Cushion Mechanics
Polymer elastomers absorb rotational force during plate contact. Offset blanket compressibility dictates how deeply rubber and fabric layers yield under static impression pressure. Lithographic presses require this resilience to transfer halftone dots across varied paper calipers without dot gain distortion.
Deflection occurs within a constrained nip where cylinder geometry forces momentary volumetric displacement. Rubber compounds react to this mechanical load by squeezing laterally into empty voids inside the carcass structure rather than pushing outward against the plate. Press operators adjust packing sheets beneath the blanket cylinder to compensate for hardness tolerances specified by manufacturers.
High resilience limits permanent deformation during long runs where millions of impressions hammer the rubber face.
Hardness Rating
Durometer readings measure the surface resistance of rubber layers against a standard indenter pin. Shore A values categorize resilient blankets from soft packings used for rough packaging boards to hard formulations designed for coated art papers. Soft blankets accommodate rough surface profiles on uncalibrated linerboard by sinking into microscopic valleys during impression.
Hard compounds maintain exact dot dimensions during high speed folding carton production where web tension remains tightly controlled. Excessive softness induces dot slur because lateral rubber creep smears ink edges across the substrate. Mill laboratories test dynamic recovery rates by dropping calibrated steel weights onto elastomer samples to record energy absorption percentages.
Impression Calibration
Mechanical nip width expands as rubber resilience increases under constant cylinder loading. Press calibration procedures balance blanket thickness against packing underlayment to maintain correct surface speed ratios between plate and blanket cylinders. Mismatched diameters create surface friction that strips ink from halftone dots or wears down metal plates prematurely.
Converters calculate total packing thickness by subtracting measured blanket caliper from the nominal gap distance between cylinder bodies. Proper adjustment prevents excessive heat buildup inside the carcass during continuous high speed printing operations. Substrate thickness variations demand precise control over nip pressure to preserve image fidelity across corrugated mediums.
