Rotary Die Scoring Stress Wave Signal Acquisition
Real-time acoustic stress wave monitoring on rotary die scoring lines detects paperboard matrix micro-cracking instantaneously, reducing convert scrap by up to 80 percent.
Roll Nip Pressure
Contact Load
Hydraulic force applied across the rotating steel and resilient polymer elements of a calender stack determines the degree of calendering a paper web receives before final winding. Roll nip pressure governs caliper reduction, smoothness development and gloss generation across newsprint, coated art papers and packaging boards. Excessive force crushes internal fibre bonds, reducing tear resistance and causing internal delamination known as blackening, while insufficient force leaves surface porosity too high for high-speed offset printing.
Operators calculate this linear load by dividing total hydraulic cylinder thrust by face width, yielding units of kiloNewtons per metre. Caliper control systems adjust the hydraulic loading continuously to compensate for thermal crowning and deflection during high-speed production runs.
Surface Deformation
Plastic deformation of cellulose fibres occurs when concentrated linear loading exceeds the elastic limit of the specific sheet structure. Elastic recovery follows the compression zone as the web exits the contact area, setting the final caliper and surface smoothness profile of the substrate. Harder polymer covers concentrate the applied force into a narrower contact width, creating higher peak pressures that accelerate gloss development on coated grades without requiring excessive total load.
Softer covers distribute the force over a broader area, preserving bulk while smoothing out minor basis weight variations in uncoated packaging papers. Temperature differentials between the top and bottom rolls alter the resilience of the polymer cover, requiring real-time hydraulic adjustments to maintain uniform bulk reduction across the entire machine direction.
Deformation Limit
Structural collapse of the paper web occurs when cumulative mechanical and thermal forces exceed the internal bond strength of the sheet. Microscopic buckling of fibre walls occurs when linear loading pushes past the critical threshold for a given grammage and moisture content, causing irreversible loss of stiffness and tensile strength. Converting plants measure this degradation through ring crush tests and bending resistance measurements on finished corrugated board liners.
Exceeding the maximum threshold also causes rapid thermal degradation of polymer roll covers through excessive hysteresis heating, leading to permanent cover failure and unscheduled machine downtime. Operating windows remain narrow because moisture variations in incoming webs alter compressibility, demanding precise control loops to prevent web breaks and runability failures in subsequent converting machinery.