Study On The Air Drawing In Spunbonding Nonwoven Process

In spunbonding, the molten polymers are attenuated into fine filament fibers by the action of high velocity cooling air, and with the air flow the fibers are randomly gathered on the collector to form nonwoven webs. Because the spunbonding process is an one-step technology. It is introduced (adopted or employed) air drawing in spunbonding, and with the help of high velocity cooling air to attenuating filament fiber provided by drawing apparatus. Due to the polymer filament spinning, drawing, laydown and bonding are fed continuously. It is needed a little time to attenuating into fine filament fiber. There are much great difference between common chemical fiber roller drafting and spunbonding air drawing method. There are many factors that influencing on the spunbonding polymer air drawing and there are complex relations among them. The further study of the technology in spunbonding nonwoven industry have a better practical significance and owns a clearer understanding on spunbonding nonwoven processing. For this reason, a series of items are studied with the action of air drawing model of polymer and air drafting mechanism i.e. of spunbonding, which essentially determines the web structure, being taken as the main subject. This study is an important component of the theory of spunbonding process, and is a guide of how to improve the web quality. Therefore, considering it is needed to realizing the characteristics and the influencing effects and mastering regulations. The theoretical basis of improving nonwoven product quality is established.The work content of the thesis covers three parts. The first part is theoretical study, which is the emphasis of our work, including modeling and numerical simulation of the air jet flow field in spunbonding. The second part is the foundation of the air drawing model of the spunbonding polymer in which the theoretical model of the air jet flow field is established. The third part is on the basis of those theories mentioned above the effects of process parameters on fiber diameters etc of simulation experiments and discussions are given.In chapter 1, the background of topic selection of the thesis is mentioned. Firstly, the theoretical model of the air jet flow field of drafting assembly in spunbonding and the geometry of drafting assembly are simply reviewed. Then, from two aspects of oversea and domestic, the research characteristics, the research trend, the research progress and current status and development prospect on the mechanism of the air drag in the polymer spunbonding process etc. are reviewed. The oversea researches of spunbonding technology was introduced, the summarization of research status of spunbonding air drawing technology is conducted comparing with them between advantages and disadvantages. The problems in the research spunbonding technology were analyzed. It was pointed out that there was a great difference between them. At the same time, the present research situation of china was analyzed, the mathematical models of the air drag in the spunbonding etc. are analyzed and evaluated. The developing trend and application prospects for spunbonding technology were predicted. The development of new technology should be stimulated and be focused on the spunbonding nonwovens. The directions for further research in this field are pointed out. Secondly, the process type, raw material, new technology, development direction, and the characteristics of the various basic typical new-type spunbonding nonwoven technology etc. are introduced.In chapter 2, the basic knowledge is introduced, including the finite difference methods, i.e. the Taylor series expansion method and the control volume method, and the methods common used for solving the algebraic equations which is the sequent of the governing differential equations discretization.The theoretical model of the air jet flow field of drafting assembly in spunbonding is established. According to the characteristics, mechanism and methods to study the air drag in the polymer spunbonding process. The air drawing model of spunbonding consists of the continuity equation, momentum equation, and boundary conditions i.e. On the basis of the characteristic of the air jet flow field, the k-εmodel is adopted. The governing equations are discretized by the control volume method and the corresponding finite difference equations are obtained.In chapter 3, the numerical simulation solving method of the theoretical model of the air jet flow field in spunbonding is discussed. The air jet flow fields of several spunbonding drafting assembly with different design parameters are simulated numerically and the corresponding vectors diagrams of the air jet flow field etc. are demonstrated. It is found from the several diagrams that appropriate design drawing device shrinkage ratio which are beneficial to the air drawing of the spunbonding polymer melt and can also produce finer fibers.In chapter 4, the performance and characteristics of Particle Image Velocimetry are introduced. With Particle Image Velocimetry the air velocity of the air jet flow field of drafting assembly in spunbonding are measured. Five air jet flow field with different design parameters are surveyed. Both the experimental data and computation numerical simulation results, which are fit well with between them and shows that the complete set of the numerical simulation algorithm founded here can be used in the prediction of the air jet flow field of drafting assembly.In chapter 5, the theoretical model established and solved of the air drawing in spunbonding polymer and the effect of process parameters on final fiber diameter are discussed. Firstly, the fundamental rules of the air drawing in spunbonding process are analyzed. Secondly, on the basis of this, the former model of spunbonding polymer air drawing is improved and a complete spunbonding polymer air drawing model is also established, which is integrated with the model of air jet flow field of drafting assembly. The model is solved by using fifth order Runge-Kutta method and the numerical simulation results coincide quite well with the experimental data.The air drawing model of a polymer in the spunbonding process is presented. This model includes the continuity equation, momentum equation, energy equation, constitutive equation and crystallization kinetics equation. The model is solved by introduced the numerical computation results of air jet flow field of drafting assembly, and the predicted fiber diameter and crystallization agree with the experimental data. The effects of the processing parameters and drafting assembly design parameters on the fiber diameter etc. have been investigated. It is found that lower polymer throughput rate, higher initial polymer melt temperature, higher primary air speed, and higher primary air temperature can all produce finer fibers, which can also produce better and finer fibers. The results also show the great potential of this research for the computer-assisted design of spunbonding technology.In summary, as the complete polymer air drawing in spunbonding process is developed, which based on the numerical simulation results of the air jet flow field of drafting assembly. The simulation of the air jet flow field within drafting assembly is performed. Meanwhile, the characteristics of high speed cooling air flow in the drafting assembly are shown by numerical simulation. It is possible to predict the final fiber diameter etc. The study of the thesis develops a clearer understanding on nonwoven processing.