How to Use a Bursting Strength Tester Step by Step

Learning how to use a bursting strength tester comes down to four things: condition the board, check the instrument, run enough valid bursts and record the result properly. This guide follows ISO 2759 for board and notes which materials ISO 2758 and the TAPPI methods apply to.

What a bursting strength tester measures

A bursting strength tester clamps a test piece over a round rubber diaphragm. A motor-driven piston pumps hydraulic fluid behind the diaphragm at a constant rate until the test piece ruptures. The peak hydraulic pressure at that moment is the bursting strength.

ISO 2759 defines it as the maximum pressure the hydraulic system develops in forcing the diaphragm through a circular area of the board. The indicated value includes the pressure needed to stretch the diaphragm itself.

Pick the method that matches the material. ISO 2759 covers board, including corrugated and solid fibreboard, from 350 kPa to 5,500 kPa. ISO 2758 covers paper from 70 kPa to 1,400 kPa and is not meant for liner or fluting taken from combined board.

In North America, TAPPI T 810 covers single wall and double wall corrugated board from 690 kPa (100 psi) to 4,825 kPa (700 psi). It does not apply to triple wall board. TAPPI T 403 is the paper method.

Before the test

Several error sources can be checked before the first test piece goes in the clamp. Start with the moisture state of the board and the condition of the diaphragm and clamps.

Conditioning the board

Paper and board change strength with moisture, so ISO 2759 requires test pieces to be conditioned to ISO 187 and tested in the same atmosphere. The ISO 187 standard atmosphere is (23 ± 1) °C and (50 ± 2) % RH. Tropical countries may use (27 ± 1) °C and (65 ± 2) % RH.

TAPPI T 402 uses the same 23 ± 1 °C and 50 ± 2 % RH for paper test rooms. Match the atmosphere to the method your customer names, and write it in the report.

Where moisture hysteresis could cause errors, ISO 187 asks for 24 h of preconditioning at 10 % to 35 % RH and no more than 40 °C. The sample then comes up to the standard atmosphere from the dry side.

Conditioning is complete when two weighings at least 1 h apart differ by no more than 0.25 %. ISO 187 notes that heavier boards can need 48 h or longer, so do not cut the time short on thick combined board.

Checking the diaphragm and clamp

The diaphragm wears with use. ISO 2759 sets two bulge checks for the board method: 170 kPa to 220 kPa at a bulge height of 10 mm, and 250 kPa to 350 kPa at 18 mm. Replace the diaphragm when it falls outside these limits.

The clamp should hold the test piece firmly between two flat, parallel, grooved rings. ISO 2759 asks for openings concentric within 0.25 mm and a clamping system able to apply 700 kPa to 1,200 kPa.

Check the pumping rate too. The board method calls for 170 ml/min ± 15 ml/min, and the hydraulic fluid and lines should hold no air bubbles. Aluminium foil test pieces can confirm the instrument works, but ISO 2759 says they should not be used as calibration standards.

Questions about a model or a test? Email Amy Zhao, Export Manager, at [email protected].

Running the test step by step

The sequence below follows clause 8 of ISO 2759. Your instrument manual covers the controls; the method covers what has to happen.

1. Warm up the instrument if it is electronic, as the manufacturer's instructions describe.
2. Select the most suitable pressure range. Run a preliminary test on the highest range if you are unsure.
3. Set the lowest clamping pressure that stops the test piece slipping.
4. Raise the clamp and insert the test piece so the full clamping area is used.
5. Apply full clamping pressure, then zero the hydraulic pressure reading if required.
6. Apply hydraulic pressure until the test piece bursts.
7. Retract the piston until the diaphragm sits below the clamping plate, then read the burst pressure to the nearest kilopascal.
8. Release the clamp and prepare for the next test piece.

As a guide for step 3, ISO 2759 suggests 400 kPa of clamping pressure for board bursting up to 1,500 kPa. It suggests 1,000 kPa for board above 2,500 kPa.

Our NPD-2D burst strength tester is one of the burst testers we supply. Tell us which test method your customer specifies and our factory team can reply by email.

Reading and recording the result

ISO 2759 asks for 20 valid tests when you do not need separate results for each face. When each face matters, run at least 10 valid tests per side. The face against the diaphragm is the face under test.

Report the mean bursting strength to the nearest 1 kPa together with the standard deviation. If grammage was measured to ISO 536, you can also report burst index rounded to three significant digits. Our guide to bursting strength units explains burst index and how kPa converts to psi and kgf/cm2.

The ISO 2759 test report also lists these items:

• Reference to the method and the date and place of testing
• Full identification of the sample
• Make and type of instrument used
• Conditioning atmosphere used
• Any deviation from the method

Common mistakes that skew burst results

ISO 2759 names the main sources of error. Several of them push the reading up, which can make weak board look acceptable.

• A pumping rate that is too fast, which gives an apparent increase in bursting strength.
• A stiff or inelastic diaphragm, which gives an apparent increase in bursting strength.
• A defective diaphragm, or one set too high or too low relative to the clamping plate.
• Inadequate or uneven clamping, which generally reads high.
• Air in the hydraulic system, which generally reads low.
• Incorrect calibration of the pressure measuring system.

Reject any reading where the test piece visibly slipped, shown by movement outside the clamps or creasing in the clamped area. Also reject readings where the break pattern, such as severance at the edge of the test zone, shows clamp damage.

Frequently asked questions

Can I use ISO 2758 and ISO 2759 results interchangeably?

No. Both standards note that, because the apparatus differs, tests on the same material will not necessarily give the same results. Report which method you used and compare results only within one method.

How often should a burst tester be calibrated?

ISO 2759 asks for calibration before first use and often enough to keep the specified accuracy. A pressure sensor that was overloaded must be recalibrated before further use. Set the interval in your own quality system.

Talk to our factory team

We sell direct from our factory, so you work directly with our factory team. Questions about a model or a test? Email Amy Zhao, Export Manager, at [email protected].