挤出制品熔接缝形成的构象分析

从挤出制品熔接缝形成的原理进行细致的分析，制品的不良熔接缝有“V形槽及弱连接”两种形式。其中熔接缝的强度及物理机械性能远远低于产品其它部位。研究发现熔接缝的结构与材料的配方、挤出机头模具的结构和加工工艺参数均有关系。     

减小熔接缝对注塑件损害的方法

分析、讨论了从注塑件设计、模具设计、塑料选材到工艺参数调节，以及其它方面避免熔接缝或改善熔接缝强度的方法。     

注塑件熔接缝力学性能研究

从注塑件熔接缝力学性能的实验研究、数学模型的建立和数值模拟三方面．介绍了注塑件熔接缝力学性能的研究概况。     

塑料注塑件熔接缝影响浅析

热塑性塑料有很多成型方法，注塑成型是其中最重要的成型方法之一，其最大优点是可以一次成型结构复杂、尺寸精密、外观精美的制品，因此应用范围广。但是，注塑件不可避免地会产生各种缺陷，其中熔接缝是注塑件最常见的缺陷之一。熔接缝的存在不仅影响制品的外观质量，出现翘曲变形，而且会使注塑件的力学性能明显降低。熔接缝受成型工艺的影响很大，在不同的工艺条件下，熔接缝区的强度可以是原始材料的10％～90％，严重影响和限制了注塑制品的正常使用。     

热塑性塑料注塑件熔接缝影响因素分析

分析了热塑性塑料注塑件中熔接缝的分类和特征。从材料选择、制品结构设计、模具设计、成型工艺、热处理几个方面分析了影响熔接缝的因素；并针对不同因素，提出了相应的对策和改善熔接缝力学性能的方法。     

注塑件熔接缝结构,性能评价及影响因素

文章介绍了熔接缝形成的原因，接缝类型，接缝外观和断口形态特征以及接缝性能评价方法。分析了接缝类型，塑料材料性质，工艺参数和其它因素对接缝性能的影响。     

注塑参数优化研究方法

对参数优化方法在注塑研究中的应用进行了综述，阐述了各方法的基本原理和主要特点，着重讨论了优化方法所适用的优化问题的类型和其对注塑翘曲、收缩、熔接缝及强度的预测能力以及模拟软件的应用，探讨了不同优化方法相结合对搜索效率和优化结果的影响。     

大型中空吹塑挤出系统设计及其关键技术研究

通过对大型中空挤出系统的分析,针对目前大型中空成型机的熔料融合不均匀问题,对机头内部流道进行了结构设计和优化;根据其模头体积大、储料多、短时间需要大流量的工作特点,设计了一种大型储料式中空成型机挤出系统;介绍了模头系统的工作过程,并对模头内流道进行了设计和研究,成功地解决了熔料融合不充分,理论接缝等问题。该设计与研究保证了制品强度,大幅提高了产品质量,节省了原材料。     

超高性能混凝土湿接缝界面粘结性能EI北大核心CSCD

研究了超高性能混凝土(UHPC)湿接缝界面破坏特性、拉伸强度以及拉伸强度比(接缝试件界面拉伸强度相对于整体试件的比值)等。结果表明:所有UHPC湿接缝试件的破坏模式均为脆性破坏;相比于未掺纤维湿接缝试件(界面拉伸强度2.24 MPa),掺纤维UHPC湿接缝试件具有更好的界面粘结性能(界面拉伸强度可达6.64 MPa,拉伸强度比可达68.6%);当纤维体积掺量不大于2.5%时,湿接缝试件的界面拉伸强度、拉伸强度比以及界面断裂韧性均随纤维体积掺量的增大而增大,最佳纤维体积掺量为2.5%;长纤维对UHPC湿接缝界面拉伸强度、拉伸强度比以及界面断裂韧性的提升效果优于短纤维,异形纤维优于平直形纤维;配筋UHPC湿接缝试件延性特征显著优于未配筋试件,增加钢筋锚固长度、界面配筋率是提高UHPC湿接缝延性特征和界面拉伸强度的较有效方法;当钢筋锚固长度达到6倍钢筋直径时,湿接缝处界面拉伸强度大于整体浇筑UHPC拉伸强度。此外,构建了不同纤维参数下UHPC湿接缝界面拉伸应力-相对位移简化模型。     

充模过程熔接缝形成的数值模拟

本文在分析注塑周期熔接缝形成过程的基础上，在充模阶段，利用前沿区喷泉流动的概念，建立“喷泉遭遇流”的物理模型和数学模型，并运用MAC的数值差分方法模拟了“喷泉遭遇流”的流场。为深入了解注塑充模阶段熔接缝的形成机理提供了理论基础。     

Fracture toughness of weldlines in thermoplastic injection molding

Weldlines are fatal defects in many injection moldings of thermosetting resins and thermoplastics. Significant strength reduction by weldlines in thermoplastics is caused by poor adhesion, molecular orientation, and a V-notch effect. These factors have been little investigated in detail, in spite of being well known. In the present article, the V-notch effect on strength is discussed for two types of thermoplastics, polystyrene and polycarbonate. The depth of weldlines was obtained by milling on the weldline surface, and the fracture toughness was measured with a double edge notched specimen. Polystryrene, which was drastically weakened by weldlines, had relatively deeper V-notch regions and the fracture toughness was also reduced by weldlines. Although polycarbonate had the same fracture toughness as polystyrene, it had strong weldlines since the depth of weldlines was negligibly small.     

Weldline strength in glass fiber reinforced polyamide 66

Presence of weldlines introduces an element of uncertainty to the performance of injection molded parts. Weldlines are particularly problematic in reinforced plastics because, unlike molecular orientation in neat polymers, the flow induced fiber orientation does not relax. This paper deals with the structure and mechanical behavior of weldlines in glass fiber reinforced nylon 66, a plastic known for excellent fiber-matrix adhesion. Two molds were used to generate weldlines: a double gated tensile sample shaped cavity in which the weldline is formed by a head-on collision of melt fronts flowing in opposite directions and a film gated rectangular plaque with a circular insert in which the weldline formation behind the insert is followed by additional flow. In both cases the weldline zone is several millimetres wide: in the plane where the melts fronts have met fibers are oriented parallel to this plane (random-in-plane in the double-gated cavity and unidirectional in the cavity with insert). The transition zone between the weldline plane and the rest of the sample is characterized by an increased presence of microvoids. Weldline tensile depends little on the fiber concentration and on the sample shape or thickness: values close to the matrix strength are found: in samples without weldlines strength increases with the fiber content. However, in instrumented impact penetration test during which the material is subjected to multiaxial loading, the weldline effect appears negligible.     

Weldline strength in injection molded glass fiber-reinforced polypropylene

Weldlines are inescapable byproducts of the injection molding process. They represent potentially fatal flaws particularly in multiphase materials. In this work weldlines in injection molded glass fiber-reinforced polypropylene (0 to 40wt%) were studied as a function of the cavity shapes and depths. It was found that the weldline is a zone between 2 and 8 mm wide extending throughout the thickness in which the fibers are oriented almost perfectly in a plane parallel to the weldline. While the strength of moldings without weldlines depends on the mold shape and on the fiber concentration, the weldline strength is a function of fiber content only. A simple model based on the assumption of complete debonding of the fiber-matrix interface when failure occurs can be used to predict the strength loss in the weldline.     

Effects of Processing Parameters on Tensile Strength of Thin-Wall HDPE Parts Injection Molded by Ultra High-Speed Process

This study explores how ultra high-speed processing parameters affect the melt flow length and tensile strength of thin-wall injection molded parts. A spiral shaped mold with a specimen thickness of 0.4 mm and a width of 6 mm was first constructed to test the melt flow length as an index of process capability for ultra high-speed injection molding. It was observed that the flow length increases with increasing injection speed. High-density polyethylene (HDPE) tensile test specimens with different thicknesses (0.6 mm and 2 mm) were also molded for tensile tests. Both single gate and double gates were used to form parts without and with weldlines. Injection molding trials were executed by systematically adjusting related parameters setting including mold temperature, melt temperature, and injection speed. The parts’ tensile strengths were measured experimentally. It was found that tensile strengths of 0.6 mm thick parts both with and without weldlines were higher than those of 2 mm thick parts. The tensile strength of 0.6 mm thick specimens increases with increasing mold temperature, melt temperature and injection speed, whereas tensile strength in 2 mm thick specimens was only weakly dependent on the corresponding processing parameters. Furthermore, 0.6 mm thick specimens with weldlines had tensile strengths lowered about 9.6% compared to parts without weldlines. For 2 mm thick part the corresponding reduction is 4.3%.     

带有矩形嵌件薄壁型腔内熔接过程动态模拟

为了准确模拟具有对称结构的带有矩形嵌件的薄壁型腔内熔接线的动态形成过程,采用Level Set/Ghost方法追踪充填阶段聚合物熔体前沿界面。引入具有高阶精度且数值稳定无振荡的5WENO（the fifth order weighted essentially nonoscillatory）格式对Level Set/Ghost方程进行数值求解,耦合求解物理量控制方程的一般差分格式实现熔接过程的动态模拟。数值算例对整个流场的压力、温度及速度进行了分析和讨论,并将熔接区域的压力、温度和非熔接区域的压力、温度进行了比较。数值结果与理论分析结果一致,且与前人数值结果相比有很好的精度。     

Weldline integrity of reinforced plastics: Effect of filler shape

The paper is a preliminary report on glass fiber and glass flake orientation in the weldline zone of injection molded reinforced polypropylene. Two types of weldlines were studied using simple shape molds: one where two melt streams meet head-on and become immobilized, the other where the weldline formation is followed by additional flow. In the weldlines of the first type, which are characteristic of current standard molds used to test weldline strength, the anisometric particles are almost perfectly oriented perpendicular to flow. As a result, the weldlines of this type tend to be weak and brittle. In the second case when the weldline is formed by merging of melt streams separated by an insert, particle orientation in the weldline area remains different from other areas of the sample for long distances from the insert. It is shown that in molds where the weldline formation is followed by laterally expanding flow the change of particle orientation is faster than for unidirectional flow.     

Performance prediction of weldline structure in amorphous polymers

The presence of a weldline generally reduces the mechanical strength of injection molded parts. A typical remedy to eliminate the problem of weak weldline structure has been to increase the melt temperature. This, however, is not an acceptable solution in some situations. A general solution to the weak weldline problem requires an in-depth understanding of the thermomechanical history of the injection molding process. A theoretical model for the strength of weldlines is presented that provides a comprehensive physical insight of the bonding process at the weldline interface. The model is based on the self-diffusion of molecular chains across the polymer-polymer interface and the frozen-in orientation that remains parallel to the interface. Both factors are analyzed separately and then superimposed to predict the strength of weldlines from known processing conditions and geometry. Experimental results show good correlation with predictions.     

Influence of Wood Welding Frequency on Wood Constituents Chemical Modifications

Interesting chemical differences betwen weldlines obtained at 100 Hz and 150 Hz frequencies in linear vibration wood welding were observed by FT-IR and ¹³C NMR. An increase in the proportion of unoxidized phenolic groups in the lignin is observed by FT-IR and the increased joint strength observed is ascribed to the improved adhesion derived from this. The much decreased level of oxidation due to the much shorter welding time possible at 150 Hz was clearly observed by ¹³C NMR by a marked decrease, even disappearance, of the presence of dark coloured quinones in the weldline at 150 Hz. This yielded colourless weldlines.     

Effects of filler contents and processing parameters on the weldline strength of compression molded natural rubber

The presence of weldlines in rubber products is regarded as a one of the most undesirable phenomena, since it results in poor mechanical properties. Compression molding of large or complicated products are prepared by multiple charges, which produces weldlines once the melt fronts are joined by the impingement flow. In this work, the effects of curing systems, processing parameters, filler types, and contents on weldline strength of compression molded natural rubber (NR) were investigated. Furthermore, the effects of curing systems on the aging properties of NR vulcanizates were studied in details. The results show that an increased amount of calcium carbonate does not affect the weldline strength. However, the difference in tensile strength between weldline and nonweldline specimens becomes larger with the high loading of silica and carbon black. In addition, for the factors selected in the experiments, clamping pressure, and curing system were found to be the principal factors affecting the weldline property of vulcanizates. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Fracture behavior of glass bead-filled poly(oxymethylene) injection moldings

The mechanical properties of glass bead filled poly(oxymethylene) were investigated as a function of glass bead content and glass bead diameter using injection molded test pieces. Fracture toughness measurements were made using single edge-notched tension and single edge-notched bend specimens. The effect of notch orientation with respect to the mold fill direction on fracture toughness was studied using single gate and double gate moldings. Tensile strength and flexural modulus were measured using standard test pieces. It was found that; (i) fracture toughness of the filled and unfilled polymer was relatively independent of notch orientation, (ii) the presence of weldlines in the molded test pieces did not affect the fracture toughness of unfilled polymer or its composites, (iii) fracture toughness of filled polymer was always considerably lower than that of the unfilled polymer; fracture toughness decreased sharply with increasing bead concentration, (iv) fracture toughness was not a sensitive function of glass bead diameter; it decreased slightly as bead diameter increased, (v) strain energy release rate as measured under impact decreased with increasing bead concentration, (vi) tensile strength decreased linearly with increasing glass bead concentration and was inversely proportional to the square root of the bead diameter, (vii) weldlines did not affect the tensile strength of the polymer or its composities, (viii) flexural modulus increased linearly with increasing glass bead concentration according to the Einstein equation.