Tightening torque of bolt for a static coupling and dynamic coupling. 1

One again, virtually zero information .. What is being driven by the coupling and what is the driver ?

What is the nature of your dynamic loadings ?

Does the coupling attach to a TEFC motor or a steam turbine ?.... or a sad old donkey going in a circle ?

Who makes the coupling ? ..Can you read the rusty tag ?.. What model...?.... Provide the coupling specification !

...Or provide a photograph ... did you find the coupling in the "bone-yard" behind the plant or will it be purcased new ?

Why will you ignore my questions ?

Najeeb, whatever you do ...

NEVER, EVER, EVER say please or thank you

MJCronin
Sr. Process Engineer

I'm going to assume you mean a rigid coupling with a bolted flange, because there are dozens of different devices called a "coupling" and that's the first one that came to my mind.

The torque on a rigid coupling bolt is generally calculated using the strength and size of the bolt material, coupling material, and frictional conditions. This results in a calculated preload that the bolt provide in a wide range of conditions.

The design of a coupling generally relies on having a list of bolt sizes and the preload for each size. The designer should know the materials and frictional conditions and then be able to select from the range of bolt sizes to suit the coupling design. The preload provided must exceed the requirement and the sizing must fit physically in the assembly.

I cannot offer insight into the "static" vs. "dynamic" angle because I don't know what kind of coupling you're talking about and what the static and dynamic load cases would represent.

That's as much as I'll say because I already made a bunch of guesses and my attention span has ended.

Tightening torque is typically dependent on the bolt properties and static or dynamic loading are irrelevant.

I have not clearly mentioned the question.
The objective is to estimate the tightening torque required for stationary components and rotating components.
stationary components (ex: gear casing) and rotating components (ex: rotating gear shaft coupled with turbine rotor).

How to calculate the tightening torque required for the case of stationary and rotating components(dynamic components). What is the relationship between these two cases?

There is no relationship. Fastener torque charts dont specify usage bc a properly designed bolted joint doesn't fail under any condition.

Tight as you can get it, then one more time around

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

Ask how much force you need to hold those things together, then figure fastner torque to produce those forces.

Ted

Likely somewhere between 0.2Nm and 20000Nm, based on the description of the problem so far.

Details fer chrissakes. So far, we know you have some things moving and other things not moving. Fantastic.

Are they M2 bolts, or M24? What material? What grade or that material? What are they clamping? Are the threads lubricated? What is the thread coarseness? Is a threadlocker being employed? Are they subject to large temperature swings? Is the joint a true bolted joint, using clamp load to develop friction? Or is it also subject to axial loading?

Draw a free body diagram and let's get some forces going on here. Holy smokes this is painful.

As a cross check for my calculations I'd look at commercially available couplings of similar size and torque rating.
I'd expect to find installation instructions on-line, and that they'd include fastener sizes and torque specs for reliable service.

Buying a commercial off the shelf product might save a bunch of time that could be better used elsewhere on the project too.

While reviewing the installation instructions pay special attention to the shaft tolerances.
Reliably afixing a coupling hub to a shaft is not a trivial matter.

@orange_kun

if he gives you all that information, what are you planning to do with it? if you have a source that utilizes that information please share it. it sounds very informative. Shigley perhaps?

have a look at VDI 2230. it might not answer all your questions, but it will definitely answer some of them.

@orange_kun
optimum tightening torque required for bolt under static and dynamic conditions

Bolt size: M30,
Material: AISI4340 alloy steel
Grade (property class): 12.9
All Bolt threads to be lubricated with MoS2 grease during torque tightening.
Temperature variations will not be there.
Bolts are not subjected to any external loads.
If these bolts are used as foundation bolts of gear casing (static condition), What is the optimum tightening torque required?
suppose, if these bolts are used in flange coupling to connect the gear shaft with shaft of generator (dynamic condition). What is the optimum tightening torque required?

I calculate the same torque for a 'fastener arrangement' (I'm defining this as a combination of bolt material and size, base materials, head size/washers, friction, temperature conditions, thread lubrication) regardless of whether it is part of a static or dynamic assembly. Except in extreme cases (high RPM, high shock maybe?) the fastener doesn't know if it's moving or not.

In my industry, the rotating parts and stationary parts are not made of the same base materials. Housings, mounting plates, etc are cast iron or plain steel. Rotating parts are usually 316 stainless steel. Gearbox internals are plain steel or alloy steel. So a 3/4" bolt in each of those situations gets a different torque.
 
The location, quantity, and fastener size are what vary for the joint. In a dynamic application there might be an additional margin added to the loads to account for fluctuations or upset conditions, but otherwise it's the same as a static condition. (In a static application, there could also be additional margin to account for things like seismic.)

If you're using the same fastener arrangement with different torques, you're de-rating the fastener if you apply less torque than it can handle. That seems silly to me. I calculate the torque and load capacity of a variety of fastener arrangements and choose the fastener arrangement that is required for the joint.