Sustainability - a stretchable definition?

Shorter product-to-market-times and higher expectations for sustainability, reliability and quality have ensured that product tests form an important link in the development process of products.

The use of high value materials in today’s products has led to longer periods of use, so that it is no longer possible to do lifespan tests under normal operating conditions and therefore accelerated testing is more appropriate. For years now engineers and product developers have used accelerated testing to predict the lifespan of materials. A lifespan guarantee is of little value if it has not been tested in practice.

Accelerated lab tests

Accelerated testing demonstrates the reliability of the components to be tested, as well as product certification, and also allows comparisons to be made with other products from different suppliers, as well as estimating the lifespan of a component.

Sirris Coating Application Lab receives many enquiries about the durability of protective coatings. For instance: how long does the antibacterial coating remain active? After how many cleaning cycles should an easy-to-clean coating be refreshed? How long does an anti-corrosion layer remain effective?

Many of these questions are difficult to answer because both wear and weathering often arise as a result of many different factors. For instance, coatings facing north on a building don’t weather as quickly as a result of the sun’s rays as the same coating facing south, and driving rain can lead to the premature failure of a layer of paint.

Coating producers rely on the earlier experiences of previous generations of coatings when offering product lifespan guarantees. New types of coatings are often developed by testing new formulas against existing recipes in standardised testing environments.

When coatings of a similar quality are compared with each other, a highly enforced form of accelerated testing is possible, because the coating degradation processes are similar.

However, with accelerated testing there must not be any additional influences present when the testing is intended to predict the lifespan of the product. This could be heat generated by lengthy friction tests, or the release and loss of components caused by testing at extremely high temperatures.

Correlation with the actual situation

There are various ways of interpreting the results of accelerated testing and attempting to convert these into an actual lifespan. Results of accelerated testing are often compared with the results from normal weathering tests with which a correlation factor is determined. This correlation factor is given a value of between 0 (no correlation) and 1 (perfect correlation). In general the correlation factor reduces when the duration of the accelerated test is reduced.

Other methods are based on predictive models that convert the results of the short term testing to a predictable lifespan.

Rules of thumb are applied in specific types of tests which are based on a collection of results. Below are some of the rules of thumb used for organic coating systems.

Test

Rules of thumb

Acceleration factor

QUV test UV-A340 lamps, medium intensity

1,000 hours => 1 to 1.5 years European Mediterranean climate

8 – 13

Neutral salt spray test ASTM B117

Test in compliance with corrosion classification described in ISO 12944

12 to 100

Cyclical salt spray test SAEJ2334

60-80 cycles => 5 years (Montreal and Quebec)

3 to 4

We can immediately see that a higher acceleration factor leads to a lower correlation factor. When setting up a test plan a balance should always found between these concepts. Sirris would like to help you make the right choices.

Would you be interested in ageing tests for your products? Just contact us or come along on 15 or 16 May during the Eurofinish trade show in Leuven and ask our experts.