Silent Paper Grade Furnish Substitution Mechanics at Machine Gate
Furnish substitutions at the machine gate require wet end NIR tracking and ISO 1924 tensile verification to prevent runnability failures and yield losses
ISO 8791-2
Roughness Determination
Air-leak roughness testing calculates surface smoothness by measuring airflow rates between a flat land and a paper specimen. Quality control units perform ISO 8791-2 using Bendtsen instruments to characterize surface profile characteristics across paper and board grades. The standard governs air-leak roughness evaluations for uncoated and coated paper surfaces.
The procedure stops applying to highly porous tissue papers or soft wadding where air leaks through the substrate bulk rather than across the surface interface.
Pneumatic Measurement
Measuring heads apply a standardized contact pressure against the paper surface held on a flat glass reference plate. Compressed air flows at a fixed pressure into the central chamber of the measuring head, escaping across the land contact area through surface micro-valleys. Flow meters measure the air volume leaking across the surface interface in millilitres per minute.
Smooth paper surfaces yield low air leakage rates, whereas rough substrates produce high volumetric flow readings. Adhering to ISO 8791-2 ensures consistent smoothness measurements across different testing facilities and production shifts.
Printability Factor
Substrate surface smoothness determines ink transfer fidelity and print sharpness in gravure and offset printing processes. Rough surfaces cause dot gain variation and poor ink coverage during high-speed print runs. Coating formulations and supercalendering operations improve surface smoothness to meet strict printing standards.