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Box Compression

By Ralph Young

May 17, 2024

Over the past 15 years, we have published several AskRalph blog posts and BoxScore articles on this often forgotten significant variable to box compression/box performance, which is four-point bending stiffness. To review those pieces, you can go to the search bar on AICC NOW, NOW.AICCbox.org, and enter this subject or contact me directly.

The definition in the Technical Association of the Pulp and Paper Industry T 836 states that “bending stiffness measurements of the combined board when used with the edge crush test and box dimensions can accurately predict the top-to-bottom compression strength of a box.” McKee’s short formula makes an estimation of this property by using the caliper of the combined board. As we will see in the example below, the equal compression strength is improved by moving from a 69/23C/69 combination to 35/23E/35/23N/35.

We have known of the edge crush test (ECT) inclusion for almost 35 years now, but we often ignore or never understood the other major characteristic of corrugated in building box performance. This seldom considered property, while not as significant as ECT, still has a contribution to top-to-bottom compression—also, but not discussed here, the measurement of torsional stiffness as determined by dynamic stiffness tester (DST) instrumentation. This is not an issue of virgin/semichemical fiber versus recycled fiber as one would obtain the same results.

My associate, Tom Weber, and I led a webinar in June 2022 titled “Testing Requirements to Guarantee Board Strength” that covered many physical properties of corrugated, folding carton, and rigid box. One of these properties was four-point bending stiffness for corrugated and taper stiffness for paperboards. It needs to be emphasized that the bulging resistance of the corrugated vertical side panels has an impact on box compression.

A third consideration of the impact of transport on the corrugated box is flexing or twisting. The way to measure this and the contribution of proper combining and converting is the use of a DST. More than 70 are in use in North America but very few among the independent portion of the corrugated industry. What do the big companies know?

The program above was a follow-up to a major 2018 national meeting presentation titled “Fluted vs. Paperboard,” with a panel discussion with converting experts. After this face-to-face presentation, we published an extensive white paper that includes a chart of some bending stiffness values for a few combined board combinations.

This particular member combiner and converter does not have access to lower substance linerboards like 29# or 21#, so we were not able to run other permutations. Additional resources are available at AICC, including expected values of containerboards such as SCT and CFC, to assist you in coming up with multiple options in reengineering the corrugated structure and box.

Although the environmental sustainability savings is less than 10% fiber reduction, the financial sustainability savings is 25%. What would your customer benefit from most? Consider the marketing advantage! Not many have all these flutes and options, but some do, and you can do something with small-flute double-wall and low-substance linerboard and medium.


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.

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