Fraunhofer Institute for Nondestructive Testing IZFP
© 2012, Dr. Jochen Kurz, Dr. Klaus Szielasko, Fraunhofer IZFP
The testing of wire ropes by magnetic flux leakage testing is common practice. This particularly applies to cable cars, lifts and cranes. Here, after the rope is exposed to a magnetic field the flaw stray fields are measured. The measurement is carried out e.g. by coils, wherein the movement of the cable through the coil (or vice versa) is assumed (that is, the coil must envelop the rope tightly), or by magnetic field sensors (e.g. Hall sensors).
In the building industrie tension absorbing elements ropes of different design (diameter, surface coating) and bundling are applied. Therefore, test systems which have to envelop the rope are only used in rare situations and in a limited range of diameters. Moreover, in many cases, no exact location of the angular position of the flaw is possible.
Inspection of Ropes and Tension Wires
At Fraunhofer IZFP, within the Fraunhofer-Carnot project "FilameNDT" (partner: IFSTTAR, Nantes, France) a flux leakage inspection system was developed which can operate battery-driven and in contact technique rope surfaces. Testable rope diameters are between about 4 cm and 20 cm. Controlled by long-range Bluetooth with a PC, the system scans cylindrical surfaces by revolving the rope once. On the rope surface it moves by a caterpillar-like movement over a defined distance. The computer creates a picture of the stray magnetic field over the entire surface of the rope. Due to the caterpillar movement of the crawler slip is small, so that the accurate retrieval of striking positions is ensured. Unlike existing systems, the FluxCrawler sticks at a wire because of the magnetic attraction force and don´t require to include the it.