Light Slewing Bearing Maintenance
Since the bearing is so critical, careful maintenance is necessary. More than 96% of slewing ring bearing failures are due to surface-originated lubrication problems, contamination, overloading, and improper installation and mounting fits. These surface failures occur much earlier than classical fatigue failures and are less predictable.
Inadequate lubrication is the most common cause of premature light bearing failures. In light slewing ring bearings, a heavy-duty, extreme pressure grease is required. When lubrication is inadequate, surface damage in the form of roughening or waviness occurs. Later, fine cracks develop, followed by flaking. Failures due to contamination are fairly common. Dirt or other debris within the lubrication system act as an abrasive and accelerate the wear. Usually the bearing raceways are scratched or indented, again leading to fine cracking and, ultimately, spalling.
So a suitable lubrication is essential for the longevity of the raceways and gears. The operating conditions such as loads, temperatures, speeds, vibrations, etc... determine the choice of lubricant.
Unless otherwise specified, the slewing rings are delivered greased.
Standard grease : Mobilux EP2 or equivalent.
Main properties required for multipurpose grease :
As being a significant component of the bearing,
grease will improve the bearing capabilities and longevity.
Recommendations for bearing lubricant :
• Lithium-base soap.
• Minimum viscosity of the base : 150 mm 2 /sec.
• Grade NLGI 2.
• Anti-wear and extreme pressure additives.
• Service temperature :
– 40 ° C to + 120 ° C
• 4 ball test : weld load : ASTM D 2596 (NT24) > 300
• Maximum NDM :
for balls = 60 000
for rollers = 30 000
Raceway and gear.
The greasing frequency varies according to utilization and environment. We recommend regreasing every 150 hours in normal usage. This frequency is to be reduced to 50 hours when the conditions of application are severe or if the environment is dusty or wet.
Greasing is required, before and after a long idle period.
Regrease every 6 months, while rotating, during prolonged idle periods.
The grease quantity is defined by the Engineering Department whenever a detailed bearing calculation is provided.
Approximate practical formula to determine the minimum necessary quantity "Q" in cm 3 :
Q = 0,005/3 x D x H with :
D = raceway mean Ø of the bearing in mm.
H = overall height of the ring in mm.
In all cases, a light extrusion of new grease must appear at the protection seal lips.