From Shearography to Pressure Testing

During the last decade Germany’s SDS has contribute to tyre quality via its Interferometric Tire Tester (ITT) range. The product line extends from applications for motorcycle, race, car, truck, bus and aircraft tyres through to special applications for OTR tyres with an outer diameter of up to 4.2 metres. But what exactly takes place during the SDS sheography process?

The ITT series’ state of the art technology employs “Speckle Shearing” through the use of a single or multiple closed measuring set-up that contains an interferometer with CCD camera and multiple laser diodes with integrated optics. During the measuring procedure the tyre in the vacuum chamber is subjected to pressure differential stress. Two phase-shifted images are superimposed upon each other and processed. The test result of this process can be used to detect anomalies such as separations, delaminations and trapped air pockets. However, anomolies are only detectable if they remain sealed from the atmosphere. A complete test cycle typically consists of three scans and the tyre has to be flipped – either manually or automatically. At this point shearography comes up against its limits. Not only does a complete bead to bead inspection require more time, critical sidewall anomalies and other structural anomalies do not necessarily cause separations and so they remain undetected.

“SDS has made it its business to find a new test procedure where the tyre structure is inspected, so that these faults become discernible,“ the company writes in a release. An obvious means by which these abnomolities become identifiable is to inflate the tyre. In 2008, SDS introduced such a solution, its “Pressure Test System“ (PTS). The PTS is a non-destructive and non-contacting method that operates automatically. In addition, the system is also able to measure tyre geometry and variation.

In the first step of the PTS test procedure both sidewalls are simultaneously measured with different inflation pressure rates. Afterwards, the different measuring results are compared and converted into a linear coordination system. The result displays irregular deformations that point out that the presence of defects such as fatigue or broken cords.

“For the first time there is a solution which automatically indicates structural anomalies clearly and reliably. It is the perfect addition to a SDS Interferometric Tire Tester and gives a comprehensive understanding of casing condition for the maximum reliability of the final product,“ the German company adds.