What's new
What's new

Long Life, High Reliability Bearing Design Problem

Bcavender

Plastic
Joined
Aug 1, 2017
I need suggestions and advice on a permanently lubricated bearing selection for a lightly loaded, low speed, but continuous remote application that I can make as reliable as possible through higher quality hardware or clever design.

I am shooting for a zero maintenance design with higher end, but still off the shelf technology without going to some impossibly expensive exotic hardware if possible. In other words, the situation can justify 3-5 times higher bearing investment over typical decent quality bearings to extend the system's serviceable life.

The design requires a 12" x 3/4" shaft with only thirty lbs of stable, radial load shared equally between two bearings about 2.5" from the ends. Axial load <5 lbs.

Operation: Continuous 24x7x365. Shaft: Torque runs a stable, 50 ft-lbs at 600 rpm.

The environment: Closed room air quality, air temp 70-95 degrees F, humidity 50-70% non-condensing, no chips, flying dirt/dust/etc. I expect shaft temp to stay below 100-110 degrees.

I would like to hit a design life of 20 years. That might be doable or not (or maybe it could go longer), but this is outside my experience level and my digging around the Internet doesn't turn up anything like this. Maybe I am Alice dreaming here for that kind of life performance, but I can't help but wonder that someone out there in this community has seen a case like this that actually worked ... like back before when business 'managers' required stuff to be designed only so that would last until the end of the short warrantee period.

Any suggestions for bearing types, vendors, comments, other ideas, etc. are greatly appreciated!

Thanks!

B
 
I need suggestions and advice on a permanently lubricated bearing selection for a lightly loaded, low speed, but continuous remote application that I can make as reliable as possible through higher quality hardware or clever design.

I am shooting for a zero maintenance design with higher end, but still off the shelf technology without going to some impossibly expensive exotic hardware if possible. In other words, the situation can justify 3-5 times higher bearing investment over typical decent quality bearings to extend the system's serviceable life.

The design requires a 12" x 3/4" shaft with only thirty lbs of stable, radial load shared equally between two bearings about 2.5" from the ends. Axial load <5 lbs.

Operation: Continuous 24x7x365. Shaft: Torque runs a stable, 50 ft-lbs at 600 rpm.

The environment: Closed room air quality, air temp 70-95 degrees F, humidity 50-70% non-condensing, no chips, flying dirt/dust/etc. I expect shaft temp to stay below 100-110 degrees.

I would like to hit a design life of 20 years. That might be doable or not (or maybe it could go longer), but this is outside my experience level and my digging around the Internet doesn't turn up anything like this. Maybe I am Alice dreaming here for that kind of life performance, but I can't help but wonder that someone out there in this community has seen a case like this that actually worked ... like back before when business 'managers' required stuff to be designed only so that would last until the end of the short warrantee period.

Any suggestions for bearing types, vendors, comments, other ideas, etc. are greatly appreciated!

Thanks!

B

.
grease is soap and oil and it tends to break down in 5 to 10 years. many fans and pumps designed for long life have large reservoirs of oil or grease. never seen sealed bearings last longer than 10 years. all sealed bearings slowly loose lubricating oil though the seals. at least thats been my experience
 
I need suggestions and advice on a permanently lubricated bearing selection for a lightly loaded, low speed, but continuous remote application that I can make as reliable as possible through higher quality hardware or clever design.

I am shooting for a zero maintenance design with higher end, but still off the shelf technology without going to some impossibly expensive exotic hardware if possible. In other words, the situation can justify 3-5 times higher bearing investment over typical decent quality bearings to extend the system's serviceable life.

The design requires a 12" x 3/4" shaft with only thirty lbs of stable, radial load shared equally between two bearings about 2.5" from the ends. Axial load <5 lbs.

Operation: Continuous 24x7x365. Shaft: Torque runs a stable, 50 ft-lbs at 600 rpm.

The environment: Closed room air quality, air temp 70-95 degrees F, humidity 50-70% non-condensing, no chips, flying dirt/dust/etc. I expect shaft temp to stay below 100-110 degrees.

I would like to hit a design life of 20 years. That might be doable or not (or maybe it could go longer), but this is outside my experience level and my digging around the Internet doesn't turn up anything like this. Maybe I am Alice dreaming here for that kind of life performance, but I can't help but wonder that someone out there in this community has seen a case like this that actually worked ... like back before when business 'managers' required stuff to be designed only so that would last until the end of the short warrantee period.

Any suggestions for bearing types, vendors, comments, other ideas, etc. are greatly appreciated!

Thanks!

Overthinking it. You do not really have a major challenge, and would have to WORK at to NOT get a 20-year life. Examples are all around you.

The Bodine Brothers. Fractional HP motors so legendary durable their advertising once read:

"Bodine motors DO TOO wear out! They just take longer."

The vast majority of the era had plain sleeve bearings. Polished steel shaft running directly in the light metal of the housing. Just finished to a standard of excellence other motor makers considered outright insane. Reliable oiling well-captured was the rest of the "secret". And they just ran, and ran, and ran...

"Veteran" machine-tools. The DC motors and MG in the 1942 and 1944 10EE here appear to have the original, open, purge-greased, not sealed, bearings. Same age for their oil-lubed spindle bearings. Neither lathe enjoyed anything close to a "clean' nor moderate temperature life.

Published sources: Reliance Electric & Engineering recommendation that if a distributor held their motors in racks as inventory, or a customer held spares? Each idle motor should have its shaft turned over a few revolutions by hand not less than once in six months. That to prevent the grease in the sealed bearings from gradually slumping all to the low side.
YOUR shaft never stops, so...

Legends: In a lower gallery of the now-mostly "tourist attraction" Obersalzberg salt mine sits a near-as-dammit all-solid Copper steam brine pump. They shut that pump down after one hundred years of non-stop operation. Nothing wrong with it, even so. They just had gotten wired for electricity, no longer needed to MESS with steam.

Dumb stuff: Blower motors on residential HVAC "air handlers". The AC "outside" unit may lose a fan motor or compressor at fewer years than 20. The air handlers usually last longer.

You have a more-favourable than average environment, low/no corrosion. Most any sealed bearing will give you 20 years of life so long as it is not "overstressed" against its ratings.

Mind - it is not MEANT to do. Greases deteriorate at under ten years. Sealed bearings are expected to fail. They are cheaply replaced. ONE service call in 20 years OK?

An under-stressed "premium" NON sealed bearing with decent reservoirs of a sort similar to these old Reliance motors on elevators & 10EE lathes ... that never got the memo that it was SUPPOSED TO FAIL ... might go fifty years and more. Not rebellious, mind. Just ignorant.

:)
 
If it really will run continously that long then I would consider a plain bearing. Should be simple enough to incorporate an oil reservoir and pump, which could be quite small. There would be no metal to metal contact and 20 years would be nothing for such an arrangement.

I see Thermite beat me to it. I might add that my home central air/heat blower is at 24 years on Oilite bushings.
 
Tom,

Ten year grease addition would be a workable option if available.

Do you have a favorite bearing company from past experience?

Bruce
 
depends on environmental conditions. i have often seen sealed bearing loose grease and dry out in 2 weeks on a printing press.
.
seals are not 100%. tripled sealed farm bearing to keep the manure and dirt out are very hard to turn cause they got triple contacting or rubbing seals.
.
usually longest lasting industrial equipment got lubricant going in periodically and a way for excess lubricant to come out. if nothing else the lubricant purges out the dirt and old lubricant (and metal particles coming off the bearings).
.
much of industrial equipment i had job to change the oil or if greased to try to remove most of old grease( often black) and replace with fresh red, blue or white grease. color often used to indicate age or condition of lubricant.
.
sure if you change lubricant periodically just like on a car, equipment last longer. try never changing oil on a car and see how long it lasts
.
automatic oilers that drip a drop every few seconds from a large reservoir been around a long time. often not noticed on equipment unless its your job to keep them full. from experience let then run out of oil and the bearings will fail.
 
depends on environmental conditions. i have often seen sealed bearing loose grease and dry out in 2 weeks on a printing press.
.
seals are not 100%. tripled sealed farm bearing to keep the manure and dirt out are very hard to turn cause they got triple contacting or rubbing seals.
.
usually longest lasting industrial equipment got lubricant going in periodically and a way for excess lubricant to come out. if nothing else the lubricant purges out the dirt and old lubricant (and metal particles coming off the bearings).
.
much of industrial equipment i had job to change the oil or it greased to try to remove most of old grease( often black) and replace with fresh red, blue or white grease. color often used to indicate age or condition of lubricant.
.
sure if you change lubricant periodically just like on a car, equipment last longer. try never changing oil on a car and see how long it lasts
.
automatic oilers that drip a drop every few seconds from a large reservoir been around a long time. often not noticed on equipment unless its your job to keep them full

Such bullshit. And you forgot to tell us how much money you make.
 
i have been a millwright and maintenance machinist for 32 years. did my share of lubricating equipment and changing bearings. maybe changed a few thousand bearings and lubricated at least 10,000 over the years. i have also seen hundreds of damaged bearing housings where bad bearing was spinning in bearing housing rather than turning in the bearing. we used to call it shake rattle and roll test. shake if you felt excess movement was sign of bearing housing damage. seen it many times. i had job to fill excess bearing housing clearance with polyurethane rubber to lessen machine vibration (causing sudden random bearing failures) and get big machine running. the $30,000 in replacement bearing housings took 2 months to get made and replaced. we spent less than $100 on the polyurethane. boss gave a pay raise on that one too and having machine not in production the loss would have been easily over $300,000 loss
.
on a printing press i kept of 3 foot high pile of used bearings worth easily over $30,000. nearby. i tried popping seal off and cleaning and relubricating and saved maybe $10,000 a year on bearings
.
and yes boss did give me many pay raises. i was making over $8/hr more than average worker.
.
bearing brands i cant say much. we later used to use bearings from Turkey. actually they were pretty much the same. only thing with big bearing company is they have more selection of seals and shields for bearings. i had a special sealed bearing i had to order enough for the year as they only made them once a year. bigger bearings can be $300 each (or more) it aint cheap to order enough for the whole year
 
I have repaired a lot of pump shafts using a tourch buildup rotoecing or exertion coating to return the beating surfaces and customers did that a lot vs mew pump shafts. The secrets we employed is straighten the shaft dead on,then machine the bearing surfaces just right and the after clean and checked fo total roundness and concentricity we would use the best bearing we could and carefully press the bearings on ourselves. Other things like lubrication were the customers choice. Unless asked we went no further than that unless the customer wanted. 20 years was a lot of time back then with things made it was not always the best like American cars and trucks.
 
Thermite,

Excellent anecdotes. That gives some great insight. Very helpful.

"Understressed" ... I reran my searches using bearing 'derating' and found two interesting points I had not found before that are really helpful.

Evidently bearing life extends by the cube of derating. So if you derate its load by a factor of 2, the life goes up by 2^3 or 8 times. That is significant. The detailed calculation for axial/radial loads is pretty complex, but it opens a path for final solution here. Here is the detailed calc I found from a bearing specialty company:

Load Ratings & Bearing Life by New Hampshire Ball Bearings

Also, bearing material enters the pic at well. This chart shows a potential 3X to 20X life improvement on top of the derating improvement.

Bearing Materials.jpg

The affordability of these more durable materials remain to be seen, but discovering these two factors gets me in motion again on moving towards a design that I think I can have some confidence in.

20 years service would be 6,300 Mrevs at 600rpm continuous. If I could find a bearing with 6 million revs as expected full load life and then derate it 10:1 ... that would get me in the ballpark. Harder materials could contribute as well.

Thanks for your good comments! That's a big help on this end.

B
 
I have repaired a lot of pump shafts using a tourch buildup rotoecing or exertion coating to return the beating surfaces and customers did that a lot vs mew pump shafts. The secrets we employed is straighten the shaft dead on,then machine the bearing surfaces just right and the after clean and checked fo total roundness and concentricity we would use the best bearing we could and carefully press the bearings on ourselves. Other things like lubrication were the customers choice. Unless asked we went no further than that unless the customer wanted. 20 years was a lot of time back then with things made it was not always the best like American cars and trucks.

.
sure i have seen a lot come back for rebuild after decades. bearing housings are also sometimes plated back to size or bored and bushing pressed in. shafts get brush plated and journals reground. i literally have seen that 1000's of times. many high speed machines cannot have stuff rattling and or vibrating even when its not a outright bearing failure yet
.
seen many bearings not outright fail but were chewing up spinning in the bearing housing creating looseness issues. or spinning on the shaft.
.
big equipment often you can pick up the shaft .015 to over 0.100. not suppose to be able to do. shake test is done cause a lot of stuff looks ok from 20 feet away thats got serious problems. never know problem unless you look for it
 
Tom,
I had briefly thought about some type large oil reserve because if you can keep that film in place, the bearings would do well. However the unattended nature of this job moved me to look for some way to design that out given the light load.

Great insights on the situations you have seen.

Thanks for the comments!

B
 
Might also look at hybrid ceramic ball bearings running in steel races.

Dynamic balance of the shaft with whatever it is carrying would also be very important to long life with rolling element bearings. Fretting damage could be a limiting factor as the bearings do have the freedom to bounce around internally, even with the tiny bit of clearance they have.
 
.
sure i have seen a lot come back for rebuild after decades. bearing housings are also sometimes plated back to size or bored and bushing pressed in. shafts get brush plated and journals reground. i literally have seen that 1000's of times. many high speed machines cannot have stuff rattling and or vibrating even when its not a outright bearing failure yet
.
seen many bearings not outright fail but were chewing up spinning in the bearing housing creating looseness issues. or spinning on the shaft.
.
big equipment often you can pick up the shaft .015 to over 0.100. not suppose to be able to do. shake test is done cause a lot of stuff looks ok from 20 feet away thats got serious problems. never know problem unless you look for it

Wow if we had been able to grind the shaft with equipment it would have been great. I have also made and pressed and shrink fitted bushings also including making grease hole in the bushing and manually groove the I’d for lubrication. Brass,navy brass, and steel sleeves shrink fitted and turned to size. Back in the old days we always used Timkin bearings as they were the best we knew.
 
I need suggestions and advice on a permanently lubricated bearing selection for a lightly loaded, low speed, but continuous remote application that I can make as reliable as possible through higher quality hardware or clever design.

I am shooting for a zero maintenance design with higher end, but still off the shelf technology without going to some impossibly expensive exotic hardware if possible. In other words, the situation can justify 3-5 times higher bearing investment over typical decent quality bearings to extend the system's serviceable life.

The design requires a 12" x 3/4" shaft with only thirty lbs of stable, radial load shared equally between two bearings about 2.5" from the ends. Axial load <5 lbs.

Operation: Continuous 24x7x365. Shaft: Torque runs a stable, 50 ft-lbs at 600 rpm.
...
Any suggestions for bearing types, vendors, comments, other ideas, etc. are greatly appreciated!

Thanks!

B
Sounds like the ideal situation for igus bearings. Very helpfull on the phone to discuss options. I have used them for tricky situations in the past with great success.
 
Plain bearing, small oil reservoir and a stupidly simple slip ring to keep the bearing lubricated. Of course this means your shaft orientation has to be horizontal. There are 80-100 year old electric motors still running using this arrangement and I doubt the oil in them has ever been changed. A simple hydrodynamic bearing analysis will tell you if this will work given your shaft size, loading and speed. Might turn out you need a slightly larger diameter shaft given your radial load.
 
20 years is 175k hours....... say 5 to 10 million miles in a car....

furnace blowers don't run 24-7

you are on the right track with de rating or over specing the bearing.

I recall seeing special specs for lubrication in bearings, you could probably find a long life grease.

Keeping the dust out and the heat low I would imagine would lead to retention of lubricant.
 
light bearing load

i saw a lot of lightly loaded bearings fail early. on a paper conveyance roller the varying web tension on paper would pickup roller and ball bearing was floating in bearing housing not enough pressure to keep outer race from just turning in the housing. it would spin wear to increase bearing housing clearance and once gets up to over .002 the ball bearing would rattle around bouncing in the bearing housing.
.
this would often cause sudden bearing failure with no warning. on a 500 roller machine we get machine shutting down every day cause one of the rollers failed cause extreme vibration sometimes screws would start coming out from vibration
.
they make wavy "tolerance rings" to always grab outer bearing race and normally inner bearing race was pressed on or loctite used and or a screw to help hold inner race. it was so had maintenance guys would remove bearing housing cap and put paper on bearing to put pressure fill excess clearance gap in worn bearing housing
.
automatic drip oilers been around over 150 years. most plain bearings had them as oil would slowly come out of the bearing. not a bad things as it helps flush dirt and stuff to come out of bearing. they got automatic grease devices. i have seen some malfunction and get too little or too much used too fast. oiler is usually better as can see the oil level through the sight glass
.
automatic drip oiler
automatic drip oiler - Google Search
.
bearing tolerance ring
bearing tolerance ring - Google Search
 
I would use a high quality sealed bearing, at those speeds and loads it could well last 20 years.

Why 20 years? Is it inaccesable, or have you arbitrarily chosen 20 years as a goal?

I have the cheap chinese bearings (R8, $19.95 for 10) running in rollers I make at a local printing company, some have been in the rollers close to 10 years, probably 50-60k hours, no failures yet.
 








 
Back
Top