Mechanical Threshold
Rheological measurements define the minimum force that must be applied to a fluid or paste to make it flow. Identifying the yield stress of coatings or pulp slurries is critical for designing piping systems and determining pump specifications in converting plants. This property determines whether a coating will remain stable on the application roll or flow smoothly onto the paper web.
Coating Stability
Application of coatings onto high-speed paper webs requires the liquid to shear-thin under the blade and then recover its structure quickly. If the yield stress of the coating formulation is too high, it will not level out after being applied, which leads to defects like streaks or orange peel patterns. Conversely, too low of a threshold can cause the coating to run off the edges before drying, which makes the product unusable.
Managing this transition requires the addition of rheology modifiers that alter the liquid structure under different shear rates. This formulation work is critical for achieving a smooth surface suitable for printing.
Pumping Efficiency
Fibers suspended in water form networks that exhibit this property, especially at the high consistency levels used in modern pulp mills. Designing pumps for these high-density slurries requires calculating the energy needed to break this network and initiate flow. This mechanical knowledge ensures that the plant does not experience clogged lines or motor failures during periods of high throughput.
