TEFC motor service life?

AS long as you don't overload and/or overheat it, the bearings are first to go. Sleeve bearings last longer than ball bearings, I'd look at numbers like 50k hours for sleeve, half that for ball bearings. I'm sure that someone in the motor industry will chime in.

I have an older GE 240volt/ half horse that has a tag that reads "Relubricate every 10 years of normal service"

Ken Grunke wrote:

oh wow, I've got 24,000 hours left. Cool!

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Hi, I can't speak to that particular motor, but bearings in a small motor that size can have L10 life expectancy well into the 40,000 to 80,000 hour range. Loading is a key factor -- tighten the belts up excessively and bearings or shaft can fail in 10s of hours.

For motor winding life, heat is the key. Run at 70 or 80% of load in a cool ambient, life can easily be 100,000 hours or more. Run it at over load in a higher than rated ambient and life might be down well under 10,000 hours.

Voltage spikes can be the other killer. If motor is running from a variable frequency drive and is not properly matched to that application or if you have a lot of other power system disturbances, that can also cause problems.

My guess is that you have lots of hours left.

Mill

My 1hp tefc baldor motor bearings began to have excess play in them after running for several hours a day grinding woodchipper knives. I think during that time I consumed near to $ 8000 in abrasives on that machine. They only lasted from 1987 until this summer. I think the replacements were around 16.00 and when I replaced them the one on the fan end was still pretty good. Ball bearings. I did switch to sealed over the grease fitting bearings this time around because they should last long enough.

So the good news is they are not hard to replace, and last a long time and you have many choices when replacing them because the sizes for the different types are pretty standard.

I am curious, why would sleeve bearings last longer than ball bearings. This seems counterintuitive. If they do last longer, then how come ball bearings are advertised as superior to sleev bearings.

I'm not a bearing engineer.

That having been said - bronze bushings are frequently used in this application, and bronze is somewhat self-lubricating. Slippery by nature. There are also bronze bushings which are porous and hold oil, so the oil wicks into the bushing/shaft area to keep things slippy. Ball bearings are more precise, but I'm not sure I would agree with a global "sleeves last longer than ball bearings" statement. Sleeves are cheaper, balls are more precise, roller bearings can handle more load (and load in interesting directions). So, depending on the use, sleeves are superior, or balls are better, or rollers are better.

Dave Hinz

Thanks Dave.

I wondered about that also. I think that with sleeve bearings, there are more variables involved--the shaft finish and fit in the bearing, proper lubrication, and amount of load...

Ken Grunke

There are true sleeve bearings and some not so true. The kind found in small motors are usually sintered bronze and run in what is called boundary lubrication mode. There is some metal to metal contact (especially in belt drive applications) and thus they do wear out.

In larger industrial motors, turbines , generators, etc. true sleeve bearings are used. There is no metal to metal contact, as the shaft floats on a hydrodynamic oil film formed by the rotation of the shaft in the sleeve bearing. If the oil is kept clean and cool, there is no wear out mechanism and the machine will run until shut down for some other reason.

Antifriction bearings are common on motors up to about 500 hp ±.. The rated life can be as much as 200, 000 hrs if they are properly lubed and shielded from dirt. The bearings in small, consumer grade motors are usually as cheap as possible and not well shielded from dirt, leading to a short life.

Randy

Hey Randy, I use a small motor with the bronze bearings in a belt drive application. Little tefc motors that are welded shut. About 80$ new in Dayton brand. What I do is turn the motor 90 or 180 degrees because as the bearings wear they wear egg shaped with 3/4 of the surface unworn and a 90 degree or less segment wasted. Any way I can get 3x the life or better. And half the amount of lubrication you would think you need works better. It's on a saw chain grinder.

In my understanding, ball bearings are specifically not ecommended for residential furnace air moving because sleeve bearings are a lot more quiet.

In a properly lubricated bearing, either sleeve or antifriction (ball or roller), there is no mettal to metal contact. Moving elements are seperated by a thin film of oil. Under this condition, sleeve bearing life is effectively infinite. Even with proper lubrication, antifriction bearings have finite life because of metal fatigue. Metal fatigue is the L10 life calculation done for antifriction bearings. In reality, few bearings fail from fatigue. Usually their life is cut short by contamination or improper lubrication.

Mill