Bearing Greasing is the most common form of lubrication as it is simple and easy to use.

When operation conditions such as speed, temperature and cleanliness are within the limits indicated by the grease lubricant vendor, bearings require no special maintenance, nor subsequent topping up. This can therefore be call long-life lubrication.

Bearing Grease type selection is critical for safe bearing operation, depending on:

  • operating temperature
  • life
  • protection
  • noise level

A wide range of quality synthetic grease lubricants is available commercially. Products satisfying the standards listed in the table below are frequently used.

Speed, load and operating temperature are basic parameters for grease selection.

Bearings operating at high temperatures, such as in electrospindles, must be lubricated with long life grease with a base oil of adequate viscosity and high wear resistance.

[twocol_one]APPLICATION[/twocol_one] [twocol_one_last]GREASE[/twocol_one_last]

Speed (ndm)  Load  Viscosity  NLGI Consistency  Thickener
 Up to 600,000  Light/Medium  3,000  2  Lithium
 Up to 600,000  High  4,000  2  Calcium/Lithium
 Up to 900,000  Medium  3,000/4,000  2  Calcium/Barium/Lithium
 Up to 900,000  Light  3.500/4.500  2  Calcium/Barium/Lithium

 

Grease Life

The effectiveness of a grease reduces in time due to operating conditions such as temperature, dynamic stress and contamination and to its chemical  and physical characteristics.

These parameters are hard to estimate, so grease life hours ÒLgÓ are calculated prevalently on statistical data.

Figure 2 gives the necessary elements for assessing the life of quality synthetic greases in optimum operating conditions. The upper part of the curve refers to operation in moderate temperature conditions, such as belt driven spindles; the lower part refers to applications where the presence of another heat source, such as an electric motor, increases bearing temperature markedly, with negative effects on the lubricant.

 

Running In

Grease lubricated bearing require an initial running-in period to ensure the correct lubricant distribution and to avoid bearing overheating at the starting operation.

The most common form of running-in entails gradually reaching maximum speed and achieving stable temperatures at each step. Another procedure is an intensive sequence of run and stop cycles according to a pre-set program.  The latter reduces running-in time but requires constant observation and is only recommended for automated running-in equipment. This is not advisable for bearings which have to operate at a particularly high speed.

Grease Quantities

The amount of grease to introduced into the bearing depends on operation speed. The amount is calculated by multiplying factor K (function of maximum rotation speed, expressed ndm ∆ Figure 3) by the Òreference quantityÓ showing in the diagram (bore and bearing series function; Figure 4)

In the case of small bearings where the grease quantities are very small it is advised that before greasing the bearings are immersed in a grease solution (containing 3-5% grease) then removed and allowed to drain (and the solvent to evaporate) before applying the grease. This ensures that all the bearing surfaces are covered with a thin layer of the lubricant.

 

 

Factory Greased Bearings

SNFA bearings are very often supplied with the type and amount of grease as specified by the customer. This solution offers operating and economic advantages for the user, as the bearing is greased during the manufacturing route with greater control over cleanliness, quantity and distribution.