Did you know that statistically 80% of motor failures are due to over greasing?
What is the correct amount and procedure for greasing?
Whether hand packed or applied by grease gun, the primary recommendation for rolling contact bearings is NLGI 2 or 3 grease. NLGI 0 or 1 is used where temperatures are low or if dispensed through a centralized system. Channeling soap greases are generally the first choice for high speed rolling element bearings. Complex soap greases are recommended for high temperatures.
The procedure for changing out grease in a bearing is:
1. Purge out old grease by adding new grease until old grease appears at vent.
2. Rotate bearing and add grease until new grease appears.
3. Rotate bearing and vent grease for about 20 min. to prevent over greasing.
There are several methods for determining the correct amount of grease for roller bearings. One method for calculating the amount of grease to be used in rolling contact bearings is to use the formula.
G = 0.005 DB (G = Grease quantity (grams), D = Bearing outside diameter (mm), B = Bearing width (mm))
G = 0.114 DB (G = Grease quantity (ounces), D = Bearing outside diameter (inches), B = Bearing width (inches))
Ø Fill the available space in the bearing and housing between one third and two thirds full, depending upon the speed of the bearing. The higher the speed, the less grease is necessary.
Ø Never fill bearing housings completely full of grease. When a bearing rotates, it is lubricated by a thin film of grease. Excess grease is moved into the cavities of the bearing and housing. If these cavities are already filled with grease, the excess has nowhere to go and remains in the bearing where it is "churned”. This causes overheating so the grease liquefies and can run out, starving the bearing of lubricant.
Ø When a properly packed bearing starts up, there will be an initial rise in the temperature while the grease disperses throughout the bearing and housing, before falling off to a steady operating temperature. If the temperature does not lower then there is too much grease in the bearing, or there is a problem with the bearing fit.
Greasing electric motors
Ø The bearings are the most critical lubrication points on electric motors. They are typically lubricated with high-quality NLG1 grade 2 non-EP grease that is made with a polyurea or lithium complex thickener. These motors may be lubricated for life. Some electric motors bearing run in a bath of oil, typically with a viscosity of ISO 68 when running at1800 rpm and ISO 32 at 3600 rpm.