Theoretical Study And Application Of The Effect Of Suction Box And Air-adding Slot On The Laying Of Filaments In Spunbonding Process

In spunbonding nonwoven process,the drawing and laying of filaments are controlled by airflow.The whole airflow field is formed from exhaust gas suction、quench air、adding air and suction air under the web.At the outlet of the draft duct,suction air will cause a strong negative pressure airflow which can form airflow velocity difference between inlet and air-adding port in the draft duct,so that filaments can obtain the required drawing force.However the structure of suction box under the web have a direct influence on the uniformity and stability of airflow in the draft duct;meanwhile the size of air-adding port determines the amount and the velocity of the adding air,which will influence the airflow field in the draft duct that directly determine the effect of drawing and laying of filaments,eventually affect the uniformity of fiber web.Therefore,it is very important to optimize the suction box and adjust the air-adding slot to improve the laying of filaments and the appearance quality of the fiber web.This thesis consists of the following three parts.In the first part,the 3-D simulation model of the airflow field of the suction box under the web and the draft duct in the negative pressure drawing spunbonding nonwoven process is established and analog computed by FLUENT software.The wind velocity tester is utilized to measure the velocity distribution of the airflow field in the suction box.Simulation results are compared with measured results and they show a good agreement with each other,which confirms the accuracy of the 3-D simulation computation of airflow field model of suction box.In the second part,based on the simulation results of airflow field model of suction box,different optimization schemes for the suction box are designed by CAD software,in this thesis,only three kind of most representative contrast schemes are explained.Eventually the optimal scheme is selected to optimize the suction box which under the web.Then test and compare the uniformity of fiber web samples which is obtain before and after optimize the suction box to confirm the effectiveness of improving the laying of filaments.What needed to emphasize is that the manufacture conditions of the two fiber web samples is identical.In the third part,based on the optimization schemes,change the size of the different position of the air-adding slot in the web width direction so that form different contrast models which are3-D simulation computed to analyze the effect rule of air-adding slot on the draft duct airflow field,eventually summarize the influence mechanism of air-adding slot on the laying of filaments.To sum up,in this thesis,the numerical simulation method is used to research the airflow field of suction box which under the web and draft duct.Meanwhile the laying of filament and the uniformity of fiber web are improved by optimizing the suction box.What’s more,the influence rule of air-adding slot on the laying of filaments is summarized so that can provide a theoretical basis for debugging the spunbonding process in practical production.