MULTILAYERING OF FINE PAPER WITH 3-LAYER HEADBOX AND ROLL AND BLADE GAP FORMER
The aim of this study was on the layering of fine paper with a 3-layer headbox and roll blade gap former. It consisted of methodological development and laboratory scale studies, as well as layering studies on the pilot paper machine scale. The potential of layered structures in papermaking and the phenomena affecting layer mixing were also studied. Filler distributions were characterized by two parameters filler distribution shape and symmetry factors. The method developed made it possible to apply a statistical approach to experiments when studying the impact of typical wet end control parameters on the control of filler distributions and the contribution of filler distributions to paper quality parameters. A method by which the center layer fiber distribution may be characterized from the final paper is also presented. The method is based on the use of dyed fibers and a spectrofotometer. In addition, a laboratory device, a multilayer handsheet former for making layered structures, is presented. The process closely resembles a real continuous multilayer process by providing water phase interactions between layers during forming and two-sided dewatering characteristics. In a case study, retention chemical and filler layering with WFC base paper was performed by the multilayer handsheet former. Surface roughness decreased and brightness increased when the filler content in paper surfaces was increased. At constant filler content, paper strength increased as the filler concentration in the paper surfaces increased. The distinction between roll dewatering and blade dewatering in terms of layer mixing as well as differences in the mixing behavior of fibers and fillers in different dewatering phases was studied. Major fiber mixing takes place during the free jet and roll dewatering phase. In blade dewatering, fiber movements are related to formation improvements. The greatest mobility differences between fibers and fillers were found in the blade dewatering phase in roll and blade dewatering. Filler distributions were significantly affected during blade dewatering, with the mobility of the fibers remaining insignificant. The relationship between typical fine paper quality parameters and filler distributions was studied. Formation improvement and densification of the paper were achievable at the same running conditions. Low porosity was achieved by evenly distributed constituents (good formation) and a local rich filler concentration somewhere in the paper structure in the paper thickness direction. Oil absorption two-sidedness was minimized by symmetrical filler distributions. The combination of all these quality factors required the filler distribution to be symmetrical and as uor turned u-shaped as possible. The use of additives layering as a part of paper quality control was also studied. Multilayering was found to be an effective tool for the control of filler distributions. On the other hand it was shown that, in order to get optimized impact of the multilayering on quality properties, the other process variables also need to be controlled.
LEPPÄNEN Effect of Fiber Orientation on Cockling of Paper
Cockling of paper is small-scale out-of-plane deformation. This undesired phenomenon appears in paper already in the manufacturing process. Cockling continues due to moisture changes during the storage, transportation and end-use of paper. Although all paper suffers from cockling, the scale of cockling varies a lot. Sometimes the cockling tendency of paper is so small that it does not create any problems in the end-use of paper, while some other paper may have a great tendency for cockling. Although many potential factors influencing the cockling tendency of paper are known, the significance of various factors is not clear. In this thesis, the effect of locally varying fiber orientation on cockling is researched via modelling. This is done by two different modelling approaches. The first approach is the continuum mechanical model, which takes into account only the local fiber orientation. The validation of the model can clearly show that significant correlation exists between the local fiber orientation and the cockling tendency of paper. The second approach is a method, which is based on the calculation of local curls. These local curls are determined by the local fiber orientation. The results of this approach also confirm the significance of local fiber orientation for the cockling phenomenon. In addition to being very efficient compared to the continuum mechanical model, this method will give an insight into the mechanism of structure-based cockling. The fiber orientation structure of paper is determined by several variables of the papermaking process, and the structure is always a compromise between many factors. Controlling individual fibers in the papermaking process is a more difficult task than controlling fiber orientation on a larger scale. The continuum mechanical model is used to predict the effect of large-scale changes of the fiber orientation structure on the scale of cockling. This study shows the significance of standard deviation of the local fiber orientation angles and the mean of the local anisotropies on the cockling tendency of paper. In addition, the results predict that small changes in the thickness directional fiber orientation distribution do not cause significant changes on paper cockling if only the fiber orientation structure is considered. PACS Classification: 02.70.Dh, 45.10.-b, 46.15.-x, 46.70.-p, 61.43.-j, 62.20.Dc, 81.05.Lg Universal Decimal Classification: 539.387, 676.017.27, 676.026.21, 676.019.1, 620.191.35 INSPEC Thesaurus: paper; paper industry; paper making; fibres; mechanical properties; deformation; modelling; simulation; continuum mechanics; finite element analysis; quality control
Numerical Simulation of Induction Heating Process of Continuous Casting Slab
Compared with traditional blazing furnace, the Continuous Casting-Direct Rolling is an advanced manufacturing steel technology, which can reduce energy waste, decrease pollution and enhance efficiency. The characteristics of steels during induction heating are complex, the change of material properties with temperature makes exact analysis methods very difficult to implement. Therefore, a powerful computer aided numerical tool (i.e., finite difference analysis) is selected to numerically model the induction heating process in this paper. The mathematic model coupling with electromagnetic field and thermal field was established, and it was solved by finite difference method (FDM), thus the slab temperature distribution and its variation with time were obtained, and the characteristics in whole induction heating process were studied. To validate the program feasible, the results were evaluated and compared with experiment results, which showed that the simulation results are reliable and effective. The skin effect in heating process from the two results was studied and demonstrated, the temperature change caused by different parameters such as the induced power intensity and the corner radian were also presented, which indicate that the slab temperature can be heated uniformly through adjusting these parameters, thus the continuous casting slab can meet the rolling requirement.