Dynamic Tension Stress Analysis in Laminated Boxboard Folder Gluers
Matching folder gluer carrier belt speeds within one percent prevents surface shear from delaminating film coatings on scoring hinges.
Dynamic Tension
Mechanical Strain Rate
Tensile load per unit width exerted continuously on a moving web of paper or paperboard during winding, printing, coating, or laminating operations characterizes running web stability. Fluctuations in dynamic tension arise from roll eccentricities, variations in reel caliper, machine speed shifts, and drive inertia. When dynamic tension exceeds the elastic limit of the paper substrate, local web breaks occur.
Conversely, an excessive drop in tension causes web flutter, misregistration, and slitter jams. The parameter governs tension zones within continuous roll-fed processing equipment up to the final rewinding nip.
Web Instability Variable
Transient acceleration changes the load profile instantaneously across unsupported spans. Closed-loop load cell rollers or dancing roll systems measure this running force, converting mechanical displacement into electrical signals that adjust drive motor torque. Caliper profile variations across the reel profile produce differential strain along the web width.
That cross-direction variation forces one edge to bear a disproportionate share of the dynamic load while the opposite edge goes slack. Moisture absorption during wet offset printing or aqueous coating operations lowers the elastic modulus of cellulose fibres, decreasing tensile strength under dynamic conditions. If unwinding reels possess structural defects such as moisture welts or bagged edges, localized strain concentrations multiply, producing web bursts.
Tension control systems must adjust damping factors to match substrate basis weight, converting speed, and roll diameter changes.
Converting Threshold
Process specifications establish tight upper and lower boundary thresholds for continuous paperboard webs. Boxboard grades spanning two hundred to four hundred grams per square metre require distinct mechanical tension bands compared to lightweight publication stocks. Excessive strain during slitting causes microscopic edge cracks that develop into tears downstream.
An insufficient load causes loose rewinds, leading to telescoping or dished rolls in warehouse storage. Operating within verified boundaries ensures dimensional accuracy through rotary die cutters and high-speed multi-colour gravure stations.