Automated Gate Rejection Algorithms for Real Time Recycled Fiber Blend Variations
Real-time NIR spectroscopy coupled with automated divert gate algorithms stabilizes furnish quality, rejecting off-spec recycled stock before pulper entry.
Freeness Control
Drainage Resistance
Drainage resistance measures the rate at which water separates from an aqueous suspension of cellulose fibres through a perforated screen under standardized conditions. Freeness control governs this filtration property during stock preparation to prevent uneven web formation on the paper machine wire. Refining mechanical pulps bruises and fibrillates the outer cell walls, which increases specific surface area and reduces the speed of water drainage.
Slowness values rise when excessive fines accumulate or when high levels of recycled furnish introduce collapsed ribbon fragments that clog interstitial channels. Papermakers monitor these hydraulic parameters continuously because overly closed stock causes sheet blowing in the press section and limits maximum machine speeds.
Refining Dynamics
Mechanical energy input alters fibre morphology to modify drainage resistance before the stock reaches the headbox. Low freeness targets suit dense glassine and security papers where high opacity and smooth surface contours outweigh drying constraints. High freeness targets remain mandatory for bulky packaging boards and fluting mediums that require rapid water release and high bending stiffness.
Operators adjust disc refiner gap settings or specific edge load parameters when drainage readings deviate from grade specifications. Temperature variations in the stock chest also shift viscosity and alter filtration rates independently of mechanical treatment, which requires thermal compensation during continuous logging.
Web Formation
Drainage kinetics directly influence grammage distribution and particle retention across the moving forming fabric. Rapid water removal on the Fourdrinier table freezes fibre orientation prematurely, which reduces tensile strength in the cross direction and increases dimensional instability during subsequent converting operations. Slow drainage permits excessive flocculation unless chemical retention aids and shear fields disrupt fibre clusters immediately before the slice lip.
Finished corrugated containers depend on optimized drainage profiles to maintain adequate ring crush resistance and box compression strength under humid storage conditions.
Low Consistency Refining Energy Distribution across Fractionated Recycled Furnish
Splitting recycled furnish into long and short fractions before refining concentrates mechanical energy on long kraft fibres, cutting power use while boosting compression.