Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Rotary shaft seal gets very hot

Rotary shaft seal gets very hot

Rotary shaft seal gets very hot

I have a tool that attaches to a CNC mill called a "right angle head".

Its just a 90 degree adapter so you can point the tool sideways.

Made internally just how you'd think..taper bearings on input shaft, angular bearings on output shaft.

And a rubber lip seal on the end of the output shaft that gets exposed to the outside world.

The tool is new to me, and in new condition.

It gets VERY hot after operating for a few minutes. The whole body of the tool probably gets to 150F.

The part of the output shaft right next to the lip seal probably gets to 200F in a matter of SECONDS at 4000 rpm.

I dont know much about lip seals, but from what I can tell, this may be normal?

The internal bearings require grease. so the lip seal gets lubed with grease.

Its the simplest lip seal, one contact point, no spring backup. Probably nitrile.

I tried replacing the seal, no change.

The lubricant is premium spindle bearing grease, Isoflex NBU15.

I isolated the overheating to the lip seal by making a spacer so the output shaft gets pushed out beyond the lip seal so its not touching. Things never got above 115F even after 15 minutes at 6000 rpm.

So whats the deal here? Is this lip seal badly designed, or maybe the grease isnt right? Or maybe I'm supposed to put a TON of grease behind it?

This isnt a cheap tool, they go for $2000 USD new, although the manufacturer of this one seemed to know very little about it, like it was some rarity. Maybe this is why..

I'm thinking of replacing the rubber lip seal with a PTFE seal which I believe would run at a lower temperature?

Help please!!

RE: Rotary shaft seal gets very hot

I don't quite understand what you did with the spacer experiment so I'll ignore that. It sounds like you believe the seal is producing the heat? Are you sure it's not produced elsewhere and the shaft is getting hot because of that?

RE: Rotary shaft seal gets very hot

The spacer test made it so the lip seal was not touching anything and therefore could not generate heat, but all the bearings in the unit were still preloaded and as normal. In that case, nothing got hot. So the lip seal is generating the heat. Plus, the output shaft right next to the seal gets very hot within seconds of turning on.

RE: Rotary shaft seal gets very hot

What shaft diameter is it? Above about 3000 fpm, the speed is getting high for general seals. Nitrile is good to about 225 Deg F. Other materials can handle much higher temperatures. Make sure you have grease between the shaft and seal (don't want to run dry).

These measurements were done without any load on the spindle? That does sound bad. The attachment is rated for that speed?

RE: Rotary shaft seal gets very hot

Are you sure it's not coming from the gearing? Small right-angle reducers like that can be lossy and lack appropriate cooling, leading to runaway thermal properties.

I'd suggest a non-contacting bearing isolator but since it's probably filled full with grease that would inevitably leak. A PTFE seal is not a bad idea.


RE: Rotary shaft seal gets very hot

Sounds like the lip seal is running dry.

I can't see from the pictures but if any moving part is in contact with the lip seal I would expect that there is insufficient lubrication. Meaning what ever you are using is getting wiped away. PTFE should work better.

Is there much of a contact force on the seal to surface? You may be able to form the PTFE better to keep a small clearance but not actually touching.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close