Slotted Headbox Screening for Fine, Publication and Newsprint Grades, 1990 Papermakers Conference Proceedings

Oliver Heise--The technical concept for headbox screens is to design them with conically drilled holed baskets. A costly problem for paper mills, especially those producing fine, publication and newsprint grades are in-house and virgin pulp contamination. This problem of contamination has forced paper mills to review their present screening systems, including the traditional concept. One solution to the problem was to install fine slotted screens, which are located between blend and machine chest. Papermakers refer to this as a thick stock screening application. An economic and technical alternative to a separate thick stock screening system is to use fine slotted screens in the approach flow. Fine and newsprint mills will significantly reduce breaks and sheet quality problems in the size press calender, winder slitter and printing press area by utilizing fine slotted reject screens in the approach flow screening system. Coated paper mills have to consider a three-stage fine slotted screening system to prevent streaks and breaks due to a contaminated base sheet. The paper will cover the following topics of contamination: - Typical sources of contamination - Operational problem areas - Solutions to virgin pulp and in-house contamination - Results from a coated paper and newsprint machine experience