AGMA 11FTM12 PDF

The international calculation method for micropitting, ISO/TR 15144, was recently published. It is the first official international calculation method to check for the risk of micropitting ever published. Years ago AGMA published a method for the calculation of the specific oil film thickness containing some comments about micropitting, and the German FVA published a calculation method based on intensive research results. The FVA and the AGMA are close to the ISO/TR. New is the calculation of the micropitting safety factors. The technical report presents two calculation rules, method A and B. Method A needs as input the Hertzian pressure on every point of the tooth flank, based on an accurate calculation of the meshing of the gear pair, considering tooth and shaft deflections to get the load distribution over the flank line in every meshing position. Method B is much simpler; the load distribution is defined for different cases as spur or helical gears, with and without profile modifications. The risk of micropitting is highly influenced by profile and flank line modifications. A new software tool can evaluate the risk of micropitting for gears by automatically varying different combinations of tip reliefs, other profile modifications and flank line modifications, in combination with different torque levels, using method A. The user can define the number of steps for variation of the amount of modification. Then all possible combinations are checked combined with different (user defined) torque levels. Any modifications including flank twist, arc-like profile modifications, etc. can be combined. The result is presented in a table, showing the safety factor against micropitting for different subsets of profile/flank modifications, depending on the torque level. Some applications from wind turbine and industrial gearboxes, known to the author, will be discussed.