Numerical and experimental study of injection step,separation, and imbalance filling in low pressure injection molding of ceramic components

In recent years, widespread use of advanced ceramics in vast areas of the industries such as medical technology and automotive industries has led to the growth of the advanced ceramics market. Due to the difficult machining processes and the difficulty of forming complex parts, manufacturing of ceramic components has been restricted. Powder injection molding can be used to overcome these restrictions. In this paper, SiC feedstock was injected at various temperatures and flow rates. Numerical and experimental results of injection step and imbalance filling were studied. As well as the separation of powder and binder was simulated and verified by experimental tests. Thermogravimetric analyzer and rotational rheometer were employed to evaluate the separation in the green parts and rheological properties of the prepared feedstocks, respectively.     

Influence of injection temperature and pressure on the properties of alumina parts fabricated by low pressure injection molding (LPIM)

The quality of ceramics parts made by powder injection molding (PIM) method is influenced by a range of factors such as powder and binder characteristics, rheological behavior of feedstock, molding parameters and debinding and sintering conditions. In this study, to optimize the molding parameters, the effect of injection temperature and pressure on the properties of alumina ceramics in the LPIM process were thoroughly studied. Experimental tests were conducted on alumina feedstock with 60 vol% powder. Injection molding was carried out at temperatures and pressures of 70–100 °C and 0.1–0.6 MPa respectively. Results showed that increase in injection temperature and pressure and the resulting increase in flow rate leads to the formation of void which impairs the properties of molded parts. The SEM studies showed that injection at temperature of 100 °C results in evaporation of binder components. From the processing point of view, the temperature of 80 °C and pressure of 0.6 MPa seems to be the most suitable condition for injection molding. In addition, the effects of sintering conditions (temperature and time) on the microstructure and mechanical properties are discussed. The best final properties were found using injection molding under the above stated conditions, thermal debinding and sintering at 1700 °C during 3 h.     

Effect of packing pressure on fiber orientation in injection molding of fiber‐reinforced thermoplastics

Injection molding of fiber‐reinforced polymeric composites is increasing with demands of geometrically complex products possessing superior mechanical properties of high specific strength, high specific stiffness, and high impact resistance. Complex state of fiber orientation exists in injection molding of short fiber reinforced polymers. The orientation of fibers vary significantly across the thickness of injection‐molded part and can become a key feature of the finished product. Improving the mechanical properties of molded parts by managing the orientation of fibers during the process of injection molding is the basic motivation of this study. As a first step in this direction, the present results reveal the importance of packing pressure in orienting the fibers. In this study, the effects of pressure distribution and viscosity of a compressible polymeric composite melt on the state of fiber orientation after complete filling of a cavity is considered experimentally and compared with the simulation results of Moldflow analysis. POLYM. COMPOS. 28:214–223, 2007. © 2007 Society of Plastics Engineers     

保压时间和保压压力对注塑制品厚度分布的影响

通过实验研究了保压压力和保压时间对制品厚度分布的影响,所得的结论可以指导塑件和模具的设计。     

Effect of molding pressure on structural and densification behavior of microwave-sintered ceramic tool material

The die-pressed Al₂O₃-based ceramic compacts for microwave sintering were prepared using uniaxial molding pressure. Effect of molding pressure on density distribution, microstructure, and mechanical properties of both green and sintered compacts were studied by simulation and experiments. The results suggested that the density distribution of green compact showed obvious stratification phenomenon as the pressure increased. High pressure could increase the density of green compact but led to large density variation. Cracks were formed within the sintered compact due to the severe stress concentration at high molding pressure. Better mechanical properties were obtained at the pressure of 200-300°MPa. The optimal mechanical properties of Al₂O₃/Ti(C,N) ceramic tool were obtained at 1550°C with the soaking time of 10 minutes, which were as high as that of conventional sintering, but the sintering period was sharply shortened.     

Study on mechanical properties of powder impregnated glass fiber reinforced poly(phenylene sulphide) by injection molding at various temperatures

The prepreg of continuous glass fiber reinforced poly(phenylene sulphide) (PPS) was prepared using the powder impregnation technique and cut into the pellets, in which the length of glass fibers was the same as the pellets. After injection molding, the mechanical properties were tested and the effects of the pellet length, fiber content, and thermal treatment on the mechanical properties at different temperatures were studied. It is found that the tensile strength and flexural strength of 6‐mm pellet sample are slightly higher than that of 3‐ and 12‐mm pellet samples. The tensile strength, flexural strength, and modulus decrease significantly with increasing the temperature. The notched Izod impact strength at 85ºC is higher than both at 25ºC and 205ºC. At 205ºC, the glass fiber reinforced PPS composites can still keep better mechanical properties. When the fiber content ranges from 0 to 50%, the mechanical properties increase with increasing the fiber contents at different temperatures, except the notched Izod impact strength do not further increase at 145 and 205ºC with raising the fiber content from 40 to 50%. Thermal treatment could improve the mechanical properties of the composites at higher serving temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of micro-lamellar talc on dimensional accuracy and stability in injection molding of PLA/PBSA blends

The present work is aimed at developing innovative solutions to enhance mechanical and physical properties of Poly(Lactic) Acid (PLA) blends, specifically designed for melt processing applications. Attention is drawn on dimensional accuracy and stability of PLA-based components manufactured by injection molding. PLA belongs to the class of bioplastic materials, entirely relying on renewable resources. It is a semi-crystalline linear aliphatic polyester, highly prone to recrystallize in harsh temperature conditions that can arise during transportation or storage of injection-molded components. Recrystallization is known to cause shrinkage of polymeric materials and, consequently, a marked warpage of components produced from them, causing scraps or parts that do not conform to the functional requirements. In this context, the experimental investigation deals with the effect of increasing amounts of micro-lamellar talc in PLA and Poly(butylene) Succinate Co-Adipate (PBSA) blends. In particular, the role of talc aliquot on dimensional accuracy and stability of injection-molded coffee capsules manufactured by PLA/PBSA blends is studied, with emphasis on the key role of recrystallization. For that purpose, commercial grade PLA and PBSA are compounded with micro-lamellar talc and several processing additives by a twin screw co-rotating extruder. The resulting compound is reprocessed to form coffee capsules by injection molding. Characterization tests include Differential Scanning Calorimetry (DSC), Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) spectroscopy and Field Emission Gun Scanning Electron Microscopy (FEG – SEM). Measurements of the characteristic dimensions of the molded components reveals the effect of increasing amounts of talc in PLA/PBSA blends on dimensional accuracy and stability properties of coffee capsules. Brewing tests allowed to identify the formulations that can ensure the utmost geometrical accuracy of the coffee capsules and their suitability for brewing in instant coffee machine. Based on experimental evidences, lowest shrinkage and improved stability are found on components manufactured by polymeric blends that involve the highest amount of talc.     

Experiment and simulation of foaming injection molding of polypropylene/nano-calcium carbonate composites by supercritical carbon dioxide

Microcellular injection molding of neat isotactic polypropylene (iPP) and isotactic polypropylene/nano-calcium carbonate composites (iPP/nano-CaCO₃H) was performed using supercritical carbon dioxide as the physical blowing agent. The influences of filler content and operating conditions on microstructure morphology of iPP and iPP/nano-CaCO₃H microcellular samples were studied systematically. The results showed the bubble size of the microcellular samples could be effectively decreased while the cell density increased for iPP/nano-CaCO₃H composites, especially at high CO₂ concentration and back pressure, low mold temperature and injection speed, and high filler content. Then Moldex 3D was applied to simulate the microcellular injection molding process, with the application of the measured ScCO₂ solubility and diffusion data for iPP and iPP/nano-CaCO₃H composites respectively. For neat iPP, the simulated bubble size and density distribution in the center section of tensile bars showed a good agreement with the experimental values. However, for iPP/nano-CaCO₃H composites, the correction factor for nucleation activation energy F and the pre-exponential factor of nucleation rate f0 were obtained by nonlinear regression on the experimental bubble size and density distribution. The parameters F and f0 can be used to predict the microcellular injection molding process for iPP/nano-CaCO₃H composites by Moldex 3D.     

Investigations on the formation of composites by injection molding of PA6 and different grafted polypropylenes and their blends

Blends of different types of polypropylenes (PP) with polyamide 6 (PA6) were produced by extrusion. The PPs used were a PP homopolymer, a maleic anhydride‐grafted homopolymer, and an acrylic acid‐grafted homopolymer. The blends were characterized by DSC measurements, selective extraction, infrared spectroscopy, REM microscopy, melt rheology, and their mechanical properties. Three types of interactions in the blends as well as in two‐component composites mold by the core‐back process could be identified. Blends of PP with PA6 were not compatible, and two‐component bars could not be produced. Blends of PPgAA and PA6 were made compatible during reactive extrusion. Two‐component bars could be produced only with a blend containing 50 wt % PA6. The composite formation was based on the interdiffusion of PA6 in both components and the reactive compatibilization in the blends. Blends of PPgMAn were also compatibilized during reactive extrusion. The composite formation on two‐component injection molding was based on two mechanisms: the interdiffusion at sites, where PA6 chains of both the components came into contact, and an interfacial reaction, where PPgMAn and PA6 came into contact. The interfacial reaction was supported by the high mobility of the first component at the temperature of the melt of the second component. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2992–2999, 2006     

Determination of the transition temperature at different cooling rates and its influence on prediction of shrinkage and warpage in injection molding simulation

In injection molding simulation the phase change from melt to solid state is usually simplified by using a so called transition temperature. In the present work, the transition temperatures of several amorphous and semicrystalline polymers were determined using DSC‐runs at different cooling rates. The transition temperature was described as a function of cooling rate. The obtained transition temperatures of the semicrystalline polymers were used in injection molding simulations with the commercial software package Autodesk Moldflow Insight 2010 to calculate the shrinkage and warpage of box‐shaped test parts. The simulation results were compared with the experimental values of optically measured injection‐molded boxes. The results showed a strong influence of the transition temperatures on the simulation results of a 3D model and a very low influence for a 2.5D model. Transition temperatures obtained at higher cooling rates improved the 3D simulation results for several dimensions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Self‐reinforcement of high‐density polyethylene/low‐density polyethylene prepared by oscillating packing injection molding under low pressure

This article reports the toughness improvement of high‐density polyethylene (HDPE) by low‐density polyethylene (LDPE) in oscillating packing injection molding, whereas tensile strength and modulus are greatly enhanced by oscillating packing at the same time. Compared with self‐reinforced pure HDPE, the tensile strength of HDPE/LDPE (80/20 wt %) keeps at the same level, and toughness increases. Multilayer structure on the fracture surface of self‐reinforced HDPE/LDPE specimens can be observed by scanning electron microscope. The central layer of the fracture surface breaks in a ductile manner, whereas the break of shear layer is somewhat brittle. The strength and modulus increase is due to the high orientation of macromolecules along the flow direction, refined crystallization, and shish‐kebab crystals. Differential scanning calorimetry and wide‐angle X‐ray diffraction find cocrystallization occurs between HDPE and LDPE. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 799–804, 1999     

Effect of microcrystalline wax on the solvent debinding of the Sr-ferrite ceramics prepared by powder injection molding

Powder injection molding (PIM) opens new possibilities to process complex Sr-ferrite components for magnetic applications. In the present study, new binder system with the addition of microcrystalline wax (MW) was used for the Sr-ferrite powder injection molding. The optimum binder composition was determined based on rheological measurement, mircrostructure observation by SEM, thermal change by DSC and debinding process. The results indicated that MW with 10 vol.% addition in the binder system containing high density polyethylene (HDPE), paraffin wax (PW) and stearic acid (SA) decreases the defects of the green parts after solvent debinding because the distribution of the binder system between the Sr-ferrite particles becomes more homogeneous. Using the proper binder system containing MW, the defect-free and dense Sr-ferrite ceramics can be prepared after solvent and thermal debinding and sintering. Based on the experimental results, the effects of MW microcrystalline wax on the solvent debinding of the Sr-ferrite ceramics were detailed discussed.     

Damp-heat durability comparison of Al-doped ZnO transparent electrodes deposited at low temperatures on glass and PI-tape/PC substrates

Durability performances are compared for Al-doped ZnO (AZO) transparent electrodes deposited on hard slide-glass and flexible polyimide-tape attached to polycarbonate (PI-tape/PC) substrates. To identify the appropriate sputtering configuration, the AZO thin films are first deposited on the glass substrates via reactive RF-magnetron sputtering under 90 sccm of argon gas and 3 sccm of oxygen gas at room temperature (RT) with 83 to 90 W of RF power for 30 min. When deposited, only the sputtering configuration with 85 W of RF power could produce the AZO films with acceptable optoelectrical properties for transparent electrodes: 80% average visual transparency and 10 Ω/□ at the thickness of 1.1 μm. The temperature at the surface of the substrates rises from RT to 88 °C due to the sputtering with 85W of RF power for 30 min, and this configuration is successfully conducted for AZO film depositions on both the glass and PI-tape/PC substrates. After exposure to a damp-heat (DH) test at 85 °C and 85% relative humidity (RH) for 25 days, the conductivity of the AZO films on the PI-tape/PC substrates is significantly degraded: many cracks are visible on the films, significantly decreasing the Hall mobility. Conversely, the films deposited on the glass substrates exhibit durable high conductivity, no cracks, and excellent stability of the Hall mobility. Despite this significant difference in Hall mobility evolution, the films on both substrates show similar patterns of a slight decrease in carrier concentrations, suggesting that chemical characteristics, extensively reported as the key for the DH degradation of AZO films, are less involved in this durability study featuring AZO films prepared via a low oxygen-to-argon gas ratio of reactive sputtering at low temperatures.     

NaCl在不同温度下对微波法含水仪检测误差影响的试验研究

通过对同一组份的矿化度(NaCl),对微波法含水仪检测精度的影响实验研究,对实验数据进行三次多项式拟合分析,得到NaCl在同一温度下,含水仪在线检测精度会随矿化度含量的增加而降低;在同一组份矿化度(NaCl)下,不同温度会对高含水原油的介电常数产生较大的影响,呈乳化状态的油水混合物,随着温度的升高,含水仪测量精度值呈递减的趋势。最后利用粒子群改进最小二乘法向量机对高含水原油含水仪在线检测结果进行误差校正建模分析,有效的减少了单组份矿化度在不同温度下对高含水原油含水率传感器在线检测精度的影响,为校正高含水原油在线检测精度误差提供了有效的参考方法和理论依据。     

Effect of carbon coating on low temperature electrochemical performance of LiFePO4/C by using polystyrene sphere as carbon source

Carbon perfectly coated LiFePO₄ cathode materials are synthesized by carbon-thermal reduction method using polystyrene (PS) spheres as carbon source. The PS spheres with diameters of 150–300 nm used for the pyrolysis reaction not only inhibit the particle growth but also lead to uniform distribution of carbon coating on the surface of LiFePO₄ particles. Rate capability and cycling stability of LiFePO₄/C with the carbon contents ranging from 1.4 wt% to 3.7 wt% are investigated at −20 °C. The LiFePO₄/C with 3.0 wt% C exhibits excellent electrochemical capability at low temperature, which delivers 147 mAh g⁻¹ at 0.1 C. After 100 cycles at a charge–discharge rate of 1 C, there is still 100% of initial capacity retained for the LiFePO₄/C electrode at −20 °C. According to the transmission electron microscope analysis and cyclic voltammetry measurement, this can be attributed to the good carbon coating morphology and optimal carbon coating thickness.     

Influence of potassium loading at different reaction temperatures on the NOx reduction process by potassium-containing coal pellets☆

The activity of potassium-containing coal pellets and the corresponding free-metal char for NO_x reduction in an oxygen-rich environment has been investigated by temperature-programmed reactions (TPRs) up to 750 °C, 2 h isothermal reactions in the range of 250-475 °C and lifetime tests, (until the samples were completely consumed), for selected samples and temperatures. An interesting ‘reactivity window’, where NO_x reduction is observed, but carbon conversion is negligible, was found from TPRs experiment for a high potassium content sample, at moderate temperatures. This interval was not observed for the char. The catalytic effect of potassium is more dramatic at high temperatures, therefore, metal loading and reaction temperature are very much interrelated. Lifetime tests provide a very valuable information (average selectivity, profitable use of samples for NO_x reduction, etc.), allowing us to check the whole efficiency of the samples. The progressive addition of potassium to the pellets makes samples more effective in terms of: (i) capacity to reduce higher NO_x amounts; (ii) maximum NO_x conversion values and (iii) higher values of average selectivity. In general, the samples studied, exhibit a maximum temperature, very much dependent on their potassium contents, that must not be exceeded with a view to practical applications.