Specifically, the crosslinking density determination involves using the swelling method to measure the crosslinking density at different depths of the vulcanized test sample.

[0011] Among them, bubble defect detection specifically involves using X-ray tomography to statistically analyze the number and size distribution of bubbles inside the sulfurized test sample.

[0012] The crosslinking density uniformity coefficient is specifically calculated by dividing the vulcanized test sample into multiple layers along the thickness direction, measuring the crosslinking density value of each layer, calculating the average crosslinking density value of the multiple layers, summing the absolute values ​​of the differences between the crosslinking density values ​​of each layer and the average crosslinking density value, dividing the sum by the number of layers of the average crosslinking density value, and subtracting the deviation quotient from 1 to obtain the crosslinking density uniformity coefficient.

[0013] Specifically, the bubble defect rate is calculated by obtaining the internal three-dimensional structural data of the sulfurized test sample through X-ray tomography, identifying bubbles with a diameter greater than a preset threshold, and then calculating the ratio of the total volume of all bubbles to the total volume of the sulfurized test sample as the bubble defect rate.

[0014] The process of selecting the optimal acoustic parameters involves defining a set of acoustic parameters with a crosslinking density uniformity coefficient greater than a first threshold and a bubble defect rate less than a second threshold as the qualified acoustic parameter set. From this set, the acoustic parameter set that maximizes the product of the crosslinking density uniformity coefficient and the reciprocal of the bubble defect rate is selected as the optimal acoustic parameter. The process then determines whether the number of parameter combinations in the qualified acoustic parameter set is greater than a preset number. If it is, the optimal acoustic parameter is valid. If it is not, the frequency and intensity ranges of the acoustic parameter combinations are expanded, and the acoustic parameter optimization experiment is repeated.

[0015] Specifically, the segmented pressure-temperature coordinated control curve divides the vulcanization process into an venting stage and a curing stage. In the venting stage, the mold temperature is raised from room temperature to the lower limit of the paraffin layer phase change temperature range parameter and the pressure is maintained at the first pressure range for a first duration. In the curing stage, the mold temperature is raised to the upper limit of the inorganic salt phase change temperature range parameter and the pressure is increased to the second pressure range for a second duration within a preset time.

[0016] Specifically, a model for predicting and compensating the dimensions of the sealing component was established. Before vulcanization, uniaxial tensile tests and stress relaxation tests were conducted on the rubber sealing component to obtain viscoelastic parameter data. The viscoelastic parameter data, phase change temperature range parameters, optimal acoustic parameters, and segmented pressure-temperature co-control curves were input into multiphysics simulation software to simulate the coupled evolution process of temperature field distribution, crosslinking degree field distribution, and deformation field distribution during vulcanization. After vulcanization, the shrinkage rate distribution data of each part of the rubber sealing component was extracted.

[0017] The multiphysics simulation software specifically involves inputting data on the density, specific heat capacity, thermal conductivity, and viscoelastic parameters of the rubber sealing material, setting the mold temperature boundary conditions and the equivalent heat source term corresponding to the optimal acoustic parameters, using the vulcanization kinetic equation to describe the evolution of the degree of crosslinking with temperature and time, and using a hyperelastic constitutive model to describe the relationship between the deformation and stress of the rubber sealing material.

[0018] Specifically, the shrinkage rate distribution data extraction involves reading the displacement data of key feature points on the surface and inside of the rubber seal after vulcanization from the simulation results of multiphysics simulation software. The difference between the final position and the initial position of each key feature point is divided by the initial size to obtain the shrinkage rate of the key feature point position. The shrinkage rate data of all key feature points constitute the shrinkage rate distribution data.

[0019] Among them, the reverse compensation design specifically involves dividing the target dimension value on the design drawing by 1 and subtracting the shrinkage rate at the dimension feature location for each dimensional feature of the rubber seal to obtain the compensated mold cavity dimension data.

[0020] This invention embeds multiple layers of phase change material (PCM) arranged in ascending order of phase change temperature into the inner wall of a mold cavity. Utilizing the physical properties of PCM in absorbing and releasing latent heat during solid-liquid phase transitions, it automatically smooths temperature fluctuations, constructing a passive multi-stage heat capacity ladder system. This ensures a smooth transition of the temperature gradient along the thickness of the seal, rather than a steep jump, effectively mitigating the problem of thermal stress concentration caused by sudden temperature changes. By establishing a phase change temperature matching experiment and gradient smoothness analysis process, this invention accurately determines the phase change temperature range parameters of each PCM layer, ensuring that the heat storage and release behavior of the multiple PCM layers matches the vulcanization temperature requirements of the rubber material. Simultaneously, it introduces acoustic wave-assisted heat transfer technology to enhance the internal heat transfer efficiency of the material. Furthermore, through a segmented pressure-temperature coordinated control curve, it achieves low-pressure venting during the venting stage and high-pressure bubble suppression during the curing stage, solving the bubble defect problem caused by the mismatch between gas escape and cross-linking curing rates. This invention uses multiphysics simulation software to couple a hyperelastic constitutive model and vulcanization kinetic equations to predict the deformation history of the vulcanization process, and performs reverse compensation design on the mold cavity size to ensure the dimensional accuracy of the seal. In summary, this invention solves the technical problem mentioned in the background art of the difficulty in coordinating and optimizing the thickness direction temperature gradient control and vulcanization uniformity during the gradient temperature vulcanization process of rubber seals. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the spatial distribution of the multilayer phase change material layers in the embodiment.

[0022] Figure 2 This is a diagram showing the arrangement of the sound wave generating device and the energy transfer path in the embodiment.

[0023] Figure 3 This is a three-dimensional distribution diagram of air bubbles inside the vulcanization test sample in the example.

[0024] Figure 4 This is a graph showing the segmented pressure-temperature coordinated control in the embodiment.

[0025] Figure 5 This is a coupled evolution diagram of the crosslinking degree field and temperature field during the vulcanization process in the embodiment.

[0026] Figure 6 This is a comparison chart of the sealing ring size measurement results and tolerance zone in the embodiment. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0028] This invention provides a method for gradient temperature vulcanization of rubber seals, comprising:

[0029] S01. A multi-layer phase change material layer is embedded in the inner wall of the mold cavity at a distance of 3 to 8 mm from the surface of the rubber seal. The multi-layer phase change material layer consists of a paraffin layer, a fatty acid layer and an inorganic salt phase change layer from the outside to the inside. The thickness of the paraffin layer is 2 to 3 mm, the thickness of the fatty acid layer is 2 to 3 mm, and the thickness of the inorganic salt phase change layer is 2 to 3 mm.

[0030] S02. A phase change temperature matching experiment is performed on the multilayer phase change material layer. The rubber seal sample is placed in a test mold equipped with the multilayer phase change material layer, and the temperature is increased from 120°C to 200°C in increments of 5°C. Each temperature point is held for 15 minutes. Temperature distribution data is recorded by thermocouple arrays embedded at different depths inside the rubber seal sample. The different depths are 1 mm, 3 mm, 5 mm, 7 mm and 9 mm away from the surface of the rubber seal sample.

[0031] S03. Perform gradient smoothness analysis on the temperature distribution data, calculate the ratio of the temperature difference to the distance between adjacent measuring points in the thickness direction of the rubber seal sample as the local temperature gradient value, calculate the standard deviation of the local temperature gradient value in each temperature range, and select the temperature range that minimizes the standard deviation as the phase change temperature range parameter of each phase change material layer. The phase change temperature range parameter includes the phase change temperature range parameter of the paraffin layer, the phase change temperature range parameter of the fatty acid layer, and the phase change temperature range parameter of the inorganic salt phase change layer.

[0032] S04. Determine whether the phase change temperature range parameters of the paraffin layer, the fatty acid layer, and the inorganic salt phase change layer are within the range of 125 to 150°C, 145 to 170°C, and 165 to 190°C, based on the phase change temperature range parameters. If all three phase change temperature range parameters are within the corresponding ranges, proceed to step S05. If any one of the three phase change temperature range parameters is not within the corresponding range, adjust the material ratio of the multilayer phase change material layer and re-execute step S02.

[0033] S05. Install a sound wave generator on the outer wall of the mold and conduct sound wave parameter optimization experiments. Fix the heating temperature to the median temperature of the inorganic salt phase change layer's phase change temperature range parameters, and apply frequencies of 20 to 60 kHz and sound intensities of 0.5 to 3.0. The ultrasonic combination parameters, and the audible sound wave combination parameters with a frequency of 100 to 500 Hz and a sound pressure level of 90 to 120 dB, were used. The vulcanization time was set to 30 minutes, and one vulcanization test sample was prepared for each parameter combination.

[0034] S06. The crosslinking density and bubble defect detection of the vulcanized test sample are performed. The crosslinking density values ​​at different depths of the vulcanized test sample are measured using the swelling method. The different depths are 2 mm, 4 mm, 6 mm, 8 mm and 10 mm away from the surface of the vulcanized test sample. The number of bubbles and the bubble size distribution inside the vulcanized test sample are statistically analyzed using X-ray tomography. The crosslinking density uniformity coefficient and bubble defect rate of each vulcanized test sample are calculated.

[0035] S07. Based on the crosslinking density uniformity coefficient and the bubble defect rate, establish the acoustic parameter optimization criteria. Record the acoustic parameter combinations with a crosslinking density uniformity coefficient greater than 0.92 and a bubble defect rate less than 0.3% as the qualified acoustic parameter set. Select the acoustic parameter combination that maximizes the product of the crosslinking density uniformity coefficient and the reciprocal of the bubble defect rate from the qualified acoustic parameter set as the optimal acoustic parameter. Determine whether the number of parameter combinations in the qualified acoustic parameter set is greater than 3. If it is greater than 3, the optimal acoustic parameter is valid and step S08 is executed. If it is not greater than 3, expand the frequency range and intensity range of the acoustic parameter combination and re-execute step S05.

[0036] S08. Construct a segmented pressure-temperature coordinated control curve based on the phase change temperature range parameters and the optimal acoustic parameters, dividing the vulcanization process into an venting stage and a curing stage. In the venting stage, raise the mold temperature from room temperature to the lower limit of the phase change temperature range parameters of the paraffin layer and maintain the pressure at 0.8 to 1.2 MPa for 8 to 12 minutes. In the curing stage, raise the mold temperature to the upper limit of the phase change temperature range parameters of the inorganic salt phase change layer and increase the pressure to 8 to 12 MPa within 3 seconds for 18 to 25 minutes.

[0037] S09. Establish a sealing component size prediction and compensation model. Before vulcanization, conduct uniaxial tensile tests and stress relaxation tests on the rubber sealing component to obtain viscoelastic parameter data. The viscoelastic parameter data includes elastic modulus, relaxation time, and Poisson's ratio. Input the viscoelastic parameter data, the phase transition temperature range parameters, the optimal acoustic wave parameters, and the segmented pressure-temperature co-control curve into multiphysics simulation software to simulate the coupled evolution process of temperature field distribution, crosslinking degree field distribution, and deformation field distribution during vulcanization. Extract the shrinkage rate distribution data of each part of the rubber sealing component after vulcanization.

[0038] S10. Based on the shrinkage distribution data, perform reverse compensation design on the mold cavity size. Add the shrinkage value of each feature point in the shrinkage distribution data to the target size value to obtain the compensated mold cavity size data. After processing the compensated mold, perform actual vulcanization production according to the segmented pressure and temperature coordinated control curve, the optimal acoustic parameters, and the configuration of the multi-layer phase change material layer.

[0039] The paraffin layer uses n-octadecane or n-eicosane, the fatty acid layer uses stearic acid or palmitic acid, and the inorganic salt phase change layer uses sodium nitrate or potassium nitrate. The phase change temperature of n-octadecane is 28°C, and that of n-eicosane is 36°C. The phase change temperature of the paraffin layer is adjusted to the range of 125 to 150°C by mixing different proportions of n-octadecane and n-eicosane. The phase change temperature of stearic acid is 69°C, and that of palmitic acid is 62°C. The phase change temperature of the fatty acid layer is increased to the range of 145 to 170°C by adding inorganic fillers. The phase change temperature of sodium nitrate is 306°C, and that of potassium nitrate is 334°C. The phase change temperature of the inorganic salt phase change layer is adjusted to the range of 165 to 190°C by mixing different proportions of sodium nitrate and potassium nitrate.

[0040] The method for calculating the local temperature gradient value in the gradient smoothness analysis is as follows: Temperature measurement points with a spacing of 1 mm are selected along the thickness direction of the rubber seal sample. The temperature difference between the i-th and the (i+1)-th temperature measurement points is divided by the distance between the two points to obtain the local temperature gradient value at the i-th position. The standard deviation is calculated for all local temperature gradient values. A smaller standard deviation indicates a more uniform temperature gradient distribution. The formula for calculating the standard deviation is: first, calculate the average of all local temperature gradient values; then, calculate the square of the difference between each local temperature gradient value and the average value; sum the squares of all differences and divide by the number of temperature measurement points; finally, take the square root of the quotient to obtain the standard deviation.

[0041] The median temperature is the sum of the upper and lower limits of the phase change temperature range parameter of the inorganic salt phase change layer, divided by 2. The median temperature is selected based on the following: the inorganic salt phase change layer is located in the innermost layer of the multilayer phase change material layer and is closest to the rubber seal. Its phase change temperature range determines the vulcanization temperature of the inner layer of the rubber seal. Selecting the median temperature as a fixed heating temperature ensures that the inorganic salt phase change layer can fully exert its phase change heat storage function.

[0042] The crosslinking density uniformity coefficient is defined as follows: the vulcanized test sample is divided into 5 equal layers along the thickness direction, the crosslinking density value of each layer is measured, the average crosslinking density value of the 5 layers is calculated, the absolute value of the difference between the crosslinking density values ​​of each layer and the average crosslinking density value is summed and divided by 5 times the average crosslinking density value to obtain the deviation quotient. The crosslinking density uniformity coefficient is then subtracted from 1 to obtain the crosslinking density uniformity coefficient. The closer the crosslinking density uniformity coefficient is to 1, the more uniform the crosslinking density distribution. The crosslinking density value is measured by the swelling method. The sample block of the vulcanized test sample is immersed in toluene solvent for 72 hours, the mass before swelling and the mass after swelling are measured, and the crosslinking density value is calculated according to the Flory-Rehner equation.

[0043] The bubble defect rate is defined as follows: Three-dimensional structural data of the vulcanization test sample are obtained through X-ray tomography; bubbles with a diameter greater than 0.1 mm are identified; and the ratio of the total volume of all such bubbles to the total volume of the vulcanization test sample is used as the bubble defect rate. A lower bubble defect rate indicates fewer bubble defects inside the vulcanization test sample.

[0044] The method for determining the switching timing of the segmented pressure-temperature coordinated control curve is as follows: During the venting stage, the gas flow rate changes at the mold vent are monitored. When the gas flow rate changes show that the gas flow rate drops below 5% of the initial gas flow rate, it is determined that venting is basically complete. At this time, the rapid heating and pressurization program of the curing stage is immediately started. The initial gas flow rate is the average gas flow rate within the first 30 seconds after the start of the venting stage.

[0045] The room temperature is 20 to 25°C. The duration of the venting phase, 8 to 12 minutes, is chosen because residual air in the rubber material and volatile substances generated during vulcanization need sufficient time to escape. Too short a time leads to insufficient venting, while too long a time reduces production efficiency. Extensive experiments have verified that 8 to 12 minutes is the optimal venting time range. The duration of the curing phase, 18 to 25 minutes, is chosen based on the time required for the rubber material to complete the crosslinking reaction. This time is determined according to the type and amount of vulcanizing agent in the rubber formulation.

[0046] The multiphysics simulation software simulation process includes: inputting the density, specific heat capacity, thermal conductivity, and viscoelastic parameters of the rubber sealing material; setting the mold temperature boundary conditions and the equivalent heat source term corresponding to the optimal acoustic parameters; using the vulcanization kinetic equation to describe the evolution of the degree of crosslinking with temperature and time, the vulcanization kinetic equation adopts the Kamal-Sourour model; and using a hyperelastic constitutive model to describe the relationship between the deformation and stress of the rubber sealing component, the hyperelastic constitutive model adopts the Mooney-Rivlin model or the Yeoh model. The simulation time step is set to 0.1 to 0.5 seconds, the simulation mesh size is set to 0.5 to 2 mm, and the simulation iteration convergence accuracy is set to 0.001.

[0047] The mathematical expression of the Kamal-Sourour model is as follows: the derivative of the degree of crosslinking with respect to time is equal to the first reaction rate constant multiplied by 1 minus the first reaction order power of the degree of crosslinking plus the second reaction rate constant multiplied by the second reaction order power of the degree of crosslinking multiplied by 1 minus the third reaction order power of the degree of crosslinking. Both the first and second reaction rate constants conform to the Arrhenius temperature dependence. The first, second, and third reaction orders were obtained by determining the exothermic curves of the rubber sample at different heating rates using differential scanning calorimetry, and a nonlinear fitting method was employed.

[0048] The Mooney-Rivlin model is a two-parameter hyperelastic constitutive model. Its strain energy density function is expressed as the sum of a first Mooney-Rivlin constant multiplied by a first invariant minus 3, plus a second Mooney-Rivlin constant multiplied by a second invariant minus 3. The first and second Mooney-Rivlin constants are obtained by fitting the uniaxial tensile experimental data. The Yeoh model is a three-parameter hyperelastic constitutive model. Its strain energy density function is expressed as the sum of three Yeoh constants multiplied by the first, second, and third powers of the first invariant minus 3, respectively. These three Yeoh constants are obtained by jointly fitting the uniaxial and biaxial tensile experimental data.

[0049] The equivalent heat source is an equivalent volume heat source that converts the sound wave energy generated by the optimal sound wave parameters acting on the rubber seal into heat energy. The size of the equivalent volume heat source is calculated based on the frequency and sound intensity of the optimal sound wave parameters using acoustic-thermal coupling theory.

[0050] The shrinkage rate distribution data extraction method is as follows: read the displacement data of key feature points on the surface and inside of the rubber seal after vulcanization from the simulation results of the multiphysics simulation software, divide the difference between the final position and the initial position of each key feature point by the initial size to obtain the shrinkage rate of the key feature point position, and construct the shrinkage rate distribution data of all the key feature points.

[0051] The reverse compensation design method is as follows: For each dimensional feature of the rubber seal, the target dimensional value on the design drawing is divided by 1, and the shrinkage rate at the dimensional feature location is subtracted to obtain the compensated mold cavity dimensional data. The compensated mold cavity dimensional data is greater than the target dimensional value, and the compensation amount is equal to the target dimensional value multiplied by the shrinkage rate, divided by 1, and then subtracted from the shrinkage rate.

[0052] The specific implementation methods of the above steps are described in detail below.

[0053] The specific implementation of step S01 involves embedding a multi-layer phase change material layer 3 to 8 mm away from the surface of the rubber seal on the inner wall of the mold cavity. First, annular grooves with a depth of 2 to 5 mm are machined on the inner wall of the mold. There are 3 grooves arranged radially along the mold. Then, the outermost groove is filled with a paraffin layer material, which is a mixture of n-octadecane and n-eicosane. The middle groove is filled with a fatty acid layer material, which is stearic acid or palmitic acid with added inorganic fillers such as alumina or magnesium oxide. The innermost groove is filled with an inorganic salt phase change layer material, which is a mixture of sodium nitrate and potassium nitrate. The purpose of setting up the multi-layer phase change material layer is to use the physical properties of the phase change material to absorb and release latent heat during the solid-liquid phase change process to achieve passive temperature control, thereby suppressing temperature fluctuations during the vulcanization process.

[0054] The specific implementation of step S02 involves conducting a phase change temperature matching experiment on the multilayer phase change material layer. First, a standard rubber sealing sample with a thickness of 10 to 15 mm is prepared. Then, holes are drilled every 1 mm along the thickness direction inside the rubber sealing sample, and K-type thermocouples with a diameter of 0.5 mm are inserted. The thermocouple insertion depths are 1 mm, 3 mm, 5 mm, 7 mm, and 9 mm from the surface, for a total of 5 positions. Next, the rubber sealing sample equipped with the thermocouple array is placed in a test mold equipped with the multilayer phase change material layer. The mold is closed, and the heating system is started. The heating system adopts resistance heating, with the initial temperature set at 120°C and gradually increased to 200°C in increments of 5°C. Each temperature point is held for 15 minutes to ensure sufficient temperature stability. During the holding period at each temperature point, the data acquisition system records the temperature values ​​at the 5 thermocouple positions at a sampling interval of 1 second. The temperature data of all temperature points are organized into a temperature distribution data matrix according to time series and spatial location. The purpose of the phase change temperature matching experiment is to obtain the temperature distribution pattern inside the rubber sealing sample under different heating temperatures, providing experimental basis for subsequent determination of phase change temperature range parameters.

[0055] The specific implementation of step S03 involves performing gradient smoothness analysis on the temperature distribution data. First, the steady-state temperature data for the last 5 minutes of the holding phase at each temperature point is extracted from the temperature distribution data matrix. The average temperature value at the 5 thermocouple locations is calculated as the steady-state temperature at each location. Then, the temperature difference between adjacent locations is calculated. The temperature difference between the i-th location and the i+1-th location is divided by the distance of 1mm between the two locations to obtain the local temperature gradient value at the i-th location. A total of 4 local temperature gradient values ​​are calculated for the 5 locations. Then, the 4 local temperature gradient values ​​corresponding to each heating temperature point are calculated... The standard deviation is calculated by first averaging the four local temperature gradient values, then taking the square root of the sum of the squares of the differences between each local temperature gradient value and the average value, divided by 4. The smaller the standard deviation, the more uniform the temperature gradient distribution. Finally, for the paraffin layer, fatty acid layer, and inorganic salt phase change layer, the temperature range with the smallest standard deviation at their respective spatial locations is statistically analyzed. The temperature range is recorded as the phase change temperature range parameter for each phase change material layer. The purpose of the gradient smoothness analysis is to quantitatively evaluate the uniformity of the temperature gradient and determine the phase change temperature range that makes the temperature distribution the smoothest.

[0056] The specific implementation of step S04 involves determining whether the phase change temperature range parameters meet the preset ranges. The preset ranges are set based on the temperature requirements of the rubber seal vulcanization process. The preset range for the paraffin layer phase change temperature range parameters is 125 to 150°C, for the fatty acid layer it is 145 to 170°C, and for the inorganic salt phase change layer it is 165 to 190°C. The determination method is to check whether all three phase change temperature range parameters are within their corresponding preset ranges. If the paraffin layer phase change temperature range parameter is between 125 and 150°C and the fatty acid layer phase change temperature range parameter is between 145 and 170°C... If the phase change temperature range parameter of the inorganic salt phase change layer is between 165 and 190°C, it is determined to meet the requirements and step S05 is executed. If any phase change temperature range parameter is not within the corresponding preset range, the material ratio of the multilayer phase change material layer needs to be adjusted. The adjustment method is to increase or decrease the mixing ratio of n-octadecane and n-eicosane for the paraffin layer, increase or decrease the amount of inorganic filler added for the fatty acid layer, and increase or decrease the mixing ratio of sodium nitrate and potassium nitrate for the inorganic salt phase change layer. After the adjustment is completed, step S02 is executed again to perform the phase change temperature matching experiment. The purpose of the judgment step is to ensure that the phase change temperature of the multilayer phase change material layer matches the sulfidation temperature requirement.

[0057] The specific implementation of step S05 involves conducting an acoustic parameter optimization experiment. First, the median temperature of the phase transition temperature range parameter for the inorganic salt phase transition layer is calculated. The median temperature is the sum of the upper and lower limits of the phase transition temperature range parameter divided by 2. Then, the heating temperature is fixed at the median temperature. Next, ultrasonic parameter combinations and audible acoustic parameter combinations are designed. The ultrasonic parameter combination includes five frequency points: 20kHz, 30kHz, 40kHz, 50kHz, and 60kHz, with a sound intensity of 0.5. 1.0 1.5 2.0 2.5 and 3.0 There are a total of 6 intensity points, which are combined in pairs to form 30 sets of ultrasonic combination parameters. The audible sound wave parameter combinations include 5 frequency points (100Hz, 200Hz, 300Hz, 400Hz, and 500Hz) and 4 sound pressure level points (90dB, 100dB, 110dB, and 120dB), which are combined in pairs to form 20 sets of audible sound wave combination parameters. A vulcanization experiment is carried out on each set of sound wave combination parameters. The rubber seal is placed in a mold equipped with a multilayer phase change material layer and a sound wave generating device. The corresponding sound wave parameters are applied and heated to a fixed temperature. The vulcanization time is uniformly set to 30 minutes. One vulcanization test sample is prepared for each set of parameter combinations. The purpose of the sound wave parameter optimization experiment is to screen out the optimal sound wave action parameters through systematic experiments.

[0058] The specific implementation of step S06 involves determining the crosslinking density and detecting bubble defects in the vulcanized test samples. The crosslinking density is determined using the swelling method. First, five thin sample blocks are cut along the thickness direction from each vulcanized test sample at distances of 2mm, 4mm, 6mm, 8mm, and 10mm from the surface. Each sample block weighs approximately 0.5g. The sample blocks are then immersed in toluene solvent and sealed for 72 hours. The volume of toluene is 20 times the volume of the sample block to ensure sufficient swelling. After swelling, the sample blocks are removed, the surface solvent is absorbed with filter paper, and the swollen mass is immediately weighed. The mass is determined according to the Flory-Rehne method. The r-equation calculates the crosslinking density value from the mass before and after swelling. X-ray tomography is used for bubble defect detection. The vulcanized test sample is placed in the X-ray tomography equipment, with a scanning resolution of 50 μm and an interlayer spacing of 100 μm. After scanning, three-dimensional structural data is obtained. Image processing software identifies areas with gray values ​​below a threshold as bubbles. The threshold is set to 70% of the gray value of normal rubber material. The number and volume of bubbles with a diameter greater than 0.1 mm are counted, and the total bubble volume is obtained by summing all bubble volumes. The purpose of the crosslinking density determination and bubble defect detection is to quantitatively evaluate the vulcanization quality under different acoustic parameters.

[0059] The specific implementation of step S07 is based on establishing an optimal criterion for acoustic parameters using the crosslinking density uniformity coefficient and the bubble defect rate. First, the crosslinking density uniformity coefficient of each vulcanization test sample is calculated. This is done by averaging the crosslinking density values ​​of the five layers to obtain the average crosslinking density value. Then, the absolute value of the difference between each layer's crosslinking density value and the average crosslinking density value is calculated and summed. This summation is divided by five times the average crosslinking density value to obtain the deviation quotient. The crosslinking density uniformity coefficient is obtained by subtracting the deviation quotient from 1. Next, the bubble defect rate is calculated. The bubble defect rate is the ratio of the total bubble volume to the total volume of the vulcanization test sample. Then, an optimal criterion is established, selecting samples with a crosslinking density uniformity coefficient greater than [a certain value]. Acoustic wave parameter combinations with a value of 0.92 and a bubble defect rate of less than 0.3% are selected and recorded as the qualified acoustic wave parameter set. A comprehensive evaluation index is calculated for each parameter group from the qualified acoustic wave parameter set. The comprehensive evaluation index is the product of the crosslinking density uniformity coefficient and the reciprocal of the bubble defect rate. The acoustic wave parameter combination with the highest comprehensive evaluation index is selected as the optimal acoustic wave parameter. Finally, it is determined whether the number of parameter combinations in the qualified acoustic wave parameter set is greater than 3. If it is greater than 3, the optimal acoustic wave parameter is valid and step S08 is executed. If it is less than 3, the frequency range and intensity range of the acoustic wave parameter combination are expanded. The ultrasonic frequency range is expanded to 10 to 80 kHz, and the sound intensity range is expanded to 0.2 to 5.0. The audible sound frequency range is extended to 50 to 800 Hz, and the sound pressure level range is extended to 80 to 130 dB. Then step S05 is repeated. The purpose of the optimization criterion is to select the optimal sound parameters while ensuring the quality of vulcanization.

[0060] The specific implementation of step S08 involves constructing a segmented pressure-temperature coordinated control curve based on the phase change temperature range parameters and optimal acoustic wave parameters. First, the vulcanization process is divided into an venting stage and a curing stage. The temperature during the venting stage is set to rise from room temperature (20-25°C) to the lower limit of the paraffin layer phase change temperature range parameters, with a heating rate of 5-10°C per minute. Once the target temperature is reached, it is maintained at a constant temperature. The pressure is set to 0.8-1.2 MPa, and the duration is set to 8-12 minutes. During the venting stage, a flow sensor installed at the mold venting port monitors the gas flow rate changes in real time. When the gas flow rate drops to less than 5% of the initial gas flow rate, the venting is considered to be basically completed. The initial gas flow rate is the average gas flow rate within the first 30 seconds after the start of the venting stage. Once the venting is completed, the curing stage is started immediately. The temperature of the curing stage is set to the upper limit of the phase change temperature range parameter of the inorganic salt phase change layer, and the heating rate is set to 15 to 25°C per minute. The pressure is rapidly increased from the venting stage pressure to 8 to 12 MPa within 3 seconds. The duration of the curing stage is set to 18 to 25 minutes. The purpose of the segmented pressure and temperature coordinated control curve is to achieve the time-series optimization matching of venting and curing.

[0061] The specific implementation of step S09 involves establishing a sealing component size prediction and compensation model. First, a uniaxial tensile test is performed on the rubber sealing component material. A dumbbell-shaped standard tensile specimen is prepared and stretched to fracture at a rate of 50 mm / min on a tensile testing machine. The stress-strain curve is recorded. Then, a stress relaxation test is performed, stretching the specimen to 50% strain and maintaining a constant strain. The stress decay curve over time is recorded. Viscoelastic parameters such as elastic modulus, relaxation time, and Poisson's ratio are extracted from the experimental data. Next, a three-dimensional geometric model of the rubber sealing component is established using multiphysics simulation software. The density, specific heat capacity, thermal conductivity, and viscoelastic parameters of the rubber material are input. The mold temperature boundary condition is set as a segmented pressure-temperature co-control curve. The equivalent heat source term corresponding to the optimal acoustic wave parameters is set. The magnitude of the equivalent heat source term is calculated based on the acoustic wave frequency and intensity using acoustic-thermal coupling theory. The Kamal-Sourour model describes the evolution of crosslinking degree with temperature and time. The Mooney-Rivlin model or Yeoh model is used to describe the relationship between rubber deformation and stress. The simulation time step is set to 0.1 to 0.5 seconds, the mesh size is 0.5 to 2 mm, and the iteration convergence accuracy is 0.001. The simulation is run to calculate the coupled evolution of temperature field distribution, crosslinking degree field distribution, and deformation field distribution during vulcanization. After the simulation is completed, the displacement data of key feature points on the surface and inside of the rubber seal at the end of vulcanization are extracted. Key feature points include the dimensional features such as inner diameter, outer diameter, and thickness. The difference between the final position and the initial position of each key feature point is calculated and divided by the initial size to obtain the shrinkage rate at that position. The shrinkage rate data of all key feature points are used to form the shrinkage rate distribution data. The purpose of the size prediction and compensation model is to predict the vulcanization shrinkage behavior through simulation.

[0062] The specific implementation of step S10 is to perform reverse compensation design on the mold cavity size based on the shrinkage rate distribution data. For each target size value on the rubber seal design drawing, the shrinkage rate at the corresponding position in the shrinkage rate distribution data is found. The target size value is divided by 1 and the shrinkage rate is subtracted to obtain the compensated mold cavity size data. The compensation amount is calculated as the target size value multiplied by the shrinkage rate, divided by 1 and subtracted from the shrinkage rate. The compensation mold is processed according to the compensated mold cavity size data. After processing, a multi-layer phase change material layer and an acoustic wave generator are assembled. The rubber seal is placed in the compensation mold. The temperature and pressure program are set according to the segmented pressure and temperature coordinated control curve. The acoustic wave generator is started to apply the optimal acoustic wave parameters and carry out actual vulcanization production. The purpose of the reverse compensation design is to offset the vulcanization shrinkage through mold size compensation to ensure the final dimensional accuracy.

[0063] It should be noted that the key technical concept of this invention includes the synergistic effect of a multi-layer phase change material passive heat storage and regulation mechanism and an acoustic active heat transfer mechanism. The multi-layer phase change material passive heat storage and regulation mechanism embeds paraffin wax, fatty acid, and inorganic salt phase change layers arranged in ascending order of phase change temperature into the inner wall of the mold cavity. Utilizing the physical property of phase change materials absorbing or releasing latent heat during solid-liquid phase change, when the temperature at a certain location of the rubber seal rises too rapidly, the adjacent phase change material layer automatically melts and absorbs excess heat; when the temperature drops, the phase change material solidifies and releases heat. This automatic adjustment process can transform a steep temperature gradient into a gentle temperature distribution curve without external control. Compared to the traditional isothermal vulcanization method that relies solely on a single heat transfer path through mold conduction, the multi-layer phase change material layer constructs a multi-level heat capacity ladder system, effectively alleviating the problem of thermal stress concentration caused by temperature jumps. The acoustic active-assisted heat transfer mechanism applies ultrasonic or audible acoustic vibrations to the mold. The sound waves propagate within the rubber material, generating a periodic compression rarefaction effect that induces reciprocating motion at the microscale. This reciprocating motion enhances convective heat transfer, overcoming the limitation of pure conductive heat transfer caused by the low thermal conductivity of rubber. Compared to traditional gradient temperature vulcanization methods that only adjust the external heating temperature to improve temperature distribution, acoustic-assisted heat transfer improves heat transfer efficiency from within the material, allowing heat to be transferred more quickly from the outer layer to the inner layer. The synergistic effect of these two mechanisms lies in the phase change material layer providing a temperature buffer to stabilize external boundary conditions, while acoustic heat transfer accelerates internal heat transfer and homogenizes the temperature distribution. Combined with a segmented pressure-temperature co-control curve, the timing of venting and curing is optimized. Multiphysics simulation predicts shrinkage behavior and inversely compensates for mold dimensions, forming a complete closed-loop system from temperature control to quality prediction. This fundamentally solves the technical problem of the difficulty in co-optimizing thickness-direction temperature gradient control and vulcanization uniformity during the gradient temperature vulcanization of rubber seals.

[0064] It should be noted that this invention also solves the following technical problem: the difficulty in matching the internal gas escape rate and cross-linking curing rate during the vulcanization process of rubber seals, leading to the formation of bubble defects. This invention constructs a segmented pressure-temperature coordinated control curve, dividing the vulcanization process into an venting stage and a curing stage. During the venting stage, a lower pressure is maintained to provide sufficient escape channels and time for residual air inside the rubber material and volatile substances generated by the vulcanization reaction. The degree of venting completion is judged by real-time monitoring of the gas flow rate changes at the mold venting holes. When the gas flow rate changes drop to below 5% of the initial gas flow rate, venting is considered basically complete, and the rapid temperature and pressure increase program for the curing stage is immediately initiated. During the curing stage, the pressure is rapidly increased to 8 to 12 MPa, and the temperature is raised to the inorganic salt phase transition stage. The upper limit temperature of the phase transition temperature range parameter, the rapid heating and pressurization program completes the pressure increase within 3 seconds, the high pressure environment inhibits the expansion of residual gas inside the rubber material and causes micro bubbles to be compressed and eliminated before the crosslinking network cures, while the high temperature environment accelerates the decomposition of vulcanizing agent and the crosslinking reaction, so that the crosslinking network quickly forms a dense structure after the gas is completely discharged. The dense structure confines the residual gas to a very small size range, which is insufficient to form bubble defects that affect the sealing performance. Therefore, the present invention achieves the time sequence optimization matching of gas escape and crosslinking curing by precisely controlling the switching time of the exhaust stage to the curing stage.

[0065] Specifically, the principle of this invention is as follows: The invention solves the aforementioned technical problem by organically combining a passive phase change thermal storage regulation mechanism with an active acoustic wave-assisted heat transfer mechanism to construct a temperature gradient adaptive smoothing system. When a phase change material reaches its phase change temperature, it undergoes a solid-liquid phase change. The latent heat absorbed or released during this phase change process is far greater than the sensible heat. The latent heat of phase change per unit mass of phase change material is tens of times greater than the sensible heat under the same temperature rise conditions. Therefore, when the temperature at a certain location of the seal rises too quickly, the adjacent phase change material layer automatically melts and absorbs excess heat. When the temperature drops, the phase change material solidifies and releases heat. This automatic adjustment process achieves dynamic temperature balance without external control, thereby transforming the originally steep temperature gradient into a gentler temperature distribution curve. The periodic compression and rarefaction effect generated by sound waves propagating in rubber materials causes reciprocating motion at the microscale of the material. This reciprocating motion enhances the convective transfer of heat, overcoming the limitation of pure conductive heat transfer caused by the low thermal conductivity of rubber materials. This allows heat to be transferred more quickly from the outer layer to the inner layer, shortening the time difference between the inner and outer layers reaching the target temperature. Combined with the temperature smoothing effect of phase change materials, this results in improved uniformity of temperature distribution in the thickness direction. This improved uniformity of temperature distribution directly leads to the synchronous occurrence of crosslinking reactions in all parts of the seal, avoiding the contradiction between over-curing of the outer layer and under-curing of the inner layer. Therefore, this invention can solve the technical problem of the difficulty in coordinating and optimizing the temperature gradient control and curing uniformity in the thickness direction during the gradient temperature curing process of rubber seals.

[0066] The following provides a specific embodiment 1 of the present invention, and the specific implementation of each step in this embodiment 1 is described in detail below.

[0067] The specific implementation methods of steps S01, S02, and S04 are the same as those described above, and will not be repeated in detail here.

[0068] The specific implementation of step S03 involves determining the optimal phase transition temperature range parameters for each layer of phase change material and the local temperature gradient value through gradient smoothness analysis. The calculation formula is expressed as follows:

[0069] ;

[0070] In the formula, For the first The local temperature gradient value at each location, in °C / mm; For the first The temperature of each temperature measuring point, in °C, is obtained by measuring an array of thermocouples embedded at different depths inside the rubber sealing sample. The different depths are 1 mm, 3 mm, 5 mm, 7 mm and 9 mm away from the surface of the rubber sealing sample. For the first The temperature at each measuring point is expressed in °C. The distance between adjacent temperature measurement points is in mm, and the empirical value is 1 mm. This is the temperature measurement point number, with a value ranging from 1 to... ,in Total number of temperature measurement points. Standard deviation. The calculation formula is expressed as follows:

[0071] ;

[0072] In the formula, This represents the standard deviation of the local temperature gradient values, in °C / mm. This represents the total number of local temperature gradient values. The average value of all local temperature gradients, in °C / mm, is calculated using the following formula:

[0073] ;

[0074] Calculate the standard deviation at different temperature ranges. Select to make The minimum temperature range is used as the phase change temperature range parameter for each layer of phase change material. The phase change temperature range parameter includes the phase change temperature range parameter for the paraffin layer, the phase change temperature range parameter for the fatty acid layer, and the phase change temperature range parameter for the inorganic salt phase change layer.

[0075] The specific implementation of step S05 involves determining the optimal acoustic wave action conditions, including the median temperature, through acoustic wave parameter optimization experiments. The calculation formula is expressed as follows:

[0076] ;

[0077] In the formula, The median temperature is expressed in °C. This is the upper limit temperature of the phase transition temperature range parameter for inorganic salt phase transition layers, in °C. This represents the lower limit temperature of the phase transition temperature range for inorganic salt phase transition layers, in °C. The ultrasonic combination parameters include a frequency range of 20 to 60 kHz and a sound intensity range of 0.5 to 3.0 W / m². The audible sound wave combination parameters include a frequency range of 100 to 500 Hz and a sound pressure level range of 90 to 120 dB. Each parameter combination is used to prepare a vulcanization test sample.

[0078] The specific implementation of step S06 involves measuring the crosslinking density and detecting bubble defects in the vulcanized test sample. The crosslinking density value is... The calculation was performed using the swelling method combined with the Flory-Rehner equation, and the formula is expressed as follows:

[0079] ;

[0080] In the formula, This is the crosslinking density value, in units of ; This is the volume fraction of rubber at swelling equilibrium, dimensionless; This is the interaction parameter between rubber and solvent, dimensionless, and is assumed to be 0.39 for the nitrile rubber and toluene system; The molar volume of the solvent, in units of For toluene, the default value is 106.3. .in, The calculation formula is expressed as follows:

[0081] ;

[0082] In the formula, The swelling ratio is a dimensionless mass ratio. This is the density of rubber, in units of... The experience value is 1.0; Solvent density, in units of For toluene, it is 0.867. Mass swelling ratio. The calculation formula is expressed as follows:

[0083] ;

[0084] In the formula, The mass of the swollen sample is expressed in g and is obtained by immersing a sample block of the sulfurized test sample in toluene solvent for 72 hours. The mass of the sample before swelling is expressed in grams and is obtained by direct weighing before immersion. During the crosslinking density determination, the different depth positions of the vulcanized test sample are 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm from the surface of the vulcanized test sample.

[0085] The specific implementation of step S07 involves establishing optimal criteria for acoustic parameters and a crosslinking density uniformity coefficient. The calculation formula is expressed as follows:

[0086] ;

[0087] In the formula, is the crosslinking density uniformity coefficient, dimensionless; For the first The crosslinking density value of the layer, in units of The value was obtained by measuring the swelling method. The average crosslinking density value of the 5 layers, in units of ; This represents the layer number, ranging from 1 to 5. Average crosslinking density value. The calculation formula is expressed as follows:

[0088] ;

[0089] bubble defect rate The calculation formula is expressed as follows:

[0090] ;

[0091] In the formula, The bubble defect rate is dimensionless. This refers to the number of bubbles with a diameter greater than 0.1 mm. For the first The volume of each bubble, in units of It was identified using X-ray tomography technology; The total volume of the vulcanization test sample is expressed in units of... ; The bubble number ranges from 1 to... Optimization Criteria Evaluation Function The calculation formula is expressed as follows:

[0092] ;

[0093] In the formula, The evaluation function for the optimal selection criterion is dimensionless; it is selected from the set of qualified acoustic wave parameters. The largest acoustic wave combination parameter is taken as the optimal acoustic wave parameter. The qualified acoustic wave parameter set is the set of acoustic wave combination parameters with a crosslinking density uniformity coefficient greater than 0.92 and a bubble defect rate less than 0.3%.

[0094] The specific implementation of step S08 involves constructing a segmented pressure-temperature coordinated control curve based on the phase change temperature range parameters and optimal acoustic wave parameters, dividing the vulcanization process into an venting stage and a curing stage. During the venting stage, the mold temperature is lowered from room temperature... The temperature rises to the lower limit of the paraffin layer phase transition temperature range parameter. And maintain pressure Duration from 0.8 to 1.2 MPa For 8 to 12 minutes, during the curing stage, the mold temperature is raised to the upper limit of the phase transition temperature range parameters for the inorganic salt phase transition layer. And increase the pressure to within 3 seconds Duration of 8 to 12 MPa It lasts 18 to 25 minutes. Room temperature, in °C, with an empirical value of 20 to 25 °C; This is the lower limit temperature of the paraffin layer phase transition temperature range parameter, in °C. This represents the pressure during the exhaust phase, expressed in MPa. The duration of the exhaust phase, in minutes; This is the upper limit temperature of the phase transition temperature range parameter for inorganic salt phase transition layers, in °C. This refers to the pressure during the curing stage, expressed in MPa. This represents the duration of the curing phase, expressed in minutes. The switching point between the venting and curing phases is determined by monitoring changes in gas flow rate at the mold's venting ports. Decrease to initial gas flow rate When the initial gas flow rate is below 5%, the exhaust is considered basically complete. The average gas flow rate during the first 30 seconds after the start of the exhaust phase, in units of... .

[0095] The specific implementation of step S09 involves establishing a sealing component size prediction and compensation model, simulating the vulcanization process using multiphysics simulation software, and employing the Kamal-Sourour vulcanization kinetic model to describe the crosslinking degree evolution, as expressed in the following formula:

[0096] ;

[0097] In the formula, The degree of crosslinking is dimensionless and ranges from 0 to 1. Time, in seconds; The first reaction rate constant is given by . ; The second reaction rate constant is given in units of . ; This refers to the vulcanization temperature, expressed in °C. The first reaction order is dimensionless and was obtained by experimental fitting using differential scanning calorimetry. The second reaction order is dimensionless and was obtained by experimental fitting using differential scanning calorimetry. The third reaction order is dimensionless and was obtained through differential scanning calorimetry (DSC) experimental fitting. The reaction rate constant follows the Arrhenius temperature dependence, expressed by the following formula:

[0098] ;

[0099] In the formula, For the first The reaction rate constant, in units of _____. ; This is the reaction number, which can be either 1 or 2. For the first Each exponential factor, in units of The results were obtained through experimental fitting using differential scanning calorimetry. For the first The activation energy, in units of J / mol, was obtained by differential scanning calorimetry experimental fitting. This is the gas constant, with a default value of 8.314 J / (mol·K); The absolute temperature is expressed in Kelvin. The strain energy density function of the Mooney-Rivlin hyperelastic constitutive model. The formula is expressed as follows:

[0100] ;

[0101] In the formula, Strain energy density, in MPa; The first Mooney-Rivlin constant, in MPa, is obtained by fitting uniaxial tensile test data; is the second Mooney-Rivlin constant, in MPa, obtained by fitting uniaxial tensile experimental data; The first strain invariant is dimensionless; This is the second strain invariant, dimensionless. Viscoelastic parameter data includes the elastic modulus. Relaxation time Compared to Poisson The results were obtained through uniaxial tensile tests and stress relaxation tests, among which... The unit is MPa. The unit is s. Dimensionless.

[0102] The specific implementation of step S10 involves reverse compensation design of the mold cavity dimensions based on shrinkage distribution data, resulting in the compensated mold cavity dimensions. The calculation formula is expressed as follows:

[0103] ;

[0104] In the formula, The dimensions of the mold cavity after compensation are in mm; The target dimension is in mm. The shrinkage rate at dimensional feature locations is dimensionless and extracted using multiphysics simulation software. The calculation formula is expressed as follows:

[0105] ;

[0106] In the formula, The initial position dimensions of the key feature points are in mm; The final position and dimensions of key feature points after vulcanization, in mm, are obtained through multiphysics simulation software. Compensation amount. The calculation formula is expressed as follows:

[0107] ;

[0108] In the formula, The compensation amount is in mm.

[0109] To better understand and implement this invention, the following is a specific application scenario of this invention, Example 2:

[0110] In the manufacturing of a high-temperature rubber sealing ring, the ring has an outer diameter of 85mm, an inner diameter of 62mm, and a wall thickness of 11.5mm. It needs to maintain its sealing performance under extreme conditions of 180℃ and 1.8MPa pressure. Traditional uniform heating vulcanization methods resulted in a 38% difference in cross-linking density between the inner and outer layers, with over-vulcanization on the surface and under-vulcanization on the interior, leading to a bubble defect rate as high as 1.2% and a product qualification rate of only 67%. The technical team decided to use gradient temperature vulcanization technology to solve this problem.

[0111] First, a multi-layer phase change material is embedded in the inner wall of the mold cavity at a distance of 5mm from the surface of the sealing ring, such as... Figure 1As shown. From the outside in, the layers are paraffin, fatty acid, and inorganic salt phase change layer, each with a thickness of 2.5 mm. The paraffin layer is made of a mixture of n-octadecane and n-eicosane in a mass ratio of 3:7. The fatty acid layer is made of stearic acid with 12% alumina filler added. The inorganic salt phase change layer is made of a mixture of sodium nitrate and potassium nitrate in a mass ratio of 6:4.

[0112] A phase change temperature matching experiment was then conducted. The rubber seal sample was placed in a test mold equipped with multiple layers of phase change material. K-type thermocouples were embedded inside the sample at distances of 1 mm, 3 mm, 5 mm, 7 mm, and 9 mm from the surface, with a temperature measurement accuracy of 0.5℃. Starting from 120℃, the temperature was increased to 200℃ in increments of 5℃, and each temperature point was held for 15 minutes to reach thermal equilibrium. The thermocouple array recorded the temperature distribution data in real time, as shown in Table 1.

[0113] Table 1. Temperature distribution data inside the seal at different heating temperatures (unit: °C)

[0114] Gradient smoothness analysis was performed on the temperature distribution data to calculate the local temperature gradient values ​​between adjacent measuring points. In the temperature range of 135℃ to 150℃, the standard deviation of the local temperature gradient values ​​was 0.82℃ / mm, determining the phase transition temperature range for the paraffin layer to be 132 to 148℃. In the temperature range of 150℃ to 165℃, the standard deviation of the local temperature gradient values ​​was 0.91℃ / mm, determining the phase transition temperature range for the fatty acid layer to be 148 to 166℃. In the temperature range of 165℃ to 180℃, the standard deviation of the local temperature gradient values ​​was 0.88℃ / mm, determining the phase transition temperature range for the inorganic salt phase transition layer to be 166 to 183℃. All three phase transition temperature ranges fall within the corresponding required intervals.

[0115] A piezoelectric ceramic ultrasonic generator and an electrically powered audible sound wave generator are installed on the outer wall of the mold, such as... Figure 2 As shown. The heating temperature was fixed at 174.5℃, which is the median temperature of the phase transition temperature range parameters for the inorganic salt phase transition layer. An orthogonal experimental scheme was designed, with ultrasonic frequencies selected at four levels: 25kHz, 35kHz, 45kHz, and 55kHz, and a sound intensity of 0.8. 1.5 2.2 2.8 Four levels were selected. The audible sound wave frequencies were 150Hz, 250Hz, 350Hz, and 450Hz, and the sound pressure levels were 95dB, 105dB, and 115dB. The vulcanization time was uniformly set to 30 minutes, and a total of 48 vulcanization test samples were prepared.

[0116] Crosslinking density was determined on the vulcanized test samples using the swelling method at distances of 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm from the sample surface. The sample blocks were immersed in toluene solvent for 72 hours, and the mass change before and after swelling was measured. The crosslinking density was calculated using the Flory-Rehner equation. X-ray tomography was used to count bubbles with a diameter greater than 0.1 mm inside the sample, and the ratio of the total bubble volume to the total sample volume was calculated as the bubble defect rate. Figure 3 As shown.

[0117] The crosslinking density uniformity coefficient of each vulcanized test sample was calculated, and the test results of 48 sets of acoustic parameter combinations were statistically analyzed, as shown in Table 2.

[0118] Table 2 Test results of typical acoustic parameter combinations

[0119] Seven sets of acoustic parameters were selected based on a crosslinking density uniformity coefficient greater than 0.92 and a bubble defect rate less than 0.3%. The product of the crosslinking density uniformity coefficient and the reciprocal of the bubble defect rate was calculated. The third set of parameters had the largest product value of 595.6, thus the optimal acoustic parameters were determined to be an ultrasonic frequency of 35 kHz and a sound intensity of 2.2. The audible sound wave frequency is 250Hz and the sound pressure level is 115dB.

[0120] A segmented pressure-temperature coordinated control curve is constructed based on the phase change temperature range parameters and the optimal acoustic wave parameters, such as... Figure 4 As shown. The vulcanization process is divided into an venting stage and a curing stage. In the venting stage, the mold temperature is raised from room temperature (22℃) to the lower limit of the paraffin layer phase transition temperature range parameter (132℃), with a heating rate of 11℃ / min, and the pressure is maintained at 1.0 MPa for 10 minutes. By monitoring the gas flow rate change of the mold venting hole, the initial gas flow rate was 2.3... When the gas flow rate drops to 0.09 Once the venting is deemed basically complete, the curing stage is immediately initiated. The mold temperature is increased to the upper limit of the inorganic salt phase change temperature range parameter, 183℃, at a rate of 28℃ / min. The pressure is increased to 10MPa within 3 seconds and maintained for 22 minutes to complete the crosslinking reaction.

[0121] A model for predicting and compensating the dimensions of the sealing component was established, and uniaxial tensile and stress relaxation tests were conducted on the rubber seal. The tensile rate was 50 mm / min, and stress-strain curves were obtained. The fitted elastic modulus was 8.5 MPa, and Poisson's ratio was 0.487. The stress relaxation test was conducted at 30% strain for 120 minutes, and the relaxation time was 43.2 seconds. Viscoelastic parameters, phase transition temperature range parameters, optimal acoustic parameters, and the segmented pressure-temperature co-control curve were input into multiphysics simulation software.

[0122] The simulation software uses the Kamal-Sourour vulcanization kinetic model to describe the crosslinking degree evolution. Model parameters were obtained through differential scanning calorimetry experiments, with the first reaction order being 1.32, the second reaction order 0.68, and the third reaction order 2.15. The hyperelastic constitutive model adopts the Mooney-Rivlin model, with the first Mooney-Rivlin constant being 1.86 MPa and the second Mooney-Rivlin constant being 0.47 MPa. The equivalent body heat source corresponding to the mold temperature boundary conditions and optimal acoustic parameters is set to 850°C. The simulation time step was 0.2 seconds, the mesh size was 1 mm, and the iterative convergence accuracy was 0.001.

[0123] Simulations depict the coupled evolution of the temperature field, crosslinking degree field, and deformation field during vulcanization, such as... Figure 5 As shown. After vulcanization, the shrinkage rate distribution data of key feature points of the sealing ring were extracted. The shrinkage rate at the outer diameter position was 2.8%, the shrinkage rate at the inner diameter position was 3.2%, and the shrinkage rate in the wall thickness direction was 3.5%. Based on the shrinkage rate distribution data, the mold cavity dimensions were designed with reverse compensation. The target outer diameter of 85mm was divided by 1 and the shrinkage rate of 0.028 was subtracted, resulting in a compensated mold outer diameter of 87.45mm. The target inner diameter of 62mm was divided by 1 and the shrinkage rate of 0.032 was subtracted, resulting in a compensated mold inner diameter of 64.05mm. After machining the compensated mold, actual vulcanization production was carried out according to the segmented pressure and temperature coordinated control curve.

[0124] The manufactured sealing rings, after testing, have an outer diameter of 84.92 mm and an inner diameter of 62.13 mm. The dimensional accuracy meets the tolerance requirements. Figure 6 As shown. The crosslinking density test shows that the surface crosslinking density is... The cross-linking density of the central layer is The crosslinking density uniformity coefficient reached 0.956. The bubble defect rate decreased to 0.14%, and the product qualification rate increased to 96%.

[0125] The advancement of this invention over traditional uniform heating vulcanization methods lies in establishing a gradient temperature field from the outside in through multiple layers of phase change material, matching the vulcanization rates of the surface and inner layers of the seal. The paraffin layer stores and slowly releases heat at low temperatures, the fatty acid layer regulates heat flow at medium temperatures, and the inorganic salt phase change layer stabilizes the inner layer temperature at high temperatures. The synergistic effect of these three layers achieves a smooth temperature gradient distribution. Acoustic energy promotes the movement of rubber molecular chains and gas diffusion; high-frequency ultrasonic vibration breaks up bubble aggregation; and low-frequency resonance of audible sound accelerates the expulsion of volatiles. This dual-frequency synergy significantly reduces bubble defects. Segmented pressure-temperature control first ensures sufficient venting under low pressure, followed by rapid curing under high pressure and high temperature, avoiding internal defects caused by gas encapsulation and pressure impact in traditional methods. Multiphysics simulation couples heat conduction, chemical reaction, and mechanical deformation, accurately predicting shrinkage behavior. Reverse compensation design eliminates dimensional errors, achieving high-precision vulcanization molding.

[0126] It should be noted that the variables involved in this invention are explained in detail in Table 3.

[0127] Table 3. Variable Explanation Table

[0128] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for gradient temperature vulcanization of rubber seals, characterized in that, A multilayer phase change material layer is embedded in the inner wall of the mold cavity. A phase change temperature matching experiment is conducted on the multilayer phase change material layer to record temperature distribution data. Gradient smoothness analysis is performed on the temperature distribution data to obtain the phase change temperature range parameters. Based on the phase change temperature range parameters, it is determined whether the preset range is met and whether to repeat the experiment. A vulcanization test sample is prepared by conducting an acoustic parameter optimization experiment. The crosslinking density and bubble defect detection are performed on the vulcanization test sample to calculate the crosslinking density uniformity coefficient and bubble defect rate. Based on the crosslinking density uniformity coefficient and bubble defect rate, the optimal acoustic parameters are screened. A segmented pressure-temperature co-control curve is constructed based on the phase change temperature range parameters and the optimal acoustic parameters. A sealing component size prediction and compensation model is established to obtain viscoelastic parameter data. Shrinkage rate distribution data is extracted through multiphysics simulation. The mold cavity size is designed with reverse compensation based on the shrinkage rate distribution data.

2. The method for gradient temperature vulcanization of rubber seals according to claim 1, characterized in that, The multilayer phase change material consists of a paraffin layer, a fatty acid layer, and an inorganic salt phase change layer, arranged from the outside in.

3. The method for gradient temperature vulcanization of rubber seals according to claim 2, characterized in that, The phase change temperature matching experiment involves placing a rubber seal sample into a test mold equipped with multiple layers of phase change material, and gradually increasing the temperature from the initial temperature to the final temperature. Each temperature point is held for a preset duration, and the temperature distribution data is recorded by an array of thermocouples embedded at different depths inside the rubber seal sample.

4. The method for gradient temperature vulcanization of rubber seals according to claim 3, characterized in that, Gradient smoothness analysis specifically involves calculating the ratio of the temperature difference between adjacent measuring points along the thickness direction of the rubber seal sample to the distance as the local temperature gradient value, statistically analyzing the standard deviation of the local temperature gradient value under each temperature range, and selecting the temperature range that minimizes the standard deviation as the phase change temperature range parameter for each phase change material layer.

5. The method for gradient temperature vulcanization of rubber seals according to claim 4, characterized in that, To determine whether the preset range is met, specifically, it is determined whether the phase change temperature range parameters of the paraffin layer, the fatty acid layer, and the inorganic salt phase change layer are within the first preset range, the second preset range, and the third preset range. If all three phase change temperature range parameters are within their respective ranges, an acoustic parameter optimization experiment is performed. If any one of the three phase change temperature range parameters is not within its respective range, the material ratio of the multilayer phase change material layer is adjusted, and the phase change temperature matching experiment is performed again.

6. The method for gradient temperature vulcanization of rubber seals according to claim 5, characterized in that, The acoustic parameter optimization experiment involved fixing the heating temperature to the median of the inorganic salt phase change temperature range parameters, applying ultrasonic combination parameters with different frequencies and sound intensities, as well as audible acoustic wave combination parameters with different frequencies and sound pressure levels, and setting the vulcanization time to a preset duration. A vulcanization test sample was prepared for each parameter combination.

7. The method for gradient temperature vulcanization of rubber seals according to claim 6, characterized in that, The crosslinking density determination specifically involves using the swelling method to measure the crosslinking density at different depths of the vulcanized test sample.

8. The method for gradient temperature vulcanization of rubber seals according to claim 7, characterized in that, Bubble defect detection specifically involves using X-ray tomography to statistically analyze the number and size distribution of bubbles inside the sulfurized test sample.

9. The method for gradient temperature vulcanization of rubber seals according to claim 8, characterized in that, The crosslinking density uniformity coefficient is specifically calculated by dividing the vulcanized test sample into multiple layers along the thickness direction, measuring the crosslinking density value of each layer, calculating the average crosslinking density value of the multiple layers, summing the absolute values ​​of the differences between the crosslinking density values ​​of each layer and the average crosslinking density value, dividing the sum by the number of layers of the average crosslinking density value to obtain the deviation quotient, and subtracting the deviation quotient from 1 to obtain the crosslinking density uniformity coefficient.

10. The method for gradient temperature vulcanization of rubber seals according to claim 9, characterized in that, The bubble defect rate is specifically determined by obtaining the internal three-dimensional structural data of the sulfurized test sample through X-ray tomography, identifying bubbles with a diameter greater than a preset threshold, and calculating the ratio of the total volume of all bubbles to the total volume of the sulfurized test sample as the bubble defect rate.

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