Principles of Top-load Testing

Why perform top-load tests?

Product Performance

Top-load or column-crush testing ensures that products consistently meet requirements for axial load - the force exerted on products during:

  • Production - bottles, for example, must withstand the stresses of filling and closure.
  • Storage and display - Almost all packaging is stacked at some point, in both empty and filled states.
  • Transport - Extra strain is frequently experienced when packaging is subject to movement or when other products are placed on top.

Products must be sufficiently robust to maintain integrity within desired or industry standards when subject to these stresses. Failure to meet these objectives can result in unacceptable levels of packaging failure which lead to:

  • Leakage, breakage or wastage
  • High product return rates
  • Loss of income
  • Environmental impact

Cost-effective Design

In order to achieve the performance objectives above most cost-effectively, manufacturers strive to “lightweight” or “down-gauge” packaging materials in the most efficient way. The down-gauging of billions of finished products worldwide amounts to considerable cost savings. This involves not only reducing the volume of raw materials used but also designing for strength.

Plastic bottles and containers, cans, glass jars, or cardboard cartons, will all behave differently according to materials used, contents and structural design. A common example of a stacked container is the PET bottle, used globally for beverages, cooking, cleaning and other liquids. It has design features that affect axial load strength, including closure, handles, grip areas, and shoulder and base design. Some designs are made for unit-to-unit stacking to further minimise batch packaging and increase stack stability.

Top-load testing is therefore as integral a part of the design process, as it is of production line quality testing. Only reliable and repeatable top-load testing can ensure the most effective design and raw material ratio.

How is it Tested?

A top-load test essentially involves applying a downwards compression to measure resistance to crushing of a product, usually a container. Test methods define the speed of compression and extent of deformation, and peak force measurement determines the product sample strength. An appropriate top-load tester will also be able to measure accurately the initial and recovered height of the sample, for conformance to specification.

In the case of multi-wall cardboard materials, standardised samples of the material itself are assessed for rigidity by edge crush testing, since this is predictive of final construction strength. Contents, head space and weight, as well as humidity and storage conditions greatly affect the load-bearing of a cardboard container. The strength and suitability of a complete cardboard box may therefore also involve compressive burst testing under various conditions.

Mecmesin top-load testers provide a straightforward way to produce sophisticated test results that are reliable and repeatable. Behaviour recorded in tests can be displayed in highly visual graphs and provided to SPC systems for further analysis.

Crush Test Fixtures

Compression fixtures account for the behaviour of the sample. For example:

  • A plate for crush testing a bottle may be vented, or have a cone centre that prevents a bottle slipping sideways.
  • A plate for crushing a box may be self-levelling to follow the pattern of failure
  • Edge crush methods may require special fixtures, for example to retain a circular ring of cardboard
  • Filled containers such as a beverage cans require a suitable enclosure to contain the effects
  • Glass top-load testing demands additional safety enclosures

Accurate top-load testing, therefore, requires the correct selection of fixture. Mecmesin can provide a large range of accessories and customised fixtures to suit your requirements.

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A Brand You Can Trust

"We have performed top-load tests on our PET bottle production line for nearly a decade with Mecmesin equipment, which has proved extremely robust and reliable. We plan to upgrade our QC test equipment soon and I will have no hesitation in sticking with Mecmesin."

John Gilroy, Quality Manager, Esterform Packaging Ltd


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