Dear all,

I have a gearbox reducer with motor input 750 kw(about 1005.36 HP) and gear ratio 1:2.08 and on the output shaft motor the temperature 83degree celcius and 996 rpm and on the output gear reducer the temperature 82 degree celcius and 470 rpm, the temperature on both output quite high and this condition not good enough for the gears, said the OEM the temperature must 73 degree celcius..and for the lubricant i'm using ISO VG 220 and the base oil grade III(mineral oil), the cause viscosity or the base oil for this happen? if the viscosity, what's the correct and the suitable viscosity for the gears?..cause the recomended OEM are mineral oil

The issue with a number of OEM's is that they are Europe based and base their viscosities on the cooler European ambients. Compared to an oil lubricated piece of equipment with a 30C plus starting ambient then the viscosity often needs to be altered to adapt. In Australia we often have customers with the same equipment who raise the viscosity one ISO grade if they operate in the Northern part of Australia. Suggest you talk with the OEM and see if they will assist with a trial to move the viscosity up one grade.

The second issue which can occur with some large gearcases is that they rely on splash feed to lubricate the input and output shaft bearings. This is not always effective and the bearings can become starved for oil, particularly if the oil used does not have suffient film strength to seperate the metal surfaces under load.

There are some graphics called nomograms, in them you can trace a line that gives you the right viscosity if you feed it with the right data, such as the rpm and HP´s.

I will try to track them, but may be they are at google.

On the other hand, you can "avoid " this problem using a PAO or even better a polyglycol. Most mineral oils have VI around 100, a good PAO above 150.

Bearing that fact in mind, the behaviour at high temperatures is almost the next viscosity grade... i hope i am being clear, i mean a PAO ISO 220 at 100 C will have the same or higher viscosity than a mineral oil.

Widman can clear that fact better than me, i used his tools to make a viscosity comparison between 3 lubes, mineral ISO 320 and 460 and a PAO ISO 320.

By the way you can check the AGMA 9005 E02.
Also, Table flender 7300 BA

There are some useful guidelines.