多熔体多次注射成型聚苯乙烯/聚乙烯共混物的相形态结构演变规律

采用扫描电子显微镜(SEM)对多熔体多次注射成型(MMMIM)聚苯乙烯(PS)/聚乙烯(PE)共混物制品的相形态结构进行了研究,发现MMMIM制品呈现出特殊的"双皮-芯"结构,且不论是在MMMIM制品的皮层材料区域还是在芯层材料区域,分散相PS的形态结构在制品的近浇口端和远浇口端均存在着显著差异,即在近浇口端处有大量取向的纤维状结构形成,而在远浇口端只有少量椭球状或棒状结构形成。在形态分析的基础上,结合MMMIM成型原理,探讨了熔体穿透作用对多熔体多次注射成型制品形态的形成及分布的影响。     

微注塑聚丙烯制品的形态结构

微注塑成型中,聚合物熔体在型腔中的流动形态与传统注塑中有很大的不同,研究成型工艺条件对微注塑制品形态结构的影响对控制微制品形态结构、提高微制品性能具有重要的意义。文中以等规聚丙烯(iPP)为原料,采用单因素实验,研究注塑成型中熔体温度和注射速度两个主要工艺参数对1mm和200μm厚微制品形态结构的影响及微制品中的一些特殊的形态结构现象。实验结果表明,1mm厚微制品的形态分布呈典型皮芯结构,而200μm厚微制品观察不到有非晶冷冻层和球晶结构,全部是具有明显shish-kebab结构的剪切层。     

PP材料泡孔及表面品质的研究

采用注塑成型方式制备微发泡聚丙烯(PP)材料,结合电子扫描显微镜(SEM)、差示扫描量热法(DSC)及热重分析(TG)等技术,研究了发泡剂对微发泡PP的泡孔及表面品质的影响。研究结果表明:不同发泡剂对微发泡PP泡孔及表面品质有显著的影响,以FPE-20为发泡剂,制得的微发泡PP的泡孔尺寸分布均匀,泡孔尺寸较小,为53.39μm;泡孔密度较大,为8.76×10~(12)个/cm~3;同时表面明显无气痕。     

基于CAE的弹药包装箱结构分析

针对产品在使用过程中出现的失效现象,利用CAE技术对包装箱产品的成型过程和静载承压过程进行了模拟,分析和研究了制品承压时的应力分布以及不同注塑浇口位置对注塑件在静载承压情况下所造成的可能失效的问题.研究结果表明,改变注塑成型工艺参数,浇口位置、个数可使注塑制品在静载承压时破裂的危险系数降低.     

高光大平板塑件熔接痕改善方法研究

高光塑件外观要求高,表面不能出现明显的熔接痕,而大型塑件大都是多浇口注塑不可避免的会产生熔接痕,如何减轻或消除大型塑件表面熔接痕,常用的模具及注塑解决方案都存在一定的局限,如成本高,不够节能环保,效果不佳等。本文在对高光产品常见成型方法进行分析比较的基础上,提出了一种更经济、节能环保的高光大平板塑件成型方法,可有效控制熔接痕。     

微注塑成型工艺对聚丙烯制品形态结构的影响

文中基于一组薄壁微制品的微注塑成型实验,研究熔体温度和注射速度对厚度为1.0 mm和500μm微制品形态结构的影响。实验结果表明,这两种微制品都呈现出一种相似的皮芯结构,但不同于传统注塑制品4层或5层结构,微制品只有冷冻层、剪切层和芯层3层结构。随着注射速度的提高,在厚度方向上剪切层比例增大,当注射速度超过一定值后,呈现无芯层结构;随着熔体温度的提高,500μm微制品形态变化不大,1.0mm微制品芯层小幅增厚。     

基于 SEM 和 EDS 的生物质缓冲包装制品微观组织结构研究

采用SEM和EDS技术研究了生物质缓冲包装制品的微观组织结构。实验结果表明:采用模压发泡工艺的生物质缓冲包装制品内部形成了泡孔结构,其形状不仅与成分配伍有关,而且和成型工艺也有密切关系,当稻草纤维含量为10%且成型温度为225℃时,制品回弹性能达到最高值89%;植物纤维在制品内部形成具有良好性能的网状立体结构,该结构与制品中植物纤维、淀粉的含量无关;制品表面的白色颗粒团、横条状、黑色区域等3种典型形态,主要成分分别为填料、植物纤维和淀粉。     

熔体温度对注塑成型iPP制品结晶形态的影响

注塑成型聚丙烯制品的内部结晶形态对制品的最终性能起着至关重要的作用,而结晶形态的形成对成型条件(尤其是熔体温度)有一定依赖性。文中利用偏光显微镜、小角X射线散射和广角X射线衍射等实验方法,详细研究了熔体温度对注塑成型iPP制品结晶形态的影响。研究结果表明,在实验温度范围内,制品厚度方向形态呈现五层皮芯结构,即冷冻层、过渡层、剪切层、β晶层、α球晶层。随着熔体温度提高,皮层厚度减小;结晶度提高,取向度极大值并无明显变化。     

聚丙烯/弹性体共混体系流痕的形成机理及调控

利用扫描电子显微镜、衰减全反射傅里叶变换红外光谱仪和高温凝胶色谱仪研究了聚丙烯的相对分子质量及其分布、弹性体种类对聚丙烯/弹性体共混体系注塑样品流痕及流痕区结构形貌的影响。结果表明,弹性体的加入使聚丙烯缺口冲击韧性大幅提高,但聚丙烯和弹性体的微相相容性及熔体流动剪切诱导分相导致了注塑流痕的产生。茂金属催化丙烯基弹性体同聚丙烯具有更好的微相相容性;宽峰分布聚丙烯中低相对分子质量聚丙烯能提高共混体系的流动性,有利于橡胶相的解缠结和分散,能够稳定熔体的流动,避免基体与弹性体在剪切流动中发生相分离,从而有助于消除注塑流痕。     

运用SEM分析聚醚酰亚胺注射成型制品开裂

运用SEM对聚醚酰亚胺注射成型制品的微观结构进行了分析,找出了制品应力开裂的原因.对制品脆断面的SEM分析可以看出,细微的银纹和熔融料流注射充模过程的流动波纹,有助于正确判断影响制品质量的工艺因素.工程塑料的熔融行为对成型加工至关重要,正确的工艺设置需要对熔融行为进行测试.指出了影响PEI注塑件应力的成型技术的关键因素.     

变模温与型腔气体反压辅助微孔发泡注塑技术及其产品内外泡孔结构演变

建立了一种变模温和型腔气体反压协同控制的微孔发泡注塑技术,研制了相应的变模温控制系统与型腔气体反压控制系统,构建了变模温与型腔气体反压辅助微孔发泡注塑试验线,并对变模温与型腔气体反压作用下的产品内外泡孔结构演变进行了研究。结果表明,变模温与型腔气体反压辅助工艺单独施加于微孔发泡注塑技术时,对其产品内外泡孔结构均具有双重影响:变模温可以改善产品大部分的表面形貌,但其对填充过程中的熔体发泡影响不大;型腔气体反压可以基本抑制填充过程中的熔体发泡,但却对产品内部泡孔密度有比较明显的降低影响。通过变模温与型腔气体反压的协同控制,可以实现微孔发泡注塑产品表面气泡形貌和内部泡孔结构的良好调控。     

Application of Taguchi''s method on the optimal process design of an injection molded PC/PBT automobile bumper

The manufacturing process of an injection molded polycarbonate/ poly(butylene terephthalate) automobile bumper was optimized, using Taguchi's method, to eliminate silver streaks on the surface of the product. First, a set of process factors was selected and a preliminary experiment was conducted with an L₁₂ orthogonal array to screen the significant factors, check the validity of the data fitting model, and predict an improved process condition to overcome the filling difficulties. Second, using the selected control factors, a principal experiment was conducted with an L₁₈ orthogonal array to predict an optimal process condition that solve the quality problem. Finally, the predicted process condition was tested on an 2500-ton injection molding machine to confirm the prediction. The results reveal that the main factors that directly relate to the generation of silver streaks are the mold temperature, the fill time, the fill/ postfill switch over control, and the injection rate.     

加工参数对微孔注塑聚醚砜力学性能的影响

通过正交实验,考察了微孔注塑成型过程中各重要加工参数对微孔聚醚砜(PES)制品拉伸强度和冲击强度的影响,利用扫描电镜(SEM)观测了制品的泡孔结构.结果表明,受冷却和剪切的影响,制品表层到芯层的泡孔形态不同.较高的熔胶量和超临界流体(SCF)含量,适中的射胶压力和射胶速率以及较低的熔体温度和模具温度有利于提高制品的拉伸...     

气体辅助注射成型聚丙烯的多层次结构

用扫描电镜(SEM)观察了气体辅助注射成型(GAIM)和常规注射成型(CIM)等规聚丙烯(iPP)在不同部位的结晶形态。发现CIM试样的"皮-芯"结构不明显,而GAIM试样在不同部位则形成了包括球晶、串晶和取向片晶,进而表现出明显的多层次结构。在结晶形态分析的基础上,初步探讨了GAIM制品多层次结构的形成机理。     

注塑成型工艺参数对制品体收缩率变化的影响及工艺参数优化

结合CAE及Taguchi DOE技术研究工艺参数对注塑制品体收缩率变化(制品中体收缩率的最大值与最小值的差值)的影响并获得优化的工艺参数以使制品的体收缩率变化最小。文中采用L9(3^4)正交矩阵进行实验,并研究了各个参数对制品体收缩率变化的影响程度,对于所选参数,保压压力和模具温度对注塑制品的体收缩率变化的影响较大。     

An experimental study of the water-assisted injection molding of glass fiber filled poly-butylene-terephthalate (PBT) composites

The purpose of this report was to experimentally study the water-assisted injection molding process of poly-butylene-terephthalate (PBT) composites. Experiments were carried out on an 80-ton injection-molding machine equipped with a lab scale water injection system, which included a water pump, a pressure accumulator, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit. The materials included virgin PBT and a 15% glass fiber filled PBT composite, and a plate cavity with a rib across center was used. Various processing variables were examined in terms of their influence on the length of water penetration in molded parts, and mechanical property tests were performed on these parts. X-ray diffraction (XRD) was also used to identify the material and structural parameters. Finally, a comparison was made between water-assisted and gas-assisted injection molded parts. It was found that the melt fill pressure, melt temperature, and short shot size were the dominant parameters affecting water penetration behavior. Material at the mold-side exhibited a higher degree of crystallinity than that at the water-side. Parts molded by gas also showed a higher degree of crystallinity than those molded by water. Furthermore, the glass fibers near the surface of molded parts were found to be oriented mostly in the flow direction, but oriented substantially more perpendicular to the flow direction with increasing distance from the skin surface.     

Development of PLA/cellulosic fiber composite foams using injection molding: Crystallization and foaming behaviors

Poly(lactic acid) (PLA) and northern bleached softwood kraft (NBSK) or black spruce medium density fiberboard (MDF) fibers were melt compounded using a co-rotating twin screw extruder and subsequently microcellular injection molded. Poly(ethlylene glycol) (PEG) was used as a lubricant. The microcellular structure, thermal properties, and crystallization behaviors were characterized using scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, and wide angle X-ray diffraction. Results show that cellulosic fibers, acting as crystal nucleating agents, increased the crystallization temperature and the crystallinity and decreased the crystallization half time. The dissolved N₂, the shear stress, and biaxial stretching during foaming also enhanced the crystallinity of PLA. Compared to PLA/PEG, a finer and more uniform cell structure was achieved in the cellulosic fiber composite foams. The improved foam morphology was attributed to the cell nucleating effects of the fibers and the increased melt strength by the addition of cellulosic fibers and by the gas- and fiber- induced crystallization.     

长玻璃纤维/聚丙烯复合材料粒料注塑制品的拉伸强度

利用自行研制的玻璃纤维(GF)增强聚丙烯(PP)预浸装置,制备了长玻纤增强聚丙烯(LGFRP)粒料,并通过普通注塑机注塑成型。研究了界面改性、粒料长度、浸渍程度及退火处理等对注塑试样拉伸强度的影响。试验发现,用接枝马来酸酐PP作为界面相容剂,试样的拉伸强度明显提高。当接枝马来酸酐量占PP量的0.3 %左右时,试样强度达到最大值。长纤维粒料内纤维浸渍度越高,注塑试样的强度越好。15 mm和5 mm长纤维粒料注塑成型试样的拉伸强度均高于10 mm粒料注塑成型的试样。退火处理可较大程度地提高注塑试样的拉伸强度。     

Prediction of shrinkage and warpage in consideration of residual stress in integrated simulation of injection molding

The accurate prediction of shrinkage and warpage of injection molded parts is important to achieve successful mold design with high precision. In this study, the numerical analysis of shrinkage and warpage of injection molded parts made of amorphous polymers was carried out in consideration of the residual stresses produced during the packing and cooling stages of injection molding. The temperature and pressure fields were obtained from the coupled analysis of the filling and post-filling stages. For residual stress analysis, a thermo-rheologically simple viscoelastic material model was introduced to consider the stress relaxation effect and to describe the mechanical behavior according to the temperature change. The effect of the additional material supply during the packing stage was modeled by assigning the reference strain. The deformation of injection molded parts after ejection induced by the residual stress and temperature change was analyzed using a linear elastic three-dimensional finite element approach. In order to verify the numerical predictions obtained from the developed program, the simulation results were compared with the available experimental data in the literature. In the case of residual stress, it was found that the present simulation results overpredicted the tensile residual stresses at the surface of injection molded parts. However, the predicted shrinkage was found to be reasonable to describe the effects of processing conditions well. Finally, an analysis of the shrinkage and warpage was successfully extended for a part with a more complex curved shape.     

Generation of optimal parting direction based on undercut features in injection molded parts

An algorithm has been developed for the automated recognition of undercut features for determining the optimal parting direction of injection molded parts. On the basis of the 3-D solid model of a molded part described in Boundary Representation (B-Rep), the geometrical entities and the information of a solid model and their topological relationships are extracted. According to these information, the criteria under which the undercut feature is formed are set up and the undercut feature directions (the withdrawal directions of side-cores or side-cavities) are identified. The optimal parting direction is chosen based on the criterion of maximizing undercut feature volumes in each undercut feature group. Through the case studies on industrial parts, the methodology developed is found to be efficient and effective in determining the undercut features and the optimal parting direction automatically.mining the optimal parting direction of injection molded parts. On the basis of the 3-D solid model of a molded part described in Boundary Representation (B-Rep), the geometrical entities and the information of a solid model and their topological relationships are extracted. According to these information, the criteria under which the undercut feature is formed are set up and the undercut feature directions (the withdrawal directions of side-cores or side-cavities) are identified. The optimal parting direction is chosen based on the criterion of maximizing undercut feature volumes in each undercut feature group. Through the case studies on industrial parts, the methodology developed is found to be efficient and effective in determining the undercut features and the optimal parting direction automatically.