NORD Drivesystems B1000 - Manual (Page 40)

www.nord.com A38
INTRODUCTION
G1000 – Subject to Change Without Notice
Lubrication
The Importance of Oil Viscosity
Viscosity or the oil’s resistance to shear under load, is of-
ten considered the single most important property of
any gear oil.
NORD Gear Designers have selected the most appro-
priate ISO viscosity grade of oil, for each type or class
of gear reducer. Gear oil viscosity is selected by assum-
ing typical ambient conditions, at rated speed and
load conditions.
Important Considerations:
• The correct viscosity selection helps provide proper
lubrication and assures that a minimum fi lm thick-
ness is maintained between interacting surfaces.
•
The degree to which viscosity changes with
temperature or the viscosity index, varies from oil
to oil, and depends upon the type of lubricant and
additive agents used.
• Selecting too low of a viscosity can result in mixed-
boundary (partial metal-tometal contact) or
boundary lubrication (full metal-to-metal contact)
conditions, increasing internal friction heat
build-up and wear.
• Selecting too high of a viscosity results in increased
churning and squeezing losses in the load zone
and excessive heat (especially when peripheral gear
speeds are high); Ultimately, this causes the oil
temperature to rise and the viscosity to go down,
decreasing the effectiveness of the lubricant.
Considering an Oil Viscosity Change
There are three primary reasons to consider a lubrica-
tion viscosity change as follows:
1. Low temperature gear oils should be selected so
that the pour point is at least 9°F (5°C) lower than the
expected minimum ambient temperature. In extreme
cases, consider a lower ISO Viscosity rating and test
the critical performance of the gear box under cold
start-up.
2. High temperature applications may require
an increase in the lubricants viscosity to as-
sure proper lubrication conditions in the criti-
cal load zones of the gear unit. NORD also rec-
ommends switching to synthetic oil if oil sump
temperatures exceed 176-185 °F (80-85 °C).
3. In cases of extreme load conditions, gear pairs and an-
tifriction bearings may be more susceptible to scuffi ng
wear. In these operating conditions, it may be benefi cial
to consider an increased lubrication viscosity and/or
lubrication with improved antiwear additive pack-
ages.
NORD recommends that the user consult with their
primary lubrication supplier when considering
changes in oil viscosity.
Maximum Oil Sump Temperature Limit
To prevent reducer overheating, the reducer’s maxi-
mum oil sump temperature limit must not be exceed-
ed for prolonged periods of operation (up to 3 hours
continuous operation, depending upon reducer size).
Oil Type Maximum Oil Temperature Limit
NORD AGMA 9005-D94
Mineral 80-85 °C (176-185 °F) 95 °C (203 °F)
Synthetic 105 °C (220 ° F) 107 ° C (225 ° F)