Det Norske Veritas - Germanischer Lloyd

Calculation of gear rating for marine transmissions
 N CG-0036

Annotation

Scope and basic principles

The gear rating procedures given in this class guideline are mainly based on the ISO6336 Part 1 to 5 (cylindrical gears), and partly on ISO 10300 Part 1 to 3 (bevel gears) and ISO Technical Reports on Scuffing and Fatigue Damage Accumulation, but especially applied for marine purposes, such as marine propulsion and important auxiliaries onboard 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, grey staining (micropitting), etc. are given, such damages may limit the gear rating.

The class guideline applies to enclosed parallel shaft gears, epicyclic gears and bevel gears (with intersecting axis). However, open gear trains may be considered with regard to tooth strength, i.e. part 1 and 3 may apply. Even pinion-rack tooth strength may be considered, but since such gear trains often are designed with non-involute pinions, the calculation procedure of pinion-racks is described in Appendix C.

Steel is the only material considered.

The methods applied throughout this document are only valid for a transverse contact ratio 1 < < 2. If > 2, either special considerations shall be made, or suggested simplification may be used.

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