Bearing with too high temperature in summer, how to cool it? 2

[foxstar]

Hi! This subject is somewhat new to me, however I studied it quite deep at my graduation course. The case: Steel industry,i was called to meet three motors each with power of 250 kW, two bearing and a the motor shaft in between. In summer time the temperature rises up to 95 to 98 ºC. They ask me how to cool it? With new bearings having some closed circuit where cool-water from cooling-tower, will circulate as function of the bearings temperature? Or taking other approach less invasive, cheaper. Any tip, hint will be most appreciate. Tks to you All.

 

[electricpete]

One thing you should avoid is cooling the housing dramatically. That can decrease the bearing internal clearance... possibly very bad news, especially if you apply cooling before the machine is started. I think I'd rather take my changes with 95-98C (by the way is that measured on the housing?.... one ends or both? TEFC motor?).

If you have greased bearings, I don't think there is much hope to apply external cooling.
If oil, maybe you can cool the oil reservoir.



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(2B)+(2B)' ?

 

[foxstar]

Hello Electric(Pete),
As a matter of fact, there's some critical issues about the possible thermal-shocks. In fact, we have to explore the oil approach. I must confess, was thinking in this direction too and your opinion enforces it indeed, in spit of looking at the problem from other perspectives as well. I do thank you for your advice and expertise. I hope to hear from you again and the Forum, because this is a very common situation we have to deal with in process industries.
Any contribution will be welcome, thank you all.

 

[dgallup]

What is wrong with 95 to 98 C? Lots of transmissions are designed to operate just over 100 C to avoid problems with water buildup. Plenty of lubricants that work very well in this range.

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[foxstar]

Hi DGALLUP, maybe you are rigth, I'm going to check the the measured temperature profiles. I'll let you know. Tks.

 

[foxstar]

DGALLUP, I just checked the bearing temperature range. It's goes up to 98ºC, sometimes higher, 105ºC. It might be reasonable, to increase cooling the (forced pumped) circulating lubrificant outside the bearing. Thanky you.

 

[chicopee]

If the ambient temperature is lower than the 98 dC, air cool the bearings with fans mounted on the shaft.

 

[ccfowler]

foxstar,

I would want to take a closer look at the oil used in the bearings. It is not unusual for excessive viscosity to be used based on the assumption that it will provide better wear protection for the bearings. This is particularly true where elevated bearing temperatures are being experienced. You may find that substituting a suitable lower viscosity oil with good thin film strength properties may cure the problem. The needlessly high viscosity oil can lead to high temperature problems or even cause the high temperature problem due to the greater fluid friction involved.

I've encountered cases where the effects of using a lower viscosity oil eliminated all of the previous bearing cooling problems, and bearing life increased.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[foxstar]

Hello my Good Fellows!
Thank you for your expertise and advice! No doubt we are approaching to the solution, "I can feel it", something in the line of what CCFOWLER wisely expressed in his post.

My "technical feeling" says that the main solution is related with the oil system and its lubrication capacity in those almost extreme conditions, if we have to increase the oil rate or not and one important aspect said by CCFOWER, the oil viscocity. Maybe we can use it of a bit lower viscocity without compromise the "wear protection for the bearings.",as CCFOWLER has mentioned as well.

ASnd if this is not enough the CHICOPEE's suggestion can work pretty good, I would applied in a second approach to the problem, in addition, if you allow me to say so. Thanks so much.

 

[romke]

one way to lower the operating temperature would be to use a less viscous oil. that will increase the lubricant flow through the bearings. that will reduce the shearinduced temperature rise and because per unit of time more oil is flowing through the bearings the amount of heat to be dissipated per unit of time will also decrease.

are you sure the oil you use is in accordance with the manufacturers instructions for this type of operation? most times instructions are given ofi a more general nature together with a suitable viscosity at 40 degrees C. those do not necessarily apply in specific cases.

 

[racookpe1978]

What is the air circulation in through AND around the motor? Can you increase air flow without getting water inside the motor?

Is the air restricted excessively to try to prevent the moist cooling-water-entrapped air from getting near the motor/ 100 C - if not needed for some other reason - is high based on my experience in power plants.