B2CV-6-C ign of the gear units Overview tables Technical sp Bevel-helical gear box B2

Flender/Flender Gear Units/Bevel-helical gear box B2

ments introduced in the surface layer and the concentration towards the core. These can be controlled and slightly adapted by the process parameters of the diffusion treatment. Nitrogen and carbon have proved to be suitable enriching elements for gears in many process variants. 6.3.4.2 Nitriding Nitriding processes can always be applied when thin, very hard, wear-resistant nitrided and nitrocarburized layers tend best to meet the expected stresses. Only very slight distortions are expected because of the low process tempera- tures. However, the hardness curve in the layer and its small thickness limit the Fig. 6.1 Residual and bending stresses in the tooth root2 6 Manufacturing Process amount of stock which can be removed in subsequent hard nishing operation. In practice, nitrided gears receive their nal tooth ank geometry and surface duringsoft machining, such that the gear is nished after nitriding. Enriching the surface layer of the material with elemental nitrogen increases the hardness and strength of the base material. Unlike martensitic hardening, thisprocess relies on the mechanism of precipitation hardening where strengthincreases with hardness in the nitrogen-enriched surface layer. In addition, as arule compressive residual stresses appear in the surface layer. Ductility is inverselyproportional to hardness. This latter characteristic indicates what the main problem is with nitrided gears: as result of their high hardness and inadequate ductility, micro-cracks propagate very quickly when there is local overload. There is high probability that the type of damage after sudden overload will be fracture in the root. Nitriding layers aretherefore preferably used where the main focus is protection against adhesive andabrasive wear and corrosion. If carbon as well as nitrogen is added to the surface ina nitrocarburizing process, surface layer with very small coefcient of friction isproduced. This increases efciency in the gearbox along with tooth ank load