Purchasing gear lubricants: be careful when playing the numbers game
Written by John Sander
8. Consider Gear Speed
Viscosity often is related proportionally to the speed at which the gearbox is operating. The general belief is that high-speed applications require low-viscosity lubricants, and low-speed applications require high-viscosity lubricants. AGMA provided a general guideline in its 9005-94 specification, which can serve a good rule of thumb. When referring to its viscosity grades shown in Table 3, AGMA stated:
"These guidelines are directly applicable to … gears that operate at or below 3,600 revolutions per minute, or a pitchline velocity of not more than 40 meters per second (8,000 feet per minute) … and worm gears that operate at or below 2,400 rpm worm speed or 10 meters per second (2,000 feet per minute) sliding velocity".
Anything above these gear speeds is considered a high-speed gear, and it is best to consult the OEM recommendations for lubricant recommendations. Figure 2 is a simple schematic that summarizes how load, speed and viscosity come together during the lubricant selection process.
