Torque to be applied 3

[Guardiano]

Dear Forum Members,
I don't know if this is the right forum but I'm sure the gurus present would shed some light. We have a gearbox arrangement and the motor/gearbox assembly drives a shaft which itself drives a conveyor. The gearbox was removed for maintenance and now it has just been put into position. We are looking for the right procedure and the correct torque to tighten the shrink disc bolts on the gearbox. See the attached picture. We contacted the OEM but without much success. The gearbox is rated @ 3200 k Nm.

Thank you.
Guardiano

 

[dik]

I'm out of my league, here, but what strength do the fasteners have? I would torque them for about 75% of their tensile capacity. I'd also torque them by partially tightening them is a sequence where one is partially tightened and the fastener opposite is partially tightened, then the one at quarter point is tightened, then the one opposite it, until they have all been snugged to part (say 33%) of their total tightening stress... I then proceed and retighten them in the same sequence to say 67% of their final torque value. and then on to the final. In this manner, the clamping effect is fairly uniform. Real mechanical guys may have a better solution.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[TugboatEng]

Basic flanged connection. Use your standard bolt torque tables based on thread diameter, pitch, and fastener grade.

https://www.coastalfasteners.co.nz/torque-data

Remember, torquing is a very crude exercise, if the clamping force required anything more than ballpark you wouldn't be using torque.

 

[desertfox]

Hi Guardiano

Firstly I would check any maintenance manuals for the gearbox and see if that gives any torque figures and whether or not the bolts are lubricated prior to tightening, lubricating bolts will have a dramatic affect on the tightening torque.
Failing to find any figures from the manufacturer the first thing I would do is replace all the bolts with new ones because the old ones might have been tightened to 90% of yield.
Next I would ensure that the bolts and mating threads were clear of oil or any other lubricant and then proceed to torque bolts to 70% of yield stress as dik stated.
I would torque the bolts in a sequential order like this site recommends

https://www.boltscience.com/pages/tsequence.htm.

However that said is there a gasket held between the flanges? If so that could also change the torque figure I would use.
We would need details of the gasket and it’s material to really help you further.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[mfgenggear]

Agree with TugboatEng and Desertfox, crisscross pattern, and with with the values posted. after starting gearbox, recheck torque.

 

[dik]

Thanks for the added info...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Can you get tension indicating washers for this type of connection?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[JS_]

I have seen two different ways to deal with shrink disk or Ringfeder couplings.

One way is continuous tightening in 1/4 turn increments.

The second is a crisscross pattern.

The last one, I worked with the mechanics would pull through the torque wrench click with a little extra.

That day it was adjust torque wrench only after a few times around and the click was consistent.

And then it was a 50 Lb-ft increase all the way to the final.

 

[dvd]

Is the shrink disc somewhat similar to what is shown below from the Ringfeder website? It seems like, absent any other information, you should use available installation literature as a general guide. Are you using new fasteners?

 

[dik]

If using new fasteners, they should be the same 'grade' to prevent over torquing... you may damage the material the bolts thread into... if you use a higher grade, then in the future if someone is going through the same exercise, they may inadvertently torque to the higher value.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[TugboatEng]

I'm sorry, I may have missed that this is a shrink disk. The picture appeared to be a basic flanged connection. If it is a tapered fit connection, there should be a certain draw up distance. This is more reliable than torque. Without support from the manufacturer you may be able to see witness marks on the shafts from the previous installation.

 

[Guardiano]

Thanks All for the great posts.
Dear Desertfox, I quote what you wrote. "Firstly I would check any maintenance manuals for the gearbox and see if that gives any torque figures and whether or not the bolts are lubricated prior to tightening, lubricating bolts will have a dramatic affect on the tightening torque."What effects have lubricating bolts on the tightening torque?
Guardiano

 

[dik]

Well lubricated fasteners can increase the tension load on the fastener significantly.

https://www.portlandbolt.com/technical/faqs/tension-vs-torque-explained-sort-of/

https://www.boltscience.com/pages/nutorbolttightening.htm

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[mfgenggear]

tapers are self locking and is used often on lathes and mills for tooling. it changes nothing and should be self centering when installing.
and thanks to DVD for pointing that out. The grade of the bolts should be stamped on the heads, engraved or what ever on the heads. for exact replacement.
and thanks for DIK for pointing out the warning about the parent material tensile strength. and it should be taking into account for torque requirements.
I assumed because the OP was looking for help here because of no manual. which gets precarious when we try to come up with torque requirements.
such makes me un-easy. when over torqueing damages the threads or under torqueing could cause bolts becoming loose and cause damage,
the torqueing sequence should be as to keep the flange level as inserting into the mating parts and have equal tension.

 

[desertfox]

Hi Guardiano

As dik mentioned in his post ( I haven’t checked the links he posted yet) for a given torque the tensile load in the bolt can be doubled if the bolt is lubricated or gets contaminated with oil or grease which reduces the friction factor (K) used in a very simple torque - tension formula for bolts :- T = k*d*F Where d = bolt dia
T = Torque
K = Friction factor 0.2 for dry threads (unit less)
When a bolt or screw is tightened friction between mating threads, underside of bolt heads, washer faces etc must be overcome however if the surfaces are lubricated then the amount of friction to overcome is reduced and so that reduction allows more tension to be stored in the fastener for a given torque. I experienced this once when working as an engineer and had specified a dry torque for some fasteners, I had a call to say threads were getting stripped, when I arrived I found the bolts were getting contaminated with grease from the fitters hands, they were amazed that after I got them to clean there hands, tools etc there were no more failures.

https://roymech.org/Useful_Tables/Screws/Preloading.html#Initial_Bolt_Tension

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[TugboatEng]

Desertfox, can you give us a few more details about your experience? Particularly the thread diameters material, and coatings?

 

[dik]

df... excellent link. thanks.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[desertfox]

Hi TugboatEng

It was on some high voltage switch gear and they were bolting some copper electrical contacts onto a brass threaded insert, which was moulded into a plastic insulated bushing. I had specified a dry torque for the steel bolt which screwed in to the brass insert and was confident there would be no problem. After I got the call about them failing, I went to site to observe and spoke to the fitters assembling the contacts, they informed me the first set of connections went fine and no problems but every other set of contacts they assembled the breast insert thread failed in shear and after doing another two or three sets they decided to give me a call.
I asked what there procedure was and they said well we bolted the first set of contacts and then got some electrical contact grease which they smeared with their hands onto the copper contact after bolting it together. What subsequently followed was everything they handled after that got contaminated with grease ie bolt,tools, brass insert etc.
So I explained to them what I thought was happening and asked them to degrease everything and not to put the electrical contact grease on the contacts until all the joints were made, this they duly did and we had no more failures.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Guardiano]

Hi All,
We finally found the manual and the recommended torque is 3400 Nm. We already torqued to 3600 Nm but the outer and inner rings are still not aligned, see the picture in my initial post. There is a gap of about 30 mm between the outer and inner rings. The gearbox was removed because the main shaft was replaced. There is no difference in diameter(730 mm) between the old and new shaft. A school of thought on site is claiming to set the required torqued(3400 Nm) and to tighten one bolt after the other until the required torque is achieved. The manual has been translated from German to English and recommend to tighten the bolt successively that is one after the other. Any comment?
Thanks
Guardiano

 

[BrianE22]

Ringfeder style clamps are very sensitive to the order of the bolt tightening and the increment of the torque applied. Years ago I tried tightening one up and an experienced worker nearby laughed a bit when I told him how quickly I did it. The assembly wouldn't transmit much torque at all. He redid it for me. He took quite a bit more time to tighten it. I think the taper pieces get easily cocked in the stiff assembly.

If you can't find the instructions for this one then take a look at a Ringfeder instruction sheet. You'll see it has to be done in the proper order and with increments of torque.