There are two "invisible" and unavoidable factors that have a huge impact on the service life of rubber conveyor belts. These factors are ozone (O 3) and ultraviolet (UV) light. Contrary to popular belief, the damage they cause is not limited to high altitudes or sunny climates.
Ozone (O 3) is naturally present in the upper atmosphere. It is continuously formed by the action of solar ultraviolet radiation on molecular oxygen (O 2). At high altitudes, ozone acts as a protective barrier by absorbing harmful UV rays. Wind currents carry O 3 into the atmosphere at the Earth's surface. At lower altitudes, ozone becomes a pollutant. Ground-level or "bad" ozone is not emitted directly into the air, but is produced by the photolysis of nitrogen dioxide (NO 2 ) from vehicle exhaust and industrial emissions. This is called ozone decomposition. Ozonolysis is a reaction between molecular structures (double bonds) and ozone.
Even trace amounts of ozone in the air can damage the molecular structure of rubber. It increases the acidity of the carbon black surface, of which natural rubber, polybutadiene, butadiene rubber and nitrile rubber are the most sensitive to degradation. The first visible sign is the beginning of cracks on the rubber surface. Further attack then occurs within the newly exposed cracks, which continue to grow steadily until they complete the "cycle" and the product separates or fails. The cracks are always at right angles to the strain axis. The dynamic stresses to which the conveyor belt is subjected during operation are considerable. Ozone attack occurs at the point of maximum strain.
Although ozone concentration varies from place to place, ground-level ozone pollution is always present and its effects should not be underestimated.
UV light from sunlight and fluorescent lamps also has serious adverse effects on rubber, as it accelerates rubber deterioration by producing photochemical reactions that promote oxidation of the rubber surface, leading to loss of mechanical strength. This is known as "UV degradation". In belts that are not fully resistant, the combined effect of ozone and UV light not only significantly shortens service life, but also causes serious environmental, health and safety problems as fine dust particles penetrate cracks and are then discharged (shaken off) onto the belt. Return (lower side) belt operation.
Damage caused by ozone and UV rays is completely preventable. We have equipped a laboratory with the latest ozone testing equipment and introduced mandatory testing to EN/ISO 1431 international standards for all Dunlop rubber products.
As a direct result, special antioxidant additives, which are highly effective anti-ozone agents and prevent the damaging effects of ozone and UV rays, are an essential component of every Dunlop rubber compound without exception.
To scientifically measure resistance to ozone according to the EN/ISO 1431 test method, samples are placed under tension (e.g. 20% elongation) in an ozone test cabinet and exposed to high concentrations of ozone for up to 96 hours (@ 40°C, 50 pphm and 20% strain).
The samples were carefully checked every two hours for signs of cracking, and the results were carefully measured and recorded. Experience has shown that in order for the rubber to be sufficiently resistant, the qualifying criterion must be that the rubber sample does not show any signs of cracking within 96 hours.
Although it is critical, conveyor belt manufacturers and suppliers rarely, if ever, mention ozone and UV resistance. This is because ozone resistances cost money. The best advice is to always require ozone and UV resistance when selecting any rubber conveyor belt.