Seal Direction

[John C.]

I got called failure analysis on a vibrating grisly on a Power Screen crushing and screening plant. The eccentric shaft was just rebuilt and put back together and had less than fifty hours of run time. It started running slower and slower. Client removed the hydraulic drive motor and tried to turn the shaft by hand and it would barely move. We removed the shaft and found dirt that have been left in the shaft housing had been pushed through the grease seal and into the shaft bearing packing into the bearing and locking thing up. We know for a fact that the dirt in the housing was part of the prior failure so that part of the issue is not in dispute. When I looked at the seals in both sides of the bearing housings I noticed the lips are faced to the bearings. The bearings run in grease so I mentioned that I thought the seals were in backwards. They should have been faced so that the grease would move out of the housing and keeping the dirt from coming in. I received a lot of push back on that so I'm looking for some more input. The maintenance schedule says to grease the shaft bearings every 40 hours. My point is that the old grease needs a way to get out. The parts book shows nothing about the direction and the machine is old enough that there is no service manual for it. Give me you opinions and justifications. We are putting the machine back together on Monday.

 

[willie59]

I agree with you John C, if the bearings have grease fittings and the maintenance schedule recommends X number of hours to grease them, then yes, the grease needs somewhere to go and with lips facing inward that will prevent that, same way as the lip seals on excavator pins, lets excess grease escape, keeps dirt out.

 

[Tyler d4c]

Yes the excess grease needs to go somewhere even if it is just filled once hot it could push the seal out. Then the dirt really gets in there

 

[John C.]

Thanks Willie and Tyler, your opinions help.

 

[willie59]

I think every application has it's specific requirements, one size fits all doesn't. Take cam rods on air brakes, at the bearing support adjacent to the S cam of the rod. On the S cam side you install the lip of the seal inward to prevent grease ingress at the S cam, but on the opposite side, slack adjuster side, you install the lip outward to allow grease to escape. If you install both lip seals inward it will simply push the seals out.

 

[1466IH]

Willie brings up a good point. Is there anything outside if that seal they would not want grease on?

 

[John C.]

Willie, You are right about considering where you want the excess grease to go. I remember seeing instructions for the seals on the S cam shafts.
1466IH, one direction goes to the eccentric shaft which is inside the tube. The other side is outside between the frame and the drive coupler. Grease won’t hurt anything on either side.

 

[Bluox]

Are these bearings the ones in the screen frame or the ones on the deck mounts?
Where is the dirt coming from?
What kind of bearings are they?
Bad Bob

 

[Bluox]

You answered one of my questions while I was typing.
I don't think you would want grease going in the shaft housing.
It's common for grease to go to the outside and that works well till the discharge belt stops and the bearing gets full of dirt when the screen overflows.
I replaced a bearing on one last month and the inside seal kept grease in and the outside one let grease out.
Bad Bob

 

[John C.]

These are the bearings that support the eccentric shaft that make the grizzly vibrate. There are double roller bearings on each end of the shaft. There is nothing inside the tube that the eccentric shaft is housed in. The eccentric shaft is driven by a hydraulic motor and there are no belts involved. Dirt is loaded by a wheel loader. The prior failure happened when the tube ran loose of the frame at one end. Dirt that got into the tube on the prior failure and wasn't cleaned out when reassembled caused this failure. The inside seal on the drive end of the eccentric shaft was destroyed. We spent about two hours with a needle scaler cleaning the tube looking for a hole or crack large enough to allow the material inside the tube. There were none. The destruction I believe was caused by the dirt getting into the seal. You can see where a groove has been worn into the shaft where the seal rode. The seals will be put back into the housings with the lips facing away from the bearings.

 

[Bluox]

The bearing failure on the screen I replaced was dirt from the outside.
The seals were put back as they came out inside tube lip toward bearing outside lip away from bearing so grease goes to outside.
Checked with R D Olsen, Kelso WA. who made the screen.
Bad Bob

 

[JLarson]

I almost always put single lip seals in on grease bearings.

Some of the grease stuff we work on runs double lip or single lip out with purge valves too.

 

[56wrench]

The best seals i have seen an ag application are a triple-lip seal pressed onto a spindle and the wear ring is pressed into the hub. Then the grease purges the dirt as it is forced out. Also used on some gang shaft bearings on disc harrows that run in a lot of dirt

 

[John C.]

Put the bearings and shaft back together today. Bluox was correct on the orientation of the seals. The eccentric shaft seal area has a step up that will not allow the seal lip to slide up onto it with the lip turned toward the eccentric. The outside seal can be put in either direction. We put the drive side of seal towards the eccentric because we could get access to use a tool that would allow lifting the seal lip up over the step in the shaft.



This is the drive side assembled. What you see is the housing that carries the big double roller self aligning bearing and the seals. It can be assembled with the shaft pulled partially out of the tube.

 

[John C.]

This is the opposite end. The bearings and seals are pressed into the housing and then the housing is installed on the shaft and into the frame bore. We used the ready rods to support the housing and was able to get the bearing to start onto the shaft. We used a pipe on the small part of the shaft to lift it enough to get it all started. The bearings had to be installed onto the shaft using a hammer an punch. There is no provision for using any kind of press.



We rigged this strongback to the opposite end so as not to send shock of hammering the bearing on the opposite side into the housing on the drive side.







This all came about because someone previously used soft washers and 8.8 bolts with nylon nuts to hold the bearing housings in place. The washers flattened out and the housings moved around in the frame wallowing out the bolt holes and breaking up the tube.

 

[John C.]

For a better reference are a couple of photos or the two parts of the grizzly.

 

[Tones]

The shaft and bearing setup is very similar to what forestry mulchers use including spherical roller bearings. On those things both bearings had to be knocked in. Labyrinth seals were used to keep the dirt out. One of the worst things bearings hate in this environment is to much grease, it creates to much heat. A little bit of grease often lengthens bearing life astronomically.