Gearbox

[Guardiano]

Hi,

First of all I`m not a mechanical guy. I`m looking for a mechanical advice about an epicyclic gearbox. We have on site an epicyclic gearbox, installed brand new two years ago,which nameplate reads as follows :
P=50 kW
T2-=3175 kNm
N1/N2= 10105/1
The gearbox is driven by a 75 kW 4 pole motor itself powered through a VSD. We have been running this gearbox constantly at >60 k W and torque between 3500 and 3900 kNm.The mechanical gurus on site are claiming that the working range is normal for a gearbox of this size.My question is simple, what the P and T2 ratings on the gearbox mean ?

Thanks.

Guardiano

 

[hydromech]

P is input power

T2 is output torque in kilonewton meters.

The nameplate states the safe working load and although the gearbox may well work for several years, it is working in its safety factor and not within its rated load.

The gearbox is effectively overloaded and in these cases the working life is much shorter and the risk of catastrophic failure is higher.

There are also implications with warranty and health and safety risk assesments to be considered.

Adrian

 

[MintJulep]

They mean that you should buy a spare.

 

[MikeHalloran]

Buy two spares. Now.



Mike Halloran
Pembroke Pines, FL, USA

 

[spciesla]

Buy a spare that meets the process requirements.

 

[BrianPetersen]

... and hope it fits the original mounting arrangement.

 

[zekeman]

I would fire the socalled "mechanical gurus" and immediately replace both the gurus and the gearbox with a larger gearbox, or you may soon be picking up ground and broken pieces of gear
YOU NEVER EXCEED RATED TORQUE BY 25%.

 

[Guardiano]

Thanks to all for the replies. Zekeman, is it a standard practice the 1.25 service factor for a gearbox which in our case is still ok,the gearbox is working within the sfety margin.

Guardiano

 

[MikeHalloran]

I don't think that's how a 'service factor' works.

You might want to review the sizing/application pages of your catalog again.





Mike Halloran
Pembroke Pines, FL, USA

 

[hydromech]

Guardiano

The safety margin is there to allow for minor differences is materials and manufacturing techniques. It gives the manufacturer a bit of an allowance.

The safety factor also allows for human error.

What is doesn't do is allow people to cut corners by using a cheaper and smaller gearbox than is required by the application.

If the gearbox fails and people get hurt, the investigators will look for evidence and there is plenty right here on this page.

 

[boo1]

The American Gear Manufacturers Association (AGMA) is an association of the large gear manufacturers in the United States, very similar to ASME in that they promulgate standards under which their members manufacture gearing.

This association has developed a series of calculations and formulae which can be applied to any gearbox to arrive at its AGMA Rated Mechanical Horsepower. They have also developed a table of recommended minimum service factors to be used with these horsepower ratings. The 1.25 service factor indicates the GB is designed for, (example normal loading operating 10 to 24 hours a day with lessthen 10 starts / hour).

http://www.transmatix.com/service_factor.html

GB service factor is not Safety Factor.
GB rated max mechanical input torque / service factor = GB allowed minimum required rated torque

 

[IceStationZebra]

A gear box (or many other mechanical things for that matter) may be under rated to account for load spikes. If your load is constant with very few load spikes this would help to explain your long live while being overloaded.

ISZ