Structural Distortion
The dimensional distortion in corrugated board caused by unequal expansion or contraction of the inner and outer liners defines a common manufacturing defect in packaging mills. This flute warp typically arises during the corrugating process when the temperature or moisture levels of the paper webs are unbalanced. It results in a curved or twisted board that does not lie flat.
Moisture Balance
Achieving a balanced sheet requires careful control of the pre-heaters and moisture sprays as the linerboards are bonded to the corrugated medium. When the liner on one side contains more moisture than the other, it will shrink more as the finished board dries. This differential shrinkage pulls the board into a concave or convex shape.
Standard corrective actions include adjusting the steam flow to the pre-heater drums or modifying the application of starch adhesive to the flute tips.
Converting Difficulty
Downstream processing of warped sheets is difficult because the curved board cannot easily be fed into flexo folder-gluers or die-cutters. Automatic suction cups and feeder gates frequently jam when presented with curved boards, resulting in reduced running speeds and high reject rates. Beyond runnability issues, warped board can lead to weak glue joints and poorly aligned manufacturer joints during box assembly.
Maintaining strict control over the moisture profile of incoming paper rolls prevents these production delays and ensures the structural integrity of the shipping containers.
