Deep Dive into Bursting Strength Testing: A Technical Guide for Packaging Safety

In the packaging and papermaking industries, Bursting Strength is one of the most critical indicators for measuring a material's physical performance. Whether for international trade or domestic logistics, understanding the ultimate strength of a material under pressure is essential to reducing transportation losses. This article provides a deep technical analysis of this key test.

1、What is the Mullen Test?

Bursting strength testing is academically known as the Mullen Test. It is defined as the maximum pressure a material can withstand under an increasing hydraulic force applied perpendicular to its surface until it ruptures.

• Test Subjects: Primarily paper, corrugated board, aluminum foil, textiles, and leather.
• Units: Usually expressed in kilopascals (kPa), pounds per square inch (psi), or kilograms per square centimeter (kg/cm²).

2、Technical Principle: Hydraulic Power & Diaphragm

he core of a bursting strength tester lies in its hydraulic system. During the test, the specimen is clamped between two annular plates, with a flexible rubber diaphragm located beneath the lower plate.

1. Hydraulic Drive: The machine injects glycerin or silicone oil at a constant rate.
2. Diaphragm Expansion: Hydraulic pressure pushes the diaphragm upward against the specimen.
3. Peak Recording: At the moment of rupture, the system records the peak hydraulic pressure and subtracts the diaphragm's own resistance to calculate the net bursting strength.

3、Core Standards：ISO 2758 vs ISO 2759

To ensure international credibility, specific testing standards must be followed:

• ISO 2758 (Paper): Applicable to single-layer paper with bursting strength between 70kPa and 1400kPa.
• ISO 2759 (Board): Applicable to corrugated board, paperboard, and multi-layer paper with strength between 350kPa and 5500kPa.
• ASTM D3786: The standard test method specifically for textile fabrics.

4、Key Factors Affecting Accuracy

1. Clamping Pressure: If the pressure is insufficient, the specimen may slip, leading to falsely high readings; if excessive, it may damage the fibers.
2. Air Bubbles: Air trapped in the hydraulic system causes unstable pressure transmission and significant data fluctuations.
3. Diaphragm Condition: An aging, hardened, or cracked diaphragm alters its inherent resistance and must be replaced regularly.

5、Maintenance & Calibration Tips

To maintain high precision, Zhongyi Instruments recommends:

• Daily Calibration: Use the standard aluminum foil calibration sheets provided to verify zero points and measurement accuracy.
• Oil Management: Regularly check if the glycerin is cloudy or depleted; replace and bleed the air as necessary.
• Grip Cleaning: Prevent paper scraps or impurities from entering the hydraulic chamber.