Reduction Of Twist On Board Machines, PaperCon2017

This paper presents some of the benefits of measuring a proxy for twist on multilayer board machines. In particular, it presents the improvement possible in twist for machines making liquid packaging and folding boxboard using FotoFiber sensors. The proxy for twist is defined as the difference in fiber orientation angles between the top layer and the bottom layer. Measurements of the surface fiber orientation are required on both surfaces, which provide an angle and an anisotropy as profiles. Although most paper makers know that the amplitude of a twist profile can be controlled (to some extent) by changing the jet to wire ratio setpoint, some do not know that twist profiles can be controlled quite precisely by the top and bottom slice lips.

A closed-loop CD control for the twist proxy is also possible, if the mill has retained motorized slice lip actuators with positional feedback on the top and bottom headbox slice lip. Provided one of the headboxes is a dilution headbox, the fiber orientation can be controlled independent of the basis weight or caliper to a considerable extent. Otherwise, the controls are coupled quite tightly. If the mill has slice actuators, but they are not motorized, then manual control is possible. Results from both of these are presented. 

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