Total indicated runout and its impact on combined board quality, Technical Information Paper TIP 0304-56 (2009)
In the process of making corrugated board, there are several steps in the process that require precise applications of pressure between rolls, or consistent gaps between rolls in order to meter precise amounts of adhesive to the flutes. In order for these requirements to be met, rolls have to be parallel to each other and also must be as close to perfectly round as possible. Bearings or journals must also be operating in such a manner as to allow the rolls to turn as close to perfect circular motion as possible.
If a pressure roll is not rotating in a perfectly round manner, then as the roll turns against the corrugating roll there will be areas where the pressure applied to the singlefacer web at the rolls' nip point will be lessened. If the pressure is lessened enough, the singlefacer bond can be compromised and, thus, affect board quality. An adjustment to increase pressure to compensate for the problem could lead to another problem−pressure roll cutting of the medium and possibly box failure in compression and/or mullen (burst).
Similarly, if the adhesive applicator roll and/or metering roll are not perfectly round, then as the rolls turn against each other the gap between them will open and close in proportion to how much the rolls are out of round. Thus, for any one revolution, starch application can run heavy to light, leading to moisture and probable warp problems, as well as areas of possibly substandard bonding. To some degree the same effect can be seen between a rider roll and applicator roll at the doublebacker (DB) glue station. The heavy/light adhesive patterns and the potential fluttering of the singleface (SF) web through the nip point can lead to high-lows (or something that looks like them) on the doubleface side of the board. "High-lows" are often "corrected" then by narrowing the gap between the rider roll and applicator roll, crushing the flutes into the glue roll. This leads to lost caliper and possible losses in flat crush, edge crush or stacking strength.