March 20, 2025
It was an honor to once again attend SuperCorrExpo® in 2024 and reconnect face-to-face with so many members and associates. It was also refreshing to have so many Ask Ralph live questions.
One member asked about replacing 33# medium with 30# medium, which resulted in an unexpected performance. They added that the lighter option “should meet” the required edge crush test (ECT) target and that they knew some but not all of the physical properties.
Since this question involved a containerboard mill integrated system, addressing the issue from a solution property perspective may take longer to analyze given the different factions in that organization.
Our first level of investigation was on the combined board strength at three different test sites. The three labs found very different results.
We then started to examine the age of the corrugating rolls and their flute profile. While this is a newer corrugator and a newer paper machine, that does not mean each element has the best technology. It’s difficult to look at a potential solution in Europe because medium manufacturers there have different recycled fiber sources for their containerboards. Changing flute profiles and flutes per foot is expensive but needs to be considered.
It could be that the single face operators did not make adjustments for differences in caliper with the lower basis weight sheet, and the web is not “flowing” or forming through the labyrinth properly. Other combined board tests would be beneficial to perform such as a dimensional stiffness evaluation for the combined board.
I am also talking to corrugating roll manufacturers for their input.
More comprehensive evaluations of medium properties should be considered. Understanding the different thermal forming (modulus of elasticity) properties of the medium with different fiber combinations and chemical additives is a tough one to determine, but we know it exists. Most papers want to return to their relative “flat” natural form after any process that attempts to shape the sheet into something that is not normal.
The difference between sheets with neutral sulphite semi-chemical pulp and those with 100% recovered fiber can result in high and low flutes. The height differences in flutes have an impact on combined board bonding as well as flat crush strength and edge crush strength.
Our thoughts then went to the possible cost advantages and maybe mill discounts offered by a lower basis weight and a reduced fluting cost adjustment. If the 30# medium is the sweet spot on the paper machine and has the highest contribution revenue, then a mill may be willing to share its increased income for this grade with the converter.
As a final thought, we have developed data, spreadsheets, and other resources that may be of value to you. We also retain third-party research from the U.S. and Europe. We are currently working with a member on glue tab strength and its impact on box performance.
Ralph Young is the principal of Alternative Paper Solutions and is AICC’s technical advisor. Contact Ralph directly about technical issues that impact our industry at askralph@AICCbox.org.
