大直径中间相沥青纤维纺制时的剪切速率

考察了大直径中间相沥青纤维熔纺过程中中间相沥青在喷丝板微孔区内的流动特性及剪切速率。随熔纺温度及挤出流量的增加,中国相沥青在喷丝板微孔区内剪切速率相应增加。熔纺时控制了挤出流量和牵伸速率的良好匹配,获得了丝径均匀的大直径中间相沥青炭单丝。两种中间相沥青在剪切速率和由其纺制获得纤维的离散系数方面的差异,归结为常压与加压齐聚反应后中间相沥青在本性上的差异。     

PP/CHA熔喷非织造布制备工艺及其性能研究

介绍了PP/CHA熔喷非织造布的加工研制过程.通过对所制PP/CHA熔喷非织造布进行纤维细度、力学性能、透气性能、过滤效率和亲水性能测试,分析热空气温度和压力、接收距离等熔喷工艺参数对产品性能的影响.结果表明:纤维直径随热空气温度增加,先减小后增大;随热空气压力增大而减小.强度随热空气压力增大而增大,随接收距离增大而减小.透气率随热空气温度升高而增大,过滤效率随热空气压力增大而增大,吸液率随接收距离增大而增大.     

空气过滤用电纺聚偏氟乙烯-聚丙烯腈/熔喷聚丙烯无纺布复合材料的制备及过滤性能

为开发高效低阻的空气过滤材料,采用静电纺丝技术制备了聚偏氟乙烯（PVDF）-聚丙烯腈（PAN）复合纳米纤维,并与聚丙烯熔喷非织造布复合制得高效复合过滤材料,研究了PVDF与PAN的质量比对溶液性质、表面形貌、比表面积、透气性和过滤性能的影响。结果表明,当PVDF与PAN质量比为3:5时,其溶液可纺性最好,所得纤维直径均匀,约为0.59 μm;利用BET比表面积分析仪测试可得其比表面积约为PVDF与PAN质量比为2:1时的两倍;利用滤料测试仪对PVDF-PAN/熔喷聚丙烯（PP）无纺布复合滤材的过滤性能进行测试,结果表明,静电纺PVDF-PAN纳米纤维层可显著提高聚丙烯熔喷非织造布的过滤性能,PVDF-PAN/熔喷PP无纺布过滤效率可达99.95%,明显高于熔喷无纺布的过滤效率（65%）,过滤阻力为77 mmH₂O（1 mmH₂O=9.8 Pa）,过滤品质因子达0.0987,远高于熔喷无纺布的过滤品质因子0.0168,过滤效果得到显著提升。      

静电纺聚乳酸纳米纤维复合滤料的过滤性能研究

将聚乳酸颗粒加入到质量比为8:2的三氯甲烷与N-N-二甲基甲酰胺的混合溶剂中,室温下配置质量分数为10%的纺丝液,采用静电纺丝法制备了平均直径在620nm左右的聚乳酸纤维。以聚乳酸熔喷非织造布为基布,通过控制纺丝时间的不同得到了负载不同厚度纳米纤维层的可生物降解的复合过滤材料。通过对各试样的孔隙率、孔径及孔径分布、过滤效率的测试发现:随着纺丝时间的增加,复合材料孔隙率不断下降,孔径不断减小,纺丝3h时,孔径基本减小到原先的一半,且分布相对集中,大大地提高了普通过滤材料的过滤效率。     

神经网络模型在SiC涂层制备中的应用

材料表面抗氧化涂层的质量是限制碳／碳复合材料作为高温结构材料使用的关键．本文运用人工神经网络技术建立了CVD－SiC涂层制备工艺的过程模型,以解决该过程影响因素众多、相互作用关系复杂、难以对制备过程进行有效的预测和控制的问题．研究结果表明：所建立的神经网络模型,可以比较准确和全面地反映各工艺因素对SiC-CVD过程的影响大小及内在规律;模型对工艺参数与沉积速率之间关系的预测与实验结果相吻合;证实了将人工神经网络模型应用于抗氧化涂层的制备过程的控制和工艺优化是有效和可行的．     

石英玻璃纤维/气凝胶复合材料的热导率计算及优化

纤维含量和直径是影响纤维/气凝胶复合材料热导率的重要参数。采用常压干燥工艺实验制备了石英玻璃纤维/SiO_2气凝胶复合材料,基于材料微观结构表征结果建立了纤维/气凝胶复合材料总体热导率的计算模型,研究了纤维含量和纤维直径对复合材料热导率的影响规律。通过二元优化(即同时优化纤维体积分数和直径)获得了复合材料的最小总体热导率,与单一优化纤维含量或纤维直径相比总体热导率可分别减少50%和20%(以1000K为例);并探讨了在不同温度条件下复合材料中最优纤维含量和纤维直径的变化规律,发现随温度升高最优纤维含量增大而最优纤维直径减小。研究结果可用于指导纤维/SiO_2气凝胶复合材料的结构设计和性能优化,促进气凝胶复合材料在航空航天、工业、建筑等领域的节能应用。     

静电纺聚丙烯腈复合滤料的制备与性能

将聚丙烯腈粉末加入到N,N-二甲基甲酰胺中,制备12%(wt,质量分数)的纺丝液。以聚丙烯熔喷非织造布为基布,通过改变纺丝时间,制得不同厚度的复合滤料。通过扫描电子显微镜观察熔喷布和纳米纤维的外观形貌,并对复合滤料的孔径、孔径分布、过滤效率、透气性进行表征。结果表明:采用静电纺丝的方法纺制了平均直径为220nm的聚丙烯腈纳米纤维。随着纺丝时间的增加,复合滤料的孔径不断减小,过滤效率逐渐提高,透气性下降。当纺丝时间为60min时,复合滤料的孔径尺寸集中分布在2~5μm,对粒径"≥1.0μm2.0μm"颗粒的过滤效率为99.85%,压力降为200Pa,符合医用防护口罩技术要求,过滤性能达到2级。     

电纺PLA/BioMIL-5复合纤维膜的制备及其吸附过滤性能研究

采用静电纺丝技术制备聚乳酸(PLA)/锌基金属有机骨架(BioMIL-5)复合纤维膜，探讨了不同含量BioMIL-5对复合纤维膜纤维形貌和性能的影响，并研究了复合纤维膜的吸附过滤性能和抗菌性能。结果表明：随着BioMIL-5含量的增加，纤维平均直径先增大后减小，复合纤维膜的断裂伸长率和疏水性不断提高。与熔喷布相比，复合纤维膜可高效吸附PM_2.5和PM₁₀,BioMIL-5质量分数为4%的复合纤维膜对PM_2.5和PM₁₀的平均过滤效率分别可达99.93%、99.96%,并且对大肠杆菌和金黄色葡萄球菌具有一定的抗菌性。     

中间相沥青熔融纺制异形纤维的研究

用热缩聚和催化缩聚两种不同工艺制备的中间相沥青及自行设计的五种喷丝板,熔融纺制出中空、条形、Y 形和圆形截面的沥青纤维。实验证明,沥青熔体的出口膨胀性是影响异形纤维特别是中空纤维纺丝成形的重要流变学参数。这一参数随中间相沥青的性质和熔体温度而变化,在较高温度下,沥青熔体的出口膨胀性减小,使得所纺制异形纤维截面的异形度降低。X 射线衍射分析结果表明,不同形状的喷丝板因其不同的当量直径,在纺丝时对熔体产生不同的剪切作用;当量直径越小,剪切作用越强,沥青分子沿纤维轴的取向度越高,因此可使其炭纤维的力学性能提高。     

人工神经网络在钢铁材料研究中的应用

人工神经网络是近年发展起来的模拟人脑生物过程的具有人工智能的系统,在钢铁材料研究中有着广阔的应用前景.人工神经网络可根据钢的化学成分和/或加工工艺参数对微观组织、相变温度和时间及性能等做出快速准确预测,并可用于研究钢的上述各影响因素间的相互关系.研究人工神经网络也可用于钢的冶金过程及钢的表面处理过程工艺参数的预测及控制.     

A nonlinear system model for electrospinning sub-100 nm polyacrylonitrile fibres

Solutions of polyacrylonitrile (PAN) were electrospun using a range of process parameters, resulting in fibre diameters from 10 to 320?nm. A nonlinear neural network system model was used to analyse the dependence of the fibre diameter on the process parameters, and used to simulate conditions for electrospinning 40-60?nm diameter fibres. These results indicated that flow rate is most important for determining fibre diameter. It was not possible to find the appropriate conditions for electrospinning sub-25?nm fibres. Precise control of the ambient temperature and relative humidity will be critical to producing electrospun fibres that are sub-25?nm. Further, it is unlikely that sub-25?nm fibres will be produced without significant changes in the electrospinning apparatus, for example, by use of focusing and jet-steering fields, alternate carrier gases to modify the discharge characteristics, or patterned electrospinning.     

Nanofibre fabrication in a temperature and humidity controlled environment for improved fibre consistency

Fabricating nanofibres with reproducible characteristics is an important demand in the membrane industry in order to establish commercial viability. In this study, the effect of controlled atmospheric conditions on electrospun cellulose acetate (CA) nanofibres was evaluated for temperatures ranging 17.5–32.5 °C and relative humidity ranging 20–70%. CA solution (0.2 g/mL) in a solvent mixture of acetone/dimethylformamide/ethanol (2:2:1) was electrospun into nonwoven fibre mesh with the fibre diameter ranging from 150 nm to 1 μm. The resulting nanofibres were analysed by differential scanning calorimetry, showing a correlation of reducing melt enthalpy with increasing atmospheric temperature. The opposite was seen with increasing atmospheric humidity, which conferred increasing melt enthalpy. Analysis of scanning electron microscopy images provided a correlation of reducing average fibre diameter with increasing atmospheric temperature and increasing fibre diameter with increasing atmospheric humidity. These results correlate with the melt enthalpy results, suggesting that finer CA nanofibres infer a lower melt enthalpy. Together these studies provide strong evidence that the controlled atmospheric conditions affect the fibre diameter of the resulting electrospun nanofibres. A salient observation in this study was that increased humidity reduced the effect of fibre beading yielding a more consistent and therefore better quality of fibre. This has apparent implications for the reproducibility of nanofibre production and offers a new method of controlling fibre morphology. This study has highlighted the requirement to control atmospheric conditions during the electrospinning process to fabricate reproducible fibre mats.     

闭式高洁净取注浆机的设计开发

为保证取注浆机在取出和运送过程中金属浆料的洁净度和温度,研发设计了一种由浆罐、浆罐移动系统和机架等3部分组成的闭式高洁净取注浆机,包括方案设计、浆罐移动系统的设计和机架的设计.闭式高洁净取注浆机提高了取注浆过程的安全性、准确性,原料质量处于受控状态,在生产对浆料质量要求较高的压铸件时,闭式高洁净取注浆机可以替代传统的浇汤机,使压铸件产品的质量得到进一步提升.     

PET薄膜挤出成型有限元模拟和阻流分析

设计了厚度为0.12mm的聚对苯二甲酸乙二醇酯(PET)薄膜衣架式挤出流道,使用有限元软件模拟了聚合物熔体的流动规律,获得了流道内部的压力场、速度场和温度场的分布,分析了阻流设计对流场的影响。研究表明,流道结构对压力分布影响显著,对速度、温度分布影响不明显;流道阻流部分尺寸较小的改变,会引起流道内部熔体压力较大的变化,易导致挤出成型过程的不稳定,从而显著影响产品质量。此外,挤出流量对流场压力分布影响很小。     

A mathematical model of the edge-defined film-fed growth process

A model is presented to simulate the steady-state growth of a fiber produced by the edge-defined film-fed growth (EFG) process. Equations describing the axisymmetric transport of heat in the melt and fiber are discussed. Heat transfer between the system and the surrounding environment is assumed to take place via convection and radiation. Given the fiber translation velocity, the external temperature profile, the die temperature, and the input flow rate or the pressure, asymptotic solutions for the temperature profiles in the melt and fiber, and the melt/gas and solidifying interfacial shapes are developed in the limit of a small melt slenderness ratio (fiber radius/approximate melt height). The effect of process parameters on the shape of the fiber system is investigated.     

Prediction of die casting process parameters by using an artificial neural network model for zinc alloys

Pressure die casting is an important production process. In pressure die casting, the first setting of process parameters is established through guess work. Experts use their previous experience and knowledge to develop a solution for a new application. Due to rapid expansion in the die casting process to produce better quality products in a short period of time, there is ever increasing demand to replace the time-consuming and expert-reliant traditional trial and error methods of establishing process parameters. A neural network system is developed to generate the process parameters for the pressure die casting process. The system aims to replace the existing high-cost, time-consuming and expertdependent trial and error approach for determining the process parameters. The scope of this work includes analysing a physical model of the pressure die casting filling stage based on governing equations of die cavity filling and the collection of feasible casting data for the training of the network. The training data were generated by using ZN-DA3 material on a hot chamber die casting machine with a plunger diameter of 60 mm. The present network was developed using the MATLAB application toolbox. In this work, the neural network was developed by comparing three different training algorithms: i.e. error backpropagation algorithm; momentum and adaptive learning algorithm; and Levenberg-Marquardt approximation algorithm. It was found that the Levenberg-Marquardt approximation algorithm was the preferred method for this application as it reduced the sum-squared error to a small value. The accuracy of the developed network was tested by comparing the data generated from the network with those of an expert from a local die casting industry. It was established that by using this network the selection of process parameters becomes much easier, so that it can be used by a novice user without prior knowledge of the die casting process or optimization techniques.     

籽晶边长对SAPMAC法蓝宝石晶体放肩阶段生长质量的影响

温度场的控制是蓝宝石生长过程关键技术问题。采用有限元方法研究了冷心放肩微量提拉法蓝宝石单晶生长过程中籽晶的边长对晶体生长放肩阶段温度场内温度分布、流场分布和晶体的等效应力分布的影响。结果表明:当籽晶边长为24mm时,放肩阶段熔体的轴径向温度变化平缓,温度场内温度分布均匀,熔体的流动和晶体的热应力均适合晶体的生长。     

神经网络与混合遗传算法结合的注塑成型工艺优化

注塑成型中,工艺参数直接影响到模具内熔体的流动状态和最终制品的质量,而工艺参数与制品质量之间的关系非常复杂,因此如何建立制品质量与工艺参数之间的关系模型井获得优化的工艺参数是改善制品质量的关键。收缩是衡量制品质量的一个重要指标,制品在型腔中的非均匀收缩是引起制品翘曲的主要原因。文中基于成型过程的数值模拟,采用人工神经网络与混合遗传算法结合优化注塑成型工艺,以改善制品质量。对一工业产品进行分析,以制品内的体收缩率差值为质量指标优化工艺,改善了制品内的体收缩率分布,获得了满意效果。     

Optical measurement and modelling of parison sag and swell in blow moulding

Blow moulding is a process whereby a cylindrical parison is extruded first, then pinched between the two halves of a mould and, finally, blown into the product. Parison size and shape result from complex interactions between mandrel and die geometries, processing parameters and viscoelastic properties of the polymeric material. Moreover, parison size changes with time due to sag. An innovative, contactless and online measurement technique of the parison is shown to be an effective tool to measure precisely parison diameter and thickness and to capture dimensional changes with time. This technique employs laser lighting of the parison and hinges on the refractive properties of molten polymer. Images taken with a digital camera are processed to give a precise measurement of diameter and thickness, at different time step during extrusion. Thus, parison swell and sag have been recorded for a commercial HDPE. Influence of processing parameters such as the rotational screw speed or die gap width can be brought forward. From the measurements, thickness swell is found to possess a different behaviour from diameter swell. Moreover, sag has been measured and can be modelled from a Newtonian perspective using one dimensional convected coordinates. Parison sag is shown to be governed by two parameters: an extrusion velocity and a a single coefficient of sagging susceptibility which value has been deduced from experiments.     

挤管用螺旋芯模机头内熔体流动分析

本文以B.Procter的简化模型(方法Ⅰ)为基础,考虑流动指数与剪切速率的关系(方法Ⅱ)和垂直于轴的截面上的压力平衡(方法Ⅲ),用迭代法分配计算单元的轴向和沿螺旋流道方向的体积流率。编制了模拟螺旋芯模机头内熔体流量、压力降和剪切速率分布的计算机程序。模拟结果表明,根据漏流分布曲线的特性选择几何参数的螺旋芯模机头对熔体的分配效果不受更换物料和改变机头温度及挤出速率的影响。用高密度聚乙烯进行挤管实验时测定的机头压力降和管材壁厚偏差介于用方法Ⅱ和方法Ⅲ模拟结果之间,实验测定结果与用方法Ⅰ模拟结果的差别最大。高密度聚乙烯管的内、外表层的结晶不同,其差别随挤管时的牵引速度的提高而降低。