What Is Stacking Strength and Why Is It Important?

If you work in an industry that uses a lot of cardboard for packaging, then you rely heavily on the stacking strength of corrugated boxes to protect your products — even if you don’t realize it. Whether you store your products in a warehouse or transport them by vehicle, the strength of your boxes ensures the continued safety of their contents. For more information on the stacking strength of corrugated cardboard boxes, here’s a review of what the strength means and what can influence it.

What Is Stacking Strength?

Stacking strength is a measure of how much weight can be placed on top of a container during its lifetime without starting to crush. Given how many containers are intended for vertical stacking in warehouses, it is important to know the maximum amount of weight the box on the bottom can endure. By doing so, one can ensure the safety of the products inside for as long as they are stored — and, by extension, prevent the stack of boxes from toppling over.

In addition, the stacking strength of corrugated boxes also takes the environment into account. For example, increased moisture content can result in a loss of stacking strength and become a problem. Therefore, any containers that will be used in humid climates with high moisture levels must have an excess amount of stacking strength to accommodate any that is lost.

How Is the Stacking Strength of Corrugated Boxes Determined?

It is important to carefully measure and calculate the stacking strength of boxes so that the items it contains does not exceed the maximum weight limit. To ensure the containers are as safe and secure as possible, they are designed to have three to seven times the strength necessary for their anticipated stacking weight — although the field conditions will not have the same level of control as there will be with test boxes.

There are several methods that are used to measure the stacking strength of boxes, including the Edge Crush and Mullen Test. With the Edge Crush Test, force is applied to the edges of the box to examine how much the material can endure without being crushed. The Mullen Burst Test, meanwhile, suspends a piece of the material and measures how much force is necessary to burst the face of the container using a machine to apply an increasing amount of force.

What Factors Can Influence Stacking Strength?

A wide array of factors exist that can influence the stacking strength of corrugated boxes. Given how many ways force can be applied or the strength can be altered, it is essential that as many facets as possible are taken into account to ensure the contents stored inside remain safe. Some of the many factors measured and considered include:

  • What kind of stacking the box uses
  • The number of layers in the unit
  • Size of the box flutes
  • The weight of the product the box will contain
  • The weight distribution of the contained product — unevenness can apply more force in certain areas
  • How many units will be stacked on top of the box
  • The temperature, humidity, and other environmental conditions the box will be used in
  • What direction is the box loaded in
  • The kind of transportation and distribution the box will experience

What Is Compression Strength?

Another important factor that determines the durability of cardboard boxes is their compression strength. Unlike stacking strength — which determines the maximum weight that can be placed on top of the box — compression strength tests a container’s capacity to withstand compressive loads before breaking down and deforming. Given how both dictate the overall strength of a material, it is essential that both stacking strength and compression strength are taken into account when using corrugated cardboard to store and transport goods.

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