One of the most important factors in box design is also one of the least understood: Load sharing.
Load sharing is the extent to which a box’s contents contribute to crush resistance, or its ability to stand up to weight placed on top of it. Because box stacking is common practice, designers need to understand a box’s contents (which determine load share) and the box’s end use (which determines the need for load share) before they can start designing it.
“Box design is more complex and critical than many people realize,” explains Jeff Bittner, Business Development Manager at Acme Corrugated Box. “It’s why our design team does a deep dive with customers before they design any made-to-order corrugated product. From transit to storage conditions to warehouse practices to end use, there are many factors to consider, and many of these factors brush up against the topic of load share.”
A TOP TO BOTTOM LOOK AT LOAD SHARING
High load share is achieved when a box’s contents are sturdy enough and packed tightly enough to enhance a box’s stacking strength beyond the box’s standard crush resistance rating. A box packed tightly with books, for example, has near-infinite load share.
“Assuming every cubic inch of that box is filled with books, it would take vast amounts of pressure to crush it, because books are practically crush-resistant,” Bittner says. “Theoretically, you could stack these boxes to the sky without crushing the books or the bottom-most boxes. We call this absolute load share. The product is doing all of the work; the box is really just a protective wrapper, freed from the burden of stacking strength.”
Load share decreases when there’s empty space between the top of contents and the top of the box (known as head space) or if there’s empty space between or around contents (known as air channels).
“A box packed three-quarters high with books offers limited load share because while the books’ sturdiness could help with the structural integrity of the box, the head space could invite crushing if the boxes are stacked too high or if too much weight is placed on top,” according to Bittner. “Limited load share also occurs in boxes packed unevenly, packed with fragile or breakable contents, or packed with substantial air channels between contents.” Contents prone to bulging or settling during transit (for example, boxes containing bags of ground spices or juice concentrates) also find themselves in this common middle ground.
At the bottom end of the load share spectrum are boxes containing breakable contents or contents that compress under pressure, like towels, sponges, or tortilla chips. In these scenarios, the box itself needs to provide all of the crush resistance to protect both the box and its contents from the effects of weight.
Which brings us to load share’s bearing on design.
LOAD SHARE AND BOX DESIGN
Once you understand load share, it’s clear why Acme Corrugated Box needs to know a future box’s entire story in order to design for optimal performance. After load share and other essential elements have been discussed from all angles, the design team can recommend box characteristics including a board grade. The sturdiest board grades are used in scenarios where a box’s contents will offer low or no load share.
“When contents aren’t contributing to load share as needed, Acme Corrugated Box often turns to its proprietary grades, such as BD, ED, Powerwall 100 and Powerwall 60,” Bittner says. “These offer greater crush resistance than what most other box manufacturers can provide. Our designers can also work with customers to minimize complicating factors like head space and air channels.” Interior packaging elements such as pads and dividers can also be used to increase a box’s crush resistance.
“Boxes might seem like a commodity, but they’re not, and load share often helps our customers understand why. Customization is key to optimal box performance as well as optimal business outcomes.”
Want to learn more about Acme Corrugated Box customized box solutions? Contact us for more information.