Monitoring and controlling the web structure is of primary concern to the papermaker. Nevertheless, quality degradation due to bad formation or large-scale variations in the basis weight is not uncommon.
Previously, it has only been possible to examine the web structure by offline laboratory methods, or online using equipment installed on measurement frames in the dry end of the machine.
The STFI Online Forming Analyser (SOFA) is now available as a tool to determine the fibre mass distribution online in the wet end of both single-wire and twin-wire paper machines. This provides a number of advantages:
- Direct access to the forming process, without influence of downstream operations.
- Separate analysis of each layer on multi-ply machines.
- The effects of individual forming components can be isolated.
- Shorter feedback times in forming control loops.
Typical applications include online formation monitoring and detection of large scale basis weight variations (for example streaks).
The SOFA system can help the paper and board mills to get control of the variations in product quality. Research has shown the potential of saving as much as 5% of fibre raw material. For an average Nordic board mill (500.000 t/year), this could mean saving SEK 125 millions per year. A reduced fibre utilisation of 25.000 t/year also implies a reduced energy consumption by 50 GWh/year.
SOFA systems are also being used both within the Innventia research activities and for contract work. Development work is continuously done to improve its functionality for the benefit of Innventia and its partners.
A SOFA system installed after a top wire unit. The high-speed camera captures images of the light transmitted through the wire and the web. Image analysis then yields the web structure. A full-scale installation includes a system of cameras in a row across the web.