Glass bulbs are compression-tested

Two twin column materials testing machines are being used for compression testing of glass bulbs used in automatic sprinkler systems as part of a manufacturer's rigorous quality programme.

Quality control of components used in automatic sprinkler systems is of huge importance.

These systems are used more than any other fixed fire protection method and over 80 million sprinklers are fitted worldwide each year.

The outstanding quality of the components used is reflected by the fact that accidental discharge of water due to manufacturing defects is 1 in 14,000,000 per year of service.

Norbulb , a world leader in glass bulb technology, is using two EZ20 twin column materials testing machines from Lloyd Instruments for compression testing of its glass bulbs used in automatic sprinkler systems as part of its rigorous quality programme.

The test routine is fully automated using pneumatic robotic sampling methods.

In use, the glass bulbs are filled with a coloured liquid of known co-efficient of expansion.

The bulbs are part of a pressurised system and must be strong enough to withstand the pressure of the water behind them in ambient conditions.

However, expansion of the liquid on reaching the trigger temperature due to a fire, causes the bulb to fracture, thereby releasing the water, The EZ20 test machines are fitted with 20kN loadcells and the fully automated test routine was developed by Norbulb using Lloyd Instruments' NEXYGEN MT materials test and data analysis software, Ondio's application builder and the batch tester software.

The test is performed under load rate control, showing a linear rise in load until the sample breaks.

* Sample handling is fully automated - twenty-five glass bulbs are loaded into a rotary sample holder and the test sequence is started.

Jaws on a sliding arm are opened by compressed air and a bulb drops into them.

The jaws then close and the arm moves forward to position the sample between the compression plates.

The crosshead drives to secure the sample in position and the jaws open and the arm retracts.

A cover slides down over the sample and a slight vacuum is applied through a suction tube.

The test is then performed and when the sample breaks, any glass fragments are removed by the suction tube.

The cover lifts and the sample holder rotates to allow the next sample to drop into the jaws.

A complete test cycle for one sample takes around 40 seconds.

The systems run continuously during production and have been working without any trouble for 3 years.

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