模拟研究超细旦涤纶长丝纺丝工艺

基于熔融纺丝动力学模型及理论,建立了超细旦长丝纺丝成形工程数学模型,模拟纤维温度、速度、应力、取向在纺程上的变化情况,分析超细旦涤纶成形特点,进一步研究了缓冷区温度对超细旦纤维纺丝成形的影响,为制备高品质超细旦涤纶长丝提供理论依据。     

Simulation of dry‐spinning process of polyimide fibers

As one type of high‐performance fibers, the polyimide fibers can be prepared from the precursor polyamic acid via dry‐spinning technology. Unlike the dry‐spinning process of cellulose acetate fiber or polyurethane fiber, thermal cyclization reaction of the precursor in spinline with high temperature results in the relative complex in the dry‐spinning process. However, the spinning process is considered as a steady state due to a slight degree of the imidization reaction from polyamic acid to polyimide, and therefore a one‐dimensional model based on White‐Metzer viscoelastic constitutive equation is adopted to simulate the formation of the fibers. The changes of solvent mass fraction, temperature, axial velocity, tensile stress, imidization degree, and glass transition temperature of the filament along the spinline were predicted. The effects of spinning parameters on glass transition temperature and imidization degree were thus discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

熔体静电纺丝的工艺条件对纺丝纤维直径的影响

主要研究纺丝温度、纺丝电压、接收距离等参数对聚丙烯(PP)熔体静电纺丝纤维直径的影响。采用了只变一个参数,其它参数固定的常规实验方法。在实验条件范围内,随着纺丝温度的升高,纤维的平均直径逐渐减小,得到PP的最佳纺丝温度240℃。在固定电压的情况下,得到最佳接收距离7cm。在固定接收距离的情况下,随着电压的增加,电场中的喷射流熔体受到的电场力逐渐增大,得出最佳纺丝电压35kV。     

Structure development during melt spinning of linear polyethylene fibers

Apparatus has been developed for studying the development of crystallinity and orientation during the melt spinning of synthetic fibers. Tension in the fiber and temperature, diameter, and x-ray diffraction patterns are measured as a function of distance from the spinneret for a running monofilament. Measurements are presented for linear polyethylene over a range of spinning variables together with other investigations carried out on the final as-spun fibers. These data indicate that the development of crystallinity in polyethylene is controlled by a balance between increased crystallization kinetics caused by the stress in the fiber and a tendency for increased supercooling with change in any spinning variable that increases cooling rates in the fiber. The type of crystalline orientation observed, its development during the spinning process, and the changes observed with changes in spinning conditions suggest a model for the as-spun fiber structure in which varying amounts of row nucleation and twisting of lamellar, folded-chain crystal overgrowths occur depending on the spinning conditions. As-spun fiber birefringence was shown to depend primarily on the crystalline orientation. Mechanical properties correlated well with c-axis crystalline orientation function and spinline stress.     

Model of Oxidation‐Induced Fiber Fracture in SiC/SiC Composites

Stress rupture of SiC/SiC composites at intermediate temperatures in oxidizing environments is the result of a series of internal chemical and thermomechanical processes that lead to premature, localized fiber fracture. This article presents analytical models for two potentially critical steps in this process. The first involves the generation of tensile stresses in the fibers due to SiO₂ scale formation (following removal of fiber coatings) and the associated reduction in the applied stress required for fiber fracture. The second occurs once the gaps produced by coating removal are filled with oxide and subsequent oxidation occurs subject to the constraints imposed by the matrix crack faces. In this domain, the failure model is couched in terms of the stress intensification within the fibers caused by constrained oxidation. The models incorporate the combined kinetic effects of oxide growth and viscous flow. The competing effects of increased oxidation rate and accelerated stress relaxation with increasing temperature on fiber stress feature prominently in the results. The results suggest that, in dry air environments, the highest risk of fiber fracture occurs at temperatures in the range 840°C–940°C. In this range, the oxide scales grow at appreciable rates yet the resulting growth stresses cannot be mitigated sufficiently rapidly by viscous flow.     

细旦腈纶的生产

研究细旦腈纶的纺丝工艺条件。并在纺丝线上进行试生产。讨论了纺丝原液温度、凝固浴条件、喷丝板负拉伸率、总收缩率、总拉伸倍数、纺丝速度对细旦腈纶质量和生产稳定性的影响。工业化试验表明:纺制0.89 dtex细旦腈纶的主要工艺条件为,纺丝原液温度74~76℃,喷丝板负拉伸率70％,总收缩率23%~25％,总拉伸倍数15,纺丝速度155m/min以及适当的凝固浴条件。     

Neutron Diffraction and Finite-Element Analysis of Thermal Residual Stresses on Diffusion-Bonded Silicon Carbide-Molybdenum Joints

Various approaches can be used to minimize residual stresses in ceramic-metal joining, such as a refractory-metal interlayer in a hot-pressed joint. Nonetheless, it is still necessary to characterize the stresses at and near the interface between the interlayer and the ceramic, as a function of the hot-pressing parameters. This study combines two techniques to assess the stress distribution of hot-pressed silicon carbide-molybdenum joints: neutron diffraction and finite-element (FEM) analysis. The results demonstrate that the joining temperature greatly influences the final stress distribution, and that significant stress accommodation is achieved by controlling the cooling rate of the diffusion couples. FEM analysis provides a broad view of stress distribution profiles, whereas experimental stress values that are obtained via neutron diffraction allow a better assessment of the effects of parameters that are not easily reproduced using a mathematical model.     

Studies on the melt spinning process of noncircular fiber by numerical and experimental methods

The spinning process of noncircular fiber was investigated in this work. A combination of numerical simulations and experiments made it possible to find out the optimum processing condition for shaped fiber. First, an inverse method which combined two‐dimensional/three‐dimensional simulation with experiments was utilized to find out the temperature and draw ratio dependent surface tension in melt spinning of shaped fiber. The surface tension as a function of temperature and draw ratio was found to be decisive to the change of cross‐section. Second, an orthogonal numerical experiment and statistics analysis were carried out to determine the optimum spinning condition for the desired noncircular fiber. The optimum spinning condition was well validated by experiments. It was then proved that the integrated method in this work, including the numerical method, the inverse method to determining the surface tension, and the orthogonal analysis, can be a good solution for the design and processing of profiled fibers. POLYM. ENG. SCI., 50:1935–1944, 2010. © 2010 Society of Plastics Engineers     

纺程加张力对PET纤维结构形成的影响

在熔融纺丝过程中,纺程张力是控制纤维结构形成的重要结果参数之一。大多数工艺参数都间接地或直接地反应在张力上,而张力又直接影响纤维的结构形成过程。本文采用在纺程上施加一定张力(0.10～0.15GPa)的方法,获得了强力较高的纤维。借助经典的测试分析方法,研究纺程加张力对纤维结构形成及性能的影响。结果表明:纺程加张力对纤维的结晶形成影响较小;而对纤维的取向结构,尤其是无定形取向结构有很大的促进作用。在施加的张力范围内,纤维的无定形取向因子f_(am)可达到0.53～0.72,比常规速纺PET纤维的无定形取向f_(am)高得多。这说明了PET在一定条件下取向与结晶可以分别进行;高取向的纤维更容易结晶.     

Prediction of the influence of flow‐enhanced crystallization on the dynamics of fiber spinning

A linearized sensitivity and stability analysis of fiber spinning of semi‐crystalline polymers has been carried out for both low‐ and high‐speed spinning conditions to investigate the relative roles of flow‐enhanced crystallization (FEC) and thermal‐induced crystallization (TIC) on the process dynamics. The analysis is based on an earlier‐developed two‐phase constitutive model for FEC that utilizes either the Giesekus or the Extended Pom‐Pom constitutive equations for the amorphous phase and a rigid‐rod model for the semi‐crystalline phase, combined with the transport balances for the 1‐D fiber spinning model. Model parameters from fits of the steady‐state low‐ and high‐speed spinning of Nylon and L ‐polylactic acid are used to illustrate the effects of changes in various process variables (principally air cooling rate and temperature) on the system sensitivity. Results show that higher crystallization, whether from TIC or FEC, generally equates to lower spinline sensitivity. However, factors such as high‐speed necking induced by FEC, viscoelastic stresses, and thermal transport properties are also shown to impact trends in the sensitivity. Because of the specific nature of the FEC model and lack of a general theory for determining model parameters from first principles, calculations and conclusions are necessarily system specific. POLYM. ENG. SCI., 48:88–96, 2008. © 2007 Society of Plastics Engineers     

熔体直纺多孔超细涤纶POY纺丝成形工艺研究

研究了熔体直纺多孔超细涤纶POY的成形加工条件。重点探讨了直纺熔体品质、纺丝温度、冷却成形条件和卷绕速度对多孔超细涤纶POY纺丝成形过程中的流变性、可纺性和结构性能以及纤维品质的影响。     

聚碳硅烷可纺性与纺丝工艺探讨

本文研究了聚碳硅烷的特性与其可纺性的关系,并对连续聚碳硅烷原丝制备过程中的纺丝温度、纺丝压力、过滤方式、气流收丝方式与速度等进行了探讨。     

涤纶低弹网络丝的研制

研究了纺 62dtex/ 72f细旦涤纶低弹网络丝的工艺。结果表明 ,纺丝温度 2 91℃ ,上油率控制在 0 .7%～ 0 .8% ,条干不匀率小于 3 .8% ,网络工艺控制要防止出现飘丝 ,可生产出优质细旦涤纶低弹网络丝。     

聚苯硫醚-聚酯复合纤维的成形及性能

聚苯硫醚(PPS)由于其优异的耐热性能使其在高温滤袋中得到了广泛的应用。采用复合纺丝技术,制备PPS-聚酯(PET)皮芯复合纤维,并系统研究纤维成形的牵伸温度、拉伸比对复合纤维力学性能的影响。结果发现:控制皮芯纤维的纺丝速度小于1000 m/min,可制备出力学性能与PPS相近的PPS-PET复合纤维。在成形过程中,随着牵伸温度的提高,纤维的强度降低,断裂伸长率增大,沸水收缩率减小,强度和断裂伸长率在牵伸温度高于105℃时产生突变;经过180℃干热松弛处理48 h后,PPS-PET复合纤维的强力降低6%左右。     

Computer simulation of melt spinning of polypropylene fibers using a steady-state model

A mathematical model that includes crystallization in the spinline and the effect of crystallization on the extensional viscosity and the various physical properties of polypropylene has been developed and used to help in identifying the various factors that can affect the spun yarn characteristics. The model is used to simulate effects of spinning parameters on fiber physical properties, temperature, and stresses. The experimental observation of a minimum in density of the spun yarn at high throughput rates, when density is plotted as a function of take up velocity, has been investigated in some detail. It has been found that all conditions which can substantially affect the rate of cooling and the orientation of the polymer in the spinline, viz, throughput rate, spinning temperature, and spinning speed have an important bearing on the temperature range in which crystallization can take place in the spinline and thus affect the density. It is suggested that in addition to these factors, the formation of different crystal modifications at different spinning speeds could also contribute to the reduction in density of these samples. The model cannot reflect the observation of density changes occurring due to the formation of different crystal modifications. Nevertheless, it can be of use in understanding the effects of various process conditions on the cooling rate and the orientation of the polymer in the spinline. © 1995 John Wiley & Sons, Inc.     

Effects of imperfect adhesion on thermal micro-residual stresses in polymer matrix composites

This paper investigates the influences of imperfect bonding between the fiber and matrix on thermal micro-residual stress fields in polymer matrix composites. For this purpose, a representative volume element consisting of a three-phase composite material subjected to a uniform temperature change is considered. Based on the energy method, a three-dimensional closed-form solution for micro-residual stresses is obtained. Besides, a finite element model is developed and the results are compared with the analytical solution. Both the energy method and finite element analysis show similar trend for thermal stress distribution along the fiber length, while due to the stress singularity, the interfacial shear stress from the finite element solution cannot satisfy the stress-free condition at the fiber end. The analysis shows that the magnitude of thermal stresses and their distribution mainly depend on the bonding efficiency parameter. An increase in thermal and elastic properties bonding efficiencies leads to a considerable decrease in composite axial and shear residual stresses, while the Poisson's ratio bonding efficiency does not affect the thermal stress fields. The interfacial radial residual stress distribution is approximately independent of the bonding conditions. Inefficient bonding may result in higher residual stresses in comparison with the perfect bonding condition. It means that in cases of low bonding efficiency conditions, the ability of composites to sustain and transmit load decreases drastically. Thermal stress concentration occurs at the vicinity of the fiber ends, although peak values depend on the bonding efficiency value.     

压力容器筒体与平封头多级焊缝残余应力数值模拟

采用有限元软件ANSYS中生死单元技术对压力容器筒体与平封头单面焊焊接过程进行数值模拟,得出焊缝焊接残余应力、温度场及位移场的分布情况。经过分析可以得出：在焊缝区及熔合区温度极高;远离焊缝,温度峰值急剧下降。在熔舍区焊接残余应力达最大值;焊根处残余应力较小;在热影响区,沿焊缝方向多为拉应力,垂直焊缝方向多为压应力。     

CDP／PA6桔瓣型复合纤维纺丝工艺

研究了阳离子染料可染PET与PA6复合纤维纺丝工艺,讨论了两组分复合比、纺丝温度、卷绕工艺等对复合纤维的生产过程及产品品质的影响。发现二者的复合比为80／20、纺丝温度为278℃及266℃、卷绕速度为3150m／min时,纺丝顺利,产品品质较好。     

耐高温强色牢度FDY的研制

在纺制普通涤纶FDY的基础上,采用共混纺丝的方法将结晶过的母粒加入到PET中,纺制出带色、并具有耐高温、抗日晒、色牢度性能强的纤维。对干燥工艺、纺丝温度、上油、侧吹风、组件砂配比、卷绕等工艺过程进行了探讨。     

热管一步法仿真丝的研究

采用热管纺丝，通过改变纺程温度，摸索热管一步法仿真丝的工艺；应用强伸仪、Ｘ一衍射仪及沸水收缩测试等手段对热管纺丝纺制的纤维结构及性能进行了测试．着重探讨了纺丝速度及热管温度对纤维的影响．