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Preventing bearing wear

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tonyfell

Mechanical
Mar 27, 2002
3
DE
Hi,
I have a drum containing pressurised oil that rotates on a vertical shaft on either bronze or PEEK bushes. The leakage of the oil through the journal / bush clearance lubricates the surfaces and in effect creates a form hydrostatic bearing on either end of the drum. On occasions the oil in the drum can be highly contaminated with particles having a hardness upto approximately 65 Rc which understandably cause considerable damage to the bearing surfaces. I cannot prevent the particles form getting into the oil and so am looking for a way of keeping the particles from getting into the bearings. Also, I cannot introduce a great deal of additional friction into the system as this will causes the drum to slow down so conventional sealing techniques may be out of the question. Anybody have any ideas or know of any means to prevent / reduce the ingress of particles into the bearing?
 
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Maybe you can try to use a labrinyth seal design....the fingers are not exactly touching each other so should not induce great amount of friction as compared to contact rubber oils seals.
 
check out Ignore the rope cutter stuff & scroll to the moving picture of the Sandstopper. The red dots represent the sand. The blue dots represent clean water. Provided you can fit the Sandstopper (which is actually a clever kind of continuous centrifuge particle separator) inside your tank and before the oil gets to the bearings,It will very efficiently process out the heavier abrasive particles. Quickwater Marine have developed a way of drawing clean lubricant to the bearing. The system works on tranquil separation and particle dwell time, and as I do not expect you want oil flowing through your bearings at a high flow rate, there will be plenty of dwell time to allow even fine particles to separate.
 
I neglected to mention that in the drawing a pump is also depicted. (for moving drawing click on integrated sysyem)It is only neccessary to pull lubricant down the bearing with a bi-directional pump when the shaft is required to rotate in both directions, as is the case for a boat propeller shaft.
 
tonyfell
What sort of rotational speed is involved?
You seem to indicate both top and bottom bearings are affected, is this correct?
israelkk
A filter would have to be internal and although effective for a while -I wonder how long a while is?- will clog. Cleaning/replacing might be quite a project. Seals (assuming both bearings are affected)will be required to secure the filters around the shaft.

Clearly keeping abrasive matter out would be the logical route.
 
rnd2
The rotational speed is approx. 4500 rpm. The both bearings are affected, although the bottom is affected to a greater extent than the top.
 
tonyfell
Boomerang points to an elegant solution.
4500rpm, density differential approx 7:1 and "tranquil" separating conditions indicate amenable conditions for efficient separation, subject to oil vicosity.
No dependency on filters
No contact seal
Self cleaning separator
The only limiting factor would seem to be whether or not the tank design is able to accomodate the separator.

 
unclesyd
tonyfell says: "The leakage of the oil through the journal / bush clearance lubricates the surfaces and in effect creates a form hydrostatic bearing on either end of the drum."
This precludes use of a classic "seal" as the oil is also sealed off.
 
I would suggest using a bearing, with a material combination of two much harder materials then the particles.
Bearings made of Silicium Carbide Ceramic might work very well. We at Ceratec have many years of experience producing, and engineering ceramic / metal bearings, wich are most of the time medium lubricated. Often there are solid particles in the lubricant, and the bearing surface are hardly touched. SiC bearings have a hardness of 2800 HV.

Hope to have helped

 
Are the particles magnetic? How often can you service the device that protects the bearings?
 
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