Chapter 14
AGMA 925 - Scoring

The AGMA925-A03 Effect of Lubrication on Gear Surface Distress is currently the only standard that calculates the conditions in the lubrication gap over the tooth contact. AGMA925 describes the calculation of the height of the lubrication gap taking into account the curvature of the flanks, properties of the lubricant, sliding speed and the local stress load. On this basis, the standard calculates the probability of wear (by means of metallic contact by the surfaces if the lubrication gap is too small).The standard itself does not provide any notes on protection against micropitting. It is known, however, from literature and research results that there is a direct correlation between the minimum lubrication gap size and the occurrence of micropitting. The calculation method can therefore be used when gearing is to be optimized to resist micropitting.

The probability of the occurrence of scuffing is also determined in accordance with AGMA925. This calculation has the same basis (Blok’s equation) as the calculation of scuffing in accordance with the flash temperature criteria under DIN3990 part 4. The determination of the permitted scuffing temperature under AGMA925 is somewhat problematic because comprehensive or generally applicable notes are missing in this area. In particular there is no reference to the scuffing load load capacity specification according to the FZG test. Oils with active EP additives therefore have a tendency to be undervalued.


Figure 14.1: GEARCALC - AGMA 925

 14.1 Type of lubrication
 14.2 Oil
 14.3 Profile modification
 14.4 Oil temperature
 14.5 Tooth temperature
 14.6 Scuffing temperature
 14.7 Standard deviation of scuffing temperature
 14.8 Dynamic viscocity at ΘM
 14.9 Coefficient for pressure viscocity)
 14.10 Coefficient of friction
 14.11 Thermal contact coefficient
 14.12 Surface roughness
 14.13 Filter cut-off of wavelength