sheared layshaft in gearbox 3

[blkbk]

Hi,
I have had the same layshaft shear 3 times.Gearbox manufacturer say nothing wrong with their design,the gearbox should suffice for torque produced.Anybody similar problems. The gearbox drives a reciprocating compressor.

 

[MikeHalloran]

It smells like you called the gearbox mfgr with a torque number, and they said the box is good for that torque.

... but you failed to mention that big ol' recip, so they used the wrong service factor, and got the wrong answer.


Am I wrong?




Mike Halloran
Pembroke Pines, FL, USA

 

[blkbk]

Mike,
I agree, problem is how to explain to mfgr it was their error.

 

[MikeHalloran]

You had to assert that you were an engineer to gain entry to this site.
Engineers should know about service factors.
Therefore, it wasn't the gearbox mfgr's error that the box was misapplied.
That's my opinion.

If you talk nice to them, maybe they'll give you a "nice guy discount" on the gearbox that you actually need.


Mike Halloran
Pembroke Pines, FL, USA

 

[BrianPetersen]

Whose error it was depends on whether they were told that the gearbox was operating a reciprocating compressor (or that it needed a certain service factor on top of the nominal torque load).

If the gearbox supplier were told that in writing but didn't make use of it then perhaps it is the gearbox supplier's fault.

If the gearbox supplier was only told a torque rating but not given either a service factor or told that it was operating a reciprocating compressor then it is probably the selection engineer's fault (yours?).

 

[blkbk]

Brian,
Unfortunately this was a completed project I have inherited,Mfgr and previous Engineer both claim to have mis-laid information that was submitted for gearbox selection. So I am starting cold on this with no information. As previous reply suggests maybe bite the bullet and start again.

 

[MikeHalloran]

Bilateral selective amnesia suggests that both parties were complicit in the mis-selection process.

None of that matters now.
You need a stronger gearbox.

Ask if the gearbox mfgr. can sell you an uprated shaft, e.g. 'heavy duty', or one from a stronger box that happens to interchange, or give you a good price on a stronger complete box.

... Do that after you go through a sizing exercise with several other gearbox mfgrs.

Email or fax all of them a spreadsheet set up as an RFQ, outlining the complete specs required and the environmental factors that affect SF, and asking specifically for firm price and delivery time in writing on a replacement.

Don't let any of them know who else is bidding, but do let them know there are other bidders, e.g. by marking each RFQ as a BCC: .



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

...So I am starting cold on this with no information...

You are not starting cold and you have plenty of information available to begin diagnosing your problem.

First, you could review the manufacturer's documentation for the compressor, gearbox and prime mover. Are they all compatible in terms of speed, torque, fatigue, shaft dynamics, etc? Second, document the condition of each of the failed components and compile any available operating/service records for the drivetrain. Did all three gearbox shafts fail in the same manner? Third, check the installation conditions of the compressor and gearbox. Is there excessive misalignment between the mating shafts? Do the compressor and gearbox mounts provide adequate stiffness? How are the shafts coupled?

Before assessing blame, it would be prudent to thoroughly study the situation. If you would provide specific details about the compressor, gearbox and installation, I'm sure the members of this forum would be quite happy to assist you in diagnosing your problem.

Good luck to you.
Terry