English (United Kingdom)
Print

Detect irregularities in the process

By performing some simple measurements now and then it's possible to detect irregularities in the process that can limit the production and the product quality. The following is an example of what was found in a linerboard machine recently. The customer experienced runnability problem with loose edges and web breaks.

By using L&W TSO Tester, an ultrasonic measurement of paper stiffness and fiber orientation, rather large variations of fiber orientation in both cross and machine direction was found in the produced paper. This could come from pulsations in the headbox and or forming section. To define the cause of these variations measurements of the jet speed from the headbox and the wire speed was done with laser technique. Dantec SensorLine is such an instrument that can be used to exactly measure both these speeds and thus determine the Jet to Wire Ratio. The customer claimed the J/W ratio was +1.023 but actual measurements showed 1.000. What the measurements also showed was machine directional variations of both the stock speed and the wire speed. As the average J/W ratio was 1 this caused the machine to run randomly in rush (higher jet speed) and drag (higher wire speed).

Conclusion; Variations in jet and wire speeds were the explanation to the variations of fiber orientation and paper stiffness and can also explain the runnability issues.

Measurements of the two press fabrics were done of moisture content and water permeability. The sensors used were L&W Felt Moisture Meter and L&W Felt Permeability Meter. The first press felt indicated two streaks of very low permeability that in turn caused moisture streaks in the same positions. This will cause water streaks in the paper and reason is insufficient cleaning of the felt in these positions. Measurement of the second press felt indicated extremely low felt permeability at both paper edges. This again is caused of not sufficient cleaning in these positions.

Conclusion; Moisture streaks and fiber clogging of felts in these positions can and will cause web breaks!

Summary
Simple and fast measurements with portable instruments will help papermakers to optimize production, minimize variations and to produce paper with high quality.

Lars Kånge

Product Manager

Click here  to read the complete report.