The influence of gas‐assisted injection molding parameters on the structure and thermomechanical properties of hollow parts

The purpose of the work was to estimate an influence of gas‐assisted injection conditions (the temperature of plastic material, switch time‐delay time, gas injection time) of shape, position and dimension of gas channel, and structure of injection molded parts. The change in the value of the dynamic Young modulus and the mechanical loss tangent in function of temperature and oscillation frequency by the dynamic mechanical thermal analysis (DMTA) method was determined. It was found that injection molding parameters: injection molding temperature, switching time and gas injection time influenced significantly mass, wall thickness, and thermomechanical properties of parts. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Foaming of EPDM with water as blowing agent in injection molding

Chemical foaming of elastomers is state of the art and preferred to the more complex systems engineering of physical foaming, yet, many commonly used chemical blowing agents often are hazardous. In current investigations, we introduced water bound to carrying substances (silica, carbon black) into elastomer compounds. A stable, reproducible foaming process can be implemented using water as physical blowing agent. In first tests, the average cell diameters in injection molded elastomer parts exceed the average cell diameters of chemically foamed parts. Yet, varied amounts of blowing agent can reduce the cell diameters. Furthermore, nucleating agents and water carriers are being examined to reduce cell diameters and reach cellular structures and mechanical properties of chemically foamed parts. In conclusion, foaming of elastomers with water is a promising. Yet, further examinations have to cover the effect mechanism of foaming and vulcanization as well as continuous processing and compounding. Rear end of an EPDM part foamed with water carried on silica in injection molding process (mold temperature 195 °C, breathing mold opening 2 mm) © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43613.     

Morphological evolution of HDPE parts in the microinjection molding: Comparison with conventional injection molding

To compare the difference of morphological evolution of HDPE micropart and macropart, micropart with 200 μm thickness and macropart with 2000 μm thickness were prepared. The PLM images of micropart and macropart exhibited a similar “skin–core” structure, but the micropart showed a much larger fraction of orientation layer. The SEM observation of core layer of micropart featured an unoriented lamellae structure and shear layer of micropart showed a highly oriented shish‐kebab structure. The 2D‐WAXD patterns of shear layer of macropart indicated twisted oriented shish‐kebab (KM‐I) structures, however that of micropart indicated untwisted oriented shish‐kebab (KM‐II) structures which was firstly found in microinjection molding. The diffraction pattern of the micropart exhibited stronger azimuthal dependence than the shear layer of macropart, indicating the most pronounced orientation of HDPE chains within lamellae. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Hierarchical crystalline structure of HDPE molded by gas-assisted injection molding

To understand the crystalline morphology of the parts molded by gas-assisted injection molding (GAIM), in this work, the hierarchical structures and the crystalline morphology of gas-assisted injection molded high-density polyethylene (HDPE) were investigated. According to the comparison between the results of the GAIM part and those of the conventional injection molded counterpart, it is found that gas penetration can remarkably enhance the shear rate during GAIM process and oriented lamellar structure, shish-kebab structure and common spherulites arise in the skin, subskin and gas channel region, respectively, owing to the different shear rate in these regions. Meanwhile, cooling rate also plays an important role in the formation of the oriented crystalline structure.     

The effect of vibration injection molding on mechanical properties of polyolefin parts

In this paper an experimental study of vibration field effect on molded polymers specimens is carried out. A self‐made vibration injection device is employed to mold the experiment samples. In the experiment some polyolefin materials are investigated, and property tests for the specimens are carried out. The results show that the tensile strength of high‐density polyethylene (HDPE) and polypropylene (PP) have an obvious increase, but polystyrene (PS) does not. The effect of vibration on the strength is related to the temperature, pressure, and gate. Lastly, the test results are analyzed and conclusions are presented. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1514–1518, 2004     

Rheology studies of polyethylene/chemical blowing agent solutions within an injection molding machine

An in‐line capillary rheometer nozzle equipped to a conventional reciprocating 55‐ton injection molding machine was used to study the viscosity of single phase low density polyethylene (LDPE)/chemical blowing agent (CBA) solutions under high shear rate in the concentration range of 0 to 5 wt%. The steady shear viscosity of LDPE with endothermic and exothermic chemical blowing agents was measured for shear rates ranging from 170 to 200,000 s^?1 and under pressure conditions up to 36 MPa. Pressure‐volume‐temperature (pvT) measurements were determined to account for the pressure effects and the changes of the free volume during processing. The viscosity reduction of the polymer‐CBA solution was found to be dependent on the concentration of the chemical blowing agent and melt pressure. A model based on a simplified Cross‐Carreau model, incorporating the pvT behavior of LDPE, and the free volume concept was proposed to estimate the viscosity reduction resulting from the addition of a chemical blowing agent. The model employs a scaling method based on concentration‐dependent and pressure‐dependent shift factors to collapse the viscosity measurement to a master curve at each temperature. POLYM. ENG. SCI., 45:1108–1118, 2005. © 2005 Society of Plastics Engineers     

Gloss and surface topography of ABS: A study on the influence of the injection molding parameters

Acrylonitrile butadiene styrene is used in applications where the surface appearance is important. Plates with surface texture, varying from highly smooth to very rough, were injection molded with various processing conditions. Morphology, roughness, and gloss of the surface were assessed in relation to the processing parameters. The surface characterization of the moldings was done using reflected differential interference contrast microscopy and laser microtopography. It was observed that the surface properties are affected by the molding parameters. The mold temperature, followed by the injection temperature and the holding pressure are the more influent parameters. The contribution of each parameter to the gloss varies with the type of surface, but for most of the surfaces the contribution of the mold temperature was above 90%. In general, higher values of these parameters improve the replication accuracy that reduce the roughness (and increase the gloss) of very smooth surfaces and cause the opposite effect in other surfaces. In surfaces with an anisotropic texture the gloss depends on the measuring direction. POLYM. ENG. SCI. 46:1394–1401, 2006. © 2006 Society of Plastics Engineers.     

The influence of knit-lines on the tensile properties of injection molded parts

When injection molding complex parts, often knit-lines are formed during the mold filling stage. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter and the effects of the knit-lines on the tensile properties of injection molded plates with holes is quantified by the variation of a socalled knit-line-factor a_k1. Finally, for PS a comparison of the influence of knit-line-formation by a splitted melt stream and by multi-gating on the mechanical level is given.     

Analysis of the influence of the injection molding process on the crystallization kinetics of a HDPE

Thermal analyses of microparts in high density polyethylene (HDPE) have shown that the specific processing conditions used in microinjection molding have irreversible consequences on the polymer morphology. This result has been demonstrated with the analysis of the non‐isothermal crystallization behavior of a HDPE with different thermal histories. The evolution of the absolute crystallinity has been analyzed with a relevant model able to separate the primary and secondary mechanisms all over the crystallization duration. This model has emphasized that the evolution of the primary crystallinity with time is different for the microparts compared to the conventional objects. These differences were attributed to variations of the crystallization mechanisms, especially within the nucleation phase, where a persistent melt memory effect of the former chains orientation/extension was assumed. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44239.     

薄壁塑件注塑压缩成型多指标工艺参数的优化

基于Minitab软件建立6因素5水平的田口试验并与模糊数学中的综合评判法相结合,以电脑显示器外壳为研究对象,对不同工艺条件下的注塑压缩成型过程进行模拟分析,对塑件成型后的最大翘曲变形量、平均熔接线和平均体积收缩率等3个目标值进行综合评判。通过对综合评分进行极差分析,确定了模具温度、熔体温度、压缩力、压缩速度、压缩距离和压缩时间等对注塑压缩成型的影响程度,得出了最优注塑压缩成型工艺参数组合方案,并对该工艺参数组合方案进行了模拟验证。最终得出最优工艺参数:模具温度为75℃,熔体温度为260℃,压缩力为60 t,压缩速度为14 mm/s,压缩距离为1.5 mm,压缩时间为7 s。     

The influence of surface heating on the birefringence distribution in injection molded parts

In order to reduce the frozen-in orientation, which is usually present in injection molded products, the effect of high-performance mold surface heaters was investigated. The heaters are capable of changing their surface temperature by 70°C within a few tenths of a second typically, which minimizes their effect on the cooling time. The effects of the heating time, the instant of heating, and the heating power on the birefringence distribution of a polystyrene resin were studied. Reductions of the birefringence peak by a factor 4 to 7 were observed. The birefringence is removed most effectively by heating briefly before and during the injection stage. A heating pulse of about one second and with a power density of 20 W/cm² then seems to be sufficient. A minimum power density of 10 W/cm² is needed for the relaxation to occur in this specific system.     

薄壁塑件注射成型翘曲变形的工艺优化

本文以注射成型照相机前壳为研究对象,以注塑成型中的翘曲量为优化目标,利用正交试验结合CAE模拟技术,研究模具温度、熔体温度、注射时间、保压时间、保压压力和冷却时间对制品翘曲的影响规律。用均值分析法得到最小翘曲变形的一组优化工艺参数组合,并进行CAE模拟验证。再运用方差分析确定各个工艺参数对翘曲变形的影响程度。     

薄壁塑件注射成型翘曲变形的工艺优化

本文以注射成型照相机前壳为研究对象,以注塑成型中的翘曲量为优化目标,利用正交试验结合CAE模拟技术,研究模具温度、熔体温度、注射时间、保压时间、保压压力和冷却时间对制品翘曲的影响规律。用均值分析法得到最小翘曲变形的一组优化工艺参数组合,并进行CAE模拟验证。再运用方差分析确定各个工艺参数对翘曲变形的影响程度。     

橡胶注射成型机注射装置结构分析研究

主要介绍了橡胶注射成型机及其注射装置的发展情况,阐述了橡胶注射成型的特点以及注射装置设计要求,并对三种常用的注射装置的结构特点及应用作系统的分析比较.     

Banded spherulites of HDPE molded by gas-assisted and conventional injection molding

Crystal morphologies of high density polyethylene (HDPE) with low molecular weight obtained by gas-assisted injection molding (GAIM), conventional injection molding (CIM), and spontaneous cooling, respectively, were studied by scanning electronic microscopy (SEM). It is found that banded spherulites are generated in the inner zone of GAIM parts and the outer zone of CIM parts but are absent in quiescent parts. According to the results, the representative morphologies of crystal change with gradual increment of instantaneous flow field in crystallization from non-banded spherulite to banded spherulite and then to oriented lamellae. This morphological evolution indicates that banded spherulites could be induced by flow field with certain intensity, which is confined by both an upper critical value and a lower one.     

冷凝态下高MFR HDPE注塑专用树脂开发中的问题分析

分析了在气相流化床工艺高负荷冷凝态下开发生产高熔体流动速率(MFR)高密度聚乙烯树脂存在的问题。当氢气摩尔分数超过18%以后,树脂平均粒径大幅下降,聚合反应循环系统细粉的浓度大幅增加,易造成夹带,循环过程中在反应器扩大段部分易沉降粘壁,堵塞反应换热器和分布板。抑制细粉的产生主要采取选择催化剂、控制催化剂活性、控制反应温度等措施。     

Effect of powders and binders on material properties and molding parameters in iron and stainless steel powder injection molding process

It is essential to study and optimize multiple objective functions such as binder system design, feedstock, part geometry, mold design, and processing conditions in order to develop a successful powder injection molding process. A powder with different combinations of binder systems and a binder system with different combinations of powder systems were investigated with a combined experimental and simulation study. First, an experimental rheological study was performed to evaluate the influence of the powder/binder combinations on the rheological behavior and thermal stability of carbonyl iron and stainless steel powder injection molding (PIM) feedstocks. Second, based on the characterization of the feedstock, the simulation study revealed that the pressure-related parameters such as wall shear stress, injection pressure, and clamping force were mainly dependent on the binder system and not much on the powder characteristics, in the range of particle attributes studied. Third, to the temperature-related parameters such as melt front temperature difference and cooling time, binder selection is more critical than powder selection. Fourth, for the velocity-related parameter, maximum shear rate, the selection of both powder and binder system is critical in control. It is demonstrated that the simulation study is essential in the development stage for successful PIM.     

气辅注射成型工艺参数的优化

气辅注射成型的影响因素有很多,选取四因素三水平正交表,通过正交试验法,利用CAE软件Moldflow分析了不同工艺参数对气体穿透的影响,用极差法分析了各因素对气体穿透的影响程度,最后对工艺参数进行了优化组合.     

填充白炭黑的闭孔海绵橡胶——发泡剂、温度、频率和应变对其结构和性能的影响

聚烯烃弹性体（POE）结构规整,无毒害成分,应用广泛。对乙烯-辛烯共聚物硫化胶的结构与性能关系的研究已日趋成熟。文中分析了填充沉淀法白炭黑的闭孔乙烯-辛烯共聚物硫化胶的动态力学特性,研究了发泡剂用量、填充剂用量、频率、温度对动态力学特性的影响。