Hi All, Can anyone tell me the r

[AB85]

Hi All,

Can anyone tell me the reason for having to rotate shafts of motors while they are sitting idle. (i.e. newly installed shafts that are waiting to be hooked up) I know its to prevent the shaft from seizing up, but are there any other reasons.

Thanks

 

[Scipio]

It also prevents bearing damage in larger machinery with heavy shafts. It's not just required for motors, any type of heavy rotating equipment should have periodic shaft rotations while in long term storage or standby condition.

Ball and roller bearings can suffer brinnelling at the contact point, since a single point on one or two ball bearings could be supporting the majority of the weight.

This is the reason you rarely want rotate in multiples of 360°. Usually you'll want to rotate one and a quarter or one and a half full turns. With sleeve type bearings, I don't think it's as critical, but it will help ensure you've got a good film of oil on the contact surfaces when you crank it over.

 

[Kawartha]

AB85,

I think Scipio has covered most of the requirements for shaft rotation, but I'd like to add a couple of additional points.

1. The requirement for shaft rotation can be either bearing or shaft deformation related. Although not a problem with smaller size rotating assemblies, as the size increases and unsupported shaft lengths increase, it becomes necessary to continuously turn the rotating assembly when not in use. For example, a large steam turbine rotating assembly requires continuous rotation even when not in operation. Without rotation, shaft sag can occur, which would result in shaft deformation. Therefore the larger the equipment, the more important it is to rotate the shaft on a regular basis.

2. Even with smaller pump or other rotating equipment, if the equipment is stored in a location which has a high vibration level, the bearing damage can be seriously increased. The brinnelling effect mentioned by Scipio occurs at a much increased rate when vibration of the site is also an issue.

 

[dadfap]

all

This has been recognised as a problem by the marine industry for some time. I spent a previous life in the Australian Navy and bearings that were stored aboard ship were regularly thrown out as being suspect, just from sitting in their packaging and vibrating merrily away.

dadfap