Need more info on rivets cooled before they are installed for a tight fit. 1

[DasKleineWunder]

I tried Googling it and found almost no info.
So far only found student exercises to use thermal expansion coefficients and formulas.

Does cooling a rivet before installing actually helps ensure a tight fit thus preventing it from coming loose?
Or does it actually adds stress when it expands?

 

[dhengr]

DasKleineWunder
The holes are likely to be slightly misaligned due to manufacturing tolerances, so a cold rivet will not necessarily fit better or fill the holes during the driving/bucking process. When the rivet is hot, it will deform a bit to fit the holes and then deform (expand) more when it is being driven and headed. This fills the holes more completely even if they are slightly misaligned. And, the total contraction due to final cooling is really quite small in the scheme of things. Because of this, riveted joints tend to slip less than bolted joints, which must slip to some extent to bring all the bolts into bearing.

 

[MikeHalloran]

It has nothing to do with shrink fits and such.

Some aluminum aircraft rivets must be refrigerated in storage to prevent them from age-hardening before they are bucked. I.e., they are supplied in a soft condition that allows them to be upset. Some time after they are installed, and allowed to warm to room temperature, their metallurgy changes in a way that makes them stronger, and incidentally too hard to upset properly.



Mike Halloran
Pembroke Pines, FL, USA

 

[racookpe1978]

Two problems here:
(1) aircraft rivets requiring refrigeration BECAUSE of their metalurgy;
and
(2) older structural and shipbuilding and pressure vessel iron/steel rivets that HAD TO BE kept red-hot because of their metallurgy to be driven in hot and to shrink tight to forma good joint.

Which is your concern. A cold-driven structural rivet will always fail and must be replaced. A too-cool structural rivet will often fail.

 

[paddingtongreen]

Your (2). The rivets are driven hot because they are at maximum malleability.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[tbuelna]

I agree with paddingtongreen, large diameter steel rivets are driven hot because they are more malleable and require much less effort to form when hot. Rivets are designed to transfer loads in shear. Thus it is important when installing rivets to expand the body sufficiently to completely fill the mating holes the rivet is installed into.