Bursting Strength Tester (Paperboard)

Bursting strength tester is use to test the burst strength of a paper board. The machine expresses the burst strength in pressure, usually the unit is kgf/cm2, psi or bar.

There are some common problems/issues associate with bursting strength tester, whether problem is from the machine or from other factors, we will share some of the problems and how we solve it.

1. Test result too high or too low

When we have this condition, we need to test standard aluminium foil. If the value is larger than the spec, we need to replace the rubber membrane.

If the value is low, we need to check if there were air traps inside the rubber membrane or the oil system. We also need to confirm there are no leaks in the system.

To remove the air in the system, we need to perform bleeding process:

1. First, we remove the rubber membrane, then fill up the pocket of oil to the brim.

2. Carefully, we install the rubber membrane without introduce air.

3. Compressed the cover with the hand wheel or pneumatic cylinder, hand tight the locking ring.

4. Loosen the oil cap on the top reservoir.

5. Press the rubber membrane a few times to purge any remaining air.

6. If there are no visible air anymore, tighten the oil cap.

7. The bleeding process is completed.

2. Sample cannot burst/break

This problem can happen due to few reasons. The most common cause is low fluid level. What we need to do is remove the rubber membrane. Return the piston to the initial/neutral position, fill up the glycerin oil up to the brim. Reinstall the membrane and ensure no air is trapped inside. We should able to burst the sample.

The second reason is potential oil leak is in place. We should check for any visible oil leak, check and tighten all joint and connection. It can happen due to internal leak as well. We need to replace the seals inside the cylinder.

Another reason is a broken gearbox, the motor is running but the piston is not moving. For this problem, the gear box should be inspected.

A broken belt is uncommon, what we need to do is to confirm the belt condition for any slippage or looseness. A loose belt may not transmit the necessary torque to push the piston and burst the sample.

3. Oil leak

Oil leakage is common is bursting tester. What we usually do is we need to confirm the leak location.

If the leaks were from joint or connection, we can tighten it or add some teflon tape to stop the leak.

If the leaks come from the cylinder/piston area, we need to overhaul the assembly. We dismantle the cylinder, replace the seals on the piston and put some new gaskets on the joint surface. Check the piston positioning, stopper and the gearbox neutral position.

Reinstall everything and the machine should have no more leak.

4. Rubber membrane damaged/burst

If this scenario sounds familiar to you, you might have tested with a paperboard which is too thick.

Most bursting tester indicated capacity is 100kgf/cm2. Unfortunately, the limitation depends on the rubber membrane. A common safe operation limit lies around 50kgf/cm2. If we test some tri-wall paperboard with high grammage. The machine will unable to burst the sample.

Another reason is the rubber membrane was damaged or aged, even a small invisible cut on the membrane can lower its strength significantly. It is a good practice to replace the membrane and perform verification periodically.

5. Machine cannot run/operate

The first thing we need to check is the power supply, check with a test pen or mutimeter. Next, we check if the fuse is in good condition.

If the power supply is present, we check if any emergency switch is activated and we need to deactivate the switch.

Check if the motor is running, if the motor is not running after we press start, the motor or capacitor might have damaged.

Check if the belt is broken, replace belt or adjust tension if found the tension is too loose.

For semi-automated tester, check if the photo sensor is in good shape. Normally, when the sensor detects the specimen, the upper die will clamp down and start the test.

6. Machine cannot display test value / Machine does not stop after sample burst

Both of these problems happen due to a damaged pressure cell. We can check the pressure cell condition or the wiring connection. It can also happen if the calibration file/value was corrupted/altered.