Non-Contact Caliper Measurement Systems on High Speed Packaging Board Lines
Non-contact optical gauges eliminate mechanical board compression on high-speed lines, enabling tighter cross-machine caliper targets and reduced fiber mass.
Terahertz Spectroscopy
Spectral Resolution
Optical testing using terahertz spectroscopy evaluates internal packaging structure by measuring the absorption of electromagnetic waves within a specific frequency band between infrared and microwave radiation. This analytical method detects hidden delamination within laminated paperboards and measures precise moisture distribution across containerboard webs without physical contact. High frequency emitters generate pulsed radiation directed through the moving substrate, and receivers capture the transmitted or reflected waveform after interaction with the material.
Delay lines alter the optical path length to map the temporal electric field profile with femtosecond precision. Data processing algorithms convert recorded time domain waveforms into frequency spectra through Fourier transformations. Water vapor absorption lines provide absolute frequency references for wavelength calibration during continuous production runs.
Sensor heads mount directly above web transport lines to inspect corrugated medium without interrupting high speed manufacturing speeds. Calibrated reference standards establish baseline transmission coefficients for specific grammages before production monitoring begins.
Adhesive Penetration
Packaging converters apply terahertz spectroscopy to quantify hidden adhesive laydown inside multiwall paper bags and corrugated fluting bonds. Adhesive layers absorb terahertz radiation differently than virgin cellulose fibers, allowing non destructive quantification of glue line thickness beneath opaque outer liners. Extrusion coaters use the resulting absorption profiles to verify uniform polymer coverage on liquid packaging board before converting operations proceed.
Signal processors extract amplitude attenuation values corresponding directly to coating mass per unit area. Excessive adhesive application creates broader absorption peaks that signal potential waste on high volume production lines. Insufficient glue deposition produces weak attenuation signatures that fail structural strength thresholds during drop testing.
Production technicians adjust applicator nozzles immediately when the measured absorption falls outside established tolerance bands.
Moisture Gradient
Containerboard manufacture requires strict control over internal water content to prevent dimensional distortion during subsequent printing and die cutting processes. Terahertz spectroscopy measures bound and free water within thick paper substrates by exploiting distinct absorption coefficients associated with hydrogen bonding states. Water molecules absorb electromagnetic energy strongly in this frequency band, yielding high sensitivity to small moisture fluctuations within dense paper matrices.
Drying cylinders evaporate excess moisture until absorption signals match target specifications for specific basis weights. Finished reels maintain flatness and rigidity when internal moisture gradients remain below specified limits across the entire width. Environmental humidity changes alter baseline readings, requiring continuous temperature and humidity compensation algorithms within the spectrometer control unit.