Loading factors within the strength calculation procedure for involute marine gears with parallel axes

Unified Requirement UR M56, prescribing the calculation of geometry, surface durability (pitting) and tooth root bending strength of gear pairs implemented in marine propulsion and auxiliary machinery was revised by the International Association of Classification Societies (IACS) in 2013. In the previous paper, published at the CIET 2014 Conference, the author who had taken place in the development of the UR M56 within the task of the IACS Machinery Panel, presented the background of that task, the results, its final outcome and the benefits gained. The most important benefit was the development of the verified and validated MS Excel/VBA calculation program based upon UR M56, developed by that author, which was handed over to the IACS Machinery Panel members to verify the UR M56 proposed calculation procedure itself. One of the drawbacks of the calculation procedure prescribed in UR M56 is that it does not present the way to calculate the loading factors (so called Kfactors) for a gear pair, other than referring to the ISO 6336-1 standard. This standard has also inherited the problem of certain ambiguities in the calculations of loading factors. The calculation procedure itself is rather extensive and complicated, so the K-factors were also omitted in the then developed version of the MS Excel/VBA calculation program. For this reason, additional efforts have been made later to improve the program introducing the entire calculation of loading factors, with all the necessary details. The aim of the present paper is to present the methodology used in the development of this part of the program, methodology of the verification (based upon the recently published technical report ISO/TR 6336-30:2017) and the future validation of the program results.