In order to achieve optimum performance from bearings, and prevent premature bearing failure, correct handling procedures and mounting methods using the proper tools is imperative. Bearings must be mounted correctly. Incorrect mounting will not only affect the bearing precision and life, but also affect the performance of the equipment where it is installed. The recommended procedure for the bearing installation is as follows:
- Preparing for mounting
- Inspecting the shaft & housing
- Unpacking (washing the bearing, when needed)
- Mounting the bearing
- Test running of the equipment
Preparing for mounting
When preparing for mounting, select an appropriate and clean work place to proceed. All of the necessary parts, tools, and equipment should be at hand before beginning the procedure.
Absolute cleanliness is essential at all times! Dirt and humidity are dangerous offenders, since even the smallest particles entering the bearing will damage the rolling surfaces.
Inspecting the shaft & housing
Inspect the shaft and housing to confirm that they are free of burrs, flashes or any other defects. Check to confirm that the shaft and housing meet specifications using properly selected tolerances in accordance with American Bearing Manufactures Association (AMBA) Standard 7, "Shaft and Housing Fits for Metric Ball and Roller Bearings." This includes dimensions, perpendicularity of the shoulder and fillet radii. Non-observance of proper shaft and housing conformity will impair bearing performance leading to premature bearing failure. The cause of such failures is not always easy to establish and much time can be lost looking for the cause of failure.
Check the shaft diameter at two positions (A and B) in four planes.
Record these measurements for future reference.
Check the housing bore diameter at two positions (A and B) in four planes.
Record these measurements for future reference.
Unpacking (washing the bearing, when needed)
Unpack the bearing just before mounting.
Handling with bare hands may cause rust, it is advised that you use a clean pair of vinyl gloves. Dirty gloves are a possible source of dust and dirt which may enter the bearing and cause future problems. Normally a bearing need not be washed after unpacking as the anti-rust preservative coating is compatible with most lubricants. However, high speed and high precision bearings which are used for special applications or when the grease is incompatible with the preservative, the bearing may have to be washed to remove the rust prevention fluid.
When cleaning the bearing it is necessary to use a fresh kerosene, free of impurities such as dust and dirt. Wash the bearing with a filter shower. When a shower is not available use a net to dip the bearing in kerosene.
The cleaning process should be divided into rough cleaning and final cleaning. A separate kerosene container should be used for each process. The bearings should then be carefully dried. After cleaning immediately cover the bearings preferably with plastic.
Mounting the bearing - Methods of Mounting
Press method :
This is the most common method to mount a bearing and can be used on bearings up to a maximum bore diameter of 80 mm. When mounting with an interference between the shaft and inner ring,use a mounting dolly according to the size of the inner ring.
It is recommended that a thin film of gear oil should be applied to the shaft.
When force is to be applied on the rolling bearing for mounting, it must be applied in a straight line and evenly. Make sure that bearing is centered correctly.
When a press is not available, hammer in the bearing, using only a dead blow hammer and a mounting dolly to minimize the shock to the bearing and evenly distribute the mounting forces.
The bearing should not be hammered directly and pressure should be applied only to the inner ring.
When you are mounting the inner and outer rings at same time, use a metal buffer and apply a force simultaneously on both rings.
The Thermal expansion method:
If the interference between the inner ring and shaft is large,a thermal expansion method is recommended.
This method of mounting is simple if a heat tank or induction heater is available.
Absolutely never heat a bearing using an open flame!
- Reduce Friction
- Reduce Wear
- Rust Prevention
- Inhibit Corrosion
- Protection Against Contamination
Composition of Grease
Advantages Convenience: factory sealed and greased bearings require no maintenance. Cost effective: A sealed & greased bearing reduces the number of parts in an application. Grease is less apt to leak compared to oil. Grease acts as a seal preventing the entry of contaminants.
- NACHI standard grease fill for sealed & shielded bearing is 20 ~ 30 %.
- Too much grease can cause excess friction, thereby overheating the bearing and causing failure.
- Only a small amount of grease is required to lubricate a bearing in motion.
- When a bearing is in motion, most of the grease is pushed to the side (channeling) leaving a thin film of oil between the raceways and rolling elements.
- When using grease with open bearings, pack the bearing as follows: