replacing a journal with rolling element bearing 1

[sabermostafavi]

Hi to everyone
I have a shaft with velocity almost 7000 which always attaches to it's upper journal and causes to fail. Now I want to change it with one or two rolling element bearings. I want some help to know if it is possible in such a kind of speeds and what's the procedure of changing?

Thanks

 

[MikeHalloran]

Drag out the thickest rolling element bearing catalog you have, and start reading in the back.

Or, call and ask for a sales engineer to show up on site and help you in person.





Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

Like Mike H said, its best to get an application engineer involved for the first few bearing design projects.

Among the info the application engineer will provide are specs for bearing seat and housing tolerances. The recommended Fits and accuracy are likely to have your shop and supplier huffing and puffing.

Have there been multiple failures of the same (repaired) machine?

Or is this a standard product, or a design you have created or inherited?

Without knowing a lot more about the application, history and the failure(s) I'm wondering if it is a design problem, or a workmanship problem. Sometimes oil lines become kinked or restricted. Replacement bearings may be of a different material, or incorrect design. If the bearings are not colinear, or the shaft is bent, edge loading will result, and pump a lot of heat into a small section of the bearing.

It's a shame to re-engineer something to correct problem that is really a manufacturing or basic workmanship "issue."

 

[electricpete]

You haven't given any units for velocity 7000. How about telling us the shaft rpm and diameter With units instead.


=====================================
(2B)+(2B)' ?

 

[electricpete]

Also an idea of application as tmoose said including load lub environment

=====================================
(2B)+(2B)' ?

 

[sabermostafavi]

hi to everyone
thanks for your tips. speed is almost 7000 rpm and this problem happens occasionally. I think the problem is from wrong usage. sudden shocks cause to idler moves in up direction. this movement causes to idler upper point touches journal. this touch in this speed brings journal fail. Idler shaft attaches to upper journal so it can not move any more so input gear which is coupled to motor will be destroied. We want to change journal with rolling element bearing such as deep grow ball bearing. I want to know if you have any experience.

Thanks

 

[MikeHalloran]

There's probably at least a couple centurys' experience available here, but nobody can make sense of what you are talking about without a decent drawing and/or some photographs.



Mike Halloran
Pembroke Pines, FL, USA

 

[electricpete]

What is the journal diameter?


=====================================
(2B)+(2B)' ?

 

[sabermostafavi]

Dear Mike and Electric
let me explain the problem in detail. we have designed a pump with increasing gearbox. Pump is vertical so gearbox is to. Our gear box has three shafts which are all vertical: Input shaft, Idler shaft and High speed shaft.Input shaft is coupled with electromotor with velocity almost 3000 rpm. Input shaft transmits the power to idler shaft with a pair of helical gear. Idler shaft rotates with speed about 7000 rpm. It transmits power to high speed shaft via a pair of spur gear. So there are two gears on Idler shaft: helical on the head of shaft and spur on the end of the shaft. High speed shaft speed is 20000 rpm and an impeller is mounted on its end which is located in pump casing and the rest of the story...
Idler shaft rotates in two bearings: an upper journal and a deep grow ball bearing for down of it. Our design is completely precise undoubtedly. Main problem is in process condition where some unmodelled loads from fluid and via high speed shaft influences the idler shaft behavior and causes idler attaches to upper journal and... journal diameter is almost 50 mm and idler shaft length is almost 250 mm.
Now we want change the upper journal with one or two rolling element bearings like the other side of shaft in order to prevent from contacting the idler shaft and journal. Idler must bear radial and axial load simultaneously. I want to know how many bearings I have to use and from which class. If you need more data such as loads at bearings I can tell you.

Best regards
Mostafavi

 

[MikeHalloran]

Are you trying to say that the idler shaft journal is seizing in its bushing?

Regardless, HOLY CRAP! That's a very ambitious design.

Are you sure you're not having a critical speed problem?



Mike Halloran
Pembroke Pines, FL, USA

 

[sabermostafavi]

Hi mike
Exactly!!!
I want to know in a centrifugal high speed pump class OH6 which has an increasing gearbox with shaft rotational speed almost 7000 rpm with distinct loads on it HOW CAN SOMEONE CHANGES UPPER BUSH WITH BEARING? WHAT'S THE PROCEDURE?

THANKS

 

[MikeHalloran]

I'm looking at a cutaway of a Sundyne LMV-341, which I suspect is similar to the pump you're trying to hack. I got it here:

http://www.archimedemilano.com/gallery/.../Sundyne LMV-341.pdf

You could have saved a little time by giving us the model number of your pump in your first message. You had me thinking you were re-engineering a design at a pump factory, now clearly not the case.

If I were investigating seizure of the intermediate shaft's upper bushing in that Sundyne pump, I would suspect insufficient head in the gearbox's internal lube oil channel. That would lead me to investigate these other possibilities:
- That the gearbox's lube oil pump, tied to the input shaft, may be worn out or broken, and not pumping enough oil.
- That the lube oil pump's inlet tube is cracked or its attachment is loosened, causing the pump to pump air with whatever oil it is still managing to suck out of the gearbox sump.
- That the lube oil pump's inlet tube is clogged, or kinked from being stepped on, or otherwise starving the pump.
** After first investigating the really obvious culprits,
- has the oil filter _ever_ been changed?
- is there _any_ oil in the gearbox?


The last thing I would consider is changing the bearing design in such a high-speed gearbox. The journal bearings are there for a reason.




Mike Halloran
Pembroke Pines, FL, USA

 

[sabermostafavi]

Hi Dear mike
Happy new year
I will think on your suggestion about lubrication oil and oil pump.I will inform you about what happens.

Sincerely yours
Mostafavi

 

[sabermostafavi]

Dear mike
We found the problem. bush had been designed to bear just radial forces not axial and trust bearing mounted in other end was designed to bear axial loads. helical Gears where manufactured in wrong direction so all axial loads were on bush causing temperature rising up and shaft seizing in upper bush.
Now because we have ordered some pairs of these gears we have to use them with wrong direction of forces. So again!!! we must change the upper bush with a bearing able to bear axial force either! What's your suggestion?

Sincerely yours
Mostafavi

 

[MikeHalloran]

I'm guessing the impellers are not symmetrical, and the volutes certainly aren't, so you can't just reverse the motor rotation and be done with it.

Propose to the gear supplier that you have some special impellers and special volutes made, of the opposite hand, to be paid for by him. Chances are he'll propose to supply the right gears instead.



Mike Halloran
Pembroke Pines, FL, USA

 

[sabermostafavi]

Dear Mike
Gears are manufactured in other countries such as turkey and Spain and it seems to be ineffective to communicate them. We must use these wrong hand expensive gears!!! What's your suggestion for one double act rolling element bearing able to bear below forces
Radial force: 11.9 KN
Axial force: 2.92 KN Direction: Upward (in a vertical shaft)

 

[sabermostafavi]

What's more shaft diameter is 40 mm

 

[MikeHalloran]

If you accept bad parts, you will _never_ get good parts.

Changing your design to use bad parts compounds the mistake.

Whose mistake was it, really?

Is it your design?

What is your actual role in this expensive disaster?

Did you call a bearing application engineer yet?


Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

So it was the axial face of the bushing that seized to the shaft ?

What detail or feature limits the upward motion of the shaft?

============

"Idler shaft rotates in two bearings: an upper journal and a deep gro(ove) ball bearing for down of it."

**IF** that deep groove (not an angular contact) ball bearing is properly sized to handle a thrust loads if applied downward (maybe even a little more, as the shaft/gear weight will be opposing vertical upward thrust), it should be able to handle those same loads applied upward. I'd look at it's retaining and locating features on the shaft and housing, and if it's a style the uses "filling slots" as it may need to be reversed.

 

[sabermostafavi]

Dear Mike
It was not any of our company members mistake. What 's important now is that being out of service of this pump causes almost 700000 dollars a day damage to country income and it's not important to find the guilty. We don't have any other options and have to use these wrong hand helical gears however.
So just pray for me to find right answer. I would let you know the end of story.

Best regards