Headbox flow analysis

Cross-machine fiber orientation and basis weight profiles depend on the headbox design and operation, which makes a headbox system critical to a successful papermaking system. The objective of this paper is to examine the relationship between the headbox flow characteristics and the fiber orientation by systematically analyzing different headbox flow control devices such as slice profiling, edge valve, tube inserts, pondside bleeds, and header balancing. To correlate the headbox flow characteristics to the measured fiber orientation, CFD (Computational Fluid Dynamics) was employed. Through the CFD analysis, the headbox flow characteristic in terms of the so called flow angle was obtained from the CFD solutions. The measured fiber orientation data were recorded and compared to the computed flow angle. The comparison indicated that the fiber orientation mimicked the flow angle, and both showed consistent response to the adjustments of headbox control devices. The present work also identified three basic transformation modes between the flow angle and the fiber orientation, namely, translation, linear augmentation, and rotation modes. Understanding these different mechanisms can definitely help improve both headbox and former designs for better fiber orientation controls. This work demonstrated that the CFD can be used for not only trouble shooting, but also design improvements. The current approach serves as an effective means for lowering design costs and design cycle time instead of the time consuming trial-and-error process.