Oil Flingers

[rads]

Good afternoon.

I have a gearbox design which is showing signs of gentle incontinence (note NOT incompetence ;-) ).
Oil is seeping trough a sealed bearing (which is way above the static oil level, we thought the "seals" in the bearing should resist the occasional splash of oil but that appears not to be the case).
I think an oil flinger, mounted inside the case, adjacent to the bearing should keep most of the oil off the bearing and prevent seepage.
I presume there is some science to the design of oil flingers? Anyone care to shed some insights?

David

 

[GregLocock]

Can't help you directly, but in the marine electronics design environment sealing against splashes is the hardest thing to get right. The problem is that there is no static pressure to press the sealing lip (of whatever form) against the other surface, and the dynamic impact of the splashes creates reverse loads in the seal, opening them up.

So, I'm not surprised you've got a problem, but I can't help!

Having said that, a static ring attached to the casing, covered by a rotating cap attached to the shaft, ought to do the job. If you know your oil viscosity it ought to be fairly easy to calculate the necessary dimensions.


Cheers

Greg Locock

 

Talk to Parker technical dept. You should be able to seal up no problem with a loaded lip seal (p designation for rotary) I have found that you almost can never rely upon the bearing seal to do the job completely, as they are very light seals. You almost always need a secondary shaft seal. Do you have a gearbox vent or breather? If you don't, as the machinery and oil warms up, you are pressurizing the case, and you will have oil-laden mist and air forcing its way out on the path of least resistance. A slinger should not be necessary, unless you want added turbulence inside the case for all-points lubrication.

 

[skeptic]

Hi David,

I had a similar problem years ago with a custom gearbox design. I asked an engineer from the bearing company to explain to me why his sealed bearing was not preventing oil from seeping outside the gearbox. His reply was something like, "The bearing seals are designed to exclude contaminants and retain lubricant. They are not designed prevent migration of lubricant from one side of the bearing to the other." He went on to say that the seals weren't perfect, but that they generally did a good job at what they were designed for.

From that point on, I quit trying to use sealed bearings in that application, and used shaft seals instead. On any shaft that penetrates the gearbox housing, I now use an open bearing with a shaft seal positioned immediately next to it. The open bearing receives lube from splash or bath, and the shaft seal is lubed through the open bearing. The seals are often available with OD's that are sized the same as the bearing. So if there is no axial bearing load, the seal and bearing can be installed in the same through bore. If an axial load is present, then a shoulder or retaining ring must be present.

I've had much success with this approach. The shaft seals last a long time, and they are easy to replace. Many seal designs incorporate springs that press the rubber lip to the shaft. Such a seal won't leak a drop until it is badly worn. The only downside that I am aware of is that the housing must be thicker in the vicinity of the shaft penetration to accommodate both the bearing and the seal.

Also be sure to provide lubricant to the seal. This usually occurrs automatically (from splash) in oil-filled gearboxes.

I hope I haven't wasted your time with something you already knew all about.

 

[rads]

Gentlemen,

Thanks for replies.

Unfortunately, the design has always been tight on axial space (the reason for using a sealed bearing in the first place, rather than a separate seal). Also we are keen to maximise efficiency and minimise seal drag.

The shaft in question is well above the oil level, though oil may be pumped towards the sealed bearing by the action of the adjacent gear pair.

A breather is a possibility, I will investigate.

However, I am still keen on a flinger, mounted between the bearing and the spur pinion, designed to overlap the outside diameter of the sealed bearing thus direct oil away.

Any further comments?

 

[wijnand]

Try a bearing isolator, check with Flowserve