Spindle Knowledge

Grease distribution run

With bearings lubricated with grease, correct commissioning primarily determines the durability, service life and the performance of the spindle bearing. An optimum grease distribution run will optimise the characteristic value of the rotational speed, reduce the operating temperature in the bearing, achieve a long service life and ensure high operational reliability. During the grease distribution run, the grease is displaced from the running track and the base oil which is continuously added can build up the separating oil film between the balls and the running tracks required for lubrication.
The grease distribution run can be split into short intervals and continuous operation.  Initially, the system is run at various speeds for ½ – 1 min. and then allowed to stand still for approx. 2 min. This is repeated approx. 5 times for each selected speed. During the standstill period, there is a settling of the temperature in the bearing and this prevents damaging increases of the pre-tensioning within the bearing.   Speed intervals
can be 0.33× nmax , 0.66 × nmax  and 1× nmax  or 0.5 × nmax , 0.75× nmax  and 1× nmax  .
These are stipulated by the spindle manufacturer or by the spindle bearing manufacturer. Another important aspect of the grease distribution run is the continuous monitoring of the bearing temperature and the bearing noise, so that the grease distribution run can be interrupted in the event of extreme noise development or a housing temperature in excess of 60°C. The grease distribution run is influenced by both the viscosity and the quantity of the grease being used. Selection of the grease depends on the operating speed and the bearing's reference diameter:
n × dm= (n × (D + d)/2) (mm/min)

n  Operating speed of the bearing [rpm]
D  External diameter of the bearing [mm]
d  Bore diameter of the bearing [mm]

For the standard greases, the n ×dm  values are given in the table and this facilitates the selection of the optimum grease for lubricating the spindle bearing. A grease distribution run is not necessary for main spindles with oil-air lubrication. However, when commissioning the machine it should be noted that there could be a dead period due to the length of the line between the lubrication unit and the main spindle, before the lubricant reaches the bearing. For this reason, it is recommended to let the lubricating unit run for a time before switching on the main spindle. [FAG], [GMN]