New type of bearing?

[Leffe]

Has anyone like me felt the need of a new type of ball/roller - bearing with an integrated sealing. Very often when designing some type of gearbox or other casing with a shaft coming out of it, one needs a sealing to keep the oil on the inside. To do this with a separate sealing makes the design bigger and more clumsy. It also makes it more expensive to manufacture. When it's time for repair it is easy to change the bearing but sometimes the sealing has wearn in to the shaft witch then needs to be exchanged or repaired. Wouldn't it be great with a ballbearing with an integrated sealing that seals between the inner and outer rings in the bearing? I understand that it needs to be fitted either over a o-ring or with some kind of glue or silicone to prevent leakage between the shaft and the inner ring as well as between the housing and the outer ring. It still would be a more effective design and it would be possible to use it in a lot of applications.
When I have asked people working for SKF, FAG or INA aboute this I have got what I think a very stupid answer: "We don't do it because no one asks for it." Ofcause no one asks for it since there isn't any such bearing.

WHAT DO YOU THINK?

Leffe

 

[FrenchCAD]

I think it would be a very difficult bearing to make, but it sure could be usefull in some cases.

Cyril Guichard
Mechanical Engineer

 

[diamondjim]

Leffe,
I have seen this type of design on large
tunnel boring equipment and also some
mooring buoy equipment. The seals were
very large and special welding technique
was applied to the wear surface to allow
a very hard rubbing surface and then
ground. It was expensive and the running
torques were out of sight, but the customers
had plenty of drive to overcome this.
To effectively seal out oil the lip pressure
of the seals must be very high. I have
seen a seal act as a pump and actually pump
the oil out of the bearing. I do not know if
it was because of excess axial play or not.
Most bearing manufacturer do not make these
exotic seals and expect seal manufacturers
to come up with suitable designs. Often they
are spring loaded and difficult to assure the
accuracy required to effectively seal out oil.
If you have enough money and insist that these
be incorporated into the design and can assure
enough sales volume to warrant the production costs
and assembly problems, I think any bearing
manufacturer would help you. The cost of developing
a prototype can be extremely high and then may
not effectively seal out the oil depending on
clearances and runout of the seal with respect
to the raceway system and accuracy of the installation
at your sight. Also the disadvantage is that if
it does leak, you have to replace the whole assembly
instead of only the seal. Yes, it can be done.

 

[EnglishMuffin]

You can get sealed ball bearings from all the major manufacturers, such as SKF, FAG etc, either with a true lip seal, or a non contacting shield, either on both sides of the bearing, or one side only. I can't imagine you are not aware of this, since you have apparently spoken to them - so there must be some reason why these are not adequate. The contacting seal type can get hot, and their speeds are derated because of it. Most electric motors use some type of integral sealed bearing, but in this case its mostly to retain the grease.

 

[Leffe]

Apearently I need to clarify this.

So what I want to compare with is not a ballbearing but a ballbearing and a sealing. Compared to a traditional design this shaft can be machined to a rugher surface, (cheaper)the sealing runs against a smother hardened surface (no leak) (less wear)(longer lifetime)(less friction)and when I change the bearing I also have the sealing and the surface it is running against, changed without problems with the sealing has worn in to the shaft.
Leffe

 

[EnglishMuffin]

The advantages you state are all absolutely valid. But what is the difference between that and a standard sealed ball bearing - other than the static seal you have added ?
The only difference I can see is that the lip seal in yours is physically bigger (more reliable?), and so yours is longer. I have used sealed ball bearings with a seal on only one side to retain oil in gearboxes - worked fine. Yours could work better - but unless you have a problem when using a sealed bearing, why bother? Have you tried a standard sealed ball bearing ?

 

[automatic2]

We frequently pulled the box side seal out of sealed bearings, leaving one side sealed. Works excellent in retaining lubricant. As with Muffin, I can't understand that you are not aware of this, unless you are thinking of a seal to keep out contaminants. In that case, you'll need to turn your lip around to the exterior. An SKF redisleeve works wonders in overcoming shaft wear, and you don't have to incure the bearing expense to replace seals.

 

[EnglishMuffin]

This is off the subject a bit I know, - but there are even special sealed machine tool spindle bearings you can get now from FAG, although they are actually shielded rather than sealed. And some German machine tool makers are using grease sealed bearings even in oil lubricated gearboxes. They have very elaborate slingers to keep the oil from washing the grease out.

 

[Leffe]

The difference to a "standard sealed ball bearing" is very big. If I would suggest to my customers to rely on such a solution to keep an essetial part of a machine filled with oil they would fire me.
Leffe

 

[EnglishMuffin]

Exactly how does one get "fired" by ones customers, since they are not your employers ? But kidding aside, all I can say is this :

1. The only part of a lip seal that actually does anything is the tiny area that contacts the shaft, so just because your proposal "looks" more reliable does not necessarily make it so - although it may very well be.

2. If you are saying that the advantage of your proposal is "customer perception", I can't argue with you, but its not an engineering issue.

3. Have you ever tested a single sealed bearing?

 

[EnglishMuffin]

Oh - one other thing - if you really want to get some of these made - talk to Kaydon. They will make anything for you - for a price !

 

[Hippo41]

For agricultural use you get bal bearing inserts with what is called a tri-lip seal, or triple lip. This is effective in keeping dust out in very dirty conditions.

The same seal is/could be applied to specially made ball bearings, but they are generally wider than normal beairngs.

This would improve sealing, but your friction levels would increase.

On some big gearboxes we used a lbayrinth seal similar to that found in a standard SNU bearing housing. There was a bit of machine work involved, but it worled extremeluy wel in reality.

Hope this helps!


Lester Milton
NBC Group Ltd, Telford, Shropshire, UK

 

[IRstuff]

You seem to have drawn the bearings into a very deep groove to get the low profile.

Is what's shown actually been assembled? I can't see how you can get the balls into the race groove.

TTFN

 

[EnglishMuffin]

IRstuff :
If you're going to get really picky, there doesn't even seem to be a cage - it looks like it's full complement, so without a split inner race it would be unassemblable whatever the groove depth was. I expect its just for illustration purposes.

 

[Leffe]

Thankyou for all responce. I think we should clarify that we are not talking bearings sealed to keep dust out, like 2RSR or ZZ. Everybody knows them allready. The picture is just an illustration, it's the standard resemblence of a 6004 bearing as Ironcad makes it modified to have a sealing and chamfered corners to allow o-rings to seal against the shaft and housing. The question is: Every time we design something with a shaft sticking out of something with oil in it we need both a bearing and a sealing. Why not standardize this into one unit? If they were available I would certainly use them. Would you?
Leffe

 

[EnglishMuffin]

There is one other advantage that I don't know whether you mentioned, which is that the housing machining would be simplified in many cases. But the problem I see with something like this, from a bearing manufacturers perspective, is that you can't retrofit them into existing equipment, 'cause at the moment there are so many different dimensional variations. I still think that you would have more interest if you could make something like a current sealed bearing with standard ISO dimensions, but perhaps with a more effective lip seal than those currently available - if that's the problem. Its not obvious to me that the bearing has to be any longer. Of course, then it becomes a seal development thing as well, rather than just a bearing development thing.

 

[EnglishMuffin]

Leffe - it's also interesting to speculate on whether it's patentable, and how one would structure the claims such that it could be distinguished from a standard sealed bearing. Early disclosure before seeing a patent attorney (which this appears to be) can lead to problems sometimes. Perhaps you have no intention of patenting it, but patentability is another feature that might generate interest among bearing manufacturers. Its amazing what you can patent when you look into it. Its also true of course that the strength of a patent is sometimes directly proportional to the size of your wallet.

 

[automatic2]

I would not. At a dozen dollars for parts and half an hour to replace a leaking seal, I would be in a tenuous position if I called for a half day and a sixty five dollar part for the same repair if the seal was integrated. When a bearing fails, it is typically evidenced by a leaking seal (stand alone). When a seal (stand alone) fails, subsequent bearing failure is not a given. Do the math. Consider as well;
- the generalities built into bearing usage. A floating race would be difficult to seal, yet is common. Allowable temperatures for heat fits would compromise seal materials.
- One of reasons that modern day bearings are so successfull is their compactness.
- A box flush would be hard considering that the flush mediums require seal changes.
- throughbox shafting is typically designed to avoid flooding of bearings, avoiding lub pressure issues.
- increased maintenance expenses without any real advantages would move a manufacturers box down on the desirability list.
- If your sprung a seal leak with your design, and you told your manager that the box needs to come apart for a bearing replacement because of an oil leak, you still might be subject to job loss.
- if no one else has asked for such a configuration, you will likely bear the entire cost of manufacturer/supply. You will loose your job.

 

[EnglishMuffin]

automatic2
Be fair to this guy - if its a standard seal incorporated into this bearing, and its accessible from the outside, you don't necessarily have to replace the whole bearing or disassemble everything if the seal itself fails. And a standard seal that fails because of shaft wear would be much more expensive to fix than just replacing the bearing - unless you maybe use a speedi-sleeve.

 

[automatic2]

' if its a standard seal incorporated into this bearing,' and it fails, how else are you going to prevent leakage without replacing the bearing that has the incorporated seal? You must be speaking of a standard seal used in conjunction with a bearing. That is what I've described in the previous post.

My experience has shown that erosion of the seal face on shafting is almost always accompanied by erosion of the bearing seat. In fact the latter brings on the preceeding. Unless of course mechanical damage has taken place. Bearing failure will typically not destroy seal faces unless it is catastrophic, or is allowed to continue to the point that bearing seats are damaged, which will almost always lead to seal face damage. Worn seal surfaces on shafting are an indicator of other problems. Incorporating the seal into the bearing does nothing to address those problems.