Building the JU-02 gas producer

[Johansson]

Dec 9, 2018 15:12:49 GMT -5 racket said:

Hi Anders

LOL..................looks like I'd better pop the spare comp in the Post for you :-)

The good part is that lotsa bits survived.

Hopefully it wasn't the thrust bearing failing and allowing the comp to move forward and contact the housing which would have instantly untightened the nut .

Hows the turbine wheel itself look ??

Lots to be learnt from the "autopsy"

Cheers
John

Hi John,

Oh, so you had a spare X846 wheel? I´ve sent KTS a mail to hear what they would want for one, still good to know even if I don´t plan to wreck any more of them.

The thrust bearing feels tight and good, I had almost 6 bar oil pressure when the compressor came lose to it should be ok. I´ll take the shaft tunnel apart some night this week and check it out closely.

The turbine wheel looks ok except for embedded aluminum on the shaft where the comp sat, it didn´t look bent when I rotated it in the bearings but I think I´ll fit the spare shaft anyway just to be sure.

Cheers!
/Anders

[Johansson]

Dec 9, 2018 15:16:03 GMT -5 racket said:

Hi Anders

Crossed emails , I generally can't get the full amount of angular tightening as the billet comp material is "harder" than the original cast wheels , I just tighten until I can't turn any more on the T bar and socket , Locktite used as well

Cheers
John

Hi John,

I got a reply from a tractorpulling guy who sent me some drawings on a custom nut with locating pins, it won´t work for the TV94 since the thread is right handed unfortunately. He told me they run over 7 bar and 125.000rpm with a 103/141mm compressor on a 112mm turbine, crazy!

Is there no way of securing the nut for us? Perhaps using a Nordlock washer under the nut? That still won´t help if the compressor starts slipping on the shaft though.

Cheers!
/Anders

[racket]

Hi Anders

Yep , I have a spare , I thought we might have needed one somewhere along the development trail, so purchased 2 while I was at it :-)

At 4.4 PR and 3.3 lbs/sec and say 70,000 rpm the turbine wheel is producing 30 ft lbs of torque to drive the comp , we torque our comp nut down to a lot more than that, I really can't see it moving

I'll have a think on this .

Cheers
John

[Johansson]

Dec 9, 2018 15:47:00 GMT -5 racket said:

Hi Anders

Yep , I have a spare , I thought we might have needed one somewhere along the development trail, so purchased 2 while I was at it :-)

At 4.4 PR and 3.3 lbs/sec and say 70,000 rpm the turbine wheel is producing 30 ft lbs of torque to drive the comp , we torque our comp nut down to a lot more than that, I really can't see it moving

I'll have a think on this .

Cheers
John

Hi John,

Ah, you saw this coming did you?

It is difficult to tell if any of the scratches in the comp cover was from a rub that caused this whole mess, but I can´t see why the compressor can run up to 70.000rpm and suddenly hit the housing with a constant oil pressure to the axial bearing.

I didn´t bother to clean the rotor shaft or threads before assembling the engine last time, didn´t see that this would ever be an issue.

Cheers!
/Anders

[Johansson]

Since all of the mating surfaces that the compressor have contact with were slick with oil when I assembled the rotor, wouldn´t the torque needed to spin the comp on the shaft have been much smaller than if all of the surfaces were thoroughly cleaned? Might be a reason for what happened.

[racket]

Hi Anders

LOL................I went through a lotta rotors with FM-1 .............you've got a way to go before you catch me ;-) .................I can appreciate how you're feeling right now .

Yes , the thrust bearing would need to be badly worn before the comp hit the cover, there is a pretty large forward force but I can't see it distortng your housing/s to the degree needed to let the wheel hit ...............what sort of axial clearance did you give the comp ??

Can you please post some more pics of the engine bits , it might supply some answers .

I just did some quick numbers from the TV94 comp map and at its worst the turb wheel is required to produce ~300 HP at similar RPM , so ~22 ft lbs of torque , I can't see your extra 36% being enough to "overpower" the security of the fastening, especially with the Loktite , we don't run our engine long enough for the comp to heat up to a temp that would degrade the Loktite strength , you've got freezing cold air going into your engine , the comp nut would be kinda cold .

Yep , your thoughts about oily surfaces is valid , I'd better clean mine before reassembly :-)


Cheers
John

[jetjeff]

Hi Anders,

Somewhat disappointing at what happened today, but somewhat not also,,,been there done that.

Working on jet engines where we are the engineer, mathmetition and manufacturer, it's surprising we get are far as we do.

Never accept defeat, only a steep learning curve.

I'm working on Heineken II today.

Respectfully

Jeff Pittel

[racket]

Hi Anders

This might "amuse" you ...................the instructions from my turbo guy on tightening Garrett Compressor Nuts for our size wheels .


Small amount of OIL on the threads and comp wheel FACE .

Install and tighten nut to 31 Nm ( 23 lbs feet)

Loosen nut

Tighten nut to 5Nm ( 50 lbs inch)

Tighten nut 135 degrees .

Well that sorta shoots the "lubrication" option down as a possible cause of the slipage.

Cheers
John

[smithy1]

Yep, we always lubed the threads and the nut contact face on the C20 and C30 comp nuts during assembly, it's in the latest RR manual.

Anders, I wonder if there's a "transient imbalance" which may have had the comp wheel touching the inlet housing at certain rpms and then causing the nut to loosen. We often noticed a balance issue at certain RPM algorithms on the balance machines. Some of the manufacturers mention to not run constantly at certain rpm's....and to either stay under or go right through to a higher rpm.

Doesn't take much for the shaft to "bend" enough to cause grief.

Smithy.

[racket]

Hi Anders

Its in the Post.............might just get there for Christmas :-)

Cheers
John

[elventu]

If I can give a suggestion...
To clean the aluminum deposit on the shaft, you can put it into sodium hydroxide solution.
Aluminum are destroyed by it, steel are only deeply cleaned.
If the shaft isn't damaged or bent, but the problem it is only the aluminum deposit, it can solve the problem.
Be careful to wash the shaft accurately after the treatment, and oil it to avoid oxidation.

Can't you add a second nut after the main one?
It is a simple way to avoid loosening.
For sure it add some weight, but not too much, expecially if you use a low profile nut.

Hope this helps.

Davide

[dieselguy86]

My turbo guy here who builds tractor puller turbos, keys the wheels to the shafts.

[turboron]

Anders, a couple of points on centrifugal compressors based on my experience:
1) All centrifugal compressor outside diameters moved forward toward the stationary shroud/scroll during operation. This is confirmed by finite element analysis and observation. This is one of the reasons aircraft gas turbine engines use abradable coatings on the shroud/scroll.
2) Adding a bore to the center of the impeller for a shaft doubles the stress and deflection compared to a impeller without a bore.

These factors point to a couple of possible reasons for your nut coming loose. The first is that the impeller to shroud/scroll was not sufficient to prevent contact. The second is that the material strength of the billet impeller was not to specification. You may want to check the impeller bore to see if it has opened up.

Thanks, Ron

[monty]

CRAP!! Anders, I was so excited to see your post, and then my heart sank with that flame out the back... It looked like you could see aluminum filings flying around in the air right before the "big" event. How rigid is the area where the front bearing is located/supported? could that have flexed, and allowed the wheel to contact the front shroud? If you had good oil pressure everything should be fine, unless the actual bearing support area flexed and allowed the wheel to move forward. Once that wheel contacts the housing, all bets are off with a right hand nut. How do the thrust washers between the circlips and bushings look? How does the front face of the turbine facing the NGV look?

Ron=> If the wheel spun on the shaft, doubt the bore will tell much. Measuring bores that small is....well....difficult. Separating any damage from spinning on the shaft and the wheel expanding will be next to impossible.

If it spun enough to distort the bore, not much to be learned there.

Anders => glad you fixed the oil pressure issue, sorry about the difficulties.

Monty

[monty]

Dec 9, 2018 16:22:53 GMT -5 racket said:

Hi Anders

LOL................I went through a lotta rotors with FM-1 .............you've got a way to go before you catch me ;-) .................I can appreciate how you're feeling right now .

Yes , the thrust bearing would need to be badly worn before the comp hit the cover, there is a pretty large forward force but I can't see it distortng your housing/s to the degree needed to let the wheel hit ...............what sort of axial clearance did you give the comp ??

Can you please post some more pics of the engine bits , it might supply some answers .

I just did some quick numbers from the TV94 comp map and at its worst the turb wheel is required to produce ~300 HP at similar RPM , so ~22 ft lbs of torque , I can't see your extra 36% being enough to "overpower" the security of the fastening, especially with the Loktite , we don't run our engine long enough for the comp to heat up to a temp that would degrade the Loktite strength , you've got freezing cold air going into your engine , the comp nut would be kinda cold .

Yep , your thoughts about oily surfaces is valid , I'd better clean mine before reassembly :-)


Cheers
John

John,

I don't know about the oily surface theory. Usually you want to lubricate the interfaces and threads so that the installation torque is not influenced by friction between them. The goal is to stretch the male threaded portion so as to produce the designed clamping force. That is why every modern engine fastener has moved to torque to yield assembly. That guarantees a certain clamping force. If you do not lubricate the mating surfaces, then the friction can fool you, and you never get to the desired clamping force since torque is dependent on things other than stretching the male threaded member....probably clear as mud....

Monty