Interesting Vid- Torque vs. Tension

[SumpChump]

It's an industrial video but applies to us as an illustration of several things...
Torque and Tension - Real World - LINK
1. Torque isn't a measure of tension or perhaps a layman may say, "grip"
2. Tension is really what keeps your cars rims on or warps your rotors if applied unevenly
3. Keep threads clean to have them function properly in fastening
4. Lube may cause problems when torquing but it may be necessary if fastener is rusted or soiled

 

[Astro14]

Torque has always been an approximation for appropriate bolt stretch. In some engines, for example, rod bolts are tightened using a dial gauge to measure stretch, not by the torque.

 

[Shannow]

Industrially, everything that REALLY matters is tension. Either tension directly measured, or tension inferred by angle of rotation after a specific torque setting.

e.g. my turbine engineer past was 200ftlb (that's finger tight on a 4" diameter stud), plus enough rotation to install 0.15% stretch on the stud.

A 20" long stud would be stretched 0.03"either measured, mechanically or with ultrasonics, or through angle of rotation of the nut. (10 tpi, you would need 108 degrees of rotation to get the stretch)

No mortal can apply that much torque without ripping the threads/galling, so a heated rod is pssed down the stud centreline until it grows long enough to rotate the nut the right degrees...it shrinks and clamps...and never comes loose.

 

[SumpChump]

This stuff, the likes of which you mention above, is REAL fastening. I mean that in a scientific way.

To these fastener 'engineers' or other folks who work with such methods.....our automotive application and specs of fastening must look sloppy finger painting. I say that with awe for these processes.

Makes me wonder how truly unevenly tensioned our wheel studs are when working with some grit on one and some antiseeze left in another and a bit of rust on another. It's probably not real world significant but it sure is interesting!

 

[Colt45ws]

Originally Posted By: Shannow
Industrially, everything that REALLY matters is tension. Either tension directly measured, or tension inferred by angle of rotation after a specific torque setting.

e.g. my turbine engineer past was 200ftlb (that's finger tight on a 4" diameter stud), plus enough rotation to install 0.15% stretch on the stud.

A 20" long stud would be stretched 0.03"either measured, mechanically or with ultrasonics, or through angle of rotation of the nut. (10 tpi, you would need 108 degrees of rotation to get the stretch)

No mortal can apply that much torque without ripping the threads/galling, so a heated rod is pssed down the stud centreline until it grows long enough to rotate the nut the right degrees...it shrinks and clamps...and never comes loose.

 

[A_Harman]

My personal best is a 3" nut holding a 500-lb flywheel on a single-cylinder diesel test engine. 1080 ft*lbs. It took a 3:1 geared-head torque mutiplier and a 4-foot-long 450 ft*lb torque wrench to do the job. We had to build a stand to hold the wrench in alignment while applying the torque.

 

[Shannow]

Colt45ws,
superbolt...10 years as turbine engineer, and would have a superbolt rep flogging their wares every year or two.

I wouldn't use them in a fit.

The joint design is typically installed at 0.15% strain (stretch) on the bolt. The nut is massive, and has relatively small elasticity in the equation.

Throw in a superbolt with its numerous smaller shanks, and they aren't as stiff and have to be factored into the stretch equation.

If their cross sectional area is the same as the stud, then the free length of the little studs has to be added to the length of the original...e.g. if the cumulative cross section is the same as the 20" stud that I spoke of, and there's an inch of free stud beyond the threads, you need to design the joint as 'though there's a 21" stud.

Throw in an operating temperature of 350C, and minimum 4 years between unbolting, and I think you'll be undoing them with a blue flame spanner.

 

[Colt45ws]

Originally Posted By: Shannow
Colt45ws,
superbolt...10 years as turbine engineer, and would have a superbolt rep flogging their wares every year or two.

I wouldn't use them in a fit.

The joint design is typically installed at 0.15% strain (stretch) on the bolt. The nut is massive, and has relatively small elasticity in the equation.

Throw in a superbolt with its numerous smaller shanks, and they aren't as stiff and have to be factored into the stretch equation.

If their cross sectional area is the same as the stud, then the free length of the little studs has to be added to the length of the original...e.g. if the cumulative cross section is the same as the 20" stud that I spoke of, and there's an inch of free stud beyond the threads, you need to design the joint as 'though there's a 21" stud.

Throw in an operating temperature of 350C, and minimum 4 years between unbolting, and I think you'll be undoing them with a blue flame spanner.


Interesting. I doubt Ill be doing anything on bolts that large, but good info anyway. I had just seen the video on youtube and thought of it when I seen 4" bolts being talked about.

 

[Yah-Tah-Hey]

The bolts/nuts on our GE D8 hp/ip steam turbine case had to be installed with the overhead crane. I remember that they had a tapped hole for installing an eye bolt for lifting.The tightening procedure was to heat the bolt with a cal rod heater and then tighten the nut so many flats with a slugging wrench and 16# sledge hammer. The slugging wrench itself was a handful Does that sound right Shannow? It's been a lot of years.

 

[Shannow]

HosteenJorje

Yep, that's about right...Biggest of the HP studs is 5-1/2" diameter, 39" long, made of X20CrMoV12-1...250lb per stud.

Most of the GE stuff uses castle nuts I think