Computer‐aided mathematical modeling and numerical simulation and theoretical analysis of the polypropylene polymer air drawing in spunbonding nonwoven process

In this article, as a nonlinear mathematical problem, the air‐drawing model and the air jet flow field model of the polymer during spunbonding process are also presented, because the continuous filament fiber not always occurs in the spunbonding process, therefore, there exists the filament fiber breakage, the broken fibers occur in the flow field of spunbonding process is a two‐phase flow problem, we suggested a new model called the sphere–spring model that can best described the broken fibers movement features. At the same time, the air‐drawing model of the polypropylene polymer in a spunbonding process is presented and solved by introducing the numerical computation results of the air jet flow field of aerodynamic device. The model's predictions of the filament fiber diameters, crystallinities, and birefringences are coincided well with the experimental data. The effects of the processing parameters on the filament fiber diameter are discussed. A lower polymer throughput rate, lower quench air temperature, higher polymer melt initial temperature, higher air initial temperature, higher air initial speed, medium smaller venturi gap, higher air suction speed, higher quench air pressure, higher air suction speed, higher extrusion temperature, higher quench air pressure, higher cooling air temperature, and so on can all produce finer filament fiber. The results show great prospects for this research in the field of computer‐assisted design of spunbonding technology. POLYM. ENG. SCI., 54:481–492, 2014. © 2013 Society of Plastics Engineers     

Computational fluid dynamics simulation and theoretical study the air jet flow field of a wide slot positive pressure drawing assembly in the spunbonding nonwoven process

The polymer air‐drawing model of polyethylene terephthalate spunbonding nonwovens and the air jet flow field model in wide slot positive pressure spunbonding process have been established. The influence of the density and the specific heat capacity of polymer melt at constant pressure changing with polymer temperature on the fiber diameter have been studied, which is solved by introducing the numerical computation results of the air jet flow field of attenuator. It is simulated by means of the finite difference method. The predicted fiber diameter agrees with the experimental data. The effects of the processing parameters on the fiber diameter with the help of the image analysis method have been investigated. A higher inlet pressure, smaller slot width, and smaller jet angle will all cause higher z‐axis position of air velocity and air pressure, which are beneficial to the air drawing of the polymer melt and thus to reducing the fiber diameter. The experimental results show that the agreement between the results and experimental data is better, which verifies the reliability of these models. The results present great prospects for this research in the field of computer assisted design of spunbonding process, technology, and equipment. POLYM. ENG. SCI., 55:231–242, 2015. © 2014 Society of Plastics Engineers     

聚合物纺粘法非织造布的新型原料及发展趋势

简要介绍了几种纺粘法非织造布新型原料的特点,指出新型纺粘原料加工的产品具有质量优和性能独特等优点,并展望了纺粘非织造布新型原料的发展方向和应用前景。     

Influence of processing parameters on fibers diameter and web evenness of polypropylene spunbonding nonwoven fabrics in wide slot positive pressure drafting assembly of spunbonding process

The air drawing model of polymer polypropylene (PP) spunbonding nonwovens has been established. The influences of the density and the specific heat capacity of polymer melt at constant pressure changing with polymer temperature on the fiber diameter have been studied. The air drawing model of polymer in spunbonding is confirmed by the experimental results obtained with our university's equipment. The effects of the processing parameters on fibers web evenness of PP spunbonding nonwoven fabrics in wide slot positive pressure drafting assembly of spunbonding process have also been investigated. The predictions of the filament fiber diameters, crystallinities, and birefringences are coincided well with the experimental data. It is found that a medium polymer melt temperature, monomer suction wind speed, drawing pressure, cross air blow speed, and air control distance have a significant influence on the web evenness and quality, which are beneficial to produce more uniformity fibers web. The experimental results show that the agreement between the results and experimental data is very better, which verifies the reliability of these models. At the same time, the results also reveal the great potential of this research for the computer‐assisted design (CAD) of spunbonding technology. POLYM. ENG. SCI., 58:1268–1277, 2018. © 2017 Society of Plastics Engineers     

聚合物纺粘气流拉伸与射流性能的研究进展

叙述了纺粘法非织造布气流拉伸机理和水刺法中纤网射流性能等研究的进展;分析和评价了聚合物纺粘气流托伸的数学模型、水刺喷嘴对射流特性以及水刺纤网射流加固对水刺布质量等的影响,这也是纺粘法非织造布技术今后的研究方向。     

Experimental study and numerical simulation the air jet flow field of a dual slot sharp blunt die in the melt blowing nonwoven process

In this work, the physical model of a polymer in a melt blowing process is established and solved by introducing the numerical computation results of the air jet flow field of the dual slot sharp inset die. The influence of the melt blowing processing parameters and the die design parameters on the fiber diameter is also studied. A lower polymer throughput rate, higher polymer melt initial temperature, higher air initial temperature, higher air initial velocity, smaller angle between slot and axis of the spinneret, smaller width of the die head, and larger width of the slot can all produce finer fibers. At the same time, the air jet flow field model of the dual slot sharp inset die of polypropylene polymer nonwovens fabrics in melt blowing process was also established. The air jet flow field model was solved by using the finite difference method. The computational simulation results of the distributions of the z‐components of air temperature and air velocity along the spinline during melt blowing process are in accordance with the experimental data. The air drawing model of melt blowing process was simulated by means of the numerical simulation results of the air jet flow field. The predicted fiber diameter agree with the experimental data. The effects of the air initial velocity and air initial temperature on the fiber diameter were studied and discussed. The results demonstrate that a higher air initial velocity and a higher air initial temperature are beneficial to the air drawing of the polymer melt and thus to reduced fiber diameter. The results show the great potential of this research for computer assisted design in melt blowing nonwoven process and technology. POLYM. ENG. SCI., 57:417–423, 2017. © 2016 Society of Plastics Engineers     

A numerical study on warm deep drawing of polypropylene

Warm deep drawing of polypropylene, a semi-crystalline thermoplastic polymer, is studied using finite element analysis. In this process, a circular polypropylene blank is preheated to a temperature much below its melting temperature and deep drawn into the shape of a flat-bottom cylindrical cup using a punch-die combination, both initially at 25°C. The material model used for the analysis considers the effects of varying temperature and strain rate during the deep drawing process on the depth of draw. The effects of blank holder force, initial blank temperature, blank diameter, and die and punch corner radii on the depth of draw are determined. Thickness, temperature, and strain variations in the drawn cups, punch forces, and failure modes are also determined.     

A physical–mathematical model for the prediction of fiber diameter of the polyethylene terephthalate (PET) spunbonding nonwoven fabrics

A mathematical model of air drawing of a polyethylene terephthalate (PET) polymer in a spunbonding nonwoven process was established and solved by introducing the numerical computational results of the air jet flow field of the attenuator. The predicted fiber diameters, crystallinities, and birefringences agreed well with the experimental data. The air jet flow field model was solved and simulated by means of the finite difference method. The numerical simulation computation results of distributions of the air velocity matched quite well with the experimental data. The air drawing model of the polymer was solved with the help of the distributions of the air velocity measured by a particle image velocimetry. The effects of the processing parameters on the fiber diameters, measured with the aid of an image analysis method, are further discussed. A lower polymer throughput rate, higher polymer melt initial temperature, higher air initial temperature, higher air initial speed, lower venturi gap, higher air suction speed, and higher quench pressure can all produce finer filament fibers. The results demonstrated the great prospects for this research in the field of computer‐assisted design (CAD) in the spunbonding technology field. POLYM. ENG. SCI., 58:1213–1223, 2018. © 2017 Society of Plastics Engineers     

纺黏法非织造布气流拉伸模型的研究

综述了纺黏非织造布气流拉伸机理研究的特点和研究进展。介绍了国外的研究情况,比较了这些研究方法的优缺点,分析了存在的问题。同时介绍了我国在纺黏气流拉伸方面的研究情况,分析和评价了聚合物纺黏气流拉伸的数学模型。介绍了纺黏法气流拉伸完整数学模型的基本方程组：包括连续方程,动量方程,本构方程和结晶动力方程。     

Direct numerical simulation and experimental validation of flow resistivity of nonwoven fabric filter

We numerically study and then experimentally validate the flow resistivity of commercial nonwoven fabric filters used for a bag filter system. To represent a realistic flow field inside the filters during simulation, a numerical method that coordinates the filter structure obtained by X-ray computed tomography imaging with computational fluid dynamics using the immersed boundary method is developed. The effects of superficial velocity, porosity of the filter domain, and type of filter on pressure drop are investigated and analyzed based on Darcy's law. The predictions from our numerical method are quantitatively in good agreement with the experimental measurements. We demonstrate that the Kozeny constants of the filters can be estimated by utilizing the solid volume fraction. These results demonstrate that our simulation method can be used to clarify the effects of porosity, fiber arrangement, and fiber shape on the pressure drop. Finally, its application to water droplet permeation is demonstrated.     

聚合物熔体在纺黏非织造牵伸器中的气流牵伸模型 与数值模拟研究

介绍了有关纺黏非织造过程建模与数值求解的方法。首先在继承前人研究成果的基础上,给出了纺黏非织造过程理论模型;其次,对实际生产中应用的宽狭缝牵伸器的喷射流场进行数值模拟,求出了气流速度在牵伸器中的数值分布。通过对牵伸器喷射流场的数值模拟,得到了气流速度在流场中的数值分布,从而为聚合物熔体的气流牵伸模型求解提供了有利的条件。本研究也显示了在对纺黏非织造布工艺和设备进行计算机辅助设计方面具有较好的应用前景。     

Coextrusion flow of two molten polymers between parallel plates: Non isothermal computation and experimental study

A theoretical study of the one-directional coextrusion flow of two molten polymers between parallel plates has been carried out using a non-isothermal power-law model. A numerical method has been used to solve simultaneously the momentum and energy balance equations, in order to obtain the evolutions of the interface position, the pressure gradient, and the temperature profiles all along the flow. The theoretical results are in good agreement with experimental values measured on an industrial coextrusion line.     

A numerical and experimental study of fluid flow in continuous casting mold

To study removal of nonmetallic inclusion in continuous casting mold, both flow visualized experiments and computer simulations were carried out using a 1/2 scale water model of the mold. The effect of port angle of submerged nozzle on the floatability of nonmetallic inclusion was also examined. The velocity fields predicted by solving the turbulent Navier-Stokes equations using the K-ε model for turbulent viscosity were found to be in good qualitative agreement with the results of water model experiments. The result of the present work could be used to predict the characteristics of fluid flow in a continuous casting mold.     

A numerical and experimental study of aggregate-induced shrinkage cracking in cementitious composites

Aggregates in cementitious composites subject to drying lead to mechanical restraint of the matrix shrinkage, which under certain conditions may lead to internal microcracking. In the present work this phenomenon is investigated using a two-dimensional (2D) numerical model and an approximate 2D experimental approach. Experimental and simulated samples with simplified and matching spatial aggregate distributions were produced to make a quantitative comparison between experiments and model predictions. In particular, the effects of aggregate size and volume fraction on the degree of internal microcracking are assessed. The main challenges of performing a quantitative comparison are highlighted and discussed. These are related to: (i) the difficulty of designing experiments without moisture gradient effects; (ii) the experimental crack detection limit; and (iii) the role of the creep response of the matrix phase in the model. The results suggest the existence of a critical aggregate size below which aggregate-restraint does not cause detectable microcracking.     

Impact force of water jets in the hydroentanglement nonwoven process: Numerical simulation and experimental verification

The water jet flow model in the hydroentanglement nonwoven process is established and solved numerically. The impact force of water jets is calculated with aid of the model and verified with the experimental data. The numerical simulation results of the impact force coincide with the experimental data, which confirms the effectiveness of the two‐dimensional model established. Computer simulations and experiments show that higher water jet pressure, smaller water jet inclination angle, and smaller standoff distance will yield larger impact force. The results show that there is great potential for this research in field of computer‐assisted design in hydroentanglement technology and equipment. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers.     

A mathematical model to study the effect of the air jet in the film blowing process

The aerodynamic effect of the air jet that supports the polymeric films produced in the film blowing process is studied theoretically. The nonlinear coupling between the air and the polymer is examined by assuming steady, axisymmetric, and isothermal flow for both phases. The governing equations for the polymer are simplified by following the thin‐film approximation and the corresponding ones for the air are derived by applying a boundary‐layer type analysis. The latter are solved analytically by first applying the Mangler transformation that reduces the boundary layer equations for the axisymmetric case to those for a plane boundary layer. Then a similarity solution is obtained, allowing the shear stress and the pressure on the outer polymer/air interface to be evaluated in terms of the film shape only. The final set of ordinary differential equations for the film is solved numerically using finite differences. The results show that the force caused by the airflow has a significant effect on the film shape and the characteristics of the final product. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

The effects of thermomechanical coupling on the cold drawing process of glassy polymers

The source and the effects of strain-induced heating on the stress-strain behavior and corresponding cold drawing process of glassy polymers are investigated. The nature of dissipative and stored components of work are discussed where only 50 to 80% of the mechanical work of glassy polymers has been found to be dissipative. This phenomenon is demonstrated to be well-modeled by considering a portion of the work to be stored as strain-induced molecular orientation in the polymer that evokes a back stress tensor. The results of the modeling are found to be consistent with experimental measurements reported in the literature. The constitutive and corresponding heat generation model are used in fully thermomechanically coupled finite element analysis of the cold drawing of glassy polymers. The influence of applied elongation rate on the resulting temperature rise, heat transfer, thermal softening, and fiber geometry are presented, together with a full complement of the deformation field parameters related to the propagating shoulders of the drawn neck.     

纺粘非织造窄狭缝牵伸器喷射流场的研究与分析

建立了纺粘窄狭缝牵伸器喷射流场的理论模型,采用有限差分法对该模型求解,采用SIMPLE算法求解速度和压力耦合,用交错网格解决速度和压力的锯齿状分布问题,差分格式为二阶迎风格式,使用交替方向的逐线TDMA方法求得差分方程。数值计算得到了气流速度在x方向上的分量,与实验结果吻合较好。通过对几种纺粘牵伸器喷嘴的喷射流场进行了数值模拟,给出了相应的流场矢量图,显示了该研究在对纺粘设备进行计算机辅助设计方面的应用前景。     

The bending of polymers under tension as related to a deep drawing process

Two engineering plastics, an acrylonitrile-butadiene-styrene resin (ABS resin, Cycolac MS) and a rigid polyvinyl chloride resin (PVC resin, Dacovin 2082) were investigated to determine the effects of cold working. In particular, the “bending under tension” stress system of a deep drawing process was considered. The object was to determine the effect of the blank-holder pressure, the ratio of the punch radius to the material thickness, the speed of deformation and the temperature of deformation. The stress-strain characteristics of the deformed and undeformed material were markedly different. Upper yield points were lower in the deformed specimens, the tensile strengths were decreased by 10 to 15% and the %-elongation at break was higher—up to double the values for underformed specimens. An analysis indicated that these effects can be attributed to non-homogeneous yielding. The results also indicated that crazing plays an important role in permitting an ABS material to permanently conform to a radius with no geometric constraints.