The corrugated industry has moved toward higher usage levels of recycled liner and denser liners to meet customer requirements and to help the environment. These changes require plants to control their normal operating practices on the corrugator as well as in the press department to avoid score cracking problems.

All liners can crack or check under hot or dry atmospheric conditions, and even in cool moist atmospheric conditions, if the liners have been over heated on the corrugator. The cracking 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.

The retention of moisture in combined board is a very important element to successfully score corrugated board. Most plants are now checking their combined board's total moisture content, measuring it off of the dry end of the corrugator with an automatic weighing and drying oven (see Special Note). Experience has demonstrated that a target moisture from 5.8 to 7.5% total combined board moisture works well throughout the year. Corrugator operating techniques will need to be under control if liners are to be run without quality problems.

Maintenance of the press, especially in regards to Total Indicated Run out (TIR) and axial head movement in any area that applies pressure to the combined board, is critical for preventing score cracking.

This Technical Information Paper (TIP) includes recommended operating procedures to minimize incidents of score cracking.