Shaft wear caused by oil seal

[TEguy]

Oil seal creates a groove in the shaft over a period of time. What causes this problem? What can be done to reduce or eliminate the problem? Can someone suggest any useful websites on this? Thank you

 

[btrueblood]

Usually the problem is that the seals are not perfect, some liquid gets thru the seal, and carries some amount of dissolved or suspended solids with it. As it passes thru the seal, the pressure drop and heat of friction evaporates the liquid, and leaves the solids behind. The solids are trapped under the edge of the rubber seal, and you have a nice rubberized-abrasive polishing tool rubbing on the shaft for a few million revolutions.

Even the purest water or fluid can still give problems though: the rubber on most commercial seals is the cheapest possible stuff, and as such contains carbon black and other things as filler. When wet/damp, carbon can be somewhat lubricative (lubricious? lubricatorative?), but when dry (e.g. when seal is hot) it's an abrasive. You can try getting a harder shaft material, or using a seal with minimal fillers and/or lead compounds as fillers, to give better lubrication, and it will help somewhat. The latter course will have you talking to seal manufacturers, such as John Guest, who may tell you something completely different, as they are experts.

 

[btrueblood]

Geesh. Not John Guest. Wish there was an edit feature.

FWIW - take a look at pump shaft seals, these typically have a mechanical wear element built in, one side is graphite and the other is a ceramic, and the two parts are spring-loaded to maintain a seal (the rubber part that squeezes onto the shaft is static, i.e. rotates with the shaft).

 

[MikeHalloran]

To repair or re-use a seal-grooved shaft, you can use a CR Speedi-Sleeve, or shim the seal away from its original location, or use a seal that has a lip axially displaced from the original location.

To reduce wear on a good shaft, you can use a seal with a wavy lip, or install a regular lip seal with a slight tilt; both cause the seal to wear a larger area of the shaft, so it takes longer for the shaft to become unusable.

If it doesn't contaminate the fluid you're trying to contain, any lip seal will last longer if it's packed with light grease when first installed.





Mike Halloran
Pembroke Pines, FL, USA

 

[hydtools]

Select a teflon compound seal. Some teflon will transfer to the shaft. Wear will not go away, but will be reduced.

Repair the shaft with a repair sleeve. If the sleeve is harder than the shaft, sealing life will be improved.

http://www.skf.com/portal/skf/home/products?lang=en

http://www.epm.com/ptfe_oil.htm

Ted

 

[JamesBarlow]

I would sleeve the shaft with a carbide sleeve. Get a sleeve EDM'd and epoxy it in place and you are good to go.

This is what I would often do for shafts that this happened to and I would not have any more problems.

 

[Heckler]

Select a teflon compound seal. Some teflon will transfer to the shaft. Wear will not go away, but will be reduced.

Also, a codeposit of EN and Teflon on the shaft will increase seal life, reduce friction, and shaft wear. We were doing some research on a miniature electric driven pump in which seal drag was the killer. So I would contact Bal Seal

http://www.balseal.com

If you're interested in the EN/Teflon process here is the company I used

http://www.coatingtechnologiesinc.com/services_plating_np3.html

Heckler
Sr. Mechanical Engineer
SWx 2007 SP 4.0 & Pro/E 2001

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"Avoid the base hypocrisy of condemning in one man what you pass over in silence when committed by another." -- Theodor

 

[PeterCharles]

Rather than as a repair, we've used Speedi-sleeves for new designs a couple of times over the years. Never quite sure if the end users bothered to replace them of just ordered a new shaft.

 

[ClicketyClack]

I would avoid dynamic oil seals altogether and go the labyrinth oil seal route. These are non wearing, no lip/shaft contact. Inpro makes a nice one.