Posted on behalf of Helmy F


I would like to ask you some references or any engineering calculations that should be made before changing the coupling.

We have issues with some couplings such as: loose of fastening bolts, gear broken, difficult to check gear condition, etc.

From the vibration analysis, we cannot find the indication of coupling problems or maybe the analysis was wrong.

Perhaps you have some experiences that can be shared with us about changing gear flex coupling to steel flex coupling. And also what should be considered for this plan.

I wonder whether or not we will have any other problems to the motor, gearbox, fan or roll tension if we change to a wrong coupling specification.

Your advice would be much appreciated.

Thank you.

Regards,

Helmy F

Lots of related articles here:

http://www.emerson-ept.com/EPTRoot/kopflex/Engineered/Technical/techmain.asp

In particular the article on "Retrofitting gear couplings with diaphragm couplings"
http://www.emerson-ept.com/EPTRoot/public/Kopflex_tech_papers/JRM5.PDF

One way you can get in trouble is by changing the critical speed too near to operating speed.

Also the manufacturer of the new coupling should have published guidelines for acceptable application of their coupling including speed and torque transmitted, safety factors for different types of applications, interference requirements etc. If there is a sale to be made, you might be able to get them to help you with reviewing your application (ask your distributor).

Helmy,

I do a lot of vibration analysis, but the best measurement of coupling condition is airborne ultrasound. I have found it to be very effective for detecting faults in many types of couplings.

Walt

Walt - I would really like to learn more about using airborne ultrasound for coupling condition monitoring.

Can you share some details?

Terry O

quote:

Originally posted by Terrence O'Hanlon:
Walt - I would really like to learn more about using airborne ultrasound for coupling condition monitoring.

Can you share some details?

Terry O

Me Too Walt, Especially if you have some recorded Ultrasound Wave files... Seeing is to a strobe light as hearing is to Ultrasound.
Gary

Coupling selection considerations:
Thermal differences, speed and load.
Gear flex to steel flex: I assume that you're refering to a gear coupling w/drop-out switching to a steel disc such as a Thomas coupling?
Gear couplings are very versitle and cheaper but require lubrication. However, gear type coupling are much more forgiving than disc couplings (Thomas).
Disc coupling are very desirable due to their being very precision made and don't require lubrication. They do require very precise alignment and must be chosen for thermal considerations. Thermal considerations are a must and design must accomodate those deltas to maintain a 45 second angle (30 seconds is more desireable for 1800 RPM+ with 20 seconds for 3600 RPM precise machines and 10 seconds for very high RPM 8000+).

You also made comments that elude to Dodge paraflex type couplings and looseness associated with them. They require a machanic that really cares about 'getting it right'. Much care must be taken in tightening in a set manner.

While gear coupling and Thomas coupling are much easier to detect via vibration analyses; Dodge paraflex and Woods aren't so ease. But you may want to use a strobe and look for any grindings of 'rubber' on the base or around the guard.

Sam,

Steelflex is a brand name made by Falk and it is the grid-type coupling. It shouldn't be as intolerant of axial movement as the steel disc couplings.

If Helmy F is having problems with broken teeth, loose bolts, etc. with gear couplings, there is probably some cause that should be addressed rather than making a change in coupling type. Without knowing what the root problem is, it could be made much worse by a change in coupling type.

It is true, impending coupling failure is hard to detect in vibration, but I had several successful cases using convential vibration analysis.

Helmy F., could you post some vibration data for a failed coupling? May be it is telling a story?

David,

The vibration measurement here has been collected and analised by outsourcers. They didn't give us the spectrum or any data, only recommendations.

After some discussions with our local FALK coupling distributor here, I have a reference that shows Grid Coupling (Steelflex) is better than Gear Coupling. I think I will continue with my plan.

Please find the attachment.
Any comments would be much appreciated.

Regards,
Helmy

Falk_Coupling_Feature_Comparisons.doc (44 Kb, 47 downloads) Coupling Comparison

Helmy,

Having been a Falk distributor for years, I can tell you that the claims of 1/4" to 3/4" misalignment capabilities are for static misalignment only. In other words, you can assemble this coupling under these conditions, but not run it for long.

You need to find out why you are breaking gear teeth before you switch to another coupling based on loose recommendations from the guy who sells it.

Good Luck,

The gear style of coupling is the king of torque. No other coupling will handle as much torque, but as most have mentioned, something is causing the teeth to break. It could be improper gap or misalignment. Most of the coupling sales people will brag about how much misalignment their coupling can handle, but that does not say anything about how long it or any other components of the machine will last. When looking at alignment, do not forget to include changes due to thermal growth. The gap on grid style couplings is also important. Too much gap and the gird will continually flex until it breaks, too little gap and you put the grid in shear. If the root cause is not determined, changing coupling styles is only addressing the symptom.

Sure is tough with this 75 degree day here in FL.

Gary B

Gary,

Were sweatin' it out here in Richmond at a cool 70 degs.

Gary and Danny,

I don't understand the unit of your temperature. Is it in Fahrenheit? If yes, so it is ± 24 degs celcius. Here in my factory, the ambien temperature is 30 degs celcius.

About setting the coupling gap, do you know how precision the hub can be installed on the shaft to get the correct gap? Should the hub face parallel with the shaft face? Or any tolerances given?

Helmy

The correct gap tolerance is dependant on the type coupling. I think the grid type is +/- 20 mils as it is with a lot or most expect disc type and they require as close to zero axial stress as you can achieve.

Temps are F as it is uncommonly warm at this time or was at the time of writing. Woke Sat morn to snow cleaning the dish to get a signal for TV.

I have a tolerance chart I can give you if you would like picksam at juno and I'll get one to you.

Helmy,
Typically coupling hubs are are installed flush with end of shaft. I always check coupling data sheet for shaft end-gap distance. The end-gap depends on coupling type, size and speed rating. Do not rely on "rules of thumb" for this critical dimension. Some couplings have a button, disk or pad for limited end-float applications.

Walt

Sam,

Really appreciate if you could give a tolerance chart you have. If there is problem to attach the files here, you can directly send to my email below:

Helmy.Ferdiansyah@bluescopesteel.com

Thank you.
Regards,
Helmy

quote:

Originally posted by Walt Strong:
Helmy,

I do a lot of vibration analysis, but the best measurement of coupling condition is airborne ultrasound. I have found it to be very effective for detecting faults in many types of couplings.

Walt

Walt, I just happened on this old chat. I dabble in ultrasound, along with vibration and IR. Can you please describe your technique for detecting coupling faults thru ultrasound? I'm intrigued. ......much appreciated, Sharkeyrobert.sharkey@conagrafoods.com

Have you thought about magnetic couplings? We have had much success with the MagnaDrive couplings replacing Falk Steelflex couplings. Since there is no physical contact between the two drives, misalignment is never an issue.

Helmy did you adress the root cause failure of your couplings?

There is a falk document www.rexnord.com/portal/repository/falk/458910.pdf called Introduction to Lubrication Related Failures with pictures and description.

Sorry it is to big to upload here, but we had a similar problem and this document helped us to do RCFA.