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torque values for bolting !

ksarita20

New member
hi,


Can anyone suggest me some good referances where i can find the limitations for the torque that is applied in bolting a nut of different sizes and shapes.


can any one suggest how tocompare the stress developed in the bolt due to loading and how to quantify at what point the bolt will fail by over coming the compression forces created by bolting.


If i am not very clear , please let me know.


Thanks


Sarita
Edited by: ksarita20
 

BigJoe

New member
I found some good info after doing
<a href="http://www.google.com/search?q=calculate+bolt+torque&sourceid=mozilla-search&start=0&start=0&ie=utf-8&oe=utf-8&client=firefox-a&rls=org.mozilla:en-US:eek:fficial" target="_blank">a
quick google search.</a> This
<a href="http://www.efunda.com/designstandards/screws/calc_bolt_torque.cfm" target="_blank">Torque
Calculation Tool</a> from eFunda
might answer your question.
<a href="http://www.amazon.com/exec/obidos/search-handle-url/index%3Dblended%26field-keywords%3Dfundamentals%252520of%252520machine%252520design%26store-name%3Dall-product-search/102-6336325-9727311" target="_blank">There
are a ton of books that cover bolt torque.</a> We used the
<a href="http://www.amazon.com/exec/obidos/tg/detail/-/0130177067/qid=1110590748/sr=8-1/ref=sr_8_xs_ap_i1_xgl14/102-6336325-9727311?v=glance&s=books&n=507846" target="_blank">Norton
book</a> in my Mechanical Design classes and the
<a href="http://www.amazon.com/exec/obidos/tg/detail/-/0471448443/qid=1110590643/sr=8-1/ref=sr_8_xs_ap_i1_xgl14/102-6336325-9727311?v=glance&s=books&n=507846" target="_blank">Juvinall
book</a> in my Senior Design classes. Both are pretty good, but
the 1996 publication of the Norton book had some errors. Looks
like they have since published a new edition.



can any one suggest how tocompare the stress developed in the bolt due
to loading and how to quantify at what point the bolt will fail by over
coming the compression forces created by bolting.


Not the answer you want, but the failure load depends on the size of
the bolt and the material (among other things, but those are pretty
critical).



In general, the failure load is tricky to calculate, especially if your
assembly will see any fatigue loading. If you can be more
specific about your question and your application I'll try to help out
with the details.
 

Tunalover

New member
Call me during EST normal business hours and I will provide you with what you need.

Bruce Jackson aka Tunalover
 

ksarita20

New member
hi ,


efunda is really good. thanks.


but nowi want to quantify this torque into the compression force that it creates in the bolt and the plate to which they are bolted.


My aim is , when i apply a vertical load on the plate by fixing the bolt on the top.i can compare the tensile stress created at juncturewith the compression stresses ( if i can canget to know how) in deciding the failure aspect of the bolt. that is i can say that the tensile stresses created in the joint will make the bolt fail when it overcomes the compression stresses.


Do u think what i am intetnting to do is right.


thanks


sarita
 

ksarita20

New member
Thanks for ur suggestion , but i ddnt understand why u specified about gasket. how is this related to my problem.


Sarita
 

Uros

New member
Gassket calculation programs calculate bolt forces, surface stress and torques when calculating gasket joint.
 

pjw

Member
Don't know if this helps but in general it is normal to tighten the bolt to approximately 80% of the tensile yield stress. This greatly reducesthe risk of fatique failure. If a bolt is going to fail it will do so on tightening or not at all unless joint separation occurs. High pre-tension acts to prevent this. Use the following for a quick calculation for bolt torque.


Pi=Ki * At * Rp


Where Ki = constant (0.75-1) generally 0.9 for static loading


At = Tensile stress area of the bolt


Rp = Proof stress





Then use T = 0.2 Pi * d





Where T = required bolt torque,


d - nominal dia of thread for example 16mm for M16


I personally am a bit wary of this method, since friction is not taken into account and therefore one cannot be sure that the bolt load is what one thinks it is. A more reliable method is turing the bolt through a prescribed angle. You definitely know the strain in this case becasue you know the pitch of the thread, therefore you can then work out the stress.


Dont't forget to keep all units consistent!
 

pjw

Member
Myreply didn't take into account gasket factors like you will find in ASME VI (pressure vessel design). ksarita20 was probably referring to the gasket factors taken into account in bolted joint design. This is dependent upon gasket hardness, and effective seal width. Hope this helps a bit more?





pjw
 

ksarita20

New member
my main aim was to claculate the pre-load induced in the bolts for which i needed the torque claculations.


BUt thanks for the details. they increased my scope of thinking.


Sari
 

Tunalover

New member
Hello!


If you are serious about needing to know torque values, do a Google search on "TORKSENSE". I had that program a few years ago and it was tremendously useful. It was something like $US 125 then. It contains reams and reams of empirical nut factors (K), materials, material properties, and lubricants. It allows either metric or english fasteners.


Do your calculations based on the weakest material in the joint. For example, if the nut is of a material with a lower yield point than the external thread, then you will use the nut material's yield point for your calculations.


No I don't work for the people who sell the program. I'm just a design engineer grunt who has to design a lot of stuff with little time!
 

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