Observation of Fiber Orientation in a Headbox Nozzle at Low Consistency, 1997 Engineering Conference Proceedings

Many different process variables such as fiber properties, head-box geometry and forming conditions are thought to be re-sponsible for the fiber orientation distribution in the paper. This argument was recently advanced in the literature where it was demonstrated that one process variable, the headbox con-traction ratio, governed the MD/CD tensile stiffness ratio. In the present investigation construction and development of an experimental equipment to study fiber orientation in a headbox nozzle has been performed. In order to detect the fibers in the nozzle, travelling with an outlet speed of l0-15 m/s, a CCD-Camera was mounted over the outlet together with a stroboscope. Image analysis has been used in order to evaluate fiber orientation from the recorded images. The fibers, used in this investigation, were polymer fibers of uniform length and thickness. The suspension was dilute, with little interaction between particles. The contraction ratio (CR), of the headbox nozzle, was defined as the ratio of nozzle inlet area to nozzle outlet area. The con-traction ratio was changed by altering the slice opening at the nozzle end. Experiments were conducted at the three contrac-tion ratios, CR= 50, 25 and 16.7. In terms of slice opening the three experiments were conducted at 5 mm, 10 mm and 15 mm receptively. In each one of these cases a range of flow rates were investigated. The result indicates a strong relation between contraction ratio and fiber orientation in the nozzle of the headbox; changing the flow rate had a very small effect on the fiber orientation. An analytical theory treating a dilute homogeneous flow has also been compared to the experiments.