Fibre-to-Board - Validation of the Simulation Model and Development of Laboratory Methods to Receive Input Data
Fibre-to-board is a simulation model developed at Stora Enso Research Centre Karlstad. Within this model isotropic hand sheet properties are used as input data for prediction of the final multi ply board properties. In order to improve and verify the calculations from simulations in Fibre-to-board so that these will correspond better with the results from the measurements on the paper/board machine, it was requested at RCK to investigate the possibility to optimize the input data to the model.
Standardized hand sheet forming always results in sheets with properties far away from those produced on a machine. Therefore the aim with this Master thesis was to modify the laboratory procedure to receive hand sheets with properties closer to machine sheets. To achieve this, it was investigated how different parameters affect the sheet properties and if the hand sheet making process could be improved.
When freely dried sheets were investigated it was found that sheets pressed with a wire clothing between the blotting paper and the hand sheet were less cockled than sheets pressed against only blotting papers. These sheets also tend to have a higher density. The cockling i.e. as a result from shrinkage was also reduced when the sheets were dried between slightly weighted wire clothing. Neither wire clothing nor orientated blotting papers during pressing eliminate the influence of anisotropic blotters on the shrinkage for isotropic hand sheets.
It was also examined how the fine material influences sheet properties. The results showed that an increase in fines content result in higher shrinkage, higher density, increased TSI, more cockling and decreased air permeability.
Different pressing loads and an increased density did not have much influence on the shrinkage. The density for freely dried sheets increased with higher load, but the results did not reach machine sheet densities, when the laboratory platen press was used. It might be difficult to receive freely dried hand sheets with higher densities. This is because fibres in freely dried sheets tend to relax after pressing, which will influence the density. Another press than the platen press used in these studies might compensate this matter. An increased pressing load resulted in less cockled sheets.
The basis weight did not seem to have that large affect on the shrinkage when using machine chest furnish, therefore the basis weight on hand sheets used as input data to the simulation model Fibre-to-board might not be that important.
It was studied how different plies and SW/CTMP pulp in a mixture affect the shrinkage. The results showed that the shrinkage increased with a higher SW content. It was also found that there is a linear relation between the total shrinkage of a SW/CTMP pulp mixture and the shrinkage for each individual pulp.
In order to verify the Fibre-to-board model a simulation finally was performed. Furnishes and CD profiles of board were collected from a particular board machine within the Stora Enso Group. Properties from hand sheets made of furnishes were used as input data and the machine CD profiles were used as references. The CD TSI value corresponded with the value received from measurements on the machine board, but the MD TSI value did not. The shrinkage calculated on machine sheets did not coincide with the shrinkage from the simulation in Fibre-to-board.
There are insecurities in the results from shrinkage measurement on the board CD profile due to the lack of width measurement during the process, which complicates the validation of the Fibre-to-board model.
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