Dynamic Strain Rate Modeling for Multi Ply Boxboard under Rapid Compression
Dynamic strain rate modeling predicts multi-ply boxboard Z-direction compression and interlayer shear collapse during high-speed converting and package drops.
Pore Air Compression
Pneumatic Effect
Rapid consolidation of a porous fibre matrix under high-speed compression forces the air trapped within the voids of the sheet to compress. This pore air compression creates localized pressure spikes that can disrupt the structure of the paperboard or its surface coating. It occurs during the fraction of a millisecond when the paper passes through a calendering or printing nip.
If the air cannot escape quickly enough, it seeks paths of least resistance through the web.
Structure Response
Web failures and surface blistering can occur in high-temperature or high-speed operations when this compressed air cannot vent. Coated papers are particularly vulnerable because the clay layer acts as a barrier to air flow. When the pressure is released as the sheet exits the nip, the compressed air expands rapidly, which can rupture the bond between the coating and the base paper.
This behavior can be controlled by modifying the porosity of the coating or adjusting the nip width.
Venting Constraint
Lowering the production speed or using a softer backing roll can reduce the severity of the air pressure buildup. High porosity in the base sheet allows the trapped air to dissipate through the body of the paper without causing damage. The web remains stable and intact.