Numerical Simulation And Experimental Study On Non-isothermal Vulcanization Of Thick-walled Rubber Products

Vulcanization is the last process in the production of rubber products,and reasonable vulcanization time is one of the important factors that determine the quality of the product.Due to the poor conductor properties of the rubber material,the temperature history of the thick-walled products at different positions during the vulcanization process is different,resulting in different vulcanization degree in different positions at the same time.The difference becomes more obvious with the increase in thickness,which is a typical non-isothermal vulcanization process.It is usually difficult to directly determine the best vulcanization process conditions through the isothermal vulcanization curve measured by experiment.The traditional method of determining the vulcanization process for thick-walled products mainly relies on experience,and there are problems such as low accuracy and multiple mold trials.Therefore,the use of numerical simulation technology to study the vulcanization process is of great significance to the molding process of rubber.The reliability of the vulcanization simulation mainly depends on the accurate prediction of the temperature field and the high-precision vulcanization kinetic model.In this context,for the flat vulcanization molding of a typical thick-walled product,the thesis has carried out the numerical simulation and experimental research of the non-isothermal vulcanization process for rubber products,and is committed to developing a numerical prediction method for the coupled simulation of rubber heat transfer and vulcanization.Accurate prediction of temperature field and vulcanization degree during vulcanization of thick-walled rubber products.The main research work is as follows:(1)Based on the vulcanization experimental data of a certain naval nitrile rubber at different temperature,the traditional Kamal-Sourour vulcanization kinetics model was evaluated.The results show that the model has insufficient ability to predict the initial stage of vulcanization reaction and large error in characterizing vulcanization behavior in a wide temperature range.Based on this,the paper improved the vulcanization model by introducing initial vulcanization parameter and treating the reaction order as a quadratic function of temperature,and constructed an improved vulcanization model with higher accuracy.The average relative error decreased from8.68%~16.19% to 3.02%~6.17%.(2)In order to improve the simulation accuracy of the temperature field,the heat source term of the thermal conductivity differential equation and the rubber thermophysical parameters were regarded as the correlation function of vulcanization degree and temperature,and the coupled calculation equation of heat transfer and vulcanization was established.UDF subroutines were written based on C language and software pre-defined macro commands,and FLUENT was re-developed to realize the coupled calculation of heat transfer and vulcanization.(3)Based on the coupled simulation method of heat transfer and vulcanization,the simulation and verification of temperature field and vulcanization degree for typical thick-walled rubber products during vulcanization were carried out.The temperature field simulation shows that the temperature of the rubber compound close to the mold wall quickly reaches 160 ?,but when heated to 1200 s,the core of the product is less than 114 ?,and there is an obvious temperature gradient,which is a typical nonisothermal process.The vulcanization molding experiment of the product was carried out,and the temperature change history of typical positions inside the product was tested with thermocouples.The comparison between simulation and experiment shows that the predicted temperature of the simulation is in good agreement with the experimental value,which proves that the heat transfer and vulcanization coupling calculation method can accurately predict the temperature distribution of the rubber vulcanization process.(4)The vulcanization simulation study under different vulcanization heating times for thick-walled products was carried out.The results show that the temperature gradient distribution leads to the gradient distribution of the vulcanization degree.The material will continue to vulcanize to the process requirements under the effect of waste heat.If the vulcanization time is too short,it will lead to undercuring in the core of the product,and too long vulcanization heating time will lead to overcuring.Based on the same process conditions as the simulation,products with different vulcanization heating time were trial-produced,and the accuracy of the vulcanization simulation was quantitatively verified through experimental methods such as tensile testing,DSC testing,and micro-section observation.(5)Using the numerical prediction method proposed in the paper,the simulation study of a thick-walled porous rubber product for a naval vessel was carried out,and the best vulcanization heating process was determined.The vulcanization molding of the product was successfully guided to ensure that the entire product has a higher vulcanization degree,and increased production efficiency.The paper constructs a more accurate rubber vulcanization kinetic model,regards the thermal physical parameters of rubber as a function of vulcanization degree and temperature,and realizes the coupled simulation of heat transfer and vulcanization in the vulcanization process for rubber products.The thesis has enriched and developed rubber vulcanization molding simulation theory,which is of great significance for guiding the vulcanization molding of thick-walled and complex rubber products.