Standard Fiber Recovery Testing for Single Polyethylene Coated Cartonboard
Standard testing requires disintegrating 4% stock at 40°C, separating films via 0.15mm slotted screens, and confirming >80% yield with macro-stickies below thresholds.
Reject Mass
Screening Output
The dry mass of unusable material separated from the stock flow during pulp cleaning and screening operations determines the efficiency of the stock preparation system. In papermaking, the reject mass consists of heavy contaminants, shives, bark, and plastic fragments that cannot be converted into paper. It measures the amount of waste generated in the preparation of pulp before the sheet is formed.
Mill operators monitor this value to evaluate the efficiency of the pulp cleaning equipment and to minimize fiber loss.
Process Efficiency
Maximizing fiber recovery requires fine-tuning the pressure drops and slot sizes in the screening baskets. If the reject mass is too high, it indicates that too many good fibers are being discharged along with the contaminants, which increases production costs. Conversely, a low value can mean that the screen is letting through impurities that will cause paper breaks on the paper machine or print defects on the customer’s press.
By adjusting the dilution water flow and the rejection rate of the screens, the operator can keep this material flow within the specified tolerance.
Waste Management
Disposing of the recovered impurities is an important cost factor in the daily operation of a paper mill. The reject mass must be dewatered to reduce transport costs and landfill fees. Many modern mills burn this waste material in biomass boilers to generate process steam and reduce their dependence on fossil fuels.