What Is an Impact Test? A Guide to Impact and Drop Testing of Bottles and Closures
An impact test measures how well a container or a closure resists a sudden shock. A known energy is applied to the sample, by a pendulum, a falling ball or a fall of the container itself, and the sample is then inspected for breakage or cracks. Impact and drop tests are used for glass bottles and jars, PET bottles and plastic closures, which are exposed to shocks on filling lines, during transport and in the hands of consumers.
How does an impact tester work?
All impact testers rely on the same principle, the conservation of energy. A mass raised to a height stores potential energy, equal to its mass multiplied by gravity and by the height. When the mass is released, this energy becomes the energy of the impact.
Pendulum impact: a pendulum is raised to an angle and released against the bottle. The higher the angle, the higher the impact energy. On the AT2E GBIT, the energy is read directly on an energy scale, up to 2.6 J.
Falling ball: a steel ball of known mass falls through a guiding tube onto the closure. On the AT2E BIT-1, a 286 g (10.1 oz) steel ball falls through a guiding tube 762 to 1000 mm (30 to 39.4 in) high; over such a height, the theoretical impact energy (m·g·h) is about 2.1 to 2.8 J.
Drop test: the filled container itself falls from a set height onto a hard surface. The AT2E PBDT-1 drops PET bottles from 800 to 1950 mm (31.5 to 76.8 in), in vertical or horizontal position.
Main applications
Glass bottles and jars: impact resistance of the body, the shoulder or the base, with an adjustable impact point.
Plastic closures: impact resistance of caps on glass and PET bottles.
PET bottles: drop resistance of filled bottles, with a drop tester designed with reference to the ISBT requirements.
Line simulation: bottle-to-bottle contact and abrasion on packaging lines.
Stability: resistance of bottles to tilting and sliding.
Key concepts: impact energy, test method and impact point
Impact energy: the energy, expressed in joules, describes the severity of a shock better than the height alone. A heavier ball from a lower height can deliver the same energy as a lighter ball from higher up.
Test method: in a pass/fail test, all samples receive the same energy and the broken samples are counted. In a step test, the energy is increased step by step until the sample breaks, which gives the impact resistance of each sample.
Impact point and position: where the impact lands, on the body, the shoulder, the base or the edge of a cap, and how the container lands in a drop test, change the result. That is why the impact point and the drop position are set and recorded.
Resolution and losses: on the GBIT, each graduation of the energy scale is 0.1 J above 0.6 J and 0.05 J below, and the energy lost in the pendulum is 1.5 % F.S. or less.
Why a phone breaks on one fall and not another
Anyone who has dropped a phone knows that height is not the only thing that matters. A fall flat on its back may leave it intact, while a shorter fall on a corner cracks the screen. The energy is the same or lower, but it is concentrated on a small point.
Containers behave the same way. Glass breaks where the stress concentrates, often at a small surface defect or scratch, which is also why scratches from bottle-to-bottle contact on the line reduce the strength of the bottle. Impact testers control both the energy and the point of impact, so that results can be compared from one sample to the next.
Calibration of an impact tester
Since the impact energy depends on mass and height, these are the values to check:
Check the height: the drop height of a ball or a container with a calibrated rule, and the zero position and angle (energy) scale of a pendulum.
Check the mass: weigh the ball or the pendulum and compare it with its nominal value. The BIT-1 ball is specified at 286 ± 2 g and 41 ± 0.2 mm in diameter.
Check that the pendulum or the ball moves freely, record the deviations, and correct them if they exceed the acceptable limit.
An error of a few percent on the height or the mass becomes the same error on the impact energy.
AT2E impact testers
AT2E impact testers cover glass, PET and closures, and the handling conditions of the line:
GBIT: pendulum impact tester for glass bottles and jars, up to 2.6 J, for samples 30 to 130 mm in diameter, with stainless steel safety shield.
BIT-1: ball impact tester for plastic closures on glass and PET bottles, 286 g steel ball, guiding tube from 762 to 1000 mm.
PBDT-1: PET bottle drop tester, drop height from 800 to 1950 mm, bottles from 150 ml to 2.5 L, vertical or horizontal drops.
PLS: production line simulator that reproduces the friction and abrasion of packaging lines on bottles and cans 50 to 150 mm in diameter.
BTT-1: bottle tilt tester that measures the fall and slide angles of up to 10 bottles at once.
Conclusion
A bottle that passes an impact test is not unbreakable; it has withstood a known shock under known conditions. Controlling the energy, the impact point and the condition of the samples is what makes impact and drop results comparable from one batch, one supplier and one year to the next.
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AT2E is an ISO 9001 certified company (AFNOR Certification).
Request a quote: info@at2e.com
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