Dynamic Crease Stiffness Reduction Ratios under Ultra High Speed Packaging Line Strain Rates
Dynamic crease stiffness reduction ratios must be evaluated under operational strain rates of 1000°/s to 5000°/s to prevent high-speed cartoning line jams.
Matrix Shoulder Radius
Transition Geometry
Counter-die channels feature curved upper corners where the flat face of the matrix transitions into the vertical wall of the creasing groove. The radius of curvature along these top entry edges is known as matrix shoulder radius, measuring the sharpness of the transition zone in thousandths of an inch or millimeters. This geometric parameter governs the local shearing force applied to outer board fibers during score formation, and it stops applying outside the channel entrance area.
Stress Distribution
Softened channel entry shoulders allow paperboard to slide smoothly into the female matrix without scraping or cutting outer coatings. A tiny matrix shoulder radius acts like a sharp knife edge, concentrating shearing force along narrow lines and tearing the top liner or clay coating during die impression. Increasing the shoulder radius spreads the bending entry load over a wider contact area, preserving print finishes and preventing liner rupture.
However, an excessively large radius reduces the sharpness of the crease shoulders, causing carton panels to fold with wide, poorly defined fold axes. Tooling manufacturers machine precise shoulder profiles into steel plates or mold them into plastic matrix channels to balance coating protection with crease crispness.
Tooling Life
Metallic matrices preserve shoulder profiles better than plastic matrix strips. Abrasive boards wear channel edges.