Cracking Score on White Liner – update

Kaleb asks,

We are facing cracking issue in our white test liner when it is used in a particular material combination. Pictures are attached for your reference.

Kindly provide your expert opinion.

 

 Cracked Score 3 Cracked Score 2 Cracked Score 1

Allow me to make a few observations and ask a few questions that may help us find an answer to your question. Since this is double wall corrugated I assume this was converted on a rotary diecutter and not on a flat bed diecutter.

When was the last time you changed out the slotting knives and scoring heads?

Do you change scoring heads and profiles between single wall and double wall?

What was the relative humidity and board moisture at the time of converting?

It appears that the white top did not have enough tensile strength and elongation potential to survive the folding. What does the mill have as far as retained physical property tests and samples for the top sheet that you combined and converted?

Can you supply the scoring head profile so that I can review the design with some of my domestic associates?

–Ralph


Here’s an update on Kaleb’s cracking issue. After some back and forth discussion we’re still looking at Kaleb’s problem.

He has provided the following additional information on his issue.

The box is being die-cut on a rotary diecutter.

  • They change the slotting knives and scoring heads on a weekly basis, but they do not change between singlewall and doublewall orders.
  • Relative humidity of conversion area was about 45-55% and moisture of board was 7-8%.
  • Average Tensile strength and elongation values of top liner are as following:
    • Tensile Strength MD: 7.6KN/m
    • Tensile Strength CD: 5.0KN/m
    • %age Elongation MD: 2.5%
    • %age Elongation CD: 5.5%

Rick Putch of National Steel Rule provided this info…

Pre-crushing before slotting can help reduce score cracking. Also, closing the slotter head nip a little tighter than normal may create additional crush. This can reduce stretch of the outer liner when folding at 180 degrees. I would suggest asking him to run at significantly different speeds to see if that has any influences on the cracking. Also ask Kaleb to put a dial indicator on score heads to see if they are concentric. If they are running out they may not be consistently crushing the score. Have him try these things and report his findings back to us.

How does his tensile and elongation numbers compare to US kraft liner?

These elongation values should be good for any liner.

Tensile values depend on basis weights which he not provided. For example 7.6 KN/m MD tensile stiffness would be typical for DS Smith’s 150g Eurotest, their 130g Testliner 3, less than 100g SCA kraftliner, and their 100g Eurokraft.

Please feel free to share your knowledge and experience. We look forward to hearing from our readers!

—Ralph

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