Effect of headbox slice geometry during the stratified forming of woodfree paper

Abstract Stratified forming, or the simultaneous forming of a multi-layer sheet from a single headbox, can produce an heterogeneous surface due to flocs from the different layers being mixed together in the headbox jet. In this paper we investigated the effect of the slice geometry on the layer mixing process. Sharply contracting slice lips downstream of the vane tips appeared to reduce layer mixing. while parallel slice lips downstream of the vane tips appeared to increase layer mixing. However the type of slice lips had little effect on layer mixing if the vanes finished outside the headbox. A narrower slice opening reduced layer mixing in all cases. Reducing the jet speed from 830 mlmin to 540 m/min had little effect on layer mixing and paper properties. Sharply contracting slice lips improved the small scale formation. The higher consistency associated with a narrower slice opening worsened the large scale formation, but had no effect on small scale formation. The jet speed did not alter the formation within the range tested.