压榨模拟实验——宽区压榨毛毯-纸幅体系脱水机理的研究

Simulation Experiment of Pressing—the Research on the Dewatering Mechanism of Felt-sheet System for Extended Nip Press

中文关键词:  毛毯-纸幅体系  压榨模拟  脱水机理  毛毯表面平均压强  毛毯表面结构

Key Words:press felt-sheet system  model experiment of pressing  dewatering mechanism of press section  average pressure of press felt  press felt surface structure

中文摘要:

      基于宽区压榨过程中毛毯微观结构特性的分析,采用2套自制模拟实验装置,研究了压榨过程中毛毯微观组织的受压情况以及毛毯结构与纸幅定量对压榨脱水过程的影响,进而研究了毛毯-纸幅体系的脱水机理。结果表明,压榨过程中,毛毯-纸幅接触复合层在其微观组织上所受压力分布不均匀,进而影响压榨脱水效率；因毛毯植绒纤维传递的压力不均匀,毛毯-纸幅接触复合层中会形成压缩区域和未压缩区域,未压缩区域具有很高的渗透性能,是主要脱水通道；当水流经过的毛毯-纸幅接触复合层骨架空隙较畅通时,压榨脱水控制方式属于“压控主导型脱水”,反之,属于“流控主导型脱水”；在毛毯结构设计中,植绒纤维直径是提高压榨脱水效率的第一考虑要素,其次是底网结构,最后是植绒层数。对于低定量纸幅,宜采用植绒纤维直径小、多层底网、植绒层数较多的毛毯；对于较高定量纸幅,宜采用植绒纤维直径大、双层或单层底网、植绒层数较少的毛毯；压榨毛毯表面的平均压强可作为衡量其综合性能的定量化指标之一。

Abstract:

      Based on the microstructure characteristic analysis of the felt in extended nip press(ENP), two sets of simulation experimental devices were designed and used for pressing simulation study. The research focused on characterizing the micro-scale stress(MSS) variation of press felt and the influences of press felt structure and sheet grammage on dewatering process during pressing; furthermore, the dewatering mechanism of felt-sheet system(FSS) for ENP was discussed. The results suggested that MSS on the contact area (or compound layer) of press felt and wet web was non-uniform which reduced the dewatering efficiency; the nonuniform stress transfer by the felt surface batt fibers made the contact area dividing into compression and non-compression zones, and the non-compression zone had high water permeability and became the main channels for water flow; when dewatering through the unimpeded nework, the dewatering condition was called “pressing-controlled dominant dewatering”, and on the contrary, when the network was impeded, the dewatering condition was called “flowing-controlled dominant dewatering”; concerning dewatering efficiency, the most important considering factor of the felt structure was the diameter of the batt fiber, the second was the base weave design of the felt, and at last was the number of batt layers. For low grammage paper, the fine press felt was more advantageous to dewatering in pressing process which had the fine batt fibers, multiple layers of base weave and more batt layers; while for high grammage paper (especially the paper with coarse pulp fibers) which together with felt created the contact zone with high proportional non-compression zones. The press felt with coarser batt fibers, double or single layers of base weave and less batt layers was advantageous to the dewatering process. It was also suggested that the average pressure of the press felt surface could be used as one of the indicators for measuring its comprehensive performance of press felt.