Bevel-helical gear boxes B4 pecial grease protects the radial shaft seal again B4-HH-14-D

Flender/Flender Gear Units/Bevel-helical gear boxes B4

tion is carburization using carbon providing atmospheres followed by quenching in liquid media. Depending on thetime sequence and temperature prole, these are referred to as direct hardening oras single hardening, as shown in Fig. 6.2. variant form of single hardening is hardening after isothermal transformation. The double austenite-ferrite transforma-tion ensures ne austenite grain size prior to hardening.6.3 Heat Treatment 2 Direct hardening is the most economical option in terms of expected changes in size and shape. The risk of unacceptable microstructures occurs only at case hardening depths of more than 3 mm. In this case, more complex form of process management becomes necessary, thus increasing the costs. Salt melts, mineral oils and synthetic oils are possible quenching media, along with aqueous polymer solutions. When choosing the medium, compromise must always be found between cooling rate, risk of cracking, re risk, susceptibility to distortion, work safety, ecological restrictions, productivity and ergonomy. 6.3.6 Hardening Distortions Dimensional changes to the work piece always occur during heat treatment. These distortions may be regarded as the sum of all geometrical changes in the work piece. They occur as linear dimensional changes and as non-linear plastic and elastic deections. Figure 6.2 classies the distortion components. Linear dimensional changes are caused by volume increase, due to martensitic transformation, which entails growth in volume of roughly 1 %. They are classied as unavoidable changes in size and shape. Fig. 6.2 Direct hardening, single hardening and hardening after isothermal transformation [DIN-EN1 ]2 6 Manufacturing Process On the other hand, strictly speaking, non-linear changes are avoidable since they are caused by plastic and elastic deformations. They arise as result of residual stresses, non-homogeneity in the material, asymmetrical shape of the work piece, asymmetrical forging or uneven temperature proles during