Solid Bleached Sulfate Board Bending Stiffness Evaluation Methods
SBS bending stiffness scales with the third power of caliper and dictates carton bulking resistance, requiring verification via ISO 2493 load-cell testing.
Process Capability Cpk
Manufacturing Variance
Process capability cpk measures how well a converting line holds a caliper or grammage dimension within the upper and lower tolerance limits set by a customer purchase order. Statistical control establishes whether the machine runs centered between those specification boundaries or drifts toward a reject condition. Substrate variation on lightweight newsprint or heavy folding boxboard introduces natural scatter that equations quantify through standard deviation calculations.
Converting plants apply this metric to determine if a specific rewinder or die cutter is capable of meeting contractual demands before production runs begin.
Distribution Spread
Process capability cpk divides the distance from the process average to the nearer specification limit by three times the standard deviation of the sampled output. High ratios indicate that the production spread sits comfortably inside the customer thresholds without generating excessive edge trimming or sheet waste. Low ratios reveal that random machine vibration or raw material inconsistency will push finished reels outside acceptable caliper windows.
Operators monitor these dispersion metrics continuously to catch tooling wear before out of specification board reaches the sheeting stage.
Tolerance Boundary
Process capability cpk drops below acceptable thresholds when incoming paper reels exhibit uneven moisture profiles across the web width. Converting equipment running at high speeds cannot compensate for localized basis weight spikes without adjusting nip pressure or thermal drying profiles. Plant engineers rely on this index to prove that converting machinery meets quality agreements signed with packaging buyers.
Statistical thresholds define the exact point where a production line must stop for calibration adjustments.