This paper is an overview of the theory and practice of improving formation. The aim is to provide background information for mill personnel to understand the basic mechanism of formation improvement and how these mechanisms can be controlled in practice. The scope of the paper is mostly related to paper grades and concerns all headbox and forming section types. There is a lot of relevance in this discussion also for board grades although the emphasis is primarily on paper.
The principles of how formation is influenced by fibre concentration, shear, turbulence, flow elongation and drainage are explained. In the furnish and stock preparation area the influences of fibre properties, refining, wet end chemistry and formation improving additives are discussed. There is a section on formation measurement intended to brief the reader on what measuring methods are appropriate for different uses and how new measuring methods can characterize the appearance of formation. Formation improvement cannot be considered in isolation from other paper properties so while formation is the main theme of this paper the consequences of formation tuning activities on other paper properties are also described.
The emphasis on practical tuning in this paper is on how to optimize the headbox and former operation. There are sections in this paper concerned with formation fault finding, systematic tuning procedures and strategies for routine formation control. A new formation tuning technique based on measurement and control of Z direction formation profile is introduced in this paper.
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