How to Calculate Bursting Strength of 5-Ply Corrugated Boxes

The bursting strength of a corrugated box is an important characteristic for any corrugated box. Bursting strength evaluates the box's resistance against internal and external pressure before it ruptures. For packaging companies and manufacturers, this is particularly important for multi-ply boxes, including 5-ply corrugated cartons, to ensure the continued safety and performance of the goods inside during storage and transit.

For manufacturers and packaging companies, quantifying the bursting strength is a way to measure the box's performance resistance to damage caused by stacking, handling, or impact. If businesses are able to quantify the bursting strength, it allows for the quality of packaging attributes to remain consistent, industry standards to be met, and product failures caused by packaging failures to be minimized.

What is Bursting Strength and How it Measured

Bursting pressure of a substance (e.g. paper, cardboard) is the highest pressure that the material can handle before bursting, which means its resistance to stress and its strength. Bursting strength is determined by use of bursting strength tester. A sample in this test is clamped with increasing hydraulic or pneumatic pressure exerted on the sample by a rubber diaphragm. The pressure at the time the sample ruptures is then said to be the bursting strength of the sample.

How It Is Measured: Bursting strength is determined with the use of a bursting strength tester which puts more and more pressure on a material till it breaks. The sample gets clamped around a rubber diaphragm that is flexible and hydraulic or pneumatic pressure is exerted at the lower end. The diaphragm compresses the sample against the pressure. At the point when the material eventually breaks, the highest amount of pressure at that point is called the bursting strength.

• The sample is cut to standard size and clamped over a rubber diaphragm.
• Hydraulic or pneumatic pressure is applied from beneath the diaphragm.
• The diaphragm inflates, applying uniform pressure to the sample.
• The material is stressed until it bursts under pressure.
• The highest pressure recorded at the point of rupture is noted as the bursting strength.

How to Calculate Bursting Strength of 5-Ply Corrugated Boxes

A 5-Ply corrugated box is a strong, two-wall box, which consists of five separate sheets of paper: two outer-liner sheets and three inner sheets, which consist of two fluted (wavy) sheets that are bonded to two plain liners. The unique five-layer construction of a 5-Ply box is an ideal choice for packaging heavy or fragile products since the extra layer adds further strength, stacking capacity and absorbency from shock when compared to the single-wall box (3-Ply).

Bursting Strength Formula:

The bursting strength of a material helps calculate the Bursting Factor (BF), which shows how strong the material is relative to its weight. The formula goes like this:

BF = (Bursting Strength in kg/cm² × 1000) ÷ GSM (grams per square meter).

To find this, you first measure the bursting strength using a testing machine. Then, you divide that number by the material’s GSM and multiply by 1,000. This gives you a simple way to compare the strength of different materials while taking their weight into account.

Bursting Strength Measurement of 5-Ply Corrugated Boxes

• Sample preparation—Cut a sample from the 5-ply corrugated board that does not have any creases, folds, or other damage. 
• Conditioning—Subject the sample to a normal test condition (27°C ± 2°C and 65% ± 2% RH) for a duration of 24 hours or longer.
• Mounting of the Sample—Have the sample clamped in the Bursting Strength Tester, allowing no air to pass through the sample.
• Raising Pressure—Gradually raise hydraulic or pneumatic pressure with the use of the rubber diaphragm of the machine until the sample breaks.
• Documenting Findings - Make a note of the maximum pressure at which the sample failed; this is documented in kg/cm² and is called the bursting strength of the 5-ply corrugated box.     

Importance of Calculating Bursting Strength of 5-Ply Corrugated Boxes

Evaluating the bursting strength for 5-ply boxes is valuable because it offers confirmation for the safety, quality, and integrity of the products being handled or shipped. The following are the reasons explained:

• Specific Product Introduction- To determine the bursting strength allows for unique specifications of the product. So the box can be designed for specific applications or product shapes.

• Protects products from damage - a box with low bursting strength can lead to products being damaged, resulting in increased rejections and ultimately lost dollars.  

• Protects brand image - Proving that products are received in good condition is important in maintaining customer satisfaction and building a good brand image.

• Confirms the quality of materials - the testing of bursting strength is most likely the primary quality check test to confirm material performance and its functionality. 

• Helps in selecting the right packaging - it provides evidence on how the box performs under pressure, enabling manufacturers to choose the right strength for their specific use.

Presto Instrument Bursting Strength Tester for Accurate Measurement

The Presto Instrument Bursting Strength Tester is an exceptionally accurate quality control instrument for determining the bursting strength of a specific material in industries such as packaging and textiles. The unit uses a consistent pressure of hydraulic or pneumatic pressure of the sample, usually paperboard, corrugated box, or fabric by a rubber diaphragm until the sample breaks, and then the rupture pressure is recorded and displayed on the unit.   

It offers reliable and repeatable test results with features like microprocessor-based displays, digital readouts, pneumatic clamps to secure the work, and a peak hold function. This accuracy level enables manufacturers to assess whether the product meets the criteria for reliability in service, confirm that packaging meets shipping requirements, eliminate expensive rejections, and comply with international standards, ASTM and ISO.

Conclusion

Evaluating a 5-Ply corrugated box‘s bursting strength is a key component in determining the box’s quality, strength, and suitability for high-end packaging applications. The manufacturer can use a standard test method to evaluate the bursting strength of the box to determine its ability to withstand both internal and external pressure, as well as help aid in the reduction of possible damage during handling and transit.