Bearings make the world go 'round.

It occurred in a blog post at Small Dead Animals regarding windmills and why so many of them seem to be broken, that people generally don't understand how basic machinery works.

 

Dead windmill in PEI. See that brown crap on there? We're going to talk about that later.

 

This is entirely expected. Education, in my Boomer generation and ever since, does not talk about machinery. At all. I believe this to be part of the hidden class-warfare against the Commoners in our society, the sort of pervasive disdain for plumbers, carpenters, mechanics and workmen of all sorts that permeates the media and Academia, but that is a topic for another day.

Today's topic is bearings.

 

 

So many bearings.

Ten thousand years ago, some guy in ancient Sumeria got sick and tired of pulling a big bag of wheat behind him on a travois. That's two sticks tied at one end and pulled along, dragging on the ground. 

 

The noble travois, in use.

 

 

That un-recorded genius decided to put something that ROLLS on the end of his travois. So he whittled a piece of wood round, put a hole in it, and invented the wheel. He also invented the axle and the bearing, but nobody talks about that.

World's oldest surviving wooden wheel. New meaning to the phrase "I got a flat."

And then, after a little while of enjoying the beauty of reduced friction that the wheel brings to our lives, he discovered that his wheel had worn the axle in half because his bearing really sucked. His next invention was probably grease. Remember that, it's important.

 

Travois, hipster version.

(Truthfully the first wheels were probably potter's wheels, but bear with me, I'm on a roll.)

It took a long time for his idea to take hold, but eventually animals and people pulling carts became the way of the world. Humans got really good at wheels, axles and bearings. They made them out of special harder wood, and eventually out of bronze and even iron. And they used grease too.

 

Not just for hair.

Fast forward a pretty long time, and we find the Egyptians using logs to move huge blocks of stone. Everybody knows this, right? Of interest here is that everybody spends a great deal of time focusing on the logs. Nobody seems to realize the log is only half the story. The other, and more important half is the ROAD they're pulling the block along. That can't be a dirt track. You get a ten ton rock and try to pull it across your backyard, the first thing that happens is the logs dig into the dirt. Those roads in ancient Egypt had to be smooth, they had to be flat, and they had to be hard. They also had to be cheap to make and maintain. That's important as well.

See how they don't mention the freakin' road?

Fast forward a little farther, and we find that the Romans got really good at roads. Whatever the Egyptians did to pull off their moonshot, building the Pyramids, the Romans copied it and conquered Europe with it. 

 

Probably not coincidentally we find the first use of ball bearings that we know of. ~40BC, in a luxury ship recovered from Lake Nemi in Italy. Used to make a rotating table, of all things. Probably fantastically expensive, because both the ball and the track that it runs in must be smooth and hard and flat. You really can't get a round track flat and smooth without some pretty special tools, and the fitment has to be just-so. Not too tight, not too loose. The balls were metal, the tracks were wood. Super expensive custom work.

Roman ball bearing

Roman ball bearings in use..

Reproduction of the rotating table, without the bearing race.

Fast forward some more, we find detailed drawings of ball bearings and bearing races from Leonardo DaVinci and Galileo. Their designs were wooden, and Leonardo included spacers between his bearings. 

 

Leonardo. Show-off.

 

 

John Harrison invented the caged roller bearing in 1740. Philip Vaughan patented the first ball bearing system in 1794, for trains. 

Of note is Isaac Babbitt of Massachusets, who developed his famous Babbitt Metal for use in poured machine bearings in 1839. The majority of industrial machinery and trains, boats etc. used poured bushings in their moving parts because that was the only way they could get enough precision at an affordable cost. Pre-1940s cars all have Babbitt bearings throughout, except for wheel bearings. Babbitt won the race for a long time not because it was the best, or the longest lasting, but because it was Good Enough and it was cheaper.

Babbitt bearing. Note cracking and piece that fell out.

After that, FAG began precision grinding bearing balls in 1883. In 1898 Henry Timken received a patent for the tapered roller bearing. In 1907 Sven Wingquist patented the self-aligning spherical ball bearing and race. After that, everything switched to ball and roller bearing because Babbitt wasn't cheaper anymore, and also because roller and ball bearings were better. So much better.

Tapered roller bearing, extra beefy.

So here we are, 2023, and the windmill industry, of all things one would never expect, represents the bleeding edge of bearing design and manufacture. The loads on the blade, the shaft and the generators inside those huge windmills are immense, intermittent, and unpredictable. Inside the guts of that huge bird chopper are roller bearings as big around as your thigh, running in races the diameter of your living room.

Now we come to some of the limitations that bearings have exhibited over the years. Remember how the Egyptian roads had to be smooth, flat and hard? Well, the bearing race for a windmill faces exactly the same problems. The link above goes to Liebherr in Germany, the same guys who make the huge cranes. It's no mystery how they do any of this stuff, they use forgings, metal lathes, milling machines and surface grinders. Really, really, BIG ones. Machines that can achieve amazingly fine tolerances of less than 1/1000th of an inch over 20 foot diameters, all day long, every day. The precision and consistency of manufacture is near-miraculous.

My living room is smaller, as it happens.

It's fantastically expensive. Affordable only because they make many, many units. But as one might imagine, you do not want to have to change out that bearing. It's meant to last the lifetime of the machine.

 

Imagine trying to move this thing. It goes on top of a 200 foot tall tower.

Which inevitably leads us to all those idle windmills around the country, and the reason they are idle. Brinelling. Named after August Brinell, the creator of the Brinell Hardness Scale. Long story short, Brinell tested hardness by pushing a metal ball of known hardness into a metal surface with a known amount of force, then measured the diameter of the dent it made. The harder the metal, the smaller the dent. 

 

 

Scientific divot.

It turns out that if you load a ball bearing or roller bearing with a static weight, the balls or rollers will make a dent in the races just like a hardness tester. Particularly if you bang on it, or vibrate it. That's Brinelling.

You don't want to see this in a bearing.

Brinelling occurs in windmills if they stand still. This is because although the roller is large, the part that is touching the race is very small. Just like the log digging into your lawn, the roller will dig into the race. Think of a knife pushing down on a piece of cheese. You don't have to push very hard, because the knife is thin. The cheese will hold up your finger, but not the knife.

 

Brinelling, turbo-nitrous version.

 

Under the types of loads common in the largest windmills, hardened steel will behave like cheese. It'll bulge, flatten, dent, bend, do all the sorts of things you don't want it to do. This problem is solved the same way our ancient Sumerian fixed his problem, grease. In the windmills they use oil pressure to keep everything rolling nicely and keep the bearings from digging into the races. If the windmill has to sit still for a while and be buffeted by the wind, it can survive if the oil pressure is kept up. 

 

Remember this? That brown stuff is not rust. That is oil. Oopsie.

 

But if the reason it is sitting still is because the oil pressure failed? Oh, that's bad. Because now your 20 foot diameter main bearing race has divots in it, and your six-inch rollers are all flat-spotted, and she ain't going to roll no more.

 

 

The more things change, the more they remain the same.

 

According to the CBC article we were talking about way back at the beginning, six out of ten windmills installed at a Prince Edward Island wind power facility in 2014 are now defunct. Busted. Not turning. No word on why from the Powers That Be. The CBC is mystified. What could it be?

Brinelling. That's what.