Maintenance Tip:
Bearing Lubrication in Roller Hearth Furnaces
Once bearings have been properly installed and the equipment is in good condition, the most important factor regarding extended life of the bearing is lubrication. The first routine lubrication should be applied before the equipment is started for the first time.
Grease Furnace Rolls no more than once a month
Roller bearings used on furnace rolls in atmosphere type furnaces should be lubricated with one or two pumps of a grease gun NO MORE THAN ONCE A MONTH. This provides enough lubrication without damage to the atmosphere seal.
If uncertain about the amount of grease in a bearing, or if a question arises as to whether the lubrication schedule is adequate, a safe rule is as follows. With the shaft turning at normal RPM, apply grease slowly (two pumps of the grease gun, wait 30 seconds, then one more pump, etc.) until a thin sliver of grease appears at the bearing shaft seals. This bead of grease at the seals accomplishes several things. It helps prevent the entry of dirt and moisture and indicates that the bearing contains sufficient grease to lubricate the rollers. The condition of the grease (relatively clean or contaminated) indicates whether or not the bearing needs more lubrication to purge out contaminants, etc.
Applying lubricant
Applying lubricant too fast, particularly on slow turning shafts, or lubricating when bearings are stationary, can fill the bearing with grease, causing severe churning and overheating of the grease. It may also damage the atmosphere seal, resulting in atmosphere contamination. Overheating the grease may result in bearing failure. If grease has been overheated for any reason, it should be purged from the bearing with new grease. It is important to use a high quality lubricant which is free of impurities.
Selecting the correct lubricant
The selection of the correct lubricant and maintaining the correct frequency of lubrication cannot be over-stressed. Grease in cartridges is recommended because it insures clean grease. Dirt is the principal cause of bearing failure.
Some lubricants are not compatible with each other, and if mixed will develop an abrasive quality or harden into a solid. Compatibility is always a concern when lubricants are mixed. APPROVED GREASES ARE EXXON UNIREX N-2, TEXACO PREMIUM RB, AND MOBILITH 22. Although other greases may have identical specifications, only these greases have been lab and field tested and are known to work for this application.
Corrosion damage may occur at any time in the life of a bearing
Corrosion damage may occur at any time in the life of a bearing - even before it is placed in service. Corrosion marks or pitting on raceways causes stress concentrations in service and premature fatigue. Changing temperatures can cause free air space within bearings or lubricant containers to breathe moisture-laden air. Lubricant containers and replacement bearings should be stored in controlled temperature and low humidity areas.
The cleanliness of the bearing surroundings is an important factor to consider when developing a lubrication schedule. Re-lubrication, when properly performed, will extend the life of the bearings by helping to "wash out" or "push out" any contamination which may be inside the seal area of the bearings. Examine the color and consistency of the used lubricant, as compared with a fresh sample, to establish the correct lubrication interval.
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