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Hello all,
What would be the ideal greasing frequency for motor (90kW-1500rpm) and fan (2 bearing blocks-overhung - belt driven) bearings and how much grease to add? These fans are constantly running, year in, year out. Is it better to open the bearing blocks and replace old grease with new? Or is it beter to use a greasing-pump?
Is there a type of grease for motor and fan bearings that you would recommend to all?
Thanks!
Uncle

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quote:
What would be the ideal greasing frequency for motor (90kW-1500rpm) and fan (2 bearing blocks-overhung - belt driven) bearings and how much grease to add?

Here is one article which describes a relatively simple set of rules developed by EPRI that apply to motor bearing regreasing intervals and quantities, and I think it is reasonable for fans also if they are ball bearings:
http://www.machinerylubricatio...il.asp?articleid=749

For your situation >100hp, 1500-1800rpm, belt drive, assuming ambient temperature <140F, that article table will tell you to add grease every 12-18 months for the motor. Quantity of grease to be added depends on shaft size which we could figure out if you tell us the bearing type.

Of course each of the bearing manufacturers has recommendations that will differ from above. Generally the bearing manufacturers will recommend adding smaller quantities of grease at more frequent intervals than the EPRI approach described above.

The equipment OEM may also have recommendations for each individual each piece of equipment which in an ideal world trumps either of the above, but that is not always easy or practical to keep track of all of those recommendations for different OEM's and different equipment
quote:
Is it better to open the bearing blocks and replace old grease with new? Or is it beter to use a greasing-pump?


Most people just add grease periodically without ever opening the cavity until they see some evidence the cavity is full. I think this works in most cases but you get in trouble faster with high D*N bearing machines as the cavity gets full.

The bearing manufacturers recommend also periodically changing the grease (opening the cavity, removing old grease, adding new to a level somewhere around half full). For example SKF recommends I think no more than 3 intervals of addin grease before the grease is repacked. But not many people do this. Two reasons we don't do it: 1 - it is more work; 2 - I think there is serious risk of contamination during this process which could do more harm then good.

quote:
Is there a type of grease for motor and fan bearings that you would recommend to all?

I think Mobil Polyrex EM is the most universally used general purpose motor grease. Of course there are always possible special application requirements that may apply here and there, but if you're looking to standardize on one good one for the majority of your motors, that's a good one to start with.
RM
quote:
Originally posted by Uncle Repair:
Hello all,
What would be the ideal greasing frequency for motor (90kW-1500rpm) and fan (2 bearing blocks-overhung - belt driven) bearings and how much grease to add? These fans are constantly running, year in, year out. Is it better to open the bearing blocks and replace old grease with new? Or is it beter to use a greasing-pump?
Is there a type of grease for motor and fan bearings that you would recommend to all?
Thanks!
Uncle

SKF has the final words regarding relubrication interval. Pl. follow the link
http://www.skf.com/portal/skf/...g=en&maincatalogue=1
Regards
Irshad
RM
That's a pretty good link. It goes through almost all the factors which might affect greasing interval in one place. SKF's recommendations seem to continuously evolve (perhaps other OEM's as well).

Now back to the subject of repacking. As I mentioned SKF used to recommend hand repacking every three regreasing intervals (it's in the SKF Bearing Installation and Maintenance Handbook". Now their recommendation has evolved to a little more reasonable approach, but still requires periodic repack:
http://www.skf.com/portal/skf/...g=en&newlink=1_0_114

quote:
The complete grease fill should be replaced when the free space in the housing can no longer accommodate additional grease, e.g. approximately above 75% of the housing free volume. When relubricating from the side and starting with 40% initial fill of the housing, the complete grease fill should be replaced after approximately five replenishments

I know we sure don't do that. If I was inclined to do it, I would do it only for high D*N bearings. (like 6316 at 3600rpm). Do you guys do it?

Separate subject - perhaps worth to mention in some applications it makes sense to use double-sealed bearings and forget about the lubrication. For example we have an outdoor crane application 6310 bearing at 1800rpm or less which is a no-brainer for shielded bearings. It is intermittent use and low D*N so grease will last a long time. Sealing is an added plus for protecting the bearing in outdoor environment.
RM
For the fan, the re-greasing frequency may be in the order of weeks for spherical roller bearings (depending on the bearing type, size, operating conditions....)

I agree with Pete regarding sealed for life bearings. It is definitely worth considering.

Heinz Bloch has written about that. I think he recommends considering sealed for life bearing when D*N<50000
http://maintenanceforums.com/e...561041312#2561041312


SKF also has info on the matter.

Regards,

Elias
RM

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