Adjustments of relubrication intervals due to operating conditions and bearing types

Operating temperature
To account for the accelerated ageing of grease with increasing temperature, SKF recommends halving the obtained intervals (diagram 1) for every 15 °C (27 °F) increase in operating temperature above 70 °C (160 °F). The high temperature performance limit HTPL for the grease (diagram 2) should not be exceeded.

The relubrication interval tf may be extended at temperatures below 70 °C (160 °F) if the temperature is not close to the lower temperature performance limit LTPL (diagram 2). SKF does not recommend extending the relubrication interval tf by more than a factor of two.

Do not extend the obtained tf values (diagram 1) for full complement bearings or thrust roller bearings. Moreover, it is not advisable to use relubrication intervals in excess of 30 000 hours.
Vertical shafts
For bearings on vertical shafts, the intervals obtained from diagram 1 should be halved.

The use of an effective seal, shield or baffle plate is a prerequisite to prevent grease leaking from the bearing arrangement.
Moderate vibration does not have a negative effect on grease life. However, high vibration and shock levels, such as those in vibrating screen applications, cause the grease to churn. In these cases, the relubrication interval should be reduced. If, during operation, the grease becomes too soft, use a more mechanically stable grease, e.g. SKF LGHB 2 or grease with higher stiffness up to NLGI 3.
In applications where the ingress of solid contaminants is an issue, more frequent relubrication than indicated by the relubrication interval is necessary. Relubrication reduces the level of contamination while reducing the damaging effects caused by overrolling the particles. Liquid contaminants such as water and/or process fluids also require a reduced relubrication interval. In case of severe contamination, continuous relubrication should be considered.
Very slow speeds
Selecting the proper grease and grease fill is very important for slow speed applications. Bearings that operate at very slow speeds under light loads require a low consistency grease. Bearings that operate at slow speeds under heavy loads should be lubricated with a grease that has a high viscosity base oil containing EP additives.

Solid additives such as graphite and molybdenum disulfide (MoS2) can be considered for a speed factor A < 20 000 mm/min.
High speeds
Relubrication intervals for bearings used at speeds above the recommended speed factor A (table 1) should only be applied when using special greases or modified bearing executions such as hybrid bearings. In these cases, continuous relubrication techniques such as circulating oil or the oil-air method are more effective than grease.
Heavy and very heavy bearing loads
For bearings operating at a speed factor A > 20 000 mm/min and subjected to a load ratio C/P < 4, the relubrication interval is reduced to the point that SKF recommends continuous grease relubrication or the oil bath lubrication method.

In applications where the speed factor A < 20 000 mm/min and the load ratio C/P = 1–2, refer to Very slow speeds.

For heavy loads and high speeds, SKF generally recommends a circulating oil system with auxiliary cooling.
Very light bearing loads
In many cases, the relubrication interval can be extended if the loads are light, i.e. C/P = 30 to 50. To obtain satisfactory operation, the bearings should be subjected to the minimum load as stated in the relevant product chapters.
Static misalignment, within the permissible limits, does not adversely affect grease life in spherical roller bearings, self-aligning ball bearings or CARB toroidal roller bearings.
Large bearings
Large roller bearings, d > 300 mm, used in process machinery, require a proactive approach. For these critical applications, SKF recommends strict adherence to the relubrication quantities but with shorter initial relubrication intervals.

Prior to relubrication, check the used grease for both solid and liquid contaminants. Also, check the sealing system completely, looking for wear, damage and leaks. If, over time, the condition of the grease and associated components is found to be satisfactory, the relubrication interval can be increased gradually.

SKF recommends a similar procedure for spherical roller thrust bearings, prototype machines and upgrades of high-density power equipment or wherever application experience is limited.
Cylindrical roller bearings
The relubrication intervals (diagram 1) are valid for cylindrical roller bearings fitted with:
  • a glass fibre reinforced PA66 cage, roller centred, designation suffix P 
  • a machined brass cage, roller centred, designation suffix M

The obtained relubrication intervals (diagram 1) should be halved and a grease with good oil bleeding properties should be applied to cylindrical roller bearings with:
  • a stamped steel cage, roller centred, no designation suffix or suffix J 
  • a machined brass cage, inner or outer ring centred, designation suffixes MA, MB, MH, ML or MP
  • a sheet steel cage, inner or outer ring centred, designation suffixes JA or JB
If, during testing, the determined value for the relubrication interval tf is too short for a particular application, SKF recommends the following:
  • Check the bearing operating temperature.
  • Check whether the grease contains solid or liquid contaminants.
  • Check the operating conditions, e.g. load or misalignment.
  • Check whether a more suitable grease is necessary.
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