Simulation and experimental study on non-isothermal vulcanization process of thick-walled rubber products

doi:10.11949/0438-1157.20201227

Abstract

Abstract:

The vulcanization reaction process of rubber plays a decisive role in the final performance of the product, and the vulcanization of thick-walled rubber is a typical non-isothermal vulcanization process. It is usually difficult to directly determine the best vulcanization process of the product through the isothermal vulcanization curve measured by the experiment. Therefore, it is of great significance to study the vulcanization process of rubber molding by using numerical simulation technology.In view of this, based on the traditional cure kinetic modeling, an improved vulcanization model with higher accuracy was constructed by introducing initial vulcanization parameters and treating the order of reaction as a quadratic function of temperature. At the same time, the thermophysical parameters of rubber were regarded as a function of vulcanization degree and temperature. UDF(user defined function) subroutines were developed based on C language and FLUENT pre-defined macros, which realized the coupled simulation of heat transfer and vulcanization in the vulcanization process of rubber products. Aiming at the flat vulcanization molding of typical thick-walled rubber products, the reliability of the coupling algorithm for temperature field and vulcanization simulations is verified through temperature measurement experiments, product stretching of different vulcanization degrees, DSC testing and cross-sectional morphology observation. This method is more practical to guide the vulcanization molding of thick-walled and complex-structure rubber products.

Key words: rubber, vulcanization reaction, numerical simulation, kinetic modeling, coupled simulation

摘要：

橡胶的硫化反应过程对制品的最终性能起决定性作用，而厚壁橡胶的硫化是典型的非等温硫化过程，通常难以通过实验测得的等温硫化曲线来直接确定制品的最佳硫化工艺。因此，利用数值模拟技术来研究硫化过程对于橡胶的成型加工具有重要意义。鉴于此，基于传统硫化动力学模型，通过引入初始硫化参数并将反应级数视为温度的二次函数，构建了精度更高的改进硫化模型，同时将橡胶热物性参数视为硫化度和温度的函数，基于C语言和FLUENT预定义宏编写了UDF子程序，实现了橡胶制品硫化过程传热与硫化的耦合模拟。针对典型厚壁橡胶制品的平板硫化成型，通过测温实验和不同硫化程度制品拉伸、DSC测试与断面形貌观测，验证了耦合算法对温度场和硫化度模拟的可靠性。该方法对指导厚壁且结构复杂橡胶制品硫化成型更具实际意义。

关键词: 橡胶, 硫化反应, 数值模拟, 动力学模型, 耦合模拟

CLC Number:

TQ 330.6

ZHANG Mengfei, ZHANG Ling, LI Xiaochuang, ZU Yunqiu, HUANG Ming, SHI Xianzhang, LIU Chuntai. Simulation and experimental study on non-isothermal vulcanization process of thick-walled rubber products[J]. CIESC Journal, 2021, 72(4): 2065-2075.

张梦飞, 张玲, 李晓闯, 祖韵秋, 黄明, 石宪章, 刘春太. 厚壁橡胶制品非等温硫化过程模拟与实验研究[J]. 化工学报, 2021, 72(4): 2065-2075.

Figures/Tables 18

Fig.1 State-of-cure vs. time at different temperatures

Fig.2 The average relative error for K-S model

Fig.3 Temperature sensitivity experiment of n and corresponding error

Fig.4 Comparison of average relative error between K-S model and improved model

Table 1 The parameters of the improved model

t₀/s	T₀/K	E/(J·mol^-1)	k₀	a₂	b₂	c
5.94×10^-8	9238.76	2.60×10⁵	2.25×10²⁷	2.59×10^-7	-7.81×10^-3	5.23

Fig.5 Comparison of K-S model and improved model with experimental data

Fig.6 Flow chart for coupling calculation of rubber vulcanization and heat transfer

Fig.7 CAD models of product and mold

Fig.8 Grid distribution in the computational domains

Table 2 Specific heat capacity of rubber at different temperatures

温度/℃	比热容/(J·kg^-1·K^-1)
40	1419
60	1490
80	1520
100	1501
120	1477
140	1486
160	1481

Fig.9 The temperature and state-of-cure distribution at various time

Fig.10 Temperature and state-of-cure curves at the center point inside the rubber article

Fig.11 Equipment used for vulcanization temperature measurement experiment

Fig.12 Comparison between experimentally measured temperature profiles with predicted values

Fig.13 Temperature and state-of-cure curves at the center point inside the rubber article

Fig.14 Stress-strain curves

Fig.15 Vulcanization enthalpy curves

Fig.16 Tensile section morphology of rubber samples under different vulcanization heating time

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