Reactive mold filling in resin transfer molding processes with edge effects

Reactive mold filling is one of the important stages in resin transfer molding processes, in which resin curing and edge effects are important characteristics. On the basis of previous work, volume‐averaging momentum equations involving viscous and inertia terms were adopted to describe the resin flow in fiber preform, and modified governing equations derived from the Navier–Stokes equations are introduced to describe the resin flow in the edge channel. A dual‐Arrhenius viscosity model is newly introduced to describe the chemorheological behavior of a modified bismaleimide resin. The influence of the curing reaction and processing parameters on the resin flow patterns was investigated. The results indicate that, under constant‐flow velocity conditions, the curing reaction caused an obvious increase in the injection pressure and its influencing degree was greater with increasing resin temperature or preform permeability. Both a small change in the resin viscosity and the alteration of the injection flow velocity hardly affected the resin flow front. However, the variation of the preform permeability caused an obvious shape change in the resin flow front. The simulated results were in agreement with the experimental results. This study was helpful for optimizing the reactive mold‐filling conditions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Determination of corner and edge permeability in resin transfer molding

Resin flow in resin transfer molding may be strongly influenced by small heterogeneities in the fiber preform, such as narrow channels formed by bending and fitting into a mold. An evaluation of preform permeability in these regions of nonuniform packing is presented. The study incorporates an empirical and analytic approach to iteratively determine the permeability in these regions. Flowfront data were recorded for high fiber volume fraction woven fiber preforms. Edge gap width, injection pressure, and fiber volume fractions were varied. The flow front data were compared with numerical simulations to estimate enhanced permeability at the edges. The results indicate that, for high fiber volume fraction preforms, flow in the channel dominates for relatively small (≈ 2 mm) gaps.     

Process parameters estimation for structural reaction injection molding and resin transfer molding

Some design strategies for structural reaction injection molding (S-RIM) and resin transfer molding (RTM) are presented. Our approach makes use of moldability diagrams to define the parameters necessary to meet the process requirements. Moldability diagrams are presented for the filling and curing steps. The criterion for selecting the amount of fiber reinforcement, injection time, catalyst level, and process temperatures in order to optimize properties and demold time is described.     

Mold filling analysis in resin transfer molding

This study is a comparison of independently designed mold flow experiments performed at The Dow Chemical Company with simulations from a computer code developed at The Ohio State University. The experiments used in the validation study included isothermal 1-dimensional flow with line gating and end venting, isothermal 2-dimensional flow with converging flow and center venting, and two different resin systems. The simulation results were compared with experimental pressure and temperature readings and fill times. It was found that simulated fill times could be predicted within experimental error and pressure distributions could be predicted with the application of a scaling factor.     

Three-dimensional simulations of the curing step in the resin transfer molding process

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.     

Vitrification effect on the curing reaction of epoxy resin

Summary The curing reaction of diglycidyl ether of Bisphenol A(DGEBA) with triethylene tetramine(TETA) was studied by the differential scanning calorimetry(DSC). The reaction was affected as the vitrification occurred when the glass transition temperature(T_g) of the reaction mixture exceeded the curing temperature. In order to describe the curing reaction in the rubbery state as well as in the glassy state, the reaction kinetic equation containing the generalized WLF equation term was proposed and the parameters were determined from the DSC data.Nomenclature a_T time temperature shift factor, dimensionless - A_T temperature dependent frequency factor, /sec - A_Tg temperature dependent frequency factor at T_g, /sec - A_To temperature dependent frequency factor at T_g, /sec - A empirical parameter in temperature dependent frequency factor, dimensionless - B empirical parameter in temperature dependent frequency factor, K - C₁ empirical parameter in the generalized WLF equation, dimensionless - C₂ empirical parameter in the generalized WLF equation, K - D correction parameter in temperature dependent frequency factor, K - E activation energy, cal/mole - E_x/E_m ratio of lattice energies for crosslinked and uncrosslinked polymer, dimensionless - F_x/F_m ratio of segmental mobilities for crosslinked and uncrosslinked polymer, dimensionless - H_t cumulative heat generated up to time t, cal/g - H_RXN heat of reaction under complete conversion, cal/g - n reaction order, dimensionless - S _r scan rate of the DSC experiment, °C/sec - t time, second - T temperature, K - T_g glass transition temperature of the partially cured reaction mixture, K - T_go glass transition temperature of uncured reactant, 253 K - X conversion, dimensionless     

端胺基聚氨酯／环氧树脂胶粘剂的固化过程特点研究

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。     

Numerical simulation of thickness variation effect on resin transfer molding process

In this work, a computer model has been developed to investigate the effect of reinforcement thickness variation and edge effect on infiltration and mold filling in resin transfer molding (RTM) process. The developed code is able to predict the flow front location of the resin, the pressure, and the temperature distribution at each time step in a mold with complex geometries. It can also optimize the positioning of injection ports and vents. The filling stage is simulated in a full two‐dimensional space by using control volume/finite element method CV/FEM and based upon an appropriate filling algorithm. Results show that the injection time as well as flow front progression depends on the edge effect, the variation of reinforcement thickness, and the position of injection ports; this highlights that the inclusion of these effects in RTM simulation is of definite need for the better prediction and optimization of the process parameters. The validity of our developed model is evaluated in comparison with analytical solutions for simple geometries, and excellent agreements are observed. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

端胺基聚氨酯/环氧树脂胶粘剂的固化反应特征及其反应动力学研究

采用差示扫描量热法(DSC)研究了含有柔性链和刚性结构单元的端胺基聚氨酯(ATPU)对环氧树脂E-44固化反应过程特点和反应过程动力学的影响。结果表明,固化剂(ATPU)的掺加量对环氧树脂E-44固化反应过程有显著的影响,随着ATPU的增加,固化放热量增加。当ATPU的掺加量为1.6时,固化反应放热量达到最大值。固化温度研究表明,ATPU/E-44固化体系的等温固化起始温度和最高温度分别为121℃和177℃。固化反应的动力学研究表明,ATPU/E-44胶粘剂固化反应的表观活化能为81.8kJ/mol;固化反应的级数为1.3。     

Optimization of cure kinetics parameter estimation for structural reaction injection molding/resin transfer molding

A numerical method is proposed for polymer kinetic parameter estimation of either Structural Reaction Injection Molding (SRIM) or Resin Transfer Molding (RTM). The method simulates either radial flow or axial flow of reactive resins through a fiber preform inside a mold cavity. This method considers a non‐isothermal environment with different inlet boundary conditions. Based on the molding conditions, this method can find the best values of chemical kinetic parameters by comparing the simulated temperature history and the experimental temperature history. Since the kinetic parameters are estimated with the real molding conditions, the simulations using these parameter values can have better agreement with molding data than those parameters which are obtained from idealized conditions such as Differential Scanning Calorimeter (DSC). The optimization approach was verified by estimating kinetics parameters for RTM data available in the literature. Temperatures predicted by the optimized kinetics parameters are compared with experimental data for two different molding conditions: injection of a thermally activated resin into a radial mold under constant pressure flow, and injection of a mix activated resin into a radial mold under constant volume. In both cases, the optimized kinetics parameters fit the temperature data well.     

A dual-scale analysis of macroscopic resin flow in vacuum assisted resin transfer molding

In Vacuum Assisted Resin Transfer Molding (VARTM) where a sacrificial medium is used to facilitate the resin flow, the velocity of the resin varies drastically between inside the sacrificial medium and inside the fiber preform. Although the thickness-to-length ratio of a VARTM product is usually small, a 3-D analysis is required for analyzing the lead-lag flow in the two different media. The problem associated with the full 3-D analysis is the CPU time. A full 3-D numerical mesh comprising a large number of nodes requires a CPU time impractical on most computer platforms. In this study, a dual-scale analysis technique was proposed. First, the flow analysis for the entire calculation domain was conducted in 2.5-D. Using the results of the 2.5-D calculation, the 3-D analysis was performed for a small area of special concern. In some numerical examples, the local 3-D analysis could discover an eccentric flow pattern as well as the lead-lag flow that would inevitably be neglected in 2.5-D simulations. The global-local analysis technique practiced in this study can be used to analyze the intricate flow of resin through non-uniform media in affordable CPU times. Polym. Compos. 25:510–520, 2004. © 2004 Society of Plastics Engineers.     

Engineering analysis of reaction injection molding process of epoxy resin

An engineering analysis of reaction injection molding (RIM) process of epoxy resin was carried out through numerical simulation and actual experiment. In order to simulate the RIM process, and reaction kinetics and the viscosity function of the epoxy system were obtained from thermal analysis and rheological measurement, and the balance equations of the chemical species, momentum, and energy within a mold cavity were set up in cylindrical coordinates. As the result of the simulation, the temperature and conversion profiles within a disc type mold were obtained and a moldability analysis was made to find the optimum molding conditions. The temperature change during the curing reaction, at a fixed point within the mold cavity, was measured through the actual RIM experiment on a small scale, and was compared with the simulated results.     

The effect of microwave resin preheating on the quality of laminates produced by resin transfer molding

Cycle times in resin transfer molding (RTM) of an unsaturated polyester have been reduced significantly using an in-line microwave resin preheating system. Microwave preheating lowers the resin viscosity during injection and modifies the thermal age of the resin, potentially influencing the quality of RTM laminates. The tensile properties of RTM laminates have been measured with regard to improved fiber wet-out by the lower viscosity resin. Degree of cure measurements have been included to establish the effect of microwave preheating on resin conversion within the laminate. Local pressure that develops within the mold during the cure phase can lead to mold deflections. Variations in the laminate thickness associated with these deflections are presented, and the use of microwave resin preheating to reduce these variations is discussed.     

Nonisothermal simulation on pressure during resin transfer molding

High speed injection has been widely used in resin transfer molding (RTM), which improves manufacturing efficiency. This sometimes leads to excessive pressure within the mold, resulting in fiber destruction and mold deformation. Heating the mold and injection resin reduces the viscosity of resin, leading to influence on mold internal pressure. Selection of optimal mold and injection temperature for effective reduction of mold internal pressure has become a source of concern in the polymer industry. This article presents an outlook relationship between mold temperature, injection temperature, and mold internal pressure. It also showcases a temperature selection method angle to addressing this issue. The “FLUENT” software has been secondarily developed that gives an insight in using the three-dimensional nonisothermal RTM simulation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47492.     

Study on void formation in resin transfer molding

A 2-D model has been developed for the transverse impregnation of a resin into a unidirectional packed fiber mat. The model takes into account two types of flow, macro-flow around the fiber bundles and micro-flow around the fibers in the bundles, which occur simultaneously. Both flows are described by Darcy's law. Results show that if the ratio of permeability of the macro-flow to the micro-flow is more than 20, an elliptic type void is formed within the fiber bundle, and the void will shrink and disappear if vacuum assistance is applied in the mold. The capillary effect was also investigated by use of a numerical simulation based on a body-fitted finite element method and by experiment. A correlation between the capillary force and other parameters is proposed for the XT-D/O unidirectional fiber mat. The quasi-equilibrium capillary effect is limited to when the modified capillary number is about O(10^?4).     

脲醛树脂的固化研究

通过缩聚法制备出脲醛树脂,考察了制备单组分固化剂NH4C l、2%HC l、5%的H3PO4、H2O2及双组分固化剂NH4C l和2%HC l、NH4C l和5%H3PO4的使用条件,并确定了复合固化剂的配比和用量。发现双组分固化剂固化时间适宜,固化效果好。     

咪唑催化苯并噁嗪树脂固化的研究

研究了以咪唑为催化剂的苯并口恶嗪树脂的固化反应。通过平板小刀法测凝胶化时间、等温DSC和程序升温DSC等方法,表征了含有咪唑的苯并口恶嗪树脂的固化反应过程,计算了该体系的固化动力学参数。结果表明,咪唑的引入使苯并口恶嗪树脂的固化初始温度从242℃降到了130℃左右,DSC曲线出现催化固化和热固化2个放热峰;咪唑对苯并口恶嗪树脂的催化作用在一定用量范围内随着用量的增加而增加;通过等温DSC分析,含有咪唑的苯并口恶嗪树脂在150℃下的固化反应是不完全的,经过高温后处理才能固化完全;经过等温动力学计算,咪唑催化苯并口恶嗪的固化反应级数为1.72,活化能为86.3kJ/mol。     

改性双氰胺衍生物固化环氧树脂的研究

针对双氰胺固化环氧树脂时固化温度过高的缺点,从自行设计并合成的一系列改性双氰胺中筛选出一种,将其与环氧树脂复配制成单组分潜伏性环氧树脂胶粘剂,利用差示扫描量热法(DSC)和红外光谱法(FT-IR) 对单组分环氧树脂固化体系的固化反应进行了分析和研究。结果表明,改性双氰胺与双氰胺相比,具有较高的活性,显著降低了固化反应的反应温度;所配制的单组分环氧树脂胶粘剂具有较长的贮存期和良好的固化性能。     

Mechanical and dynamic mechanical analysis of hybrid composites molded by resin transfer molding

This work aims to evaluate the performance of glass/sisal hybrid composites focusing on mechanical (flexural and impact) and dynamic mechanical analyses (DMTA). Hybrid composites with different fiber loadings and different volume ratios between glass and sisal were studied. The effect of the fiber length has also been investigated. The densities of the composites were compared with the theoretical values, showing agreement with the rule of mixtures. The results obtained in the flexural and impact analysis revealed that, in general, the properties were always higher for higher overall reinforcement content. By DMTA, an increase in the storage and loss modulus was found, as well as a shift to higher values for higher glass loading and overall fiber volume. It was also noticed an increase in the efficiency of the filler and the calculated activation energy for the relaxation process in the glass transition region. The fiber length did not significantly change the results observed in all analyses carried out in this work. The calculated adhesion factor increased for higher glass loadings, meaning the equation may not be applied for the system studied and there are other factors, besides adhesion influencing energy dissipation of the composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Experimental analysis and numerical modeling of flow channel effects in resin transfer molding

Composite manufacturing by Liquid Composite Molding (LCM) processes such as Resin Transfer Molding involve the impregnation of a net‐shape fiber reinforcing perform a mold cavity by a polymeric resin. The success of the process and part manufacture depends on the complete impregnation of the dry fiber preform. Race tracking refers to the common phenomenon occurring near corners, bends, airgaps and other geometrical complexities involving sharp curvatures within a mold cavity creating fiber free and highly porous regions. These regions provide paths of low flow resistance to the resin filling the mold, and may drastically affect flow front advancement, injection and mold pressures. While racetracking has traditionally been viewed as an unwanted effect, pre‐determined racetracking due to flow channels can be used to enhance the mold filling process. Advantages obtained through controlled use of racetracking include, reduction of injection and mold pressures required to fill a mold, for constant flow rate injection, or shorter mold filling times for constant pressure injection. Flow channels may also allow for the resin to be channeled to areas of the mold that need to be filled early in the process. Modeling and integration of the flow channel effects in the available LCM flow simulations based on Darcian flow equations require the determination of equivalent permeabilities to define the resistance to flow through well‐defined flow channels. These permeabilities can then be applied directly within existing LCM flow simulations. The present work experimentally investigates mold filling during resin transfer molding in the presence of flow channels within a simple mold configuration. Experimental flow frot and pressure data measurements are employed to experimentally validate and demonstrate the positive effect of flow channels. Transient flow progression and pressure data obtained during the experiments are employed to investigate and validate the analytical predictions of equivalent permeability for a rectangular flow channel. Both experimental data and numerical simulations are presented to validate and characterize the equivalent permeability model and approach, while demonstrating the role of flow channels in reducing the injection and mold pressures and redistributing the flow.