Can any one suggest what Oil cleanliness level should be maintain in Helical Gear Box Lub Oil ISO VG 320 ?

Meshing gears have a lot more back lesh then at least 100 Micron, so does it need super clean Oil (Say NAS - 8 /7 or NAS - 6 )?

Of Course bearings are also lubricated with the same oil so cleaner the oil, better is the life of bearing. But for meshing gears does super clen oil is required ?

I will prefer your answer Yes or NO. and if yes then why ?

ANSI/AGMA 9005-E02 specifies as a minimum, 50 microns absolute for gear drives with ball or roller bearings, and 25 micron absolute for gear drives with journal bearings.

Hi Mr Dave,

Nas 8 would be nice or ISO 4407 16/13,

Your rolling bearings dictate your cleanness,
must be < ISO 16/13,
Every grade higher is twice the debris in the drive,
run up into the ISO 19/16's and you'll be spalling bearings,

Regards Rob S

Thanks to both of you for your valuable suggestions. My doubts are cleared.
Regards.

V.S.Dave.