Inside Cracking on Singleface

Fern asks:

I am curious if there is anything written regarding inside cracking on the singleface liner and how it doesn’t take away from the structural aspects of the box, or if there is an industry guideline that I can refer to.

Of course we do our best to eliminate it all together, but now we are working with more & more recycled liners (some heavily recycled) and shorter fibers, we continue to battle this.

You are not alone in this struggle.  And it’s becoming that time of year when this becomes common for many cold weather converters.

One thing we need to remember is that recycled paper gives up moisture much faster than papers made with virgin fibers. When relative humidity drops below 50% the normal board moisture content can plummet leading to a more brittle liner. And, the short fibers of recycled paper create a structure that is more brittle to begin with than long fibre virgin.

Many converters use and/or have experimented with different score profiles and for virgin and recycled paper. The more aggressive, or sharper the profile the more likely to crack the liner. While 4pt crease may be typical, 6 or 8 point can be used to distribute the pressure across the surface.

AICC published a White Paper on Score Cracking a few years back. Click here to download the White Paper. The White paper is free to AICC Members.

We have visited this topic many times in Ask Ralph. Type “Cracking Scores” or “Cracking liners” in the “Search Ask Ralph” field on this blog.

— Ralph

One Response to “Inside Cracking on Singleface”

  1. Brett Kendall (@pourlefun) Says:

    You’re talking about inside cracking of the panel scores, right? Not the flap / corrugator scores?

    Check your liner temperature right where the SF web begins it trip up the incline to the bridge. You’re looking for 195 to 215 degrees F on PR single-facers, a bit more is OK for belted single-facers. Are the SF glue lines also heavier than they should be? Is your flat crush low? These are signs that the corrugator crew is trying to buffer the excess heat using water in the adhesive.

    If the board arrives at the converting department with less than 6% moisture, it’ll likely crack.

    If we talking about cracking of RSC vertical scores on a FFG: Are all 4 scores cracking or just the 180 degree folds? If so, make sure the folding rails are properly positioned with clearance between the “elbow” of the 180 degree fold and the edge of the rail – don’t run the rail directly in the crux of the score where it acts like a dull knife.

    For die-cut items, don’t use steel rule scores in the feed / corrugation direction on RDCs. If you have no choice, bolt your SRD shell to the cylinder with the proper pattern and use every single bolt hole to make sure it’s flat.

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