Ozone & Ultra Violet Resistance
Although not an actual cover grade in its own right, there is no question that ALL rubber conveyor belts need to be fully resistant to the damaging effects of ozone and ultra violet light. This is because at ground level ozone becomes a pollutant. Exposure increases the acidity of carbon black surfaces and causes reactions to take place within the molecular structure of the rubber. This has several consequences such as a surface cracking and a marked decrease in the tensile strength of the rubber. Likewise, ultraviolet light from sunlight and fluorescent lighting also accelerates deterioration because it produces photochemical reactions that promote the oxidation of the surface of the rubber resulting in a loss in mechanical strength.
EN/ISO 1431 International Standards
To scientifically measure resistance to ozone, samples are placed under tension (eg. 20% elongation) inside the ozone testing cabinet and exposed to highly concentrated levels of ozone for a period of time (eg.up to 96 hours). Experience has determined that to be adequately resistant the pass criteria needs to be that the rubber sample does not show any signs of cracking after 96 hours (@ 40°C, 50 pphm and 20% strain) inside the ozone cabinet. Samples are closely examined for evidence of cracking at two-hourly intervals and the results carefully measured and recorded.
What to watch for: Despite its essential importance, my research has revealed that ozone and UV resistance is very rarely, if ever, mentioned by manufacturers. This is almost certainly because anti-ozonants need to be used during the mixing process of the rubber compounds and that, of course, costs money. My advice is to make ozone & UV resistance a constant requirement when selecting all conveyor belts.
Authors Comment
Quality standards and testing in the conveyor belt industry is a huge and often quite complex subject. In compiling this paper I have simply tried to provide a basic guide. Consequently, my final piece of advice would firstly be to never assume that the presence of test method reference numbers or the logos of quality organisations necessarily means what they are designed to indicate. Secondly, it is always worthwhile to ask questions and request evidence of good practice and actual performance. Taking that little bit of extra care could easily save your company an enormous amount of time and money.
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