B2-KV17-B seal Flender GmbH Flender MD Helical gear u Bevel-helical gear Reduction Boxes B2

Flender/Flender Gear Units/Bevel-helical gear Reduction Boxes B2

nk [NIEM8.2 ]1 4 Load Capacity and Efciency increase in dynamic forces and noise emission. The altered stress distribution may also have negative effect on pitting load capacity. Typical micropitting on pinion of hypoid gear set is shown in Fig. 4.8. Micropitting is mainly inuenced by surface and lubricant properties. The relative lubricant lm thickness, dened as the ratio of the minimum lubricant lm thickness to the mean tooth ank roughness [ SCHR0 ], is used as failure criterion. This ratio is compared to permissible relative lubricant lm thickness, the so-called strength of the lubricant, derived from the FZG micropitting test [FVA5 ]. The lubricant lm thickness mainly depends on speed conditions and lubricant viscosity rather than on contact stress. The sum of velocities contributes to the formation of the lubricant lm while the sliding velocity impedes it. The smallest possible prole shift for the pinion and low hypoid offset accordingly favour the formation of the lubricant lm since less frictional heat is generated in the contact resulting in higher viscosity and thicker lubricant lm. higher micropitting load capacity can be obtained by selecting suitable lubricant with low coefcient of friction. Additives in the lubricant also have signicant inuence on micropitting. In this respect, phosphorus sulphide based additives are usually more advantageous than zinc dithiophosphate based additives [NIEM8.2 ]. Because smooth ank surfaces are less at risk of micropitting, hard nishing processes or running-in procedures to smooth the active tooth ank surfaces have positive effect on micropitting load capacity. 4.1.6 Wear Wear is the continuous destructive removal of material caused by abrasion. It occurs at low circumferential speeds, and hence low lm thicknesses [NIEM8.2 ]. The different forms of wear are described with more details in [ISO1 ]. Like micropitting, wear results in tooth ank form deviations Fig. 4.8 Micropitting4.1 Gear Failure Modes 1 occurri