Composition Shift
Uncontrolled variations in the proportion of different pulp types fed into a paper machine’s headbox alter the structural and physical properties of the finished paperboard. Furnish ratio drift occurs when the automated dosing of softwood, hardwood, or recycled fibers deviates from the established recipe during a production run. This imbalance can lead to unexpected changes in sheet bulk, stiffness, and surface smoothness, which can disrupt downstream printing and converting operations.
The shift is most problematic in multi-ply board machines where each layer requires a distinct fiber mix to achieve specific functional properties.
Control Loop
The distribution of pulp slurry to the wire is managed by flow control valves linked to the mill’s distributed control system. In furnish ratio drift, a sensor malfunction or a consistency variation in the pulp chests causes the system to feed incorrect ratios of long-fiber and short-fiber pulps. This error affects the drainage rate on the forming table, which can lead to moisture variation and sheet cockling.
Automated pulp analyzers continuously check the fiber length distribution to catch these deviations before they affect the final reel.
Converting Risk
Paperboard produced during a drift event often fails to meet the specified bending stiffness or creasing performance. This failure can cause the board to crack during folding on high-speed packaging lines or to jam in the feeder of a printing press. Ensuring furnish stability is essential for maintaining consistent performance across all batches.
