LUBRICATION & OIL FOR BEARINGS

LUBRICATION Lubrication of the bearing has got such a great importance, as raw material from which from which they are made. Anticipated life of the bearing largely depends on the quality and quantity of the lubricant and its method of application. Rare lubrication and improper lubrication of a bearing result in the reduced bearing life and its premature failure. It is therefore, very essential to make a proper choice of lubricant. The advantages derived from the correct choice of lubricant are: 1. It protects the bearing from corrosion. 2. It protects the bearing to a certain extent, from the entrance of foreign matter in to the bearing. 3. It minimizes the friction between the races and rolling elements. 4. It reduces the friction arising due to elastic deformation of rolling elements when under load. 5. It facilities the smooth running of bearing by minimizing noise. 6. It creates the lubricant film on the raceway of the bearing and thereby protects the raceway from blows of the rolling elements. 7. It dissipates the heat from the bearing and also helps distribute uniformly the frictional heat throughout bearing, which is generated during operation. 8. Power losses can be saved, as internal friction can be prevented. 9. It also helps the bearing to attain the required speed. 10. It helps to attain the anticipated life of the bearing. There are TWO types of lubricants used for bearing lubrication. OIL and GREASE 1.7.1 OIL Oil lubrication is considered to be the most efficient than Grease, provided proper sealing methods are employed to prevent the leakage. Only highly refined OIL should be used as bearing lubricant. OIL is preferred when… 1. Bearing speed is very high. 2. Operating temperature is consistently high. 3. Sealing methods can be easily employed. 4. Bearing application demands that Grease is not suitable. Then during operational condition, most of the lubricant will be forced out of the bearing which can never come back into the bearing, and such lubricant is not suitable for reuse. 1.7.2 GREASE For many applications, grease is considered to be more convenient than oil. Grease used as lubricant should be of smooth texture and non-fibrous. It must be free from chemically or mechanically active ingredients. For bearing lubricants, general-purpose sodium-soap petroleum grease is preferred. It is suitable for variety of speed and temperature conditions and has rust preventive character under humid conditions. For specific working conditions and operational requirements special type of Greases are used which are… 1. Lithium soap petroleum oil grease. 2. Lithium soap di-ester grease. 3. Lithium soap silicon grease. 4. Special quality grease to withstand temperature conditions from minus 200 to 3000 F. Generally Grease lubrication is preferred when… 1. Temperature is not excessive (Not over 200 F). 2. Speeds are moderate. 3. Extra protection from Dirt, Fumes, and other foreign matter is required. 4. Long time operations without maintenance are the requirement. 1.7.3 SELECTION OF LUBRICANT 1. For small size bearing operating at high speed, low viscosity oil is used. 2. Large bearings carrying heavy loads, lubricant with higher viscosity and additional adhesive properties may be used. 3. For any application, the lubricant must have sufficient lubricating capacity at prevailing temperature. 4. It must from a load sustaining lubricating film for prevailing load conditions. 5. It must have the capacity to absorb water to a certain extent, without affecting the lubricating capacity, wherever the application demands. Thus one should ascertain the correct type of lubricant, which is suitable for operating conditions. When the lubricant quantity is inadequate, it results in the cage failure, and inadequate lubrication may heat up cage, may breakdown the ball pocket, and progressively break the whole cage. Even non-metallic cage also becomes brittle, dry and crack apart under heat and stress. Due to break down of the lubricating film on raceway and rolling element surfaces, they may also develop scoring marks, gradually resulting in bearing failure. This condition may also result in the deformation of parts, and when the bearing with deformed parts rotate under load, it will have sliding motion instead of rolling motion, and it ends up in bearing failure. Normally a medium size bearing running at the speed of 2000-6000 RPM can be sufficient lubricated with only few drops of oil per hour.