Drainage pressure oscillations during roll forming, PaperCon 2010 Conference

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In a roll-blade former the initial drainage is achieved by wrapping the tensioned fabrics over the roll surface. The dry line is located after the roll, and additional drainage is achieved in the blade section. This situation is referred to as partial roll forming.

In order to study the dynamics of partial roll forming, pressure measurements have been made in the roll-blade former of the FEX pilot machine at Innventia in Stockholm. The measurements were performed using a fibre optic pressure measurement system.

The results confirm that oscillatory flow behaviour is possible in industrial forming sections. The good agreement between the experimentally determined wavelengths of the oscillations and the theoretical analysis by Holm & Söderberg [1] strongly suggests that the oscillations are of capillary origin, and that they are controlled by a local dimensionless Weber number expressing the local balance between the momentum of the flow and the forces exerted by the fabric tension.

Pressure gradients are capable of influencing the fibre web structure, and the gradients associated with the oscillations could hence be of significance to the forming process.