振动注射成型中模腔冷却过程的研究

研究了振动注射成型中模腔内聚合物溶体产生的振动剪切热,并研究在振动作用下模腔内物料的冷却过程。结果表明,模腔内熔体的温升速率随着振动频率、应变振幅及振动剪切速率的增加而增加,随熔体温度的增加而减少。由于振动剪切换,使振动注射成型需要更长的冷却时间。     

注塑制品翘曲变形的最显著影响因素

采用Moldflow进行了塑料制品注塑过程模拟实验,分析了模具温度、熔体温度、保压时间、保压压力、冷却时间、注射时间和速度/压力控制转换（V/P转换）对注塑制品翘曲的影响,从中确定影响最显著的注塑过程参数。首先按一次因子法进行实验,根据因子效应,各因子影响权重顺序为：保压时间>冷却时间>熔体温度>注射时间> V/P转换>保压压力>模具温度,其中熔体温度、保压时间、冷却时间、注射时间对制品的翘曲有明显影响;再采用田口实验方法对这4个因素进行模拟实验,用L9（34）正交表设计实验,根据实验数据计算信噪比以评判影响因子的权重,由翘曲信噪比、体积收缩率信噪比和缩痕指数信噪比三方面分析,发现熔体温度对制品翘曲的影响最为显著。     

基于Moldflow的注射器翘曲分析

利用Moldflow软件对注射器塑料件的翘曲原因进行分析,并采用正交试验设计方法(单参数变动实验)对保压压力、熔体温度、模具温度、冷却时间等进行分析。经分析后得出影响制品翘曲变形的最主要因素是保压压力,其次则是熔体温度、模具温度、冷却时间。模拟得到本例最优成型参数分别为,模具温度35℃、熔体温度240℃、保压压力100MPa、保压时间17s、冷却时间20s。     

基于响应面传动器成型缺陷研究

传动器通过注塑成型工艺制得,其成型质量直接影响传动器的性能。在注塑成型工艺过程中,模具温度、熔体温度、保压压力以及冷却时间等工艺参数对制件的影响较显著,不合理的工艺参数导致制件出现较大的翘曲变形。通过建立响应面模型,以模具温度、熔体温度、保压压力以及冷却时间为响应参数,以制件的翘曲变形量为响应目标,优化一组最佳的成型工艺参数组合。结果表明：四个变量的影响程度分别为：模具温度>保压压力>冷却时间>熔体温度。当模具温度80℃、熔体温度180℃、保压压力90 MPa、冷却时间20 s,制件的翘曲变形量最小为1.955 mm,较未优化的翘曲变形量降低0.427 7 mm,有效地改善了制件的成型质量。     

基于 Taguchi 法的注塑制品成型收缩率最小化

运用Taguchi实验设计技术研究了熔体温度、冷却时间、保压压力、注射时间等工艺参数对聚丙烯(PP)碱性蓄电池壳注塑制品成型收缩率的影响,获得了使制品的成型收缩率最小的优化工艺参数。研究表明,在所选择的工艺参数中,对成型收缩率的影响程度按大小排序依次为熔体温度、冷却时间、保压压力、注射时间。所预测的优化工艺组合的最小成型收缩率为0.916%,与验证实验值0.908%较为吻合。     

注射压缩工艺参数对制品收缩率及其均匀度的影响

采用顺序注射压缩工艺,研究熔体温度、注射速度、压缩速度、压缩距离和冷却时间5个工艺参数对成型的聚苯乙烯长方形制品收缩率及其均匀度的影响规律。结果表明,熔体温度、注射速度和压缩距离的影响较大,压缩速度和冷却时间的影响较小,同一制品靠近浇口处的收缩率变化梯度比远离浇口处大。     

全同立构聚丙烯振动注射试样晶体结构的变化

采用自行研制的压力振动注射装置，在不同熔体温度、振动频率、振动压力下成型了全同立构聚丙烯振动注射试样，并进行了WAXD、DSC和SEM测试。结果表明，当成型温度为190℃时，在高的振动频率下，有γ晶生成；在高振动压力条件下，有β晶生成。当成型温度为230℃，无论是在高频率，还是高压力振动，都有β晶生成。同时，振动还将改变试样的熔点，提高试样结晶度，细化晶粒。     

基于计算机模拟与正交试验设计的鼓风机叶轮成型质量控制

针对某30%短玻纤增强聚丙烯材料的鼓风机叶轮,基于计算机模拟技术与正交试验法探究其优化方案。结果表明:各工艺参数对鼓风机叶轮圆柱度的影响程度排序为:保压时间熔体温度模具温度冷却时间保压压力;对叶轮熔接线状态的影响程度排序为:冷却时间保压压力熔体温度模具温度保压时间,综合分析最优工艺参数组合为A_1B_1C_2D_2E_4。依据最优工艺参数进行仿真模拟,圆柱度及熔接线状态与初始工艺相比,提高60.0%和36.2%,满足鼓风机叶轮的设计要求,并得到试模验证。     

风栅摆幅对物理钢化玻璃冷却状态的影响

通过对摆动式却风栅不同摆动振幅条件下物理钢化玻璃冷却状态及对应力均匀性影响的分析，导出了冷支风栅振动振幅的最佳值，这对于风机冷物理钢化玻璃的生产具有现实指导意义。     

基于稳健设计的汽车尾灯罩注塑工艺优化

以某汽车尾灯罩的翘曲变形量为主要优化目标，应用Moldflow软件，采用稳健设计的方法，结合随形冷却水道设计，对汽车尾灯罩注塑工艺参数进行优化，确定模具温度、熔体温度、注射时间、冷却时间、速度/压力转换作为参数，得到了各工艺参数的最优组合为：模具温度75℃，熔体温度250℃，注射时间1.8 s，冷却时间12.0 s，速度/压力转换100%。结合随形冷却水道的设计模拟优化后，翘曲变形量由最初的0.411 8 mm优化为0.154 4 mm，翘曲变形量减少了62.51%，说明稳健设计方法结合随形冷却水道设计对提升复杂零部件产品质量起到了重要作用。     

注射成型中模腔内振动剪切流动的理论模型

采用Ｌｅｏｎｏｖ本构模型,首次研究了在注射成型中模腔内聚合物熔体的振动剪切流动时所产生的振动剪切应力。结果表明,振动剪切应力的振幅随着聚合物熔体的粘度,振动频率和应变振幅的增加而增加,随着熔体温度的增加而减小。     

振动力场下聚合物熔体缠结密度理论研究

本文对Liu(1981)提出的动态速率方程加以修正 ,用修正的速率方程来研究振动剪切场下缠结密度的变化情况 ,指出当施加正统应变后 ,缠结密度的变化也呈周期性变化 ,而且施加的应变振幅与频率的大小对缠结密度的变化有很大影响 ,当施加的应变振幅或频率越大时 ,缠结密度变化的幅度越大 ,从而使熔体的粘度变化也越大。同时指出施加振动可以减少链段和整个分子链的松弛时间 ,而且初始平衡态时的平均缠结点数越少 ,施加振动后的缠结密度变化幅度越大     

并联双通道内超临界水的脉动传热特性

在压力26~30 MPa,时均质量流速420 kg·m^-2·s^-1、热通量0~130 kW·m^-2工况范围内,对垂直上升并联双通道内超临界水的脉动传热特性进行了实验研究。根据实验数据分析了流量脉动对壁温的影响,脉动振幅率(A_f)和脉动频率数（Wo）对时均Nusselt数的影响,并将脉动时均Nu与超临界传热关联式进行了比较。结果表明：壁温随流量脉动而波动,脉动周期相同,相位相反,流量脉动振幅越大,壁温波动也越大;低频脉动时均Nu随脉动振幅率的增大逐渐减小,随脉动频率数的增大先减小后基本不变;高频脉动时均Nu随脉动振幅率的增大而缓慢增大,随脉动频率数的增大而减小;关联式预测的Nu较实验值普遍偏高。     

Oscillatory and chaotic behaviour of a forced exothermic chemical reaction

An exothermic reaction takes place in a continuous stirred reactor, the cooling temperature of which is varied with time. It is shown that with an increase in the amplitude of the forcing that quasiperiodic behaviour occurs, followed by a sequence of period doubling bifurcations leading to chaos. Furthermore, multiple oscillatory states can arise, where both states are periodic or one state periodic and the other chaotic.     

Evaluation on the degrading behavior of melt polyolefin elastomer with dicumyl peroxide in oscillatory shear flow by Fourier transform rheology

The degradation of melt polyolefin elastomer (POE) at the presence of dicumyl peroxides (DCP) was estimated at elevated temperature in oscillatory shear flow. Large amplitude oscillatory shear (LAOS) experiments followed by Fourier transform rheology (FTR) were carried out to detect and evaluate the branching architecture of the products. The third complex harmonic (I₃^∗) and other two parameters, small strain elastic shear modulus (M) and large strain elastic shear modulus (L), which describe the nonlinearity and elasticity of a material obtained from FTR, are mainly used to characterize the topological structure of polymer chains. The results indicate the degradation appeared just after a large amount of the long chain branches (LCB) created rather than as soon as the reaction started when the strain was applied within the linear viscoelastic regime of the original POE at high frequencies. This is different from our previous result that the dominant reaction was coupling in linear shear flow. The threshold strain for degradation decreased with the oscillatory frequency, and the frequency owned a different acting mechanism from the strain amplitude to cause the degradation reaction. Moreover, there is a kind of selectivity of shear rate on the polymer chains for degradation. Low frequency results in short linear scission segments and a long branched chain suffers from degradation more than once. At high frequency, the possibility of degradation at the sites near the branching points of LCB increases.     

Rheological and electrical properties of carbon black‐based poly(vinylidene fluoride) composites

Carbon black (CB)–filled poly(vinylidene fluoride) composites (PCBp) were prepared by melt compounding. The linear rheology was then studied in detail. The composites show typical solid‐like response in the low‐frequency region, which is attributed to the percolation of CB particles. However, the transient percolated CB network is temperature dependent during the small amplitude oscillatory shear flow. Therefore, the principle of time–temperature superposition is invalid on the dynamic rheological responses of those percolated PCBp. A two‐phase viscoelastic model was then used to further describe the linear responses of PCBp to relate hierarchical structures of CB particles to flow responses of composites. In addition, the electrical and dielectric properties of PCBp were also investigated, aiming at further exploring the percolation behavior of CB. POLYM. ENG. SCI., 53:2541–2548, 2013. © 2013 Society of Plastics Engineers     

双组分注射成型件体积收缩的数值模拟研究

以ABS为第一次成型的内嵌件材料,PP为第二次成型的外嵌件材料,通过对双组分注射成型的数值模拟,系统研究了熔体注射温度、模具温度、注射时间、保压时间和冷却时间等工艺参数对其平均体积收缩率的影响规律,并基于流变学理论,揭示了其影响机理。结果表明,随着熔体注射温度和模具温度的升高,双组分注射成型制品的体积收缩增加,而随着注射时间、保压时间和冷却时间的增加,其平均体积收缩率减小。     

The Formation of a 12-Hydroxystearic Acid/Vegetable Oil Organogel Under Shear and Thermal Fields

External laminar oscillatory shear applied during crystallization in combination with different temperature fields was used to modify the microstructure and physical properties of edible oil organogels. Crystallization at a high cooling rate (30 °C/min) resulted in a spherulitic microstructure with a higher oil-binding capacity, lower storage modulus and lower yield stress compared with a material (with a fibrillar microstructure) crystallized at a slow cooling rate (1 °C/min). The application of an oscillatory shear resulted in the formation of novel microstructures depending on the cooling regime used. The application of an oscillatory shear (strain > 500 % and frequency = 1 Hz) resulted in the thickening of fibers observed in the slow-cooled material and an increased incidence of spherulite nucleation in the rapidly cooled material. Increasing the frequency of the oscillatory shear applied did not change the microstructure for the slow-cooled gel but further increased the incidence of nucleation for the rapidly cooled gel. The application of controlled-strain oscillatory shear to the crystallizing gel at either cooling rates resulted in an oily and very soft, paste-like material. This material had a lower storage modulus and poorer oil-binding capacity compared with the same gel crystallized statically. Reduction of the oscillatory strain from a maximum of 1500 to 500 % moderately mitigated the loss of mechanical properties and oil-binding capacity although these properties were in no way comparable to those obtained from static crystallization. The study shows that the application of oscillatory shear and different cooling regimes can be used to tailor a crystalline organogel. However, the application of continuous shear must be done with care as application of excessive shear can result in a complete breakdown in gel structure and large amounts of oil loss.     

Thermal,mechanical and rheological properties of poly (lactic acid)/epoxidized soybean oil blends

Summary  Poly(lactic acid) (PLA) was melt blended with epoxidized soybean oil (ESO) in an internal mixer and thermal, mechanical and rheological properties of the blends were investigated by means of differential scanning calorimetry, dynamic mechanical analysis, tensile test and small amplitude oscillatory shear rheometry. ESO lowered glass transition temperature and increased the ability of PLA to cold crystallization. The blend exhibited improved elongation-at-break along with a plastic deformation. The plasticization effect by ESO was also manifested by the lowering of dynamic storage modulus and viscosity in the melt state of the blends compared with neat PLA.