Paperboard Repulpability Assessment under Standard Laboratory Disintegration Conditions
Standard laboratory disintegration assesses paperboard repulpability by measuring defibering rates, fiber yield, and screen reject fractions under fixed shear.
Coarse Reject Fraction
Particle Separation
Screening equipment determines the coarse reject fraction by isolating non-fibrous contaminants or oversized material from a processed pulp slurry. This coarse reject fraction measures the proportion of input material that fails to pass through the perforated or slotted screens during the cleaning cycle. Mechanical separation relies on the difference between the physical dimensions of usable cellulose fibres and unwanted debris such as plastics, shives, or sand particles.
Manufacturers quantify this value to evaluate the efficiency of the stock preparation line and the removal rate of secondary contaminants that threaten substrate consistency.
Equipment Throughput
Heavy screens generate a higher output of tailings when the feed density rises above established operational limits. High levels of debris in the recycled furnish force a greater portion of the flow into the reject stream to maintain the purity of the accepted stock. Engineers calculate the specific volume of these rejects to determine whether secondary screening stages should recover usable fibres or if the material requires immediate disposal.
Increasing the aperture size on the screen plates leads to lower volumes in this fraction but allows more oversized contaminants into the final paper stock.
Process Efficiency
Excessive loss of long fibres into the reject stream signals an imbalance in the hydraulic pressure across the cleaning system. Correcting this involves adjusting the feed consistency or the rotor speed to prevent the trapping of good material behind the screen barrier. Stable operation minimizes the waste of valuable raw materials while ensuring that only minimal amounts of oversized particles reach the headbox.
Accurate monitoring of this outflow governs the overall yield of the mill and determines the ultimate quality of the produced paper sheet.