| The inexorable trend of spinning technology development is high-speed, automation, shortened spinning process, ecology, environmental protection and high production quality, which is a condition-prerequisite of realizing the high added value in textile industry. The high-speed whirled airflow twists the open-end trailing fibers, twined over the inlet of the hollow spindle, into a yarn in Murata vortex spinning, which is drawn extensive attention of the professional insider and is of extensive market prospect for its high speed of spinning yarn, high automation, shortened spinning process, and low energy consumption as well as excellent yarn properties.Changing the process of the vortex spun yarn will result in the change of its structure, and further changing its properties. The current research work done by previous researchers experimentally focused on yarn formation principle and yarn structure as well as the correlation between yarn formation process and yarn structure. Therefore, in this paper, the correlation between yarn formation process and yarn structure will be discussed theoretically, and then the nonlinear theories are constructed, which will be validated by designed experiments. There is a significant meaning for researching the correlation between yarn formation process and yarn structure, on the one hand, which can optimize the process of yarn formation and improve the structure of key components used to form yarn, on the other hand, which can guide theoretically the design of the yarn structure.Because the law of air current action on the fiber inside the nozzle block of air-jet vortex spinning is very complicated, if discusses the correlation between yarn formation process and yarn structure, the principle of yarn formation should be comprehensively understood, being a precondition for making clear the correlation between yarn formation process and yarn structure, which firstly requires studying the flow rule inside the nozzle block. Then, based on the flow rule, the law of air current action on the fiber and the yarn is analyzed inside the nozzle block. Finally, in air-jet vortex spinning, the effect of yarn formation process on the yarn structure is discussed by constructing the nonlinear theory. The main research contents and results can be drawn as follows:(1) Based on the air-jet vortex spinning system of Murata No.861, the computational zone of flow field inside the nozzle block is got by applying the Software Gambit, and then the Computational Fluid Dynamics (CFD) Model inside the nozzle block of Murata Vortex Machine is constructed. The CFD model adapts the standardκ-εturbulent model and uses the SIMPLE algorithm to disperse the governing equations, which is solved iteratively based on the TDMA algorithm. The process of solving the CFD model is completed in Fluid Software FLUENT 6.3. As a result, the flow rule of air current inside the nozzle block is obtained. The research results show that as follows:the compressive air through the jet orifice comes into being dimensional whirly airflow inside the nozzle block, the tangential and axial airflow is fit for the theory of swirling airflow, the tangential velocity twists open-end trailing fibers twined over the inlet of the hollow spindle; the draw effect of the axial velocity to fiber bundle may be neglected; the radial airflow makes the edge open-end trailing fibers in the twisting chamber begin to expand to let yarn get more wrapper fibers; the static pressure distributions take on the "U" shape along nozzle radius, the reason of twist irregularity of vortex yarn is that the degree twisted at different positions is different for open-end trailing fibers twined over the inlet of the hollow spindle.(2) Based on the constructed CFD model, the flow patterns affected by the nozzle structure parameters and the velocity at jet orifice exit inside the nozzle block of Murata vortex machine are investigated. The research results show that as follows: the negative pressure along the nozzle axis enhances first, and then diminishes with increasing the jet orifice angle, and the negative pressure is maximal when jet orifice angle is 30 degree; the tangential velocity decreases with increasing the jet orifice angle, however, the axial velocity increases with increasing the jet orifice angle; the tangential and axial and radial velocity as well as the negative pressure along the nozzle block axis also increase when the velocity at the exit of jet orifice enhances; the outer diameter of the hollow spindle is comparatively small effect to the velocity of airflow inside the nozzle block, but the negative pressure along the nozzle block axis will become higher for the less outer diameter of the hollow spindle; the velocity and the static pressure inside the nozzle block diminish and the negative pressure at the entrance of the nozzle block increases with increasing the distance between the hollow spindle and the entrance of the nozzle block.(3) The strength of the vortex twist action on the vortex yarn is investigated by analytical model based on simulating the flow field inside the nozzle block. The research results show that as follows:the strength of the vortex twist action on the vortex spun yarn is regard as a function of the number of jet orifices, jet orifice angle, diameter of the jet orifice, inner diameter of the nozzle block, outer diameter of the hollow spindle, velocity at the exit of the jet orifice (namely nozzle pressure), distance between the entrance of the hollow spindle and the entrance of the nozzle block, the upper height of he hollow spindle, the middle height of he hollow spindle and yarn diameter, and so on; increasing the velocity at exit of the jet orifice can increase the whirled airflow strength action on the vortex yarn; the whirled airflow strength action on the vortex yarn increases with decreasing the inlet diameter of the nozzle block and becomes weaker with increasing the distance from the inlet of the nozzle block to the inlet of the hollow spindle; the whirled airflow strength action on the vortex yarn enhances with increasing the outer diameter of the hollow spindle. The numerical and experimental results show the effectiveness of analytical model.(4) Based on the process of yarn formation in air-jet vortex spinning, the fiber spatial trajectory and the fiber configuration in vortex yarn are analyzed and discussed respectively according to the flow rule of flow field inside the twisting chamber of the nozzle block. The research results show that as follows:the spatial configuration of the fiber is affected by parameters, such as delivery speed, the distance from the nip of front roller to the inlet of the hollow spindle, fiber length, and yarn diameter, and so on; the fiber spatial trajectory shows theoretically the vortex spun yarn is of relatively less long hairiness; the hairiness of vortex spun yarn can be divided into three categories, namely head end hairiness and trailing end hairiness as well as random protruding hairiness; If the separated fibers in fiber bundle are all parallel and straight fibers, the fiber configuration in vortex spun yarn can be divided into two categories: One is the whole fiber being the core fiber, which configuration isn’t affected by process parameters, the other is the fiber that consists of the core fiber and the migration warp fiber and the surface warp fiber, accounted for most of proportion in all fibers; For latter case, the length of the core fiber is affected by the fiber length and the distance between the nip of the front rollers and the inlet of the hollow spindle; the configuration of the migration warp fiber can be characterized by its migration warp width and length, which is affected by the following parameters, such as the fiber specification, the yarn diameter, the nozzle pressure and the delivery speed; the surface warp fiber can be described by mean pitch and warp angle, which is affected the following parameters, such as the mean angular velocity of open-end trailing fiber rotating round the hollow spindle determined by the nozzle pressure and the fiber specification, the delivery speed and the yarn diameter; if the partial fiber in fiber bundle isn’t entirely parallel and straight, this fiber in vortex yarn may be formed the head hook (namely front hook), the trailing hook (namely back hook), the middle random entanglement and their combinations.(5) The attenuated law of flow field inside the nozzle block of the air-jet vortex spinning is firstly investigated by the determined numerical computation method. Secondly, based on the attenuated law of flow field inside the nozzle block, force analysis about a separated fiber in twisting chamber and the movement status of a separated fiber affected by vortex in twisting chamber are discussed. Lastly, the function relationship among the critical angular velocity of the open-end trailing fibers twined over the inlet of the hollow spindle and rotated around the vortex yarn, the fiber proceeding potion length inside the yarn’s trail and the fiber radius and so on is constructed. The critical angular velocity may judge whether the fiber proceeding potion is pulled out the yarn’s trail or not, which can explain waste fibers and thin/thick places generating. The critical angular velocity increases with increasing the fiber proceeding potion length inside the yarn’s trail and the fiber radius. On the condition of the same nozzle pressure, utilizing the coarser fiber to spin the vortex yarn, its thin/thick places and system’s waste fibers are more serious. Increasing nozzle pressure firstly can enhance the yarn strength. However when the nozzle pressure exceeds the critical point, and the waste fibers and yarn thin/thick places become more, which makes the yarn properties deteriorate. Increasing negative pressure at the inlet of nozzle block and decreasing properly the distance from the front roller to the hollow spindle can decrease the waste fibers and yarn thin/thick places generating.(6) The air-jet vortex spinning apparatus with the low waste fiber rate can be realized from two aspects as follows:one is that the structure of the trailing end of vortex yarn is compacted by the false twist effect of air current and the properly decreased inside diameter of the hollow spindle, which can increase the constraints of fiber proceeding potion just entered into the training end of vortex yarn in order to decrease the probability of the fiber proceeding potion being pulled out from the training end of vortex yarn by the whirled airflow, and then lower the waste fiber rate; the other is to minimize the effect of the whirled airflow disturbing the head end of fiber proceeding potion entering into the inlet of the hollow spindle and twisting the open-end trailing fibers inside the nozzle block by optimizing and designing the structure of nozzle block. |
PDF Full Text Request