DNV DNV CLASSIFICATION NOTES 41.2 PDF

Scope and Basic Principles

The gear rating procedures giwn in this Classification Note are mainly based on the ISO-DIS 6336 Part J-5 (cylindrical gears), and ISO-DIS 10300 Part 1-3 (bevel gears) and drafts for ISO Technical Reports on Scuffing and Fatigue Damage Accumulation, but specially applied for marine purposes. such as marine propulsion and import.ant auxiliaries onhoard ships and mobile offshore units.

The calculation procedures cover gear rating as limited by contact stresses .(pitting, spalling or case crushing), tooth root stresses (fatigue breakage or overload breakage), and scuffing resistance. Even though no calculation procedures for other damages such as wear, gray staining (micropitting), fractures starting from flanks, etc. are given, such damages may limit the gear rating. Enclosed parallel shaft gears, epicyclic gears and bevel gears (with intersecting axis), for infinite life or limited life, are applicable. Steel is the only material considered. The methods applied throughout this document are only valid for a transverse contact ratio 1 < ε_x < 2. If this does not apply, special considerations are to he made.

All int1uence factors are defined regarding their physical interpretation. Some of the influence factors are determined by the gear geometry or have heen established by conventions. These factors are to be calculated in accordance with the equations provided. Other factors are approximations, which is clearly stated in the text by terms as «may he calculated as». These approximations are substitutes for exact evaluations where such arc lacking or too extensive for practical purposcs, or factors based on experience. In principle, any suitable method may replace these approximations.

Bevel gears are calculated on basis of virtual (equivalent) cylindrical gears using the geometry of the mid.section. The virtual (helical) cylindrical gear is to he calculated by using all the factors as a real cylindrical gear with some exct: ptions. These exceptions are mentioned in connection with the applicahle factors. Wherever a factor or calculation procedure has no rcforence lo either cylindrical gears or bevel gears, it is generally valid, i.e. combined for both cylindrical aod bevel. In on.ler to minimize the volume of lhis Classification Note such combinations are widely used, and cvcrywhcrn it is necessary to distinguish. it is clearly pointed out by local headings:

Cylindrical gears

Bevel gears

The permissible contact stresses, tooth rool stresses and scuffing load capacity depend on the safoty factors as required in the respective Rule sections. Terms as enduranrn limit and static stnmgth and use  throughout this Classification Note.

Endurance limit is to he umlerstoo<l as the fatigue strength in the range of cycles beyond the lower knee of the σ-N curves, regan.lless if it is constant or drops with higher number of cycles.

Static strength is to he urH.lerstood as the fatigue strength in the range of cycles less than at the upper knee of the σ-N curves.

For gears which are subjected to a limited number of cycles at difforent load levels, a cumulative fatigue calculation applies. Information on lhis is given in 5 (Appendix A).

When the term infinite life is used, it means number of cycles in the range 10⁸-10¹⁰