Rubber storage bag preparation method capable of shortening vulcanization preheating time

Abstract

The invention provides a rubber storage bag preparation method capable of shortening vulcanization preheating time. The method comprises the following steps: arranging temperature measuring points on a mold cavity and the surface of a mold, carrying out a temperature rise test to obtain a time-temperature curve, and carrying out inversion on a convective heat transfer coefficient; establishing a heat transfer finite element model based on a mold pattern and material thermophysical properties, coupling vulcanization dynamics, calculating a temperature field and an equivalent vulcanization time field, and determining temperature rise time; vulcanization heating is divided into a preheating stage and a heat preservation stage, the preheating stage is set to be higher than the target vulcanization temperature, and the target vulcanization temperature is reduced and heat preservation is conducted when the temperature rise time is up; the heat preservation time is determined by subtracting the heating time from the equivalent positive vulcanization time, and cooling and demolding are performed after completion. The method shortens the total vulcanization time and improves the efficiency on the premise of ensuring the vulcanization quality.

Description

Technical Field

[0001] The invention belongs to the technical field of rubber preparation, and in particular relates to a method for preparing a rubber storage bag capable of shortening the vulcanization preheating time. Background Art

[0002] Numerical simulation and process control of rubber bladder vulcanization process belong to the field of rubber product molding processing and process modeling, and are mainly used in the manufacture of bladders under working conditions such as propellant storage, attitude adjustment and orbit correction in aerospace vehicles.

[0003] In actual production, rubber storage bags generally face problems such as long vulcanization cycle, uneven distribution of vulcanization degree, and inconsistent surface color. Although the commonly used full-stage constant temperature vulcanization process has stable temperature, the preheating and heating process takes a long time, and the temperature field of the mold cavity is unevenly distributed, making it difficult to quantify the vulcanization degree of various parts of the product.

[0004] The industry generally expects to achieve shorter preheating and vulcanization times, more uniform vulcanization degree distribution, and more controllable energy consumption levels while ensuring product performance indicators, while improving the repeatability and accuracy of process parameter settings.

[0005] There are two main approaches to existing technologies: one is to continue traditional constant-temperature vulcanization and adjust the heating time and mold structure through experience to improve heat transfer efficiency; the other is to use numerical simulation methods to simulate the mold heat transfer process and rubber vulcanization reaction, predict the cavity temperature and vulcanization process, and thus provide a basis for setting process parameters.

[0006] The above methods still have common limitations: the empirical method relies on on-site trial and error, and is inefficient and reproducible; although numerical simulation can provide predictions of temperature and degree of vulcanization, there are still uncertainties in parameter acquisition, model calibration and linkage with actual processes, which leads to deviations between simulation results and on-site control, making it difficult to directly convert them into operational temperature control strategies.

[0007] Therefore, it is still necessary to propose a process optimization path that can shorten the preheating stage while constraining the maximum temperature of the mold, take into account vulcanization uniformity and energy consumption control, and realize effective coupling between the simulation calculation results and the actual temperature control process. Summary of the Invention

[0008] The invention provides a method for preparing a rubber storage bag with shortened vulcanization preheating time, which is used to solve the technical problems of low vulcanization preheating efficiency and long total vulcanization time in the prior art.

[0009] In order to achieve the above object, the technical solution of the present invention is as follows:

[0010] A method for preparing a rubber sac capable of shortening vulcanization preheating time comprises:

[0011] Arrange temperature measuring points on the mold cavity and mold surface, conduct temperature rise test to obtain time-temperature curve, and determine the convective heat transfer coefficient based on it;

[0012] Based on the mold drawing and material thermal properties, a heat transfer finite element model is established, coupled with the vulcanization dynamics, to calculate the cavity temperature field and equivalent vulcanization time field;

[0013] According to the calculation results, the heating time of the heating stage is determined to be the moment when the highest temperature point of the cavity approaches the target vulcanization temperature;

[0014] The vulcanization heating process is divided into a preheating stage and a holding stage. In the preheating stage, the oven temperature is set higher than the target vulcanization temperature, and the glue-filled mold is placed in the oven for heating. When the cavity temperature reaches the temperature corresponding to the heating time, the oven door is opened or cooling measures are taken to reduce the oven temperature to the target vulcanization temperature. In the holding stage, the oven temperature is maintained at the target vulcanization temperature and heating is continued until the vulcanization is completed.

[0015] The holding time in the vulcanization stage is determined by subtracting the heating time from the equivalent positive vulcanization time, followed by cooling and demoulding.

[0016] Furthermore, the convection heat transfer coefficient is obtained by performing a temperature rise experiment in the preheated oven to obtain the cavity temperature rise curve and using the inversion method.

[0017] Furthermore, the equivalent vulcanization time is used to calculate the vulcanization rate constant based on the Arrhenius formula, which is:

[0018]

[0019] Wherein, A is the pre-exponential factor, E is the activation energy, R is the gas constant, and T is the absolute temperature; the activation energy E is obtained by fitting the equivalent positive curing time data at different temperatures.

[0020] Furthermore, the equivalent vulcanization time is calculated by calling a custom calculation unit during the finite element analysis process and recorded as a variable to characterize the degree of vulcanization.

[0021] Furthermore, the oven temperature in the preheating stage is 10°C to 20°C higher than the target vulcanization temperature; when the temperature difference between the maximum cavity temperature and the target vulcanization temperature does not exceed ±1°C, the oven door is opened and combined with forced air circulation to cool down, so that the oven temperature is reduced to the target vulcanization temperature within 3 to 8 minutes, and vulcanization is continued at this temperature.

[0022] Furthermore, the heating time is the length of time from the start of heating to the temperature difference between the maximum temperature of the cavity and the target vulcanization temperature not exceeding ±1°C, and the temperature difference judgment is calculated based on the temperature sampling results at least once per minute; the equivalent positive vulcanization time is the time value obtained by the equivalent vulcanization time calculation method.

[0023] Furthermore, the process parameters are determined through optimization to minimize the total vulcanization time, and the initial oven temperature and cooling rate are adjusted under the condition that the maximum temperature of the cavity does not exceed the target vulcanization temperature and meets the equipment performance range.

[0024] Furthermore, when establishing the heat transfer model, the initial temperature is used as the initial condition, the convective heat transfer between the mold surface and the air is used as the boundary condition, and the density, thermal conductivity and specific heat capacity of the metal and rubber are input as material parameters; the convective heat transfer coefficient is calibrated during the model calculation process using the inversion method.

[0025] Furthermore, the activation energy E is obtained by fitting the equivalent positive vulcanization time data of the rubber at 160° C., 165° C., 170° C. and 175° C.

[0026] Furthermore, it is characterized in that the convective heat transfer at the heat transfer boundary satisfies Newton's cooling law:

[0027] q=h×ΔT

[0028] Where q is the heat flux per unit area, h is the convective heat transfer coefficient, and ΔT is the temperature difference.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] Compared with the existing technology, the present invention divides the vulcanization process into two stages: preheating and insulation. By arranging temperature measuring points on the mold cavity and the mold surface to obtain a temperature rise curve, establishing a heat transfer finite element model coupled with vulcanization dynamics, and optimizing the heating and temperature control strategy, the present invention divides the vulcanization process into two stages: preheating and insulation. In the preheating stage, the temperature is quickly increased by a set temperature higher than the target vulcanization temperature. When the cavity temperature approaches the target value, the temperature is promptly lowered to the target vulcanization temperature and maintained at insulation, thereby effectively shortening the time of the heating stage and reducing the total vulcanization time. This method improves production efficiency and reduces energy consumption while ensuring vulcanization quality, and is suitable for the industrial production of rubber storage bags of various specifications.

[0031] Of course, the implementation of the various technical solutions of the present invention does not necessarily require achieving all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying any creative work, they can also obtain drawings of other embodiments based on these drawings.

[0033] Figure 1It is the rubber storage bag product in the embodiment;

[0034] Figure 2 It is the pre-buried position of the thermocouple in the temperature measurement experiment in the embodiment;

[0035] Figure 3 The temperature rise curve inside the cavity in the embodiment;

[0036] Figure 4 The temperature distribution in the mold at 9000s in the embodiment;

[0037] Figure 5 is the equivalent vulcanization time distribution in the embodiment;

[0038] Figure 6 This is the temperature rise curve of the mold preheating stage in the embodiment;

[0039] Figure 7 The temperature rise curve of the highest point of the cavity temperature predicted in the embodiment;

[0040] Figure 8 The temperature distribution in the mold at 1700s in the embodiment;

[0041] Figure 9 The temperature rise curve of the highest temperature point in the embodiment;

[0042] Figure 10 This is a graph showing the equivalent vulcanization time at the highest temperature point in the embodiment;

[0043] Figure 11 The sulfide degree distribution at 4100s in the embodiment;

[0044] Figure 12 FIG. 2 is a process route diagram in the embodiment. DETAILED DESCRIPTION

[0045] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present disclosure.

[0046] In the description of this patent, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings. They are only for the convenience of describing this patent and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on this patent.

[0047] In the description of this patent, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," "connected," and "set" should be understood in a broad sense. For example, they can refer to fixed connection or set, detachable connection or set, or integral connection or set. Those skilled in the art can understand the specific meanings of the above terms in this patent based on the specific circumstances. The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0048] Embodiment 1:

[0049] A method for preparing a rubber bladder that shortens the vulcanization preheating time involves pre-embedding thermocouples in the mold cavity and on the mold surface. The mold is not glued, and a temperature rise test is performed after preheating in the oven to obtain the time-temperature curves of the cavity interior and the upper and lower layers of the oven. Based on this curve, the inversion method is used to determine the convective heat transfer coefficient of the mold surface, and this coefficient is used to calibrate the heat transfer model. A heat transfer finite element model is established based on the mold drawing. The initial condition is room temperature, the boundary is the convective heat transfer between the mold surface and the air, and the material parameters are the density, thermal conductivity, and specific heat capacity of the metal and rubber. The average oven temperature history obtained from the temperature rise test is applied to the model, and the cavity temperature field and the temperature rise curve of the highest temperature point are calculated. Based on this, the "heating time" is determined as the moment when the highest temperature point in the cavity approaches the target vulcanization temperature.

[0050] The degree of vulcanization is characterized by the "equivalent vulcanization time" and the rate constant is calculated based on the Arrhenius formula.

[0051]

[0052] Wherein, A is the pre-exponential factor, E is the activation energy, R is the gas constant, and T is the absolute temperature; the activation energy E is obtained by fitting the equivalent positive curing time data at different temperatures.

[0053] In order to facilitate the equivalent comparison under different temperature conditions, the equivalent vulcanization time conversion relationship is adopted: if the vulcanization time at temperature T1 is t1 and the equivalent time at temperature T2 is t2, then

[0054]

[0055] Since the sulfurization reaction is a first-order reaction, the reaction rate is proportional to the concentration of the reactants.

[0056] Right now Therefore, we have:

[0057]

[0058] During the heat transfer finite element analysis process, the equivalent vulcanization time field is calculated and recorded in real time through a custom calculation unit to determine the vulcanization degree of each part.

[0059] The convection heat transfer boundary satisfies Newton's cooling law

[0060] q=h×ΔT=Q / S

[0061] Where q is the heat flux per unit area (w / m 2 ), h is the convective heat transfer coefficient [w / (m 2 ·k)], ΔT is the temperature difference (K), Q is the heat (W), S is the area (m 2 )

[0062] The convective heat transfer coefficient obtained by inversion from the temperature rise test is used to drive the model to replicate the measured temperature rise process and provide the temperature evolution and equivalent vulcanization time evolution curves of key nodes.

[0063] A certain type of rubber bladder was selected as the object. The product consists of a bladder nozzle with an O-shaped rubber ring structure and a bladder body with multiple melon-shaped segments molded. The rubber material is M301-1 and the bladder is formed by vulcanization process. Figure 1 .

[0064] To obtain the boundary and physical property parameters required for the heat transfer model, thermocouples were embedded in the experimental mold cavity and distributed on the mold surface. After preheating in the oven, a temperature increase experiment was conducted at 170°C for 9000s to obtain the cavity time-temperature curve. Figure 2 and Figure 3 Based on this curve, an inversion model is established to calculate the convective heat transfer coefficient of the mold surface, and the temperature distribution at 9000s is obtained by reproducing the experiment with the coefficient. Figure 4 ; In this embodiment, the convective heat transfer coefficient is 14W / (m2·K).

[0065] A heat transfer finite element model was established based on the mold drawing. The initial condition was room temperature (25°C), and the boundary condition was convection heat transfer between the mold surface and the air (coefficient 14W / (m2·K)). During the heating phase, the average temperature measured in the oven was used as the boundary temperature input for the model. Calculations show that the heating time required for the highest cavity temperature point to reach the target vulcanization temperature of 170°C is approximately 1700 seconds. The corresponding temperature field is shown in Figure 2. Figure 8 ; Based on this, 1700s is taken as the "heating time".

[0066] The Arrhenius relation was used for the vulcanization kinetics. The vulcanization times t90 were obtained from vulcanization tests at 160 / 165 / 170 / 175°C, which were 64.44 / 54.49 / 37.51 / 32.69 min, respectively. Based on this, the activation energy E = 72,969.3 J / mol was fitted. This activation energy and the pre-exponential factor were substituted into the Arrhenius equation.

[0067]

[0068] Calculate the vulcanization rate constant, which is used for the integral and field distribution calculation of the equivalent vulcanization time. Figure 8 The “equivalent positive vulcanization time” is 1.0 as the positive vulcanization criterion.

[0069] Table 1 Curing time (t90) at different temperatures

[0070]

[0071] The heat transfer boundary satisfies Newton's cooling law q = h × ΔT, where q is the heat flux density per unit area, h is the convection heat transfer coefficient, and ΔT is the temperature difference. The h obtained by the above inversion is used to calculate the boundary heat transfer.

[0072] The production is carried out according to the step temperature control process of "preheating-cooling-insulation": first preheat the oven to 300℃ and keep the temperature constant for 5 minutes; open the oven door, put the glue-filled mold in and close the oven within 90s to heat it up; when the calculated heating time (1700s±30s) is reached, turn off the heater and open the oven door to reduce the oven temperature to the target vulcanization temperature of 170℃, then close the oven and adjust the set temperature to 170℃ to enter insulation. The equivalent positive vulcanization time curve shows that it takes about 4100s for the highest temperature point to reach 1.0. After deducting the 1700s heating stage, the insulation stage takes 2400s±30s; then cool and demould. The temperature / equivalent vulcanization time evolution corresponding to this process can be seen in Figures 6-11 , process route see Figure 12 .

[0073] Under the above conditions, a prototype was trial-produced to produce a bladder model ZXN131. The total vulcanization time was reduced from 120 minutes in the original process to 71.5 minutes, a 40.4% reduction in total time. The product performance met all indicators.

[0074] Example 2:

[0075] The method of Example 1 was applied to another mold with different structural dimensions and heat capacity. The temperature measurement points were re-arranged and the temperature ramp test was performed to obtain a new time-temperature curve. The convective heat transfer coefficient was inverted using the same method, and the corresponding initial conditions and material thermophysical properties were input into the heat transfer finite element model. The new activation energy E was fitted using the vulcanization experimental data at different temperatures, and the vulcanization rate constant was substituted into the Arrhenius equation to calculate the vulcanization rate constant, resulting in a new equivalent vulcanization time field. Based on the calculated results, the process parameters were optimized, determining the temperature difference between the preheating oven temperature and the target vulcanization temperature, as well as the cooling rate. The total vulcanization time was minimized while ensuring that the maximum cavity temperature did not exceed the target vulcanization temperature and the equipment performance allowed. The optimized step temperature control curve was implemented in actual production. The resulting rubber bladder was tested to meet the design requirements, with a further reduction in total vulcanization time and energy consumption compared to the baseline process.

[0076] The above examples are used to illustrate the present invention, which are only used to help understand the present invention and are not intended to limit the present invention. Those skilled in the art can make several simple deductions, modifications or substitutions based on the concept of the present invention.

Claims

1. A method for preparing a rubber storage bag with a shortened vulcanization preheating time, characterized in that: include: Arrange temperature measuring points on the mold cavity and mold surface, conduct temperature rise test to obtain time-temperature curve, and determine the convective heat transfer coefficient based on it; Based on the mold drawing and material thermal properties, a heat transfer finite element model is established, coupled with the vulcanization dynamics, to calculate the cavity temperature field and equivalent vulcanization time field; According to the calculation results, the heating time of the heating stage is determined to be the moment when the highest temperature point of the cavity approaches the target vulcanization temperature; The vulcanization heating process is divided into a preheating stage and a holding stage. In the preheating stage, the oven temperature is set higher than the target vulcanization temperature, and the glue-filled mold is placed in the oven for heating. When the cavity temperature reaches the temperature corresponding to the heating time, the oven door is opened or cooling measures are taken to reduce the oven temperature to the target vulcanization temperature. In the holding stage, the oven temperature is maintained at the target vulcanization temperature and heating is continued until the vulcanization is completed. The holding time in the vulcanization stage is determined by subtracting the heating time from the equivalent positive vulcanization time, followed by cooling and demoulding.

2. The method for preparing a rubber storage bag with shortened vulcanization preheating time according to claim 1, characterized in that: The convection heat transfer coefficient is obtained by performing a temperature rise experiment in a preheated oven to obtain the cavity temperature rise curve and then using the inversion method.

3. The method for preparing a rubber storage bag with shortened vulcanization preheating time according to claim 1 or 2, characterized in that: The equivalent cure time is calculated based on the Arrhenius formula for the cure rate constant, which is: Wherein, A is the pre-exponential factor, E is the activation energy, R is the gas constant, and T is the absolute temperature; the activation energy E is obtained by fitting the equivalent positive curing time data at different temperatures.

4. The method for preparing a rubber storage bag with shortened vulcanization preheating time according to claim 3, characterized in that: The equivalent vulcanization time is calculated by calling a custom calculation unit during the finite element analysis process and recorded as a variable to characterize the degree of vulcanization.

5. The method for preparing a rubber storage bag with shortened vulcanization preheating time according to claim 1, characterized in that: The oven temperature in the preheating stage is 10℃~20℃ higher than the target vulcanization temperature; when the temperature difference between the maximum cavity temperature and the target vulcanization temperature does not exceed ±1℃, the oven door is opened and combined with forced air circulation to cool down, so that the oven temperature is reduced to the target vulcanization temperature within 3~8 minutes, and vulcanization is continued at this temperature.

6. The method for preparing a rubber storage bag with shortened vulcanization preheating time according to claim 1, characterized in that: The heating time is the time from the start of heating to the time when the temperature difference between the maximum temperature of the cavity and the target vulcanization temperature does not exceed ±1°C. The temperature difference is determined based on the temperature sampling results at least once per minute. The equivalent positive vulcanization time is the time value obtained by the equivalent vulcanization time calculation method.

7. The method for preparing a rubber storage bag with shortened vulcanization preheating time according to claim 1, characterized in that: The process parameters are determined through optimization to minimize the total vulcanization time. The initial oven temperature and cooling rate are adjusted while ensuring that the maximum temperature of the cavity does not exceed the target vulcanization temperature and meets the equipment performance range.

8. The method for preparing a rubber storage bag with shortened vulcanization preheating time according to claim 1, characterized in that: When establishing the heat transfer model, the initial temperature is used as the initial condition, the convection heat transfer between the mold surface and the air is used as the boundary condition, and the density, thermal conductivity and specific heat capacity of the metal and rubber are input as material parameters; The convective heat transfer coefficient is calibrated during the model calculation process using the inversion method.

9. The method for preparing a rubber storage bag with shortened vulcanization preheating time according to claim 3, characterized in that: The activation energy E is obtained by fitting the equivalent positive vulcanization time data of the rubber at 160° C., 165° C., 170° C. and 175° C.

10. The method for preparing a rubber storage bag with shortened vulcanization preheating time according to claim 1, characterized in that: The convective heat transfer at the heat transfer boundary satisfies Newton's law of cooling: q=h×ΔT Where q is the heat flux per unit area, h is the convective heat transfer coefficient, and ΔT is the temperature difference.

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