Study On Dispersion Performance Of Ceramic Fiber In Pulp Fluid Of Wet-laying Processing

The mechanism of wet-laying processing with special reference to the ceramic fiber as the major raw material was studied in this thesis. The factors affecting the pulp quality of wet-web were analyzed. The multi-components wetlaid nonwoven products were developed and their properties were tested. All the results obtained will be of benefit to the better understanding of the processing and machine design. The main contents of the thesis are as follows.1. Study of the dispersion behaviour of solid fiber in liquid phaseBy means of the electrodynamics, the electrodynamic potential in the liquid phase and the surface electric density of the solid fiber were calculated. The results show that the proper thickness of electrical double layer on the interface of solid-liquid two phases is essential for the solid fiber dispersing in the liquid phase uniformly. And the correct use of the dispersants according to the solid fiber properties will make the thickness of electrical double layer be required, which is due to the different kind of dispersants is capable of expend or compact the thickness of electrical double layer. A kind of negative ionO active reagent was used and added in the pulp with a low concentration in the present work because of the special characteristics of the ceramic fiber with high specific density and the high positive electricity in liquid phase, and the results were satisfied.2. Numerical simulation of the flow field in wet-laying processConsidering the irregularity of the boundary profile of the flow field, which is shaped like the pulp box, the method of mixed difference is used for the numerical simulation of the flow field in this thesis. The simplified free surface of the liquid phase was taken as the boundary condition. The SIMPLE arithmetic is used to linearize the equations. In order to improve the pitching quality a parting method is applied in such a way that the frame of grids in calculating model is irregular. Moreover, the Fluent Compact software is used to simulate the velocity and pressure of flow fields. From the numerical simulation results, it can be found that the velocity and pressure of the flow field are varied in the different area of the box. The paper gives twelve simulated examples which can show the effect on the flow field of different inlet velocity, hatch angle and pond hatch angle. It will provide a primary for furtheranalyzing the influence of the pulp flow on the properties of the wetlaid nonwoven fabrics.3. Investigation of the mechanism of the solid fiber dispersing due to the shearing action of pulp fluidAlthough the pulp is well stired and the dispersant is added in it during the upstream processing, there are still some solid fiber-assemblies and pulp faults present, which need to be disassembled further in down stream processing. Based on the numericalsimulation of the flow field, the shearing forces of the pulp liquid, which are conducive to the breakdown of the solid fiber assembly, were calculated and the factors affecting the value of shearing forces also analyzed in this thesis. The results show that the disassembly capability of the pulp fluid mainly lies on its velocity. Great velocity will improve the dispersion behaviour of the solid fiber. The fiber floes, however, will be formed again if the fluid velocity is too high and the undesirable turbulence is developed. In addition, the hatch angles of the pulp box have a remarkable effect on the value of shearing forces.4. Analysis of the diffusion, suspension and settlememt performance of the solid fiber and pulp faults in the pulp liquidWith the aid of the results of the numerical simulation of the flow field, the diffusion and suspension performance of the solid fiber and settlememt capability of the pulp faults were analyzed and calculated. The sinking velocity for all the ceramic fibers, the mixtures of the ceramic fiber and ceramic shot and pure ceramic shots were measured. The results show that in the flow field concerned the ceramic fibers can be well diffused and suspen...