New Paper Machine Gard Screening Concept for Improved Paper Quality and Paper Machine Efficiency, 1997 Papermakers Conference Proceedings

Gard TM screening involves high consistency screening of the mixed stock fed to the paper machine. The objective is to provide effective protection for the paper machine with very fine-slotted screens. This concept has shown significant improvement in paper machine operations compared to the conventional machine screening systems. Narrow slotted screens have been used already for some years in recycled fiber and mechanical pulping screening applications. However, the consistency is typically in low 0.7% to 2.0% range. In a conventional approach flow system the screening is carried out at very low headbox consistencies with high passing velocities. Any pressure disturbance from the screens will directly affect the paper quality. Screening efficiency is typically low because the screens normally are operated with large holes or slots to prevent any sudden pressure changes. Fine slots are hard to use between the machine chest and the headbox for this reason. Sunds Defibrator has developed a new screen to operate at high consistencies of 3.0% to 4.0% with high contaminant removal efficiencies. The DeltaScreen® T, allowing the use of very fine slots of 0.10mm to 0.30mm (0.004” to 0.012”) in width, is the heart of the high consistency system by providing efficient barrier screening to eliminate even the smallest elements of contamination. This paper discusses the improvements of paper quality and paper machine efficiency in tine paper, newsprint, and board applications.