DNV DNV CLASSIFICATION NOTES 41.2 PDF

Scope and Basic Principles

The gear rating procedures given in this Classification Note arc mainly based on the IS0-6336 Part 1-5 (cylindrical gears), and partly on ISO 10300 Part 1-3 (bevel gears) and £SO 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 Classification Note applies to enclosed parallel shaft gears, epicycle gears and bevel gears (with intersecting axis). However, open gear trains may be considered with regard to tooth strength, i.e. part l 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 malarial considered.

The methods applied throughout this document are only valid for a transverse contact ratio 1 < ∑_α< 2. If ∑_α >2, either special considerations are to 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 are to be calculated in accordance with the equations provided. Other factors are approximations, which are clearly stated in the text by tc1ms as «may be calculated as». These approximations are substitutes for exact evaluations where such arc lacking or too extensive for practical purposes, 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 midsection. The virtual (helical) cylindrical gear is to be calculated by using all the factors as a real cylindrical gear with some exceptions. These exceptions are mentioned in connection with the applicable factors. Wherever a factor or calculation procedure has no reference to either cylindrical gears or bevel gears, it is generally valid, i.e. combined for both cylindrical and bevel.