What is Ozone Cracking? How does it Affect the Rubber Properties?

What is ozone cracking?

The rubber tends to change its properties when exposed to different environmental conditions. When exposed to extensive ozone presence, there appears crack on the surface. These cracks appear in the right-angle orientation to the axis of strain. Thus, it hugely impacts the circumference of the material. If the rubber product is being used in a critical application like fuel pipes, they may initiate the leakage in the pipe and subsequent fire may erupt.

It is a noteworthy thing that ozone cracks appear in the sensitive zone of the product which is at the crucial position. Different types of rubber polymers have varied resistance to ozone. It has been found that air found in our surroundings have ozone, be it very less. But in the longer run, this ozone presence slowly starts degrading the rubber leading to cracks or elongations.

Depending upon the resistance of the rubber to the ozone cracking, its application is decided. Such as car door seals, O-rings, gaskets and much more. To test the rubber properties in presence of ozone, there are different testing standards issued by ASTM. For testing the deterioration of rubber, surface ozone cracking outdoors or ozone chamber, standards ASTM D1171 is followed. With this, the testing can be conducted at a predetermined rating or pass/ fail criteria. This test procedure is followed to trace the rate of growth of cracks on the surface.

In a standard process, the sample is exposed to an ozone concentration of 50pphm for approximately 72 hours. A magnification process is used to evaluate the development of cracks. The following factors are used to allow grading to the rubber samples;

·         The number of cracks developed under double magnification

·         Comparison with the predefined specifications

·         Rating allotted based on behaviour of sample at the period of 24 hours, 48 hours and 72 hours

Ozone chamber offered by Presto helps the quality manager to evaluate the performance of rubber as per the testing standards. This is the perfect machine with a glass window to peep inside the chamber.