Turbine Transmission Failure

[ChrisOlson]

The wind is blowing really good here the last 36 hours or so.  Just after lunch I was outside picking up a pile of sawdust that was behind the shop where I cut logs for our woodpile.  Suddenly my 3.2 meter turbine with the high voltage neo generator made a big CRUNCH and it locked up.  It was probably putting out 2 kW when it failed.

I figured it was a transmission problem - first time I've ever had one fail.  With the good wind I wasn't going to mess with it today because we had plenty of power without it.  But later this afternoon curiosity got the best of me.  So I went and got the tractor and lowered the tower.  I pulled the transmission cover and there was no sprocket on the PTO shaft but the chain was still laying over the shaft where the sprocket should be.

So I went and got a pan and pulled the drain plug and drained the oil out of it so I could see in the bottom.  The pieces of the sprocket were laying in the bottom of the gearcase.  They had fell down there when the sprocket split in two, got tangled up in the chain and drive sprocket, and locked it up.



This is a hardened sprocket that I get from McMaster-Carr.  It obviously wasn't tempered right - it split right thru the keyway.

In the future I'm going to build these with a one-piece PTO shaft and sprocket, with the sprocket welded to the PTO shaft full circle.
--
Chris

[Watt]

Darn the luck Chris.  Murphy could have stayed away.

Just a thought.  When we have a gear made for our draw works, various duties, we do not have the gears hardened much below the chain wear path.  We have found hardened gears always cracked and eventually break just as yours did.  As I'm sure you know, the corner of a file will easily mark a non hardened surface. 

Thanks for the update.  Now get it fixed and flying.   

[birdhouse]

bummer chris!

this reminds me of what my brother deals with to an extent.  they fab all their own snow plowing gear for 3/4 and 1 ton trucks in michigan.   he will no longer use any grade eight bolts for his rigs.  he swears they get really brittle when it's really cold out. he has settled for grade 5 bolts, and is MUCH happier with them! 

just a thought about various hardening techniques...

adam

[Dave B.]

Sorry to see that Chris but I'm sure others will agree when I say thanks for posting this failure in detail right along with the good stuff. I understand the curiosity part of needing to know what happened, that sawdust pile can wait. I'm sure you'll give everything a good looking over and have this back together flying again soon. Thanks again for helping us all learn a bit more from your experiences.  Dave B. 

[ChrisOlson]

Well, this one is the only one with this type of sprocket in it.  And it was obviously either too hard, or not tempered properly.  The sprocket is so hard you can't scratch it with a hacksaw.

The ferrite machine has the one piece shaft with the sprocket welded to it.  I never took any detailed photos of it but it's laying on the bench in this photo and it happens to have a bearing flange laying on top of it.  But it's a one piece unit with the sprocket welded right to the shaft:



That's a much better setup than using a key on the PTO sprocket.  It's nicer to use the keyed sprocket because you can position it and line everything up easier.  It takes a little precision to build a shaft/sprocket weldment and that's why I used this sprocket in this transmission - it was easier to assemble and build.
--
Chris

[Wolvenar]

Also sorry to hear you had a failure.
But  on a lighter note we get to learn something from it!

I have used two piece sprocket / puller and shims here I wonder if they would work?

These the sleeve around the shaft is keys and compressed by the sprocket, or pully as it is bolted onto the  sleeve.
The sleeve part ( if that is what it is called) is not a terribly hard metal, however the sprocket is.

I will post some pics of one if I can get some pics tomorrow for those that do not know what I am talking about.

[ChrisOlson]

Yes, tapered sleeve bore pulleys and sprockets.  Those are not made in this size.  The PTO shaft is 1" and the sprocket is only 12 tooth.  Like I said, by far the best design is a one-piece shaft/sprocket weldment.  This is the first one where I tried to "cheapen it up" and it didn't work.  In fact, this thing didn't make it barely 550 hours on the tower.

The sprocket was cracked thru the keyway long before it broke yesterday.  It was making excessive geartrain noise for the last week and the keyway in the shaft is totally worn out from the sprocket being split and "working" on the key.  When she hit full song yesterday it finally decided it had had enough and the sprocket broke.

That's why you depart from "known works" to something new you put it to The Test.

Thousands and thousands of hours on the tower with these things and I've never had one even show any signs of wear on the sprocket teeth.  So its not like you have to have the sprocket as a replaceable item.
--
Chris

[bj]

   A shame Chris, but I know you'll take the knowledge, and improve it as always.  Not surprised that
a hack saw didn't want to cut it, a fracture like that usually means very hard, but no ductility.
   Just out of curiosity, was there any other damage apparent from the sudden stop?

[ChrisOlson]

Just a big gouge in the bottom of the gearcase from when one piece of the sprocket got in between the drive and chain, pushed the chain out and jammed it against the bottom of the gearcase.  There is not room in those gearcases for any loose pieces floating around in there.  Otherwise it didn't hurt anything else.

It made some loud ticking noises before it locked up.  That caused me to look up at it and go WTF?  When it locked up it make a big CRUNCH and it stopped right NOW.  The rotor was spinning at 400+ rpm.  The energy from the spinning rotor being transferred to the input shaft and gearcase caused the whole machine to turn 90 degrees on the tower, then it swung back into the wind.

It was actually really cool   

I got another PTO shaft for another turbine I'm building.  So I welded the sprocket to it and I'm going to swap out the PTO shaft in it in a bit, with the machine right on the tower.  The sprocket teeth are a nice amber color after welding, so they're tempered now   
--
Chris

[Janne]

Nice post, it's many times the failures that teach us the most.
Hope you get it back up and running soon.

[bvan1941]

Chris,
like others have said before, "one can always count on you to report the good WITH the bad."
Nice to know you have already got an answer and will have it back on line. Thanks for giving the operating hours with this combination.


It appears to me your possibly advocating a continuous weldment "spreading out the torque or the contact pressure point (power transmission over 360 degrees) between the shaft and the gear? just trying to read between the lines here.
Bill

[ChrisOlson]

It appears to me your possibly advocating a continuous weldment "spreading out the torque or the contact pressure point (power transmission over 360 degrees) between the shaft and the gear? just trying to read between the lines here.

The machine is running again in a nice 20 mph breeze.  It was a two hour job to swap out the PTO shaft and get the tower jerked back up.

Yes, welding the sprocket distributes the load evenly around the whole thing to the shaft.  Because the sprocket is so small on a 1" shaft, this one split thru the keyway where the cross section of the sprocket is very thin.

The bottom sprocket (drive) sits up against the rear mainshaft bearing inner race and it is not adjustable forward and aft because you can't get to it after assembly without pulling the PTO shaft out.  So my idea was to use a keyed sprocket on the PTO and adjust that one for proper alignment of the sprocket set.  Well, that was a bad idea.

On my older gearcases that were side loaded, it was no problem because you could get to the drive sprocket to move it back and forth for proper alignment before tightening it up.  On the first one I welded the sprocket to the PTO like I always did in my 12G turbines.  It is required to drill and tap the forward nose of the shaft and provide a positive thrust stop up against the bearing lock ring, because the lock rings won't hold it long term.  They're not designed to handle axial load component, and they can work loose with vibration.  So everything on both shafts has to be locked in place with positive thrust stops to prevent that.

Well, with a one piece PTO weldment, shimming is required on the thrust stops to properly align the gearset.  I said, well, that's a bunch of s&*t.  So I used the keyed sprocket and that seemed simple.  Except it don't hold up   
--
Chris

[bj]

  Well Chris, usually a blown gearbox is a fairly complicated failure.  About a day from failure to
flying again?  To say impressive would be an understatement.
   Maybe I'm drinking the wrong kind of coffee?
   Glad it went so well.

[ChrisOlson]

It's pretty easy to service these gearboxes.  Four bolts and you got the cover off and can look in it.  The generators on my turbines are shimmed.  So it's a simply matter of loosening the set screws and using a hub puller to pull the rear rotor.  Pull the shim pack off the shaft that sets the air gap and lay it aside.  I went away from the threaded rod mount on the stator.  So just zip the five bolts that hold the stator with the electric impact and leave that hanging by the wires.  Loosen the set screws on the inner gen rotor and pull that off with the hub puller.

From there, there's three bolts in each PTO bearing but you don't have to take the front one out.  Loosen the lock on the front one and unscrew the bolt that holds the thrust washer, tap the shaft out of the front bearing with a brass drift, and pull the shaft out out of the rear of the case.  The inner bearing races are silicon sealed to the case and you don't even have to mess with those if you do take a bearing apart - they stay stuck right to the case.

Assembly is everything in reverse.  I think I had the old PTO out within 10-15 minutes of the start of the job.  It took longer to raise the tower and get that bolted down than it did to fix the transmission   
--
Chris

[Bryan1]

Hi Chris,
                As you would know the weak spot on any steel fixture is the corners of the keyway and thats where they will break every time. Over here when ever I replace and old sprocket or pulley it gets a new taperlock setup and to date I've never seen one failure if the unit was installed correctly. On my 1.5kw conversion the 3 metre blades are secured by a 25mm ID 50mmOD con lock and that is still going strong today.

Regards Bryan