Coupling transient torque design - how critical?
Coupling transient torque design - how critical?
(OP)
This is primarily concerned to the coupling selection / design. Usually, we do the static torque design estimations (take some safety factor!)and free torsional analysis to ensure that we are away from opertaing in resonance. The coupling manufacturers tyically gives the peak torque as twice the continuous torque!
How critical is the transient torsional analysis requirements for the couplings?. The drives can be either engine or motor and the compressor/pump on the driven side.
Thanks in advance for you contribution towards this query.
Jeyaselvan
How critical is the transient torsional analysis requirements for the couplings?. The drives can be either engine or motor and the compressor/pump on the driven side.
Thanks in advance for you contribution towards this query.
Jeyaselvan





RE: Coupling transient torque design - how critical?
1) Peak torque (low number of events for life of coupling usually at startup, usually allows stresses in the coupling approaching yield)
2) Running torque ( A static torque the coupling is designed to in conjunction with three below)
3) oscillating torque (critical for application being driven by piston engines or driving recip compressors)
The oscillating torque is almost always the driver with coupling selection as the oscillating torque dictates the fatigue requirements of the coupling. This is the reason for the running torque being so much lower than the peak torque. In order to have a coupling last a transient torsional analysis is rather critical. To get accurate values a transient dynamic analysis of the system should be performed. I can recommend a specialist if you need one.
RE: Coupling transient torque design - how critical?
RE: Coupling transient torque design - how critical?
RE: Coupling transient torque design - how critical?
In my experience industrial drive units are rather conservatively designed, and it is possible to ignore the torque ratings to some extent, at the cost of being entirely responsible when they fail in service. So if you can take that risk, go for it. However, expect to be able to justify your decision.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Coupling transient torque design - how critical?
We normally do only a static design & free torsional analysis for constant speed applications. A forced torsional response analysis is carried out for engine driven applications which has a range of operating speed. Since it is not possible to avoid opertaing at resonance, vibratory torque & power loss in the coupling are estimated and ennured to within the manufacturer's limits.
But the above are all steady state analysis. I am trying to decide on whether it would be necessary to carry out transient analysis. My observations are based on
i) For cases, I have seen with transient torques with motor applications, if we are able to push the coupling mode frequency to 20% away from the 1X & 2X motor excitations,
the estimated peak transient torque is less than or close to 2, most of the times.
ii) All the cases, the inertias of either sides of the coupling are fairly equal for the coupling mode. ( I haved some where the transient analysis is critical when the inertias are largely different on either sides)
Greg, is it a good reason for me to skip the transient analysis?
Jeyaselvan
RE: Coupling transient torque design - how critical?
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Coupling transient torque design - how critical?
I was just trying to get a feel from the experts in field on my observations.
RE: Coupling transient torque design - how critical?
A coupling for sized for a 150 HP electric motor coupled to a pump is a far different aninmal than a 1000+ HP Caterpillar diesel coupled to a recip compressor.
RE: Coupling transient torque design - how critical?
RE: Coupling transient torque design - how critical?
I am talking about power ranges from 15 HP to a maximum of 300HP, mostly the industrial compressors..I really wanted to have the coupling (commonly resilient type) as the weak link (as suggested), but at the same time do not want that to fail under normal machine opertaing conditions, steady state as well as the usual operational transients (start up & downs).
RE: Coupling transient torque design - how critical?
RE: Coupling transient torque design - how critical?