HYDRODYNAMICS OF STREAKS ON THE FORMING TABLE

In today's commercially manufactured paper and board, there are small- scale basis weight nonuniformities ranging from 5 to 20%, along with s mall-scale fiber orientation and density nonuniformities, which are ge nerally much larger. Nonuniformities in basis weight and sometimes the variations in moisture originate in the forming section due to the sm all-scale secondary flows and streaks in the forming layer. Some belie ve that the streaks in the forming jet and on the forming table are ca used by the turbulent fluctuations inside the headbox and on the formi ng table. In this paper, we show that the streaks are not caused by ra ndom turbulent fluctuations. In contrast, streaks in the forming secti on are deterministic and originate in the headbox due to small-scale s econdary flows. The secondary flows are generated, in part, by the int eraction of the jests from the tubes in the tube bank and in some inst ances are due to secondary flows through the tubes or other parts of t he headbox. The methods presented in this paper help in understanding the paper-forming process and, consequently, improving the product qua lity.