I'd like to get some of the members opinions on this topic. From experience do you prefer "lubed for life" or double sealed bearings over open or single shielded bearings. It has been our sites practice for years to use only totally sealed bearings in all of our motors and some of the other equpment (pumps, fans, and spindles). Bear in mind this is a relatively clean plant, synthetic fiber manufacturer, so contamination from outside source is not an issue.
Thanks in advance,

Here is one article by Heinz Bloch
http://www.machinerylubrication.com/article_detail.asp?...okgroup=Lubrication2

An excerpt - ‘A 1989 guideline issued by a major bearing manufacturer gives a DN value of 108,000 as the economic, although not technically required, limit for lifetime-lubrication. “

An article by Jerry Honnicut (TVA) and Wayne Johnson (EPRI):

http://www.machinerylubrication.com/article_detail.asp?...okgroup=Lubrication2

At our site we have a mixture. We took what we got from the manufacturers during construction 20 years ago. We have found we had to replace double-shielded bearings after 10-20 years of operation in twp families of motors 3600 rpm TEFC motors 75 hp and 100hp. On tese two families of machines, the inboard endbell runs hot 140F – 180F due to high machine load and the vent pattern of TEFC motors.

For smaller and slower machines we have not had many problems that I know of with double-shielded bearings.

The lfl brg will not last as long as a replenishment system brg. It doesn't have the lube capacity nor does it get replenished every so often.

If you have no lube program or poor practice and introduce contaminates and/or poor maintenance in general a lfl may prove cost justifible or if a remote location it may be justifible.

You may want to consider the gas generating replenishment lubricators as they do work and give an exact quantity per a given time interval. They are a little pricey but very well may be worth it.

Roy,
My plant has been in operation for 30 years. I've been here for the last 15 years doing Predictive work. What I have seen is that open greasable bearings (regularly lubed) seem to have a pretty much infinite life in machines with no major problems like unbalance or misalignment. Double sheilded and sealed bearings have a definitive life in the same type machines. I've looked at a lot of double shielded bearings removed from motors after 15 years or more of service and the grease is typically dry and flaky (obviously at the end of life). We used to lubricate double sheilded bearings just like open ones but have found dry grease in the bearings just the same. These findings have caused us to differentiate rebuild intervals on motors depending on the type of bearings installed. We no longer have a periodic bearing replacement interval on machines with greasable bearings, instead relying solely on PdM. Motors with non-greasable bearings have a periodic bearing replacement interval defined and in many cases, we change them over to open bearings when the replacement interval is reached. Here are some "off the cuff" observations about non-greasable bearing life based on my experience with a large number of motors both small and large.
We typically see a average bearing lifes of 10 to 12 years on 3600 rpm motors with non-greasable bearings. A few failures start to occur after 6 to 7 years.
Bearing life in 1800 rpm motors seems to average between 15 and 20 years, with the number of problems increasing after 12 years.
I've got lots of 30 year old 3600 and 1800 rpm motors with greasable bearings that have never had a problem and worry more about the life of the windings in these machines than the bearings.

I do prefer greasable bearings than sealed for life. When you detect a need of lubrication you can act on it instead monitoring it to plan a replacement before failure. A goal of our job is to maximise operating time between repair and with greasable bearings I find that I'm more in control.
J-Marc