| As a leading chemical process in the rubber products production, vulcanization is the last process of rubber production which turns unvulcanized rubbers to vulcanized rubbers and gives the vulcanized rubbers many kinds of useful properties to make rubbers becoming extensive used engineering materials. There are shortcomings in tire vulcanization technology such as the vulcanization degrees of tire are uneven. It is meaningful research improving the vulcanization technology, exploring the vulcanization mechanism, ensuring the change rule of rubbers’ thermo physical parameters during vulcanization and exploring the rule of heat absorption and release of cross-linking reaction are necessary to figure out this problem. Much work on the vulcanization medium and vulcanization equipments to improve the properties of tire. This project takes11.00R20S815tire as the object of study, determine vulcanization kinetic parameters of nine kinds of rubber, experimentally studied thermal parameters changing with temperature, and measured temperature in curing process. Based on which, tire curing process was simulated. The main conclusions are as the follows.(1) The thermal diffusion coefficients and the specific heat and the heat conductivity coefficients of rubbers that used in11.00R20S815all-steel-radial tire are measured using the LFA447laser thermal analyzer and the differential scanning calorimeter under conditions of normal pressure and2.5Mpa. The variation trend of the thermo physical parameters of the rubbers in these two conditions are the same which means hat the thermal diffusion coefficient of rubbers is decreased along with the rising of temperature. The specific heat and heat conductivity coefficients of rubbers are rose with the rise of temperature, and the relationship between temperature and the thermo physical parameters of rubbers is almost linear. The vulcanization pressure has great influence on the thermal diffusion coefficient and heat conductivity coefficients of rubbers compared to the specific heat of rubbers. The relationship between temperature and the thermo physical parameters of rubbers in the condition of2.5Mpa is linear either. The numerical simulation results based on thermo physical parameters that calculated in the normal pressure condition are more similar to that of tire vulcanization temperature measuring experiment.(2) There is a endothermic peak in the HTME rubber with the temperature interval between78.75℃to102.94℃with the peak value95.49℃and the caloric receptivity-35.3mJ. The exothermic peak is appeared between173.27℃—201.23℃and the peak value is got at184.28℃, the heat release value is81.9mJ, the HTME releases46.6mJ calories in the whole process, so the reaction of rubbers that occurred during the vulcanization is a exothermic reaction. The relationship between the cross-linking reaction endothermic and exothermic values and temperature is measured and fitted.(3) The torsion variation curves of nine kinds of rubbers that used in tire is measured using the moving die rheometer; the vulcanization kinetic parameters of charred phase, heat curing phase and flat curing phase of rubber vulcanization are calculated. The results show that the charred phase of rubbers dose not follow the first order reaction while the heat curing phase of rubbers is a typical first order reaction and in the flat curing phase some of rubbers present two first order reaction. The reaction rate of charred phase is the lowest, the reaction rate of heat curing phase is moderate and the reaction rate of flat curing phase is the highest. The activation energy that calculated by Ink and1/T is similar to that calculated by ln(1/t90) and1/T, the maximum relative deviation of these two results is8.3%. However the pre-exponential factors that calculated by regression analysis of these two methods differ from each other greatly. The Arrhenius equation that calculated by the first method is more realistic.(4) The tensile strength of rubbers increased first and then decreased along with the curing time. The elongation at break decreased first and increased with the curing time when the optimum vulcanization time peak value is got. The minimum value is got at the optimum vulcanization time. The mechanical properties are at the best during the optimum vulcanization time interval and are irrational in condition of under cure or over cure. The wear volume of tread rubber HTME decreased first and then increased with the vulcanization time, and the minimum value is got at the optimum vulcanization time.(5) The tensile strength and300%stress at definite elongation of rubbers increased with the rise of vulcanization pressure while the elongation at break, tensile set and tear strength decreased, the greater the pressure, the smaller the wear volume of tread rubber. The incidence of vulcanization pressure on the mechanical properties of all kinds of rubbers is different.(6) Because of the lower heat conductivity coefficient of rubbers and the uneven thickness of tire, the temperature rising process and the degrees of being heated of the key positions of tire are different from each other in these three vulcanization technology which leads to an uneven distribution of vulcanization degrees. Under the normal vulcanization technology, the vulcanization degrees of the crown and the tire shoulder of tire are low while the vulcanization degree of side wall is high when the internal heating vulcanization is over (54min). The after vulcanization effects of tire shoulder, bottom of crown and up and down triangle glue of tire are notable, however the surface of tire crown and the positions with a thin thickness are different, the after vulcanization effects makes the vulcanization degrees even more uneven. When the vulcanization process with pressure maintaining technology is finished, the vulcanization degree of the position that has the highest vulcanization degree is the same to the vulcanization process with normal technology, and the vulcanization degrees of each rubber are all higher than those with the normal technology. The vulcanization degrees of each rubber are lower with the setting time technology, but the uniformity of the tire is improved.(7) The temperature distributions of the tire and the influence of the thermo physical parameters on the temperature fields are researched though numerical simulation. The results show that outcomes calculated by linear thermo physical parameters are far different from that calculated by fixed thermo physical parameters. The incidence of the heat conductivity coefficients of rubbers on the simulation results is larger than the specific heat of rubbers, and the results that calculated by linear thermo physical parameters is more close to the temperature measuring experimental results. The loading of the cross-linking reaction heat values makes the simulation results are more close to the experimental results which means that the cross-linking reaction heat has great influence on the vulcanization temperature field.(8) The influence of the boundary temperatures on the vulcanization degrees of tire is analyzed through numerical simulation on the basis of existing vulcanization technology of11.00R20S815all-steel-radial tire. The temperature of superheated water has great influence on the vulcanization degrees of6#,23#,10#and18#temperature measuring points, the temperature of die sleeve has great influence on the vulcanization degrees of24#,18#and16#temperature measuring points and the temperature of hot plate has great influence on the vulcanization degrees of8#,6#and23#temperature measuring points. An optimization scheme is proposed according to the analysis results:rising the temperature of die sleeve by4K, rising the temperature of superheated water by3K and rising the temperature of hot plate by2K, and the vulcanization time of internal heating decreased from50min to45min, and the results show that the scheme can increase the tire production efficiency and ensure the vulcanization quality meanwhile.(9) There are shortcomings for traditional ways of heating such as long heating time and low heating efficiency etc. Microwave heating has a faster temperature rising rate and a more uniform temperature distribution, and the lowest temperature rising rate is8.95times of the normal heating methods. Whether in the model of circular waveguide or in the model of coaxial waveguide, the joule heat density and the temperatures are decreased along the waveguide transmission directions, the maximum value and the minimum value of joule heat density are all increased with the increase of the power of wave, and the area that has a bigger joule heat density in the middle of the rubber is enlarged with the increase of the power of wave. The highest and the lowest temperature of rubber are all increased linearly with the increase of the power of wave, and the amplification of high temperature is more obvious. The microwave heating is a way of integral heating. |
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