Examination of Technical Gear with the Help of Magnetic Passive Observer Status Maciej ROSKOSZ 1 , Miroslaw WITOS 2 , Mariusz ZIEJA 2 1 Institute of Power Engineering and Turbomachinery, Silesian University of Technology, Gliwice, Poland, Phone: +48 322371039, fax +48 322372680; e-mail: Maciej.Roskosz@polsl.pl 2 Air Force Institute of Technology, Warsaw, Poland, Phone: +48 226851353, Fax +48 226851313; e-mail: witosm@itwl.pl, mariusz.zieja@itwl.pl Abstract The paper deals with the examination of magnetization of the existing gear to detect unknown history of the effort of teeth and recognize their health/maintenance status. Discussed topics are based on the observation that: 1. Highly loaded gears are usually made of ferromagnetic materials, which are reversible and irreversible magneto-mechanical effects; 2. The microstructure and the current dislocation density strongly affect the magnetic properties of the ferromagnetic material. The expected typical symptoms of diagnosing damages to gears are material changes in the distribution of magnetization induced during the operation of the transmission in the weak magnetic field of the Earth and the accompanying changes in the distribution of the magnetic field in the close to the test object under examination. The paper presents the theory that underlies the idea of the status observer and exemplary results of diagnosing industrial and aircraft gears. The main differences of studied objects are geometric features gears and position of the test object with respect to the external magnetic field of the Earth. To observe the distribution of the magnetic field applied cheap uni-, di-, and triaxial magnetometers (magnetic passive status observer). Keywords: toothed gear, over-torque, damage, fatigue, magneto-mechanical effects, magnetovision, non- destructive evaluation (NDE), structural health monitoring (SHM), metal magnetic memory (MMM) method 1. Introduction Toothed gears are the most essential units of power transmission systems. The major components, i.e. gear (toothed) wheels, shafts, and bearings are subjected to quasi-static and dynamic loads, which proves conducive to various kinds of failures, Figure 1. Safe and efficient operation of a toothed gear requires the diagnosing of atypical operating conditions (e.g. excessive vibration, violation of permissible torque /i.e. over-torque/), but not only; also, any failures to the gear’s material should be recognized as quickly as possible, i.e. at their earliest stages. Various causes of failures may range from the excessive wear-and-tear to a catastrophic breakage. The following statement proves the only right one for few responsible structures [1]: ‘A gear has failed when it can no longer efficiently do the job for which it was designed’ The paper has been intended to present a suggestion for the application of a passive magnetic observer of the state/condition, e.g. the metal magnetic memory (MMM) method [2]. This could be used for: a) The additional verification of health/maintenance status of gear (toothed) wheels under overhaul generated conditions (after the toothed gear has been disassembled into separate subunits and structural components/parts), as a technique complementary to classical NDT methods (visual inspection (VT), and magnetic particle inspection (MT or MPI), eddy- current testing (ET), or ultrasonic testing (UT)), to detect hidden effects of: - momentary exceedance of torque limits, with no evident symptoms of any failures to the teeth, Figure 2; - accumulation of cyclic loads upon teeth, with unknown design, assembling, and operating errors simultaneously affecting the structure. 11th European Conference on Non-Destructive Testing (ECNDT 2014), October 6-10, 2014, Prague, Czech Republic