Can I safely overspeed a Baldor motor?

[NC Cams]

Some points to ponder regarding the prior comment:

"...Quite obviously an overloaded, dirty misaligned bearing running completely dry at an extreme temperature is not going to last long at anything like its full published speed or load rating..."

Re Overheating: Most motor engineers do NOT consider an operating temp of 200 to 220 deg F to be "overheated". However, for every 10 degrees you run a mineral based lubed bearing over 212 Deg F, you cut the grease life in HALF. It is not that bad for synthetics but the life does detiourate with temp none the less.

Thus, at ~220 F, you cut the life in half. At 230F, half again and at 240F, half again. Half of half of half equals about 1/8th the grease life of a bearing that runs at 180F or so which is quite substantial. I've seen engineers consider 250 deg F (Example: underhood temp of a car idler pulley or alternator can approach 400 deg F and this is "normal"). And the same engineers were surprised when a "normally" loaded bearing couldn't/wouldn't live under these "normal" 250+F conditions.

Re Misalignment: it can be rather easy for sloppy case fits and tolerance stacks AND thermal distortion to result in bearing misalignment. With misalignment of as little as 1/10 deg (6 minutes, which isn't much at all), the inner ring gets skewed and the balls speed up and slow down as they orbit arount the raceway. This is a result of the balls going up the one side of the raceway, crossing over the center and then doing the same on the other side of the raceway,

Result: the cage gets hammered by the balls constantly changing orbit speed as they instantaneously go thru a different instantaneous radii as they travel back and forth. Initially, the cages rattle from the hammering but in severe cases, and especially at high speeds, the cages can actually get pounded appart. The shorter the case, the worse this is.

I doubt that most folks would consider 6 minutes of misalignment "severe" but, sadly, it can be, ESPECIALLY at max rated speed.

Re Overload: Would you consider running a bearing at 50% to 60% of the rated capacity "overloaded"? Probably not.

HOWEVER, the load life projections are all based upon the bearings NOT being loaded anywhere near that hard, EVER. As I recall, the foundation of the load life factors is based upon what is called L10 life and this is calc'd at roughly 10% or so of the rated capacity.

If you want the bearing to "live" at the max rated speed (say 5900), you'd better only load it to a small fraction of the rated capacity (say 5% to 10%).

Re LIFE DERATING factors: there are "derating factors" that exist for bearings that are used for serious bearing load/life calculations. For each and every "off' condition, there is a sliding scale "derating" factor that, when applied to the theoretical load life calculation, will predict to some degress how much less a bearing may live when "off conditions" are unavoidable. You'd be amazed at how fast these minor "inconsequentialities" cut into the rated life of bearings.

These derating factors are NOT always published as they are somewhat empirical and they are not always politically acceptable. Customers always look for how sloppy they can get away with. Meanwhile, bearing engineers are always trying to make the client happy with bearings that can/will live in less than optimum operating environments.

The point I'm trying to make remains as follows: don't look for the number you want to see with regard to the speed or load or whatever rating for a bearing that you are planning to use/abuse.

If you study the applications and design manuals, you can often find the specs needed to tune up an application so that it can run at high speeds and loads.

But don't ever think that a SWAG perusal of and compliance with the easiest to achieve, convenient "specs" in the catalog will ever totally suffice for choosing and applying ALL the critical life affecting factors properly to bearings.

I will agree that the "recommendations" that are found in catalogs are both a function of empirical knowledge. More importantly, however, they are a result of true and proper load life calculations. These are tempered with sound judgement and the knowledge of what you can and can not get away with regarding the inevitable "off conditions" that occur.

Search out and find the load life calculations for the bearing you want to use/abuse. Do the math. When you do, then see if the bearing suppier offers a derating calculation method. Do the math with some realistic off condition assumptions or realities. You'll be amazed what you'll learn and what the calculations can predict.

We had an application where two engineering managers picked some bearings out for an application that they "knew" would work. The application was a high pressure hydraulic pump. The bearings failed in 15-20 minutes time after time. The project was dumped into my lap because of my prior "bearing experience". The first thing I had the engineers do was run the pressures thru the pump and figure out the gear loads.

To no small degree of amazement, the gear separtion forces were well over the theoretical rated capacity of the bearings. The calcs said the bearings shouldn't have lasted 5 minutes - amazingly they lasted 15~20. Seems that the "expert" managers figured that the rated capacity of the bearing was what it would be capable of tolerating so off they ran with a woefully undersized bearing.

We eventually got the thing to work but nobody EVER chose a bearing again without showing load life calculations at that company. And management scrambled like crazy to bury the costs from this abject stupidity anyway they could...

[Warpspeed]

I cannot disagree with any of that.

As a now retired electronics design engineer myself, I can certainly identify with your strong feelings and great respect for margins, tolerances, and attention to detail, as well as the value of many years practical experience in the same field.

So I bow to your superior knowledge.

But having said that, there is also a place for the amateur to sometimes push the limits of what in other circumstances may be seen as fairly risky.

The home hobbyist that has bought an ultra low cost motor on e-bay may be more inclined to "try it and see" rather than pay a consultant to do all the calculations. If he overdoes it, and the bearing becomes noisy, he can always then try a new bearing. If that fails too in a short time, then it is probably not a complete disaster.

Whereas a professional engineer working as part of a design team for a large corporation designing mass produced machinery, needs to take a much more sober approach.

There must be some middle ground to all this somewhere.

[NC Cams]

A piece of sage wisdom that has served me well both professionally and personally:

DIY'ers (and many pro's for that matter) never seem to have the time to do the calculations and/or the job right the first time BUT, BUT they always seem to have the time and $$$'s to do it over and over and over if they end up doing it wrong the first time.

Time after time, I've had clients do the latter and wish (and oh how they wish) that they'd done the former.

Caveat emptor.

[Warpspeed]

Ha-ha, yes indeed !!!

Funnily enough a recent e-mail from a friend has had me thinking about all this before I saw your last post.

As a poor but enthusiastic engineering student I used to rush headlong into projects, and usually ended up destroying things, or having to do the job twice (or more). Failed or abandoned projects were not that uncommon either.

Times change, and in maturity as a professional design engineer I had the resources and knowledge to do things properly and rigorously. It is easy to look down at the amateur tinkerer with disdain. But quite likely most of us started out that way.

Now in retirement, I have plenty of time to think things through, but very limited resources. Projects take forever to complete, but they always work.

Wouldn't it be wonderful to have both the exuberance of youth and the experience of old age.

[NC Cams]

Youth is wasted on the young.

[in2steam]

Originally Posted by NC Cams A piece of sage wisdom that has served me well both professionally and personally: DIY'ers (and many pro's for that matter) never seem to have the time to do the calculations and/or the job right the first time BUT, BUT they always seem to have the time and $$$'s to do it over and over and over if they end up doing it wrong the first time. Time after time, I've had clients do the latter and wish (and oh how they wish) that they'd done the former. Caveat emptor.

I find that statement funny, not meant as an insult, and may truly show that my experiences in life have been less then "the best" in regards to engineers as I personally know several that I wish I had at my current company and past employers also. But when I was at leeson a good amount of geuess work went into the engineers prototypes, this often showed, at least in the electrical end, the mechanical engineers seemed to have a better handle on what they were doing they were always refining(i.e. making it as cheap as possible).
Currently when I hear the words "engineering is involved" I tend start thinking of ways to fix there messes, esp if I get to see while its a work in progress(one of the benefits of being on an off shift). I long ago stopped recomending to them and quitely fix the problem(s) after they have long gone(or given up and have someone else consult them). I also like to make the documentation that they neglected to do like ladder diagrams and wire numbers for my own benefit if not theres when they come back brag about how good its working (to our customers). That is untill they open up the beast and see that its not always the way they left it, but then again they can never say for certain as they never had prints there and mine are done in language they don't understand very often,~maintenance~. More often then not though many of there projects end up as white elephants that never get used on the production floor as they never bother to ask the people who are going to use it how it should be done. This has also lead to some ergonomics and quality problems too, I can keep going....

chris

[NC Cams]

Engineering schools are NOT doing superb jobs of creating/training problem solving engineers anymore. They are, however doing a lot of "program manager" training wherein enough technology for the guy to "manage" programs is conveyed. But, not necessarliy enough info or knowledge for the technically inclined person to truly "engineer" the item sufficiently is being conveyed.

Moreover and sadly, the engineering school attentdee's are looking for answers to test problems - they are NOT appreciably interested in learning how to figure out how to solve the problems under a myriad of situations.

This is why the budding graduates don't know how to delve into a problem, learn what's going on and come up with viable solutions/alternatives to make things work properly or correctly.

Want proof?

Do a search on the topic of "bearing fits" here on the 'Zone. You'll readily find "answers" thrown around on how much press fit to install a bearing at, even though a bearing shouldn't always be pressed into the housing. How to properly fit the bearing for any particular application requires knowledge and an understanding of the loads and operating environment.

Sadly, the folks who jump on the "Zone and ask "how much press?" are looking for a quick and dirty answer, NOT the knowledge on how to properly fit the item.

Sadly, the proper answer and the knowledge required to determine the RIGHT answer are NOT always one and the same.

[Warpspeed]

Oh, this is all so very true.

My knowledge area is in electronics design, but I agree that an apprentice fitter and turner probably knows far more about fits and tolerances than many a graduate engineer simply because he is a lot more familiar with it.

In electronics, many graduate engineers go straight into design work, thinking that a few esoteric mathematical formulas and a head full of software will get the job done. Many are hopelessly impractical in their outlook, and are utterly useless for anything other than teaching. They usually end up in sales or management making everyone else's life a misery.

The best practical engineers are usually the guys that started out on the workshop floor, or as service technicians, and did some mature age part time study the hard way. Those guys have a practical hands on background and fully realize that being able to reach all of the screws, simple straightforward assembly and disassembly, and having proper documentation is all part of good equipment design.

I think we all know of nightmares where it takes five hours for an experienced service guy with all the right tools to replace a simple broken drive belt, because the original equipment designer was a complete idiot.

And if it can be fitted in backwards, eventually someone will do it. So design the bloody thing so it can only go back together one way !!! Design for manufacture is a whole other subject. Some engineers just completely lose the plot when it comes to being practical.

End of rant...

[in2steam]

Originally Posted by Warpspeed Oh, this is all so very true. I think we all know of nightmares where it takes five hours for an experienced service guy with all the right tools to replace a simple broken drive belt, because the original equipment designer was a complete idiot.

AMEN!

My personal favorite story in that right is, that me and my boss, were in on a saturday to cordinate with the engineer in charge of findng a problem with a press(which to this day some years latter has never been fixed), we got in at 6am and he showed at around 9:00, of course he promptly went to breakfast and was ready to go by 10:00 about the time we start cleaning up and go home to our families. At any rate we were replacing a linear bearing we found bad in the process of waiting for him to arive. The grease zerks and wipers on the ends were neglected for the required lubrication, since you had to disassemble the press for around 30 minutes to get at that one bearing it was neglected on my part more often then not. In of itself it was a straight forward replacement I would rate as typical. Upon arriving back from his little snack, the engineer (around a 10 year employee 5 of which as a engineer) looked at us and asked why we were wasting our time with greasing bearings? We then proceed to to tell him that this one had failed, due to lack of lubrication, and was getting replaced. He looked at us straight in the face, not more then 1 minute before me and my boss were on the computer to look at the lubrication interval (from INA)mind you, and said "linear bearings don't fail becuase of lack of lubrication, you don't need to lubricate them. And starts to go off on his pulpit about how he would have to check the alginment and build some sort of fancy jig to replace this bearing(which I had helped the people who retro fitted to not more the 6 months before, they just put it in right or wrong.) that had been mounted on a flexible piece of alum orginally using plain bearings. My boss nearly through the bearing at him, I think he was going over in his mind about the impending jail sentence and less time with his family, in my opionion I would have bailed him out.

chris