Mechanisms of drainage, retention and formation on the Laboratory Twin Former

This work studied the drainage, retention and sheet formation produced by the Laboratory Twin Former, a laboratory scale device that simulates the sheet forming process of industrial twin wire papermachines. Industrial bleached kraft pulp of consistency up to 0.8% was used for the experiments; wet webs of up to 12% consistency were produced. Drainage was shown to occur by consolidation of the suspension and then by compaction of the web; consolidation occurred by a combination of filtration and thickening, but thickening was the dominant mechanism. This behaviour was found to resemble that observed on a pilot papermachine. Fines retention and formation were also shown to be similar to industrial operation.;The Laboratory Twin Former has been used in three other successful studies involving papermaking chemistry. In all cases, the results were comparable to those obtained on industrial systems.;A theoretical model describing the drainage profile of the Laboratory Twin Former was derived. This was done by performing mass, fibre and water balances on the stock suspension and the wet web. The drainage rate through the suspension, the wet web and the fabric was described using the Forchheimer equation. The model was solved numerically using the Improved Euler method. The results showed that inertial resistance to drainage was more significant during consolidation and that viscous resistance was more significant during compaction.