Reply With QuoteHi and welcome to the forum...Could you post a sketch or model of your design? We can help better if we see what you are trying to achieve.
Thanks
Hi all,
I have a shaft of an underwater motor housing that needs a bearing. So my question, what is better 2 ball bearings at a distance of 5mm or 1 needle bearing of the same total lenght?
I need a bearing for axial and radial loads. I found the following bearing witch can have bot loads.
NX..pdf
But if I use 2 ball bearings I need to have a thrust bearing as well.
I like to use the smallest as possible bearing. So all the advice is welcome.
Arthur
Last edited by Kelly_Bramble; 10-15-2013 at 08:35 AM.
Hi and welcome to the forum...Could you post a sketch or model of your design? We can help better if we see what you are trying to achieve.
Thanks
Hi Arthur, and welcome.
As Marky has suggested if you can give us a sketch of what you are trying to do, we can advise you more accurately.
The width of the bearing does not have a significant effect on the load and performance. Two bearings side by side should be able to carry double the load providing they are a matched set. That gets expensive and probably not what you want.
The bearing you quoted does not have an inner ring so it will have to run on the hardened shaft, probably not what you want there either.
So, provide some more information and we can definitely assist you with your choice of bearings. You do not need to show us the entire thing, just the shaft and the what is going to hold the outer rings of the bearings.
Oh, and the roller you quoted has no thrust load capablility so you would need a thrust bearing, but depending on thrust loads, an anglar contact ball bearing may suffice for both thrust and axial loads.
Last edited by PinkertonD; 01-24-2012 at 06:38 PM.
When you say underwater... does this mean the bearing will be submerged in / exposed to water? If that is the case I'd go with an oil impregnated plane bearing and get a shoulder on your shaft somewhere to put a thrust bearing of same material somewhere with as much surface area as possible. If you can keep things out of the water then I'd look at the angular contact balls as was mentioned. They can be had at different angles to handle more or less thrust load / radial load. Back to back matched would take the thrust both directions. If they can be located some distance apart you can save a few bucks and skip buying matched.
If this is submerged I'd steer clear of any bearing with moving parts. Usually water means crud as well.
That's what I was thinking - when I hear submerged bearing I automatically think plane bearing. If it were me, and knowing nothing about your geometry, speeds, or loads, I would consider a plane flanged bearing as the default. Any other (rolling element) options would have to be justified for some very good reasons, and would have to be very carefully protected.
First of all thanks for the reply's.
About the water it is going to be a water proof housing were it is going to be placed in. I hope the picture in the attachment will give you a clear look on it. The shaft will be connected to a gear. I is for possition so there is no high rpm.
In the drawing you see the normal ball bearings. But when we are going to submerge the housing the shaft will have thrust inward because of the water pressure. The lip seal I chose can have a pressure of 150 bar. So that means if my shaft is 10mm it would be about 120 kg of thrust. The radial thrust of the shaft should be 200 kg or more, but that depense on the shaft lenght from the bearing
A tapered bearing would be good I think, but I can not find that small tapered bearings.
The NX10 it is a combination of a needle bearing with a thrust ball bearing.
What is the maximum axial thrust a of a anglar conact ball bearing.
bearing setup.JPG
Ahhh... Waterproof... Interesting concept.Originally Posted by Arthur
If this is submerged... and you say low rpm to boot... I'd go with a pair of oil impregnated flanged plane bearings. (Oilite or Chrysler bearings they used to call them if my memory serves...?) The bearings will outlive the seal and still function when the seal fails. (Note ... not if... but when) If you can't get a nice face finish for running on the flange then tuck a thrust bearing race in there.
Disclaimer...
I didn't do any math or convert the loads and research this at all other than past experiences and gut feel. Don't rely on what I'm about to say.
Without hesitation I would say that the plane bearings will be cheap and off the shelf and most likely the thrust washers as well. Both will handle more load than the tiny shaft could deliver before other modes of failure. Any sort of roller or mechanical bearing is going to fail after a little grit polishes into the shaft. Regardless of mechanical bearing material you'll be looking at problems. If you really feel like you need to have balls or rollers in there I'd suggest looking into a smaller compliment of balls or rollers than "normal" (one less ball) and a looser than normal running fit. Such as are used in very dirty environments... like coal conveyor rolls and the like. This way your bearings will be able to possibly chew up or run over some crud. Also put a seal on the inside as well and a zerk so you could pack this thing full of some super thick fishy friendly grease every now and then. That'd help keep the water out some too.
Arthur, at 200KG, the numbers just are not adding up. With 200Kg on a 10mm shaft? What is it made of?
Regardless of that, the design is doomed to early failure. Can you do something like this rough addition to your sketch? You would only need one bearng in the body and another in the outrigger. Is the inner end of the shaft doing anything or is this just an "Idler" situation for whatever is out in the water?
Thanks for your answer.
It is a head (cover/cap) of the housing of a tilt head for a camera.
you are right about the 200 kg. Something more like this see the drawing.
bearing setup2.JPG
Hi Arthur, Umm, then why not have the shaft machined as a straight stub-shaft off the cap and the bearing and seal on the other mating part? Infinitely more simple and no horrendous cantilevered loads on the bearing. That's why I asked about the inner end doing anything.
I have designed systems for underwater applications. We used rulon plastic bearings. Rulon does not absorb water. Materials like Nylon will absorb water and swell.
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