注塑成型制件的尺寸稳定性研究

注塑制品冷却时的收缩程度主要取决于加工材料的组份凡从事塑料加工者,均知道注塑制品冷却时会发生收缩。收缩程度主要取决于所加工材料的组份。半结晶材料的收缩率比无定形材料的收缩率大,填料可以降低各种聚合物的收缩率,降低程度取决于所添加填料的类型和添加量。制品几何结构也是影响收缩率的一大重要因素,薄壁制品要比厚壁制     

利用CAE确定精密注塑成型模具的型腔尺寸

对CAE分析的收缩结果进行了评述。给出了利用不同收缩率确定型腔关键尺寸的方法。考虑了模具受热膨胀和型腔压力对型腔尺寸的影响。利用Moldflow预测成型时的型腔压力,并用AN-SYS计算型腔压力导致的尺寸变化,给出了分析实例,为精密注塑成型模具型腔尺寸的确定提供了依据。     

确保注塑成型工艺的稳定性

在注塑成型生产中,注塑成型的稳定性对于制品质量至关重要。如何才能确保注塑成型的过程更加稳定呢？一种型腔压力传感器或许能够帮助您解决问题。     

注塑成型制品取向的研究分析

从取向应力产生机理、熔体充模流动过程、流动与取向的关系着手,分析取向对注塑制品物理机械性能的影响。同时,指出各工艺参数对取向的影响程度。改善工艺条件或优化模具设计减小取向应力,使制品截面上的取向应力均匀化,对提高注塑制品质量有着重要意义。     

注塑参数对聚碳酸酯成型收缩率的影响研究

研究了注塑参数对聚碳酸酯(PC)成型收缩率的影响，从理论上探讨了注塑参数—制品结构—收缩率之间的关系。试验结果表明，对PC成型收缩率影响最大的注塑参数是料温，其次是模具温度、注塑压力和注射速率，而保压时间、冷却时间、预塑速率在实验范围内对PC成型收缩率影响较小。     

注塑型酚醛模塑料热加工稳定性研究

讨论了低相对分子质量聚乙烯蜡、白油、切片石蜡及聚乙二醇4种稳定剂对酚醛注塑料热加工稳定性的影响，重点利用转矩流变仪研究了聚乙二醇加入前后酚醛注塑料的流变行为。结果表明：低相对分子质量聚乙烯蜡、白油、切片石蜡及聚乙二醇都可以有效地改善酚醛注塑料的流动性和热加工稳定性，但只有聚乙二醇不仅改善了酚醛注塑料的流动性和热加工稳定性，丽且还提高了酚醛注塑制品的弯曲强度。转矩时间流变曲线表明，加入聚乙二醇后酚醛注塑料具有更加宽泛的安全加工范围。     

基于Moldflow的打印机上盖制件注塑成型翘曲变形分析

以平板型薄壁注塑制件打印机上盖为研究对象,应用CAE软件Moldflow与正交试验相结合的方法,找出对平板型薄壁制件在注塑成型优化方面最重要的工艺参数.正交试验证明:对平板型注塑件而言,熔体温度和保压压力是其成型过程中影响翘曲变形的两个最重要的工艺参数.     

模具对振动注射成型制件作用效应的初步研究

采用自制的振动试验台，分别安装两个不同的试样模具，使用了不同的聚合物材料，在不同的温度，压力下变化不同的振动频率和振幅进行实验，研究了聚合物熔体在振动场中注射成型时，成型模具对聚合物振动成型效应的作用。结果表明，模具浇口及型腔尺寸不同。振动注射制件的强度不同；模具型腔尺寸大振动产生的效应弱。型腔小振动产生的效应强。     

注塑模具成型零件工作尺寸工程算法研究

针对注塑模具成型零件工作尺寸现有计算方法存在计算量大、过程复杂等问题,提出了该类尺寸的一种实用型工程算法.通过对塑件基本尺寸直接加放收缩率,再分类调整尺寸的制造公差带,同时在计算中引入修模余量,能有效避免因塑料收缩率波动导致模具的报废率,也大大简化了计算过程.     

振动力场下聚合物注塑成型过程的能量消耗

为了从理论上分析和验证振动力场引入到注塑成型过程中对注塑成型过程能量消耗的影响,在传统三大方程的基础上借助Maxwell和改进的Tanner本构方程对注塑机成型过程中的能量消耗进行了理论推导.在此基础上通过实验验证了该数学模型的正确性和可靠性.结果表明:计算结果与实验结果能够很好地吻合,振动强度越大,吻合程度越高.随着...     

注塑成型制件尺寸稳定性研究

材料吸湿性对制品尺寸的影响(4)关于尺寸稳定性的研究我们已经讨论了造成制品尺寸变小的影响因素.但是也存在一些环境因素,它们使得制品的尺寸随着时间增加.其最好的例子是尼龙制品吸收空气中的水分时会出现的尺寸增大.许多聚合物具有吸湿性,由于大气中总是存在水蒸气,因此这成为聚合物吸水的主要来源.在正常气候条件下许多吸湿性材料经过一定的时间可以吸收0.1％ ～ 0.2％的水分.但是对于尼龙材料来说,由于含有氢键,它吸水的程度更大.在相对湿度为35％～65％之间的正常环境室温条件下,未填充尼龙的平衡吸水量按重量计算大约在1.5％～2％之间.     

Dimensional stability of single‐site ethylene copolymers in rotational molding

The dimensional stability of ethylene copolymers in rotational molding was studied by comparing the warpage observed for a series of conventional and single‐site catalyzed ethylene copolymers. Bench‐scale molding trials were carried out under controlled molding conditions. The rapid cooling of the mold using a water spray resulted in greater warpage. Under such conditions, molded parts made using the single‐site resins showed less warpage compared to the Ziegler‐catalyzed copolymers with otherwise comparable densities. The Ziegler‐catalyzed copolymers were characterized by a faster crystallization rate, and were shown to generate larger crystallinity gradients through the part thickness during the cooling process. Second to temperature gradients, crystallinity gradients are a leading cause for the development of residual stresses and causing warpage. Differences in the crystallization rates between single‐site and Ziegler‐catalyzed copolymers are discussed based on their intermolecular comonomer distributions. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Dimensional stability and property gradients in thick sheet molding compound (SMC) sections

The dimensional stability of sample cylinders cured with sheet molding compound pastes was investigated. A significant amount of dimensional change was found for these samples when they were annealed. Furthermore, the amount of change varied with location from the center to the wall along the radial direction of the sample cylinder to form a strain gradient. A series of experiments were then carried out to determine property gradients along the same direction in search of the source of the dimensional instability. It was found that the sample also had a gradient in cure and a gradient in dynamic mechanical properties. But these gradients are not in full agreement. In particular, the gradient of cure appears to be opposite to the direction of the strain gradient, while the gradient of the dynamic mechanical properties coincides with it. These results, therefore, suggest that the dimensional stability may be predominantly governed by the viscoelastic behavior of the material.     

Dimensional stability of glass-ionomer cements

Factors influencing the shrinkage behaviour of glass-ionomer cements are described, with particular reference to the effects of cement age and the binding of water contained in the matrix. Dimensional changes occurring in cements exposed to alternating dry and saturated conditions are shown to be irreversible and a linear relationship is depicted between shrinkage and volume fraction of matrix. A failure mechanism involving matrix shrinkage is proposed to explain mechanical property changes which are evident when cements are maintained in environments of low relative humidity.     

Dimensional study of thermoplastic parts made using sequential injection molding

As a result of new aesthetical and economical requirements in injection molding, several processes have been developed during last years. In spite of conventional process, sequential injection molding is a versatile technique based on independent control for each gate opening. This procedure allows part filling without weld lines or, at least, these defects can be relocated in suitable positions. A short discussion about sequential principles is made introducing computer simulations. Pressure required for part filling and molding shrinkage were evaluated using experimental procedures with a prototype mold and using conventional and sequential methods. Several setting up parameters were also used to analyze the effect on injection process. Final results show that shrinkage in sequential injection is similar to conventional process but some new effects could be induced by the process asymmetry and should be investigated further. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Dimensional stability of exterior building products

Dimensional stability problems such as warpage, bowing and other changes in shape and size may occur when exterior building products (siding, windows) are heated by the sun. This paper describes the effects of material properties such as coefficient of thermal expansion, heat distortion temperature, modulus, and heat build-up, caused by the sun, on dimensional stability of the exterior building products.     

Dimensional stability of wood–polymer composites

Wood–polymer composites (WPC) were prepared by impregnation of polymeric monomers in wood and in situ polymerization. Three polymeric chemicals were chosen for this study: methyl methacrylate (MMA), hydroxyethylene methacrylate (HEMA), and ethylene glycol dimethacrylate (EGDMA). The effects of polymeric monomers and their combinations on moisture adsorption (M), anti–moisture adsorption efficiency (AME), liquid water uptake (D), water repellency efficiency (WRE), longitudinal, radial, tangential, and volumetric swelling properties (S) after soaking, and antiswelling efficiency (ASE) were investigated. It was found that M was different for different methacrylate combinations and depended not only on the composition of the impregnants, but also on wood properties. Liquid water uptake was similar regardless of the formulation of the WPC. Wood–polymer composites with high MMA content displayed enhanced dimensional stabilities, but WPCs with high HEMA content did not. Tangential and volumetric ASEs were strongly dependent on the type of treatment. Mold growth tests showed that wood treated with HEMA alone had no surface mold growth, and wood treated with MMA alone also showed less mold growth than did the control samples. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 5085–5094, 2006     

Analysis of thermal stability of acrylonitrile-acrylic elastomer-styrene terpolymer in injection molding

Acrylonitrile-acrylic elastomer-styrene terpolymer (AAS resin) was developed to improve weatherability of acrylonitrile-butadiene-styrene terpolymer (ABS resin). To compare thermal stability of both resins, test parts of AAS and ABS resins were injection molded at various temperatures and the Izod impact value of the resulting moldings was measured. A study was then made to find the relationship between this value and deterioration of the resins. AAS resin was molded at temperatures from 180°C to 280°C. The impact value of the resulting moldings was almost constant for temperatures up to 260°C, with the first major decrease occurring at 280°C. In contrast, the impact value of conventional ABS resin moldings constantly decreased as the molding temperature was elevated. To explain this phenomenon in both resins, two types of test program steps were undertaken: (1) The cause of the change in characteristics of the AAS resin was determined by obtaining its stress-strain curve in a high-speed flexural strength test; measuring its infrared absorption spectrum; and determining its flow properties with a constant-pressure extrusion type rheometer; (2) the distribution of elastomer in the resin was observed with an electron microscope. It was found that the decrease of impact values of both resins at high temperatures is caused by deterionration of the elastomer. Also, it was found that the different relationships between the impact value and molding temperatures for AAS and ABS resins are due to the difference between the rates of thermal degradation of the acrylic elastomer and butadiene elastomer.     

Dimensional stability of polystyrene/polymeric liquid crystal blends

Recovery experiments above T_g have been performed on polymeric liquid crystal (PLC) - polystyrene (PS) blend sheets obtained from extrusion and subsequent hot drawing. The data reported show that a significant improvement of the dimensional stability of a drawn thermoplastic material can be obtained by adding a low percentage of non-compatible polymeric liquid crystals that are oriented during the hot drawing process. The fibrils formed act as a constraint for a certain amount of polymer surrounding them and consequently these highly oriented sheets, once exposed to high temperature, will mainly stress relax and do not creep. This effect disappears when the melting temperature of the oriented crystalline phase is reached. Compatible PLC-PS blends do not show any improvement on the dimensional stability compared to the unfilled matrix.