Statistical Process Control Fundamentals in Packaging Substrate Converting
Statistical process control in substrate converting relies on sub-grouping across machine direction variance and isolating non-normal barrier defects.
Inline Beta Gauge
Radiation Attenuation
Radiometric scanning systems monitor paper and paperboard mass per unit area on continuous web machinery by measuring the attenuation of nuclear particles passing through the moving substrate. During web production, an inline beta gauge measures mass variations across the sheet to provide real-time feedforward control signals to the headbox dilution system.
Cross-Direction Profiling
Sealed krypton or strontium radioactive sources emit beta particles that collide with electrons inside the cellulose fibres and synthetic fillers of the moving sheet. The ratio of transmitted radiation to emitted radiation follows an exponential decay relationship proportional to total mass per unit area. Traversing heads carry the radioactive source and ionization detector back and forth across webs wider than eight metres to construct full cross-direction mass profiles.
Instantaneous feedback allows automated actuators to adjust slice lip openings or localized stock dilution valves within seconds. Fast control loops minimize basis weight variance, preventing out-of-spec paperboard from reaching downstream rewinding and converting operations.
Calibration Stability
Temperature fluctuations and air density shifts between the sensor gap alter radiation absorption and create measurement drift. Automatic standardization protocols periodically move the measuring head off-web to record clean air reference readings. Regular recalibration ensures measurement precision across continuous paper mill production campaigns.