HOW TO PREVENT SCORE CRACKING IN A BOX PLANT

In recent years the corrugated industry has moved toward higher usage levels of recycled liner and high-performance (high ring crush) liners to meet customer requirements and to help the environment. These changes will require plants to alter their normal operating practices on the corrugator as well as in the press department to avoid score cracking problems.

All liner can crack or check under hot or dry atmospheric conditions. These problems occur most frequently at the score lines. Cracking is especially evident during the drier winter months, or in heated storage environments. Today, many corrugated operations are modifying their machines to run hotter and faster, thus further increasing incidents of cracking.

Recycled and high-performance liners appear to suffer from higher levels of moisture loss during the converting process than does typical liner produced with similar moisture content. The shorter fibers in recycled liner are less forgiving when moisture is driven out, and the high-performance liners appear to release moisture more readily due to sheet densification (less air is trapped between the paper fibers). The levels of preheater wrap typically used during the past will not work on recycled or high-performance liners; up to twice the heat transfer level in liners has been measured when comparing 36-lb high-performance liner vs. a typical 42-lb liner (also see TIP 0304-43 High density liners…What are they’ and TIP 0304-40 “Techniques for bonding densified liners”). The liners measured were combined under the same conditions and had a moisture content of 7%.