Generally speaking, we are using three types of bearings:
1. Ball bearing with set screw lock
2. Spherical roller bearings with set screw lock
3. Spherical roller bearings with adapter lock/taper lock feature to attach them to the shaft
These are self-aligning bearings and should present no alignment problems with one exception: i.e., on Sealmaster bearings there is a pin beneath the grease fitting which prevents the bearings outer race from rotating. Should this pin jam, the bearing loses its alignment feature.
Common failure causes are
(1) set screws loosening and shaft turning within the bearing, and
(2) crowned bearing supports. Loosen one bolt and measure clearance between pillow block and support. Add shim to compensate.
Spherical Roller Bearings With Set Screw Lock
The self-aligning characteristic of these bearings are inherent in the spherical roller design. The closer that these bearings are to perfect alignment, the cooler they will operate.Common failure causes are the same as with ball bearings, mainly set screws loosening and crowned bearing supports.
Spherical Roller Bearings With Adapter Lock
Again, the self-aligning feature is inherent in the spherical design. Good alignment results in a cooler operating bearing. The faster the bearing operates the more critical this becomes. Common causes of failure are improper installation practice. Removing too much clearance from the bearing can result in preloading the bearing, resulting in premature failure; and removing not enough can result in the shaft rotating within the bearing. Properly tightened, this method of attaching a bearing to a shaft is second only to a press fit. Crowned bearing supports can also preload these bearings and should be checked by loosening one side of the bearing and checking for clearance.
The major cause of bearing failure is contamination of grease, insufficient grease, or incompatibility of grease. If a fan is to be stored for any length of time at the job site, the bearings immediately should be filled with grease while rotating the shaft and then the bearings should be regreased and rotated monthly. This will prevent moisture, which condenses within the bearing, from corroding the raceways. Most greases used on fan pillow blocks are lithium base. Use the greases shown on the bearing decal. Do not mix the bases without completely purging out the initial grease. Initially, follow the lubrication instruction on the side of the fan. The frequency of lubrication should be adjusted depending on the condition of the old grease being purged. This is the responsibility of the user.
If the grease is dirty, the lubrication frequency should be more often.
a. Noise — If a bearing is increasing in noise intensity and/or vibration, it will probably result in failure.
b. Temperature - If a bearing temperature begins to gradually rise, it will generally result in failure. A bearing can operate up to 200 degrees and operate satisfactorily if the temperature remains constant and the bearing receives adequate lubrication. Remember that a roller bearing under the same load and speed will be somewhat more noisy and run warmer than a ball bearing. This is normal.
Rough handling and/or dropping a fan can result in brinelling the bearing. This appears as a clicking noise at first, then gradually worsens until failure. When replacing a bearing, always align the bearings first, then bolt the pillow blocks to their support, rotate the shaft, fasten the bearings to it. If the bearing is fastened to the shaft first, tightening the pillow block bolts may bind the shaft and preload the bearings.
Read carefully before fan commissioning.
Check the oil level prior to the first commissioning. The oil fill level must be between the markings "min" and "max". If the fan is not put into operation immediately after delivery but at a later point of time, the corresponding instructions for storage and corrosion protection of radial fans must be observed. Oil has to be refilled to the maximum mark after a longer standstill period and within the prescribed maintenance intervals.
The fan shaft runs in two oil-lubricated anti-friction bearings in single bearing housings.
Depending on the design type, the sealing of the bearing is done by:
- re-greaseable labyrinth seal
- felt ring
- if necessary, additional shaft seal ring (V ring)
The bearings are designed for ambient temperatures from -5°C to +40°C. If the bearing unit is sound deadened with a noise protection cover or otherwise insulated, care must be taken that there is proper and permanent ventilation to prevent heat accumulation within the protection device.
Oil change - lubrication intervals.
The maximum oil change interval can be taken from the bearing name plate "maintenance of the bearings". Oil changes must only to be carried out when the fan is at standstill. Check the oil level regularly, at least once a month. During oil change, pay attention to cleanness and proper handling of the lubricants in view of environmental protection requirements.
Transport used oil and cleaning rags in assigned containers, take care for their proper disposal.
If mineral lubricating oil is used, change the oil every 5,000 operating hours.
The oil must be changed every 8,000 working hours but at least once per year, provided that the bearing temperature does not exceed 80°C and the ambient temperature does not exceed 40°C and also provided that the lubricating oil is not blended or mixed with other lubricating oils. If the named conditions, however, are not fulfilled, change the synthetic oil every 5,000 operating hours.
EVG Engicon Airtech Pvt. Ltd. is a forerunner in the industry of Centrifugal Fans, Centrifugal Blowers, Axial flow fans.