installation vs seating torque

[rollingcloud]

In the case of self-locking nut. Is it normal to have different definitions across different specs, within the same industry? I am so confused, AS spec should in theory be aligned with GE spec. However, I am not seeing that, am I interpreting it correctly?

AS spec says: Assembly torque is the design torque applied at final assembly. It shall include the net effect of the following:
a. The torque required to overcome kinetic friction between mating bearing faces and between mating threads.
b. The torque required to overcome the self-locking feature.
c. The torque required to apply the desired axial load to a fastener assembly.
The installation torque shall be measured only in the tightening direction. Also: Installation Torque, Tightening Torque.

Seating torque: The torque to bring the bearing surfaces into the seated position, only in the tightening direction.

My thoughts: According to the AS spec, seating torque comes before the assembly torque/installation torque. Seating torque only makes the initial bearing surface contact and does not create the final desired axial load.

In a GE spec, it says a nut is seated when the nut bearing surfaces contacts a spacer and an axial load is induced in the bolt by applying a specified seating torque or by producing a measured extension of the bolt. It also defines maximum installation torque as the highest value obtained as the nut is initially installed on and is being sized by the bolt or the max value obtained during any subsequent on or off cycle.

It says a nut is installed on a bolt when not less than the chamfer plus one-half threads and not more than the chamfer plus 5 threads of the bolt protrude through the nut. Nuts with centralized locking devices do not require the bolt to protrude through the nut provided the bolt passes through the locking device by the chamfer and one and one-half to 5 threads.

My thoughts: According to the GE spec, the installation torque is not related to bearing surface contact, but it's related to the protrusion of the bolt. The GE specs appear to define the seated state the same way as the AS spec's assembled/installed state.

I googled and found the following definition, which aligns with the GE spec, but not the AS spec

 

[SWComposites]

In the case of self-locking nut. Is it normal to have different definitions across different specs, within the same industry? > Yes. Can even happen in different specs within the same company. Ugh.

I think your interpretations are correct.

Note: engineers are often terrible spec writers.

 

[MintJulep]

AS spec should in theory be aligned with GE spec

AS =??

GE = General Electric?? If so, which of the many past and present divisions?

Why would you expect alignment?

the installation torque is not related to bearing surface contact, but it's related to the protrusion of the bolt

This is not correct. Bolt protrusion beyond the nut has exactly nothing to do with torque or preload.

 

[rollingcloud]

SWComposites,
sign...as if these countless different torque names are not confusing enough already, and who came up with these names, my god. They might as well as remove the words and name these torques with number sequences, so we know exactly what phase the torque belongs to.

 

[3DDave]

Bolt thread protrusion is used as proof that the thread has fully engaged the locking portion of the nut, accounting for the incomplete threads typically at the end of bolts.

Specs are frequently created in response to some sort of failure that preceded the writing of the spec. Different organizations will have seen different failures that prompt them to write specifications. Eventually, with enough failures, they should converge on the subjects covered, but are unlikely to converge on the terminology, or so my experience of humans and languages so far has demonstrated.

 

[rollingcloud]

MintJulep,
AS = Aerospace Standard. Pretty sure it's GE Aviation division.
GE spec's installation torque has no mention of preload/axial load at all, the protrusion is what defines the "installed" state for the max installation torque.

 

[MintJulep]

Bolt protrusion beyond the nut has exactly nothing to do with torque or preload.

faq725-1331

 

[Tmoose]

"GE spec's installation torque has no mention of preload/axial load at all, the protrusion is what defines the "installed" state for the max installation torque."

I suggest proceeding carefully.

I'd interpret protrusion as the number of screw/bolt threads visible beyond the nut.
"Producing a measured extension of the bolt" is elongation/stretch of the bolt by which it creates the desired clamp load.

For a high strength ( ~Grade 8) 3/8" fastener with a grip length of 1 inch or so, the elongation will be less than .010".

https://arp-bolts.com/i/t/stretchpreload.gif

The actual elongation stretch nearly all happens in the grip length of the bolt.

Some critical applications allow precisely measuring the change in overall length of the bolt.
That is a very convenient way to measure stretch/ elongation.
For good result the bolts must be carefully prepared with each end ground flat. Even better is a small machined center to receive special micrometer anvil and spindle faces.

 

[Gr8blu]

One form of a "self-locking" nut is to use a heat-stretched stud and nut assembly. In that case, the stud DOES NOT protrude through the nut. Applied torque is determined by the elongation of the stud itself.

Converting energy to motion for more than half a century

 

[CWB1]

IME both seated torque and thread protrusion are used for the same thing - to let the assembly folks know when all contact surfaces are fully seating against each other. If you're assembling halves of a gearbox and using fasteners to seat interference-fit bearings without smart tools, you want to know when to switch from an impact driver to a torque wrench. You can do so either by measuring seated torque or thread protrusion.