Capscrew vs Hex Head Bolt Torque 2

[rQuestionEngineering]

Is the torque same for both capscrew and hex head bolt of the same size and material ?

 

[BrianPetersen]

The head style is not the governing factor. The clamping load of the fastener doesn't depend on what style of head it is.

 

[dvd]

Read this article You can't tension all bolts

and learn more about torque versus tension

Lessons From the Field — Lesson 1: A Torqued Bolt Isn't Necessarily a Tight Bolt

excellent video

Applied Bolting - Torque isn't Tension

 

[chez311]

Actually I imagine head style can impact the torque-tension relationship ie: the torque needed to attain a certain preload - that is if the heads have different OD's at the contact surface (standard socket head vs. flanged cap screw). Under-head friction imparts a non-trivial amount to the total friction in a fastener/joint. You would have to do some testing to determine to what extent.

 

[klaus.]

you have to distinguish between
-- prestressed bolts for slip critical connections....here only special bolts with hex head are allowed
-- and prestress ( torque) in order to lock the nuts ...here 'anythng' is allowed

 

[CWB1]

So long as you're yielding neither the base nor head material via contact stress your nut factor should not change appreciably.

 

[BridgeSmith]

According to the catalogs, etc. we looked at here in the office, cap screws have a smooth raised bearing face on the underside of the head, similar to the bearing face on a nut, which a bolt does not have. Hex bolts are intended to have a washer under the head.

The allowable or required torque is dependent on the tension required for the application, the tensile strength of the bolt or cap screw, and the lubrication applied to the threads and bearing faces.

 

[chez311]

CWB1,

The long form equation for nut factor has a term devoted to underhead friction coefficient and bearing diameter. The size of the fastener head absolutely has an impact on nut factor. If you take a look at the below plot - an increase in head diameter results in an appreciable decrease in fastener preload for the same applied torque, everything else being equal. Take an example of a 1/2"-13 standard socket head cap screw vs. a hex head flanged cap screw having approximate head bearing diameters of 0.750" and 1.078" respectively. This is a 44% increase in head diameter for the flanged cap screw which results in an approximately 8% decrease in preload for the same applied torque.

This was taken from the below article.

http://www.archetypejoint.com/downloads/dissecting_the_nut_factor002.pdf

 

[Screwman1]

Cap screws are intended to be torqued from the head side (hence the washer face) and bolts are intended to be torques from the nut side (hence the washer face on the nuts). There may be slight differences between the two, but the confidence bands will likely overlap almost completely. Other factors will far out weigh this if the parts are installed as intended.