Pillow Block Bearings: Sealed? Not sealed? To grease, or not to grease....

[Drew Riley]

I'm starting this thread based on some recent discussion that I've seen brought up over and over again, but seemingly never with a solid, matter of fact answer.

There seems to be a bit of confusion surrounding the question of whether or not one should grease a pillow block bearing, especially if they are listed as "sealed". The other question is "why are there grease zercs if we're not supposed to grease them?"

Well, either we will lay both questions to rest, or create even more confusion in the process!

It is my understanding that "sealed" pillow blocks DO in fact require routine greasing and maintenance.

First, let's look at a diagram of a traditional pillow block bearing:

The "seal" of the sealed bearing is referred to in the diagram as a "special rubber seal", and this usually has a "shield" around the outside of the bearing, protecting this seal.

If you remove the bearing from the housing, you are left with something that looks like this:

Notice the groove around the circumference of the spherical outer ring, and more importantly the small hole. This hole is a grease port, which is ideally, BUT VERY RARELY lined up with the the grease zerc in the housing.
In other words, when, these bearings are set into their housing, these small grease holes are SUPPOSED to be lined up with the zircs, but rarely are. Personally, I try to line these up myself whenever I get a new PB bearing. Otherwise, when you pump grease into the zercs, you're just going to sqeeze out between the housing and the outer ring. I believe the groove is there to help compensate for this and guide the grease into the hole, but I try not to rely solely on that. Also, some bearings don't even have this groove, but just a hole.

Simply remove the zerc fitting and rotate the bearing such that the holes are centered up on eachother, and then replace the zerk.

Now, how much grease is enough?
Some say to pump it in until it starts squeezing out of the outer seal. Personally, I think this is too much, as you risk blowing your seals out, and allowing dirt and other debris to get in the bearing. This excess grease also becomes a magnet for all kinds of dirt, dust and debris which can eventually find its way into a blown seal and destroy your bearings. Finally, too much grease in a bearing can cause excess heat/friction.

Now, all that said, the seals WILL allow used/excess grease/oil to weep out of them. This is why it's important to re-grease every now and then.

Personally, I think a couple pumps of the average grease gun will suffice.

Hope this helps!

 

[KenH]

Good presentation Andrew - but I do have a question..... do you know for a fact that ALL pillow block bearings have this groove with grease weep hole? I sure was thinking I'd seen some without the hole, but I am NOT prepared to make that statement as fact. That's why I'm asking you.

I may be thinking of standard bears and not pillow block bearings at all. I do know there are many bears, such as go on the end of the small wheel rollers - these are sealed, and do NOT have any grease holes to grease inside of bearing. Now, if those bearings are sealed for life and don't require sealing - why could pillow bearings not be made the same?

Please understand, I'm not trying to be confrontation, say you are not correct - just trying in my own awkward way to seek information.

Ken H>

 

[Drew Riley]

Good presentation Andrew - but I do have a question..... do you know for a fact that ALL pillow block bearings have this groove with grease weep hole? I sure was thinking I'd seen some without the hole, but I am NOT prepared to make that statement as fact. That's why I'm asking you.

I may be thinking of standard bears and not pillow block bearings at all. I do know there are many bears, such as go on the end of the small wheel rollers - these are sealed, and do NOT have any grease holes to grease inside of bearing. Now, if those bearings are sealed for life and don't require sealing - why could pillow bearings not be made the same?

Please understand, I'm not trying to be confrontation, say you are not correct - just trying in my own awkward way to seek information.

Ken H>

Ken,
I can say this: Not all pillow block bearings with a grease hole have the circumferential groove all around the outer sleeve. Some JUST have a hole.

You can see an example in this picture:

Now, can I tell you that ALL bearings have a grease hole in the outer sleeve? No I can not. I will say that the last several sets of PB bearings I've used did have them though.

One thing to keep in mind for sealed bearings: The seals, as I undestand things, are more to keep dirt and debris OUT of the bearings more than it is to keep grease or oil IN.

For a lot of applications where PBs are used, they aren't under a great deal of load or speed, so they last weeks, months, and even years without being greased.

That said, our grinders do see a lot of speed, and as this grease heats up and it used, it may tend to "weep" or leak out of the outer seals. If you see that happening, then the grease is being depleted and needs to be replaced.

I have read of guys using a needle and injecting grease behind the outer shields/seals, or drilling their own grease holes. Personally, I'd be hesitate about drilling my own hole and getting chips inside the bearing, but then again, the alternative is running dry and suffering pre-mature failure.

 

[KenH]

Andrew - you and I do think a lot alike on those bearings. I'd sure hate to think of those metal shavings inside the race to grind on the rollers. I REALLY do like the idea of greasing bearings - and have always been concerned about the sealed bearings without a method of greasing, as in the small wheel rollers - those bears do some spinning at high RPM and really do need some grease, but without taking a chance to mess up the seal, there's just no way to grease them.

I guess it's a good thing I'm in this knifemaking just for fun and make less blades per year than ya'll full time folks do in a week or so. Lots of different in the stress on our equip.

Thanks for starting this thread and showing such detailed info.

Ken H>

Ken H>

 

[Drew Riley]

Concerning the small wheel bearings, the same principles apply. Unfortunately, those aren't set up to easily grease/lubricate like the pillow blocks with the zercs are.

That said, they are designed for light load, lower speed applications where the the lubrication they are sealed with should be adequate to maintain the bearings for quite some time.

Again, however, if you start seeing the lubrication weep out of the bearing seals, then you can bet that your bearing is going to start seeing more heat, more friction, and more wear. With these smaller (and cheaper) bearings, it probably makes more sense to just replace them and run them within their intendid operating specs, than it does to try to grease/lubricate them.

 

[scott.livesey]

the bearings we get at the office all seem to come in a cardboard box and inside the box with the bearing is a sheet of paper called "installation instructions." some like Browning dont do a seperate sheet but print the instructions on inside of box. the instructions list whether or no to install grease fittings, what kind of grease to use based on usage and location. i have also found same info online at manufacturer's website. if use is light load moderate speed, would be interesting to try bearing surfaces of oil filled nylon, PTFE(teflon), or UHMW PE(you can find em at McMaster/Carr). these are true "zero maintenance" bearings.
at the office, we grease bearings in a high rust dust environment two pumps once a week, always removing any old grease that came out.

 

[12345678910]

http://www.bladeforums.com/forums/showthread.php/527487-Greasing-a-KMG!?p=5259536#post5259536

Correct. I dropped Rob a note to let him know that my KMG arrived with one of the zerks laying in the bottom of the crate, and the other one was about to fall out as well. My other gripe was that the bearings are mounted with the zerks down and there's no way to grease them. Here's his reply:

They bearing units are 2 pieces, the outer housing and the actual bearing that is inserted in the housing.
The bearings are pre-greased and sealed for life.
In this case, the grease fitting is not applicable with the specific bearing used in this housing.
It's a standard housing that fits many choices for bearings and by its universal design, has grease fittings.
The bearing units are intentionally mounted as such so that they cannot be greased and this practice is discouraged for this application and bearing type.
This is a case where excess grease can be more damaging, than if the bearing were to run completely dry.

 

[BossDog]

Many/most of the pillow block housings have a zerk installed or at least a threaded hole plugged for a zerk. Most of today's bearing inserts I see used in pillow blocks today are sealed entirely and do not have the grease hole. If you grease a sealed bearing in this case, the grease simply flows around the sealed bearing and may cause the outer bearing race to spin inside of the pillow block housing. It shouldn't happen but I've seen it happen.

If the bearing does have the grease groove and hole, absolutely give it a squirt now and then.

One other consideration, if a non-sealed "greaseable" bearing is over greased (what ever that is), the rollers don't spin and will tend to glide on the grease eventually wearing a flat spot on one or more of the rollers. When the excess grease (eventually) seeps out and the rollers have to start rolling again, the flat one(s) really chunks along and fails the bearing prematurely. Again, unfortunately, something I have also seen personally.

These bearings are really common, cheap and easy to change out. We switch them fairly often here.