Hydrodymamics of Streaks on the Forming Table, 1996 Engineering Conference Proceedings

In today’s commercially manufactured paper and board, there are small scale basis weight nonuniformities ranging from 5% to 20%, along with, small scale fiber orientation and density nonuniformities which are generally much larger. Nonuniformities in basis weight and sometimes the variations in moisture originate in the forming section due to the small scale secondary flows and streaks in the forming layer. Some believe that the streaks in the forming jet and on the forming table are caused by the turbulent fluctuations inside the headbox and on the forming table. In this article, we show that the streaks are not caused by random turbulent fluctuations. In contract, streaks in the forming section are deterministic and originate in the headbox due to small scale secondary flows. The secondary flows are generated, in part, by the interaction of the jets from the tubes in the tube bank, and in some instances due to secondary flows though the tubes or other parts of the headbox. The methods presented in this article help in understanding the paper forming process and, consequently, improving the product quality.