oil fed bearings, pre pack with grease? 2

[simisteven]

We regularly have failure with atomiser bearings ( thrust type ball, back to back). The shaft spins at 7000 rpm and the two sets of bearings are gravity fed with hydraulic oil Engen TQH 20/32 @ a rate of 20 millilitre per hour.
The shaft is vertically mounted so the top bearings gets oil first.
The bearings are mounted on the shaft which is then wrapped and stored.
It is suspect that sometimes the bottom bearings fail soon after start up from starvation of lubrication eg if the fitter forgets to manually dose the bearings with oil.
My question is whether it is feasible to pack the bearings with grease for storage. Then install the shaft and run with oil?(without first removing the grease)
Would the grease melt away and the oil lube subsequently take over?

 

[caoimhin1]

What size of bearing are you using? Limiting speed for grease lubricated bearings is less than oil lubricated bearings, so check that 7000 rpm is ok for grease lubrication with the bearings you are using. If you do decide to grease, don't "pack" them full. 15% to 20% of the bearing internal free volume is sufficient for high speed bearings, more than this will lead to grease churning and excessive heat. Check compatability of the oil with the base oil of the grease.

 

[simisteven]

many thanks for that info caoimhin1

 

[Fugeguy]

caoimhin1's recommendations are dead on.

At those speeds if you pack them (>50% fill) in grease you will have problems.

This point will need to be emphasized to the maintenance personnel.

Most likely if they put any small amount of grease on the bearing it will run until the oil feed starts. Most of the time the tendency will be to over-grease the bearings and you will end up swapping one failure for another.