Characterization of the microinjection molding process

The commonly used plunger injection system in the microinjection molding (μIM) process has separate screw melting, metering, and injection units. As a result, extra operating parameters and complexity are introduced, in comparison with conventional injection molding. In this study, a μIM machine was used to obtain micromoldings of polyoxymethylene, high‐density polyethylene, and polycarbonate. A data acquisition system was developed to record traces of data regarding the evolution of process variables with time. Cavity filling was followed, at the millisecond time scale, using short‐shot experiments and traces of injection pressure, runner pressure, and plunger position. Six characteristic process parameters (CPPs) were defined to characterize both the cavity filling and packing stages. The method of design of experiments was used to investigate the effects of machine settings on the CPPs. Metering size, which was optimized for each set of machine variables, was also used as a CPP. Injection speed was the most significant factor affecting plunger velocity and injection pressure during cavity filling, while the effects of mold and melt temperature varied with the material and machine settings. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Study on the evaluation and compensating strategy for the wear damage of non-return valve during injection molding process

Injection molding (IM) is one of the most essential forming methods for plastics. However, some potential risks which influence part quality may occur in the molding process. A non-return valve (NRV) is a major component on the screw head whose function is to seal during the injection process to prevent the backflow of the melt. The NRV will wear in this process and cause fluctuations in parameters and quality but the wear states of NRVs cannot be monitored without the disassembly of the injection barrel. In this study, we proposed an optimization method to compensate for the wear damage of the NRVs. The V/P switchover point in each molding cycle was recalculated and output to stabilize the part quality. As a result, the wear damage of the NRV on the current machine was able to be predicted and the part quality could be initially optimized in the condition that the NRV had a degree of wear. The experimental results reveal that our proposed compensation algorithm can monitor the type of wear of NRV online, and at the same time, it can compensate the axial wear of NRV and finally improve the consistency of product weight, which established a fundamental for further research in the future.     

A simulation of the non‐isothermal resin transfer molding process

A simulation of the non‐isothermal resin transfer molding manufacturing process accounting for both the filling and the consolidation stage has been developed. The flow of an exothermally reactive resin through a porous medium has been analyzed with reference to the Darcy law, allowing for the chemorheological properties of the reacting resin. Thermal profile calculations have been extended to a three phase domain, namely the mold, the dry preform and the filled preform. The mold has been included in order to evaluate the thermal inertial effects. The energy balance equation includes the reaction term together with the conductive and convective terms, and particular attention has been devoted to setting the thermal boundary condition at the flow front surface. The moving boundary condition has been derived by a jump equation. The simulation performance has been tested by comparing the predicted temperature profiles with experimental data from literature. Further numerical analysis assessed the relevance of using the jump equation at the flow front position for both filling time and thermal profile determination.     

Replication characterization of microribs fabricated by combining ultraprecision machining and microinjection molding

This article aims to investigate the effects of five processing parameters and two geometric factors on replication quality of the microribs, as well as determination of the processing condition when different materials were used. Specifically, the considered parameters include barrel temperature, mold temperature, injection velocity, holding pressure, holding time, aspect ratio, and location of the microribs. The experiment results showed a considerable difference in replicated height of molded microribs with polymethylmethacrylate and polypropylene. Among the processing parameters, the barrel temperature and injection velocity significantly affected replication quality, whereas the holding pressure and holding time appeared to have little influence for both materials. The mold temperature was found to be a sensitive parameter only for polymethylmethacrylate. As for geometric factors, both aspect ratio and location of the microribs played important roles in achievable replication. In addition, simulation results showed good prediction on the trend of how process parameters affect replication, with a small amount of over prediction. POLYM. ENG. SCI., 50:2021–2030, 2010. © 2010 Society of Plastics Engineers     

Flatness and microstructure of a light guide plate fabricated by microinjection molding

This study photo‐etches micropatterns on mold inserts and manufactures a light guide plate with microstructures using microinjection molding. The single parameter method is used to investigate flatness and replication with different process parameters for microinjection molding. Mold temperature is the most important factor for plate flatness and microstructure replication of a light guide plate fabricated by microinjection molding. Low mold temperature increases the flatness of light guide plates, whereas a high mold temperature improves height replication of the microstructure of light guide plates. Optimal mold temperature to maintain flatness and increase microstructure replication of light guide plates is 60°C. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Modeling of the impregnation process during resin transfer molding

A model has developed for simulating isothermal mold filling during resin transfer molding (RTM) of polymeric composites. The model takes into account the anisotropic nature of the fibrous reinforcement and change in viscosity of the polymer resin as a result of chemical reaction. The flow of impregnating resin through the fibrous network is described in terms of Darcy's law. The differential equations in the model are solved numerically using the finite element technique. The Galerkin finite element method is used for obtaining the pressure distribution. A characteristics based method is used to solve the non-linear hyperbolic mass balance equation. The finite element formulation facilitates computations involving the motion of the polymer resin front characterized by a free surface flow phenomenon.     

石灰软化-絮凝法处理地下水硬度动态中试试验研究

采用石灰软化-絮凝法处理华南地区某水厂地下水硬度。动态中试试验采用一体化处理装置,考察石灰软化工艺运行效果,并进一步探索石灰投加量和PAC投加量对试验效果的影响。试验结果表明,Ca(OH)2投加量为299.1³61.3 mg/L、PAC投加量为43.6361.3 mg/L、PAC投加量为43.6⁴8.7 mg/L,处理效果较佳。处理后总硬度(以CaCO3计)降到110mg/L,总碱度(非碳酸盐碱度)降到80 mg/L,符合GB 5749—2006《生活饮用水卫生标准》要求。基于基础设施、设备投资和运行成本的分析表明,石灰软化工艺较离子交换工艺的制水成本减少0.457元/t。     

Moisture conversion and migration in single-wheat kernel during isothermal drying process by LF-NMR

Conversion among different moisture-binding types of single Hebei wheat kernels during isothermal drying processing at 60?°C was studied by low field nuclear magnetic resonance (LF-NMR), and moisture migration was studied by MRI. Water inside wheat kernels exists in four types: chemically combined water (T₂₁), strong bound water (T₂₂), loosely bound water (T₂₃), and free water (T₂₄). A new method to obtain the contents of different moisture-binding types is forwarded according to the transverse relaxation time distribution curve of dried wheat kernels. Moisture conversion inside wheat kernels during drying occurs mainly through the following mechanisms: high-temperature drives T₂₄ to diffuse to lower moisture areas and transform into other moisture-binding types, and moisture-gradient drives T₂₂ to transform into T₂₄. The drying process can be divided into two stages. Moisture migrates from endosperm to epidermis during drying. As the drying rate of the wheat kernel significantly decreases, the drying conditions and parameters need to be adjusted to improve the drying rate while ensuring the quality of wheat kernels.     

Real‐time ultrasonic monitoring of the injection‐molding process

In this study, a noninvasive and nondestructive ultrasonic technique has been used to monitor the polymer injection‐molding process in an attempt to establish a fundamental understanding of the processing/morphology/ultrasonic signal relationships. The ultrasonic technique not only can provide information on solidification affected by various temperatures and pressures but also can reflect the evolution of the crystal morphology and phase morphology of polymer blends. In addition, the periodic vibration of the dynamic‐packing injection‐molding process, in which the melt is forced to move repeatedly in a chamber by two pistons that move reversibly with the same frequency as the solidification progressively occurs from the mold wall to the molding core part, can also be monitored with the ultrasonic velocity and attenuation. Our results indicate that the ultrasonic technique is sensitive and promising for the real‐time monitoring of the injection‐molding process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Cycle time predictions for the rotational molding process with and without mold/part separation

We present a detailed theoretical heat transfer model for the entire rotational molding process (including heating and cooling stages) and identify the key dimensionless groups affecting the process cycle time. This theoretical model is employed to generate numerical results that are in very good agreement with the experimental data available in the literature. The effects of variations in the dimensionless groups on the cycle time are evaluated. In addition, part shrinkage has been incorporated in the models, and its effect on the process cycle time has been studied extensively.     

一次法混炼工艺对胎面磨耗性能的影响

胎面的耐磨性是评价成品轮胎性能优劣的一项重要指标,它取决于很多因素,但其中最关键的因素还是胎面的配方体系和胶料的混炼工艺。胶料的耐磨耗性能有磨损磨耗、疲劳磨耗、巻曲磨耗三种表现形式,本文主要从丰源轮胎推行的“一次法混炼工艺”针对炼胶工艺的提升与传统工艺进行对比,进而验证“一次法混炼工艺”所生产的胎面胶料对于胎面耐磨性的提升。     

Synthesis of indirect work exchange networks considering both isothermal and adiabatic process together with exergy analysis

In this paper, an efficient methodology for synthesizing the indirect work exchange networks (WEN) considering isothermal process and adiabatic process respectively based on transshipment model is first proposed. In contrast with superstructure method, the transshipment model is easier to obtain the minimum utility consumption taken as the objective function and more convenient for us to attain the optimal network configuration for further minimizing the number of units. Different from division of temperature intervals in heat exchange networks, different pressure intervals are gained according to the maximum compression/expansion ratio in consideration of operating principles of indirect work exchangers and the characteristics of no pressure constraints for stream matches. The presented approach for WEN synthesis is a linear programming model applied to the isothermal process, but for indirect work exchange networks with adiabatic process, a nonlinear programming model needs establishing. Additionally, temperatures should be regarded as decision variables limited to the range between inlet and outlet temperatures in each sub-network. The constructed transshipment model can be solved first to get the minimum utility consumption and further to determine the minimum number of units by merging the adjacent pressure intervals on the basis of the proposed merging methods, which is proved to be effective through exergy analysis at the level of units structures. Finally, two cases are calculated to confirm it is dramatically feasible and effective that the optimal WEN configuration can be gained by the proposed method.     

石油井下套管磨损机理与影响因素分析

测试过程中,井下套管受多种因素影响毁损问题时有发生。针对这一现象,对石油井下套管的磨损机理与影响因素进行了深入分析。套管可能存在的磨损机理主要有磨粒磨损、粘着磨损、腐蚀磨损、疲劳磨损和冲蚀磨损。而影响套管磨损的因素很多,外部因素包括载荷、速度、温度、相对运动及受力状态、磨料、介质与环境等;内部条件则主要是受磨材料的化学成分、组织和机械性能等。     

A fast computational model to the simulation of non‐isothermal mold filling process in resin transfer molding

The numerical simulation of mass and heat transfer model for the curing stage of the resin transfer molding (RTM) process is known as a useful method to analyze the process before the mold is actually built. Despite the intense interest in the modeling and simulation of this process, the relevant work is currently limited to development of flow models during filling stage. Optimization of non‐isothermal mold filling simulation time without losing the efficiency remains an important challenge in RTM process. These were some reasons that motivate our work; namely the interested on the amelioration of the performance of RTM simulation code in term of execution time and memory space occupation. Our approach is accomplished in two steps; first by the modification of the control volume/ finite element method (CV/FEM) and second by the implementation in the modified code of an adapted conjugate gradient algorithm to the compressed sparse row storage scheme. The validity of our approach is evaluated with analytical results and excellent agreement was found. The results show that our optimization strategy leads to maximum reduction in time and space memory. This allows one to deal with problems with great and complex dimensions mostly encountered in RTM application field, without interesting in the constraint of space or time. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Characterization of recycled cellulose by dynamic and isothermal thermogravimetry investigations

Isothermal thermogravimetric measurements were performed on recycled cellulosic materials. The kinetic parameters were determined with the Avrami-Erofe'ev equation from two different ways. The first one consists of the determination of n from the slope of the variations of ln(–ln(1–α)) versus ln(t) and apparent activation energy ΔE from the slope of ln(k(T)) versus 1/T. The second one also gives the values of n and ΔE from a numerical fit of the experimental data. Both methods lead to the same results and show that the reaction order of the degradation process of the cellulose is close to unity. The value of this reaction order allows the interpretation of the dynamic thermogravimetry data with the Broido method. Using this method on a series of recycled cellulose with different content of chemical and mechanical paper pulps, we show that the apparent activation energies depend linearly onto paper pulp ratio.     

Modulus and hardness evaluation of polycrystalline superconductors by dynamic microindentation technique

In this study, depth-sensing Vickers indentation tests were conducted on polycrystalline superconductors under different peak load (0.49, 0.73, 0.98, and 1.22 N). The load (P)–penetration depth (h) curves were analyzed in order to evaluate the mechanical characteristics such as microhardness and elastic modulus. It was found that both of these characteristics exhibited significant peak load dependence which suggested a need for calculation of the load-independent hardness and modulus. The load independent hardness (0.88, 0.95, and 1.12 GPa) and modulus (1.98, 3.13, and 3.33 GPa) values were then calculated for YBCO, YBCO + 0.5% ZnO, and YBCO + 1% ZnO, respectively.     

Thermooxidative stability of different polyurethanes evaluated by isothermal and dynamic methods

Two methods for the evaluation of resistance to the thermooxidation of different classes of polyurethane films (PURs) throughout thermogravimetric analyses were used. Normal and waterborne polyurethanes were characterized using either isothermal or dynamic heating. In the isothermal method, the times required to reach degradations of 0.025, 0.05, and 0.10 were determined at several temperatures in the interval of 190–250 °C. In the dynamic method, heating rates of 0.5, 1, 2, 5, and 10 °C/min were used in the range of 30–500 °C, and degradations of 0.025, 0.05, 0.10, 0.20, and 0.40 were considered. From the Arrhenius plots, activation energies were evaluated ranging between 130 and 230 kJ/mol for normal PURs and between 80 and 170 kJ/mol for waterborne PURs depending on the method, temperature interval, and degree of degradation. Advantages and disadvantages of the two methods were compared. The isothermal method requires a preliminary test, and it was more useful for degradation studies up to 0.05. The dynamic method offered evidence for the presence of different degradation processes, and it was more suitable for the evaluation of kinetics parameters at higher degrees of degradation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1216–1225, 2001     

Use of sensors and actuators to address flow disturbances during the resin transfer molding process

In Resin Transfer Molding a fiber preform is placed in a mold, the mold is closed and a thermoset polymeric resin is injected through gates into the mold to saturate the preform completely. The resin flow rate is controlled by actuators, which are usually injection machines. When one places the preform into the mold, the gap between the preform and the mold walls can create race tracking channels and provide the resin flow paths that can severely influence the flow patterns and drastically change the flow history. As this gap is unavoidable and not reproducible, one could have different strengths of this disturbance from one part to the next, some of which will cause incomplete saturation of the fibers by the resin. Hence, an active control of the filling stage is necessary that can detect and characterize the race tracking and provide the control action to redirect the flow with the aim to saturate the preform without resin starved regions (macro voids or dry spots). A methodology is proposed that intelligently places sensors in the mold to detect the resin arrival times at these locations. This information is used to determine and quantify the strength of the disturbance and used as an input parameter for the actuators to redirect the flow. This paper demonstrates this methodology on a simple mold configuration, and outlines how this technique can be generalized to any mold geometry or disturbance set in an automated RTM environment. Numerical simulations are used to establish the control methodologies, and all of the efforts are confirmed in a laboratory setting. The proposed methodology should prove useful in increasing the yield of Resin Transfer Molded parts.     

Injection molding without prior drying process by the gas counter pressure

A processing technology that facilitates quality injection molding without prior drying of polymer pellets has been proposed. The main idea is not to let the water evaporate to bubbles inside the mold. The polymer will be maintained hydrated as it was in the hopper of the injection molding machine throughout the entire molding processes by controlling the cavity pressure above the saturation pressure of water until solidified. In this work, the gas counter pressure (GCP) system has been designed and built to maintain the cavity pressure above the saturation pressure. The performance of the proposed method has been examined by checking the visual quality and the mechanical properties of the molded parts. The method has been tested with pellets of polymethyl methacrylate (PMMA), polycarbonate, polyethylene terephthalate, polybutylene terephthalate, and polyamide 66. The results show that the GCP prevents surface impairment incurred by the vapors without or with minor effects on the mechanical properties. Finally, the effects of energy saving has been examined by conducting the actual process for 1 day. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers