The Importance of Determining the Burst Strength of Corrugated Boxes
After going through the challenging process of making a product you're proud of, the last thing that's probably on your mind is how strong your packaging must be. Nonetheless, it is a critical decision. The box you put your product in transports it from you to your end customer while keeping it secure and intact.
The strength of corrugated boxes derives from a multitude of sources. Your parcel may be manufactured in various thicknesses, including single, double and triple-wall. It can also have many flute kinds ranging from A to F. The strength of each box can be measured using either a Mullen or an Edge Crush Test. However, when individuals start using terms like 200 pound burst or 32 ECT, you may need help understanding what they are talking about.
Continue reading to learn about the importance of burst strength for corrugated boxes.
What Is Burst Strength?
Bursting strength is a widely used term in the packaging industry that describes the amount of pressure or weight a corrugated box or other types of material can handle before it breaks or ruptures. If the burst strength of corrugated boxes is high, it's less prone to damage during shipping and handling. As a result, the quality of the packaging can be determined by its burst strength.
In conjunction with a box's burst strength, there are specific requirements and standards set by the American Society for Testing and Materials (ASTM) and the International Organization for Standardization (ISO) regarding package testing. These standards include the ASTM F88, ASTM F1140, ASTM F2054, ISO 11607 and ISO 2759.
When providing high-quality items to customers, it's critical to test each aspect to ensure that no harm happens to the product. You must address the burst strength of the materials you use to safely deliver items to customers. During the shipping, distribution and storage stages, some packages may experience damage due to poor packaging.
The product may be damaged if the product's primary and secondary packaging is not sturdy enough to withstand the handling conditions. As a result, it may arrive at its destination in poor shape. Measuring bursting strength is helpful because it helps assess the package's resilience and ensure it's not damaged during transit.
To see your corrugated box burst strength, look for the small circular stamp at the bottom of your box. This is its Box Manufacturer's Certificate (BMC). On the BMC, you'll see the box's manufacturer details, the box construction, the burst strength and its size and weight limits. So, how do you determine the burst strength of a box? There are two main methods — the Mullen test and the edge crush test (ECT).
What Is the Mullen Test?
The Mullen test, or the burst test, is one of two industry standards for assessing corrugated packaging. The Mullen test measures the force in pounds per square inch (psi) necessary to burst or rupture the sides of a corrugated box. For example, if a box has a burst strength of 200, it can sustain 200 psi.
The Mullen test was one of the first tests used in the industry when packages were mainly handled by hand. For many years, the governing body of the truck and rail freight industries used this standard to determine box strength.
Later, the corrugated industry saw a significant transformation. Corrugators began to utilize a greater proportion of recycled material due to its availability, cost-effectiveness and environmental benefits. However, recycled paper does not have the same properties as fresh paper. New paper fibers are long, strong and well-structured to run in the same direction. Recycled paper fibers are shorter and less structured.
Because of the differences in the properties of recycled versus new material, corrugated material began to have lower Mullen Test scores for what should be the same box structure. While the Mullen Test values changed, several observers noted that the box's vertical tensile strength remained high. In other words, the boxes could still be piled as high and heavy as before as long as the contents of the boxes did not move and impact the side walls.
The Mullen test determines a box's capacity to endure external or internal forces and how the contents will be contained during harsh handling. It specifically tests the bursting strength of the corrugated linerboard — one of the key differences compared to the ECT.
The Mullen test can mimic difficult handling situations — when shipping individual boxes via traditional carriers where the packages are tossed from one conveyor belt to another and bump into other boxes of varying shapes, sizes and rigidity.
What Is the Edge Crush Test?
The ECT is a burst strength test that measures corrugated boxes' stacking strength. As the name suggests, it's the force required in psi to crush cardboard by standing it on its edges. It measures compression strength from top to bottom. For example, a box with a 32 psi ECT result implies that the parcel can bear a force of 32 psi before crushing. The ECT is beneficial because most boxes are stacked for shipping and storing.
The ECT grew in popularity when the standard was revised by the National Motor Freight Traffic Association (NMFTA). Instead of measuring the material's "punch strength," it determines how much weight may be placed over the corrugated edge before it crushes.
Compared to the Mullen test, the ECT measured linerboard stacking strength and was the only test applicable to boxes made of recycled materials. When evaluating your package strength for business-to-business (B2B) shipping, you should generally do edge crush testing, especially if the shipments are small to medium-sized and will be stacked on top of one another.
The Different Types of Corrugated Fluting
Flutes are the s-shaped, wavy paper sandwiched between the linerboard and the corrugated sheet. It distinguishes these sheets from paperboard, providing strength and resistance to bending and pressure. Flutes differ in size and shape of their waves. They are allocated letters based on size, ranging from an A-flute with towering and broad arches to an E-flute with short and tight turns. From thickest to thinnest, below are several typical flutes:
A-flute: Type A cardboard has good compression and cushioning properties and stacking strength. It's a great option for fragile item packing and structural strength.
C-flute: Type C cardboard has compression and crush-resistant characteristics. It's most commonly used to secure shipping boxes, glass, furniture and food.
B-flute: Type B cardboard offers good crush and puncture resistance and makes an excellent printing surface. You can find this type inside packing components like dividers and cushions.
E-flute: Type E's thin structure aids in the reduction of storage space. It provides an excellent printing surface and high crush resistance. It's ideal for pizza boxes, displays, ballot boxes and consumer goods packaging like ceramics, glass and cosmetics.
F-flute: Type F-flute provides an excellent printing surface and crush resistance. Because of its thinness, it's possible to use less fiber to make stiffer boxes. It's ideal for fast food clamshell containers and consumer product packaging such as jewelry, cosmetics and shoes.
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