A PRACTICAL LOOK AT HOW TO IMPROVE SHEET FORMATION IN THE HEADBOX/APPROACH PIPING SYSTEMS

摘要

Sheet formation development is determined by a number of variables which should be satisfied. Some of these variables are more powerful than others. In a case when some are not fully optimized, they may cancel the effect of the ones that are.One of the most powerful variables is the determination of the jet speed in relationship to the wire speed. Intuitively, one may imagine that if the jet speed is faster than the wire the fibers roll forward and vice versa. In both cases, the formation suffers.Unfortunately while the majority of papermachines are equipped with sophisticated computer controls, they are still applying outdated calculations to determine the jet speed. Equations are taken off the shelf and not adapted to the specific design and application. This state of inaccuracy has left the machine operator in a state of alarming confusion. As a result, a papermachine making the same grade may run with many different process settings according to the interpretations and preferences of the current operator instead of a scientifically-based analysis. The result is like a car out of tune. The car runs but ultimately it gives poor gas mileage.This article explains the variables that determine the true jet-to-wire speed ratio which have been applied by the authors successfully over the last fifteen years in more than four hundred fifty headboxes.The article covers also other important variables that should be considered for optimum sheet formation development and structure.