Aspects in lubricating bearings

for engines, now turns its attention to lubrication of bearings.
Lubrication is an integral part of a motor vehicle especially where moving parts are concerned.
Our intention is to offer tit bits on the best ways to handle lubrication. We do not offer this as a substitute but encourage you to refer to your manual or the equipment standard procedure which is the guiding principle.
Bearings could be classified into two types: roller/rolling bearings which requires rolling friction and at times sliding friction as per the particular type of a bearing. The other type could be called a plain bearing, which requires only sliding friction. Roller bearings require both the rolling and sliding friction whereas the plain requires sliding friction only.
The lubrication of these bearings requires special attention to the lubricant recommended by the manufacturer as it could either be oil or grease.
Notwithstanding that, we believe that oil is a better lubricant than grease because oil has an advantage in reducing heat and moreso when seals are secured correctly. This usually occurs when the operating temperatures or surface speed of the ball or the rolling is high. However, it might be a disadvantage to use oil in cases of low temperature.
This is, however, notwithstanding that a large number of bearings are lubricated by grease.
Oil-lubricated units are found in machine tools and gearboxes where the oil is contained with little or no room for seepage. It is important to be able to match the operating temperatures, means of lubrication and determination on the use of the bearings for instance light, medium or heavy type, the amount of radial and axial load and whether heat is transferred from other parts.
At this stage it is hard to determine preciously what to do. As a tit bit, mineral oils of good quality should be used due to their resistance to deterioration in a service as they have a good tendency to deal with acids which might damage the highly polished working surfaces of the bearing.
Refined minerals are good on temperatures of 120-degree celsius but for those exceeding 80 degrees Celsius, these oils should contain oxidation inhibitors. Therefore, the selection of viscosity grades will depend on the relationship between operating temperature and speed factor.
In case of plain bearings the type of lubrication is predetermined by the manufacture of the equipment. In most instances grease is applied to these bearings via a grease nipple hence the need for a grease gun or oil clip and usually the manufacturer indicates the type of lubricant to be used.
In the case that choice is left to the user consider the following scenarios.
Grease is not good for bearings operating at very high speeds as in such cases heat is likely to be retained in the bearing resulting in longer lubrication intervals as compared to oil. Again grease is likely to accumulate or affect other parts of the equipment. It might be difficult for grease to start at low temperatures in comparison with oil, however, this is not a problem here in Zimbabwe as temperatures are evenly spread during the year.
Another look at oil lubricated plan bearings
A fluid film of oil is built by virtue of viscosity as a result of rotation of the journal in the bearing, purely as the journal rotates in a plan bearing as it is receiving oil in adequate quantity. Under normal operating condition oil film will prevent metallic contact between the journal and the bearing. Friction may be reduced by using oils with low viscosity.
However, speed and load, there is a lower limit of viscosity below which a fluid is not maintained and metal to metal contact is certain to occur. There should therefore be a safe margin during start up and run down.
Do not overlook the effects of operating temperatures hence at all times there should always be adequate oils. There should be equilibrium between the oil which is supplied to the bearing and which escapes. In general, the greater the load the lower the speed and the larger the clearance the higher viscosity is required. Again, conversely, light loads high speeds and small clearance requires oils of relevantly low viscosity. Correct alignment is very important in preventing overheating.
Lubrication by grease
We believe that both plain and roller bearings operate under a wide range of operating conditions and we recommend that you stick to the manufacturer’s recommendations. The type of grease for a plain bearing is affected by the method of application and clearance of the bearing as opposed to speed. Generally, use EP 1 or 2 for light vehicles and EP 3 for heavy-duty vehicles.
Extra care must be taken when choosing grease as there are some equipment which have a tendency of generating heat such that the grease will melt and fail to lubricate. Some have a melting point of 100 degrees Celsius. Lime base grease are usually smooth and buttery in texture and is water resistance. Soda-based grease is relatively smooth though fibrous in texture but has a high melting point than lime and is good for high speed, high temperature and application but has little resistance to water so should not be used where water or moisture is experienced.
Combination of soda-based grease and lime-based grease was motivated by the advantages of one type of grease over another that resulted in the creation of the two. Lithium-based grease has high temperature properties of the soda-base grease retaining the smoothness and stability of the lime base. It is highly water-resistant and to a certain extent suitable for low temperature operation a property of the aluminum base grease which resist hardening under cold conditions.
Key elements in grease are the melting point or drop point (the temperature at which grease starts to melt). The penetration measures the consistency or stiffness of grease by determining the depth to which a needle penetrates the grease under standard test conditions. In that light the higher the figure the softer it is, e.g. multi-purpose grease 3 is soft that multi-purpose grease 2.
l Let’s meet again next week for more titbits. Visit our stand at the Chitungwiza Expo today and tomorrow and let’s share our experiences. Contact us on above number or through G.Mbeya 0774 215 505. PROUDLY ZIMBABWEAN.