Influence of oil immersion depth on scuffing load capacity of cylindrical and bevel gears.

In gearboxes with labyrinth seals as they are typically used in railway applications the oil immersion depth is in many cases lower than recommended. Due to unfavourable lubrication and predominantly cooling conditions and thus increased gear bulk temperatures this may lead to scuffing failures especially at the beginning of the service life of such gears when run-in is not yet completed. Investigations in cylindrical and bevel gears showed the influence of different oil immersion depth on scuffing load capacity. Comparative tests were run with standard cylindrical A-type gears at reference oil level of centre line and different immersion depth of pinion and wheel as low as one time module only of the wheel. The scuffing load carrying capacity at lowest immersion depth was found to be only 30% of the scuffing capacity at fully flooded conditions. Parallel to the scuffing capacity measurements the gear bulk temperatures were recorded. Similar results with a drop to 20% of the scuffing capacity at fully flooded conditions were found with hypoid gears when the ring gear is immersed half of the ring gear face width. Calculation methods of scuffing load capacity in ISO 13989 are based on temperature criteria, either the total contact temperature criterion or the integral temperature criterion. Both decisive temperatures depend besides the temperatures generated in the contact also on gear bulk temperatures.