Bearing 1500 RPM @ 260¦ C 1

[pumpkind]

I am trying to solve an application where a dia 100 mm steel shaft with a dia 50 mm hole in the center rotates at 1500 RPM (vertical shaft). Service 24/7. In the center a flow of liquid at 260 ° C passes constantly. In the exterior the temperature is ambient - let's call it 40 ° C.
Trying to solve bearings problem for this application - it seem that a normal standard deep groove ball bearing - can operate 'sealed for life' only at temperature below 180 ° C.
Question : If I use a bigger ID bearing - let's say ID 200 mm - therefore having a radius of 50 mm clearance to reduce the amount of heat build ( with a spiked wheel to accomodate the bearing ) - is it reasonably to expect that the temperature of the bearing will not exceed 180 ° C?
What other measures can I take - short of cooling circuit - to be able to use a standard bearing in this service ?
Thank you for you input.

 

[Philrock]

Some grades of 440C stainless can handle this temperature. You'll have to find an appropriate high-temp lube - Dow Corning has some that would work.

Using a larger bearing to get distance between the hot fluid and the bearing is a good idea. To get a handle on what your bearing temperature would be in this configuration, I think you'll have to do a detailed heat flow analysis.

 

[electricpete]

I have never worked with an application like that. Just talking from my limited knowledge:

In addition to high temperature lubricant, you need a high-temperature bearing designed for dimensional stability at those temperatures. Also a loose internal clearance at room temperature to keep from going to negative clearance at operating temperature.

On the lubrication side, there can be a couple of advantages to oil style bearing. There are several arrangements where oil bearing is applied on top of a vertical motor. The thermal advantages are:
1 - Less heat generated from friction in the bearing.
2 - Oil can do a much better job at removing the heat. One option is a large oil bath with large reservoir enclosure surface area exposed for cooling. Also there are various ways to use the shaft itself to provide pumping action.

I would think the big 3-letter bearing manufacturers (SKF, NSK, FAG etc) would be very helpful to you in identifying a solution.

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[Tmoose]

Don't Some process rolls insulate the "hole" to keep the shaft temp and bearing temp lower. Also heat slinger fans to reduce local shaft temps.

 

[xnicke]

SKF have alot experience with high temp. apps. The high temperature deep grove ball bearing is rated at a operating temp up to: +350 °C.

 

[pumpkind]

Thanks Tmoose - I was already considering a flinger - with regard to insulation rolls- my concern is the spedd and the environment - water vapour saturated air and 1500 RPM ...still thinking ablut it.
XNICKE - thanks for the tip - already discussed with them - however the problem is not only temperature but temperature-speed combination - the temperature resistant bearings cannot take more than few hundred RPM without special lubrication/cooling circuits - something which due to financial constraints I try hard to avoid.

 

[UKpete]

The ultimate technical solution is to use active magnetic bearings. Of course these have some disadvantages such as higher cost (non-standard products) and bulk, but the temperature should not be a problem and certainly the speed won't be. And they will run and run.

 

[pumpkind]

UKpete , unless I misss somethin -> the major limit of using magnetic bearings in any application is TEMPERATURE.
I am not aware of any application where magnets can be used at temperatures above 200 ° C.

 

[UKpete]

pumpkind, active magnetic bearings don't include permanent magnets, they are energized by currents in their windings which are stator mounted. Although windings have their temperature limits, they can operate at up to 200°C (class C insulation) and being stator mounted they are more easily cooled.

The rotor bearing "journals" can be just plain steel shaft, although for very high speeds they are usually a laminated section of the outer layer of the shaft, in order to limit eddy currents. They need position sensors mounted in the stator to sense rotor position, and operate in a closed loop PID control system.
Temperature capability is certainly superior to oil bearings, the disadvantages are usually the long lead time and cost as there are no standard ranges available (each application must be individually tuned). They can also be quite bulky and require an external electronic controller.
For examples of suppliers see:

http://www.skf.com/portal/skf_rev/home

http://www.calnetix.com/bearings.cfm

http://www.s2m.fr/chap3/index.html

http://www.waukbearing.com/magnetic_bearings

(I should declare an interest here, I am an employee of the latter company).

Nearly all the applications I have heard of are for either very high speed machines (where oil bearing life is too short), or very large machines (where there is a great saving in bearing losses).

Permanent magnet bearings are described as "passive magnet bearings", which it can be shown are never stable in all axes e.g. whilst it is possible to make a passive radial bearing, the axial bearing must be a mechanical bearing. They cannot be made as stiff as active magnetic bearings. Samarium cobalt (a common rare earth magnet material) can operate at over 250°C without irreversible losses.

 

[Hippo41]

Why make things so complicated?

The SKF deep groove ball bearings for extreme temperatures don't go to 100mm shaft sizes. But you can get heat stabilised bearings (usually spherical roller bearings) for extremely high temperatures.

Your main problem will be to keep the lubricant cool (and in the housing) - but that can be solved quite easily with proper housing design.

Speak to one of the main players.

Lester Milton
Telford, Shropshire, UK

 

[pumpkind]

Thanks Hippo for the input - however, in fact SKF did found for me a dia 110 deep groove bearing for high temperature - just got their e-mail today.
Subject to the design fesibility I will go probably this route.
I must say that SKF technical help was outstanding.