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The purpose of this study was two-fold:
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The cure kinetics of a high performance PR500 epoxy resin in the temperature range of 160–197°C for the resin transfer molding (RTM) process have been investigated. The thermal analysis of the curing kinetics of PR500 resin was carried out by differential scanning calorimetry (DSC), with the ultimate heat of reaction measured in the dynamic mode and the rate of cure reaction and the degree of cure being determined under isothermal conditions. A modified Kamal's kinetic model was adapted to describe the autocatalytic and diffusion‐controlled curing behavior of the resin. A reasonable agreement between the experimental data and the kinetic model has been obtained over the whole processing temperature range, including the mold filling and the final curing stages of the RTM process. 相似文献
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Design of molding tools and molding cycles for sheet molding compounds (SMC) is often expensive and time consuming. Computer simulation of the compression molding process is a desirable approach for reducing actual experimental runs. The focus of this work is to develop a computer model that can simulate the most important features of SMC compression molding, including material flow, heat transfer, and curing. A control volume/finite element approach was used to obtain the pressure and velocity fields and to compute the flow progression during compression mold filling. The energy equation and a kinetic model were solved simultaneously for the temperature and conversion profiles differential scanning calorimetry (DSC) was used to experimentally measure the polymer zation kinetics. A rheometrics dynamic analyzer (RDA) was used to measure the rheological changes of the compound. A series of molding experiments was conducted to record the flow front location and material temperature. The results were compared to simulated flow front and temperature profiles. 相似文献
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Jyh-Dar Fan L. James Lee Junil Kim Yong-Taek Im 《Polymer Engineering and Science》1989,29(11):740-748
The effects of material flow, heat transfer, part geometry, and curing agents on the cure of sheet molding compounds (SMC) in molds with substructures were analyzed both experimentally and numerically. It was found that heat transfer during mold filling has a profound effect on the cure pattern, especially for fastcure resins molded for parts with thin dimensions. 相似文献
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Ly James Lee 《Polymer Engineering and Science》1981,21(8):483-492
A recently developed kinetic model has been applied here to describe the polyester-styrene addition copolymerization. By assuming that the termination step is negligible and the reaction rate between inhibitor and initiator free radical is much, faster than any other reactions, the kinetic mechanism can be simplified to be expressed as a single equation. The parameters, rate constant of initiator decomposition and rate constant of propagation, are estimated from the induction time and the time to the peak exotherm of isothermal differential scanning calorimetry (DSC) curves. Temperature profiles inside plate sections of SMC parts during molding are predicted by a mathematical model in which addition polymerization is coupled with heat transfer. The predicted temperature profiles compare well with the experimental results. The model is also used to predict the cure time of different part thicknesses, mold temperature and initiator concentration. Glass fibers playa role as a heat sink as well as heat conductor during curing. Adding glass fibers to SMC not only lowered the maximum exotherm but also reduced the cure time. 相似文献
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Ching-Chih Lee 《Polymer Engineering and Science》1989,29(15):1051-1058
A finite element technique has been developed for coupled reaction and heat transfer analysis in which mass diffusion is negligible. The temperature unknowns are located at nodal points, while the reaction variables (species concentrations, reaction rates) are at the Gauss points in each element. With a mechanistic kinetic model, the SMC (sheet molding compound) cure in 2-D and 3-D geometries was analyzed. The results for plate-and-rib configurations show the progression of cure and heat transfer and the influence of geometry on the progression. The analysis for a flat sheet of SMC in a mold with localized heating using bubblers indicates the thermal interaction between the mold and the curing SMC. Temperature and reaction profiles are given for each case. 相似文献
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The curing step in resin transfer molding process involves heat transfer coupled with the curing reaction of thermoset resin. In order to examine the curing behavior under a specified cure cycle in the resin transfer molding process, numerical simulations are carried out by three-dimensional finite elements method. An experimental study for isothermal cure kinetics of epoxy resin is conducted by using differential scanning calorimetry. Kinetic parameters based on the modified Kamal model are determined from the calorimetric data for the epoxy system, and by using these parameters, numerical simulations are performed for a hat-shaped mold. It is found from the simulation results that the temperature profile and the degree of cure are well predicted for the region inside the mold. This numerical study can provide a systematic tool in the curing process to find an optimum cure cycle and a uniform distribution of the degree of cure. 相似文献
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One of the major factors of concern in compression molding of fiber-reinforced thermosets is the mold cycle time which directly affects the processing cost. An ideal system would be the one which cures in a relatively short time resulting in excellent mechanical and physical properties. However, in practice, a compromise has to be made between the mold cycle time and ultimate property requirements. The effects of cure cycle time, temperature, preheating and post-cooling on mechanical properties of continuous as well as chopped glass fiber reinforced polyester and vinyl ester systems involving 1/4 to 1 in thick sections have been studied. Mold cycle time is strongly influenced by the part thickness and mold temperature. Internal heat generation due to curing reaction causes high thermal gradients across the thickness. Preheating offers advantages of reducing both the mold cycle time and the thermal gradient. The flexural and interlaminar shear strengths are strongly dependent or, the mold cycle time. Maximum strengths are obtained when the mold is opened at the instant when there is no thermal gradient across the thickness. 相似文献
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A trial and error approach reflects the state of the art in reaction injection molding. Material and process parameters determine the “moldability” of a specific system in a particular application. The concept of “molding areas” on the critical parameters plane can be extended form thermoplastic injection molding (TIM) to reaction injection molding (RIM). In this work moldability diagrams for the filling and curing stages of a RIM process are obtained based on a simplified engineering approach. The key process parameters chosen for the filling stage are initial material temperature and filling time. In the curing stage, the critical parameters are considered to be mold wall temperature and demold time. Experimental results obtained on a laboratory-scale RIM machine on a Crosslinking polyurethane system are used to check the validity of the predicted molding areas. The agreement obtained is satisfactory considering the broad range of processing parameters used. 相似文献
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端胺基聚氨酯/环氧树脂胶粘剂的固化过程特点研究 总被引:1,自引:0,他引:1
采用差示扫描量热法(DSC)研究了两种含有柔性链和刚性结构单元的端胺基聚氨酯(ATPU-2和 ATPU-1.5)对环氧树脂E-44固化反应过程特点的影响。结果表明,ATPU在胶粘剂中的含量对固化放热特征、 固化放热量和固化程度有显著的影响,随着ATPU的增加,固化放热量增加,固化度亦增加。 相似文献
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A mechanistic kinetic and heat transfer model is used to describe the cure of sheet molding compounds (SMC). Kinetic parameters such as rate constant of initiator decomposition and rate constant of propagation are estimated from the induction time and the time to reach the peak exotherm of isothermal reaction curves measured by the differential scanning calorimetry (DSC). Temperature and conversion profiles inside plate sections of SMC parts during molding are measured. The predicted results compare well with the experimental data except the limiting conversion. A set of predictive parameters are proposed from this model as guidelines for the optimal molding of SMC. Several moldability diagrams are also constructed which can be easily used to design the optimum SMC recipe for a given processing condition. 相似文献
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An experimental study was conducted on the injection molding of a thermosetting polyester resin. For the study, a general-purpose unsaturated polyester resin was used, with benzoyl peroxide as initiator. A differential scanning calorimeter (DSC) was used for studying the curing kinetics, under isothermal curing conditions. A plunger-type injection-molding apparatus was constructed, and a rectangular mold cavity with glass windows on both sides was constructed, which permitted us to record on a film the changes in stress birefringence patterns in the mold cavity during the molding operation (i.e., during the isothermal cure, post cure, and subsequent cooling), using a crossed circular polariscope. The injection-molded specimens were used to determine the distribution of the degree of cure at various positions in the flow direction, and to relate the degree of cure to the dynamic mechanical properties. 相似文献
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The longest part of the molding cycle during SMC compression molding is the curing stage. Thus it is extremely important to be able to predict its duration to estimate the cost of manufacturing a new part. During an SMC molding cycle, the mold surface temperature drops suddenly when it contacts the cold charge. The surface temperature then gradually recovers as heat is conducted from the interior of the mold and the resin releases heat during curing. In general, this exchange of heat remains locally unbalanced, causing a gradual decrease in the local surface temperature. To avoid blistering, the cure time must be increased with consecutive moldings until a steady state value is achieved (tcss). In this paper, we present a series of charts that can be used to estimate the steady state cure time for new parts. These values can then be used to estimate the manufacturing cost. 相似文献
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A series of differential scanning calorimetry (DSC) and molding experiments were carried out to measure the effect of curing agents, namely initiators and inhibitor, on the SMC reaction. Results showed that the induction time, the reaction rate, and the limiting conversion of sheet molding compounds can be modified through the change of curing agents. The SMC resin with a higher concentration of low temperature initiator and molded at higher temperature may cure in a shorter period of time and reach a higher conversion. The shortened scorch time and shelf life can be balanced by adding small amount of inhibitor. Surface quality of molded SMC parts measured by solvent extraction process showed that limiting conversion is an important factor in SMC molding. 相似文献
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《Polymer-Plastics Technology and Engineering》2013,52(5):1277-1298
Abstract The cure of unsaturated polyester was studied experimentally and by using a model of the process. The kinetic parameters were calculated from the heat flow–time curves obtained by differential scanning calorimetry (DSC, Netzsch—Simultaneous Thermal Analyzer DSC 200), working in DSC (dynamic) mode. The temperature–time histories were studied in a cylindrically shaped copper mold. Taking into account the heat transferred due to conduction through the resin, as well as the kinetics of heat generated in the cure reaction, a numerical model was constructed. The contributions to the rise in temperature from heat conduction and chemical reaction are different in different parts of the composite, which can explain the temperature–time, or conversion–time histories. Introduction of a carbon-base filler reduced the amount of heat released in the composite and, as a result, lowered the temperatures through the resin. Finally, a good agreement between experimental data and the predicted mathematical model of the curing process in the mold was observed. 相似文献
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The curing kinetics and the resulting viscosity change of a two‐part epoxy/amine resin during the mold‐filling process of resin‐transfer molding (RTM) of composites was investigated. The curing kinetics of the epoxy/amine resin was analyzed in both the dynamic and the isothermal modes with differential scanning calorimetry (DSC). The dynamic viscosity of the resin at the same temperature as in the mold‐filling process was measured. The curing kinetics of the resin was described by a modified Kamal kinetic model, accounting for the autocatalytic and the diffusion‐control effect. An empirical model correlated the resin viscosity with temperature and the degree of cure was obtained. Predictions of the rate of reaction and the resulting viscosity change by the modified Kamal model and by the empirical model agreed well with the experimental data, respectively, over the temperature range 50–80°C and up to the degree of cure α = 0.4, which are suitable for the mold‐filling stage in the RTM process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2139–2148, 2000 相似文献