[TheForge] rivets: chapter two

[Thomas A. Troszak]

On Mar 4, 2005, at 8:13 AM, Dave Smucker wrote:

> As you noted a correctly made riveted joint is as strong as a preloaded
> bolted joint.  The hot applied rivets cools and develops a preload in 
> the
> rivet just as the torque applied to the bolt develops a preload in the 
> bolt.
>

Dear Dave,

I don't think that hot rivets really contract enough to create the 
proper load, the joint has to be preloaded by bolting, and then if the 
rivets are installed correctly, they will pretty much retain the 
preload of the bolts. I think a lot of folks believe that hot rivets 
will suck a joint closed, but it just ain't so.

My gut feeling is that the hot rivets, being hot, stretch about as much 
as they shrink while they are cooling (sounds weird, but think about 
it), you only get the real clinch after the color has gone from the 
head, and only if the joint is firmly bolted first. In other words, you 
have to keep hammering and bucking until most of the color is gone. If 
you stop hammering while the head is still bright, the rivets tend to 
be looser. You have to to keep packing the hole full (upsetting) while 
the shank is still shrinking. Also, if the rivet is fairly long (8-10 
diameters or more), like a mud ring rivet, you will find that the shank 
is really only upset near the ends.

Still, in order for the riveted joint to be effective at all, the 
plates must to fit perfectly, and be bolted firmly before the rivets 
are applied. I fit my boiler plates so that a strip of paper will not 
pass through the joint between the bolts, and I bolt ALL the holes 
first.  Then when I am ready to rivet, I remove the bolt(s) where I 
wish to install the rivet, and stuff them in. You can avoid puckering 
the whole assembly by riveting the ends and center first, then keep 
splitting the difference as you go; if you start at one and and work 
along, you run the risk of cocking the plate so badly that the bolts 
won't come out, which is then a lot of extra work...

I don't have hard data to back this up, but from my personal experience 
with hand riveting ironwork (mandatory blacksmithing content here) I 
feel I can often get a tighter clinch from riveting cold than hot. I 
think the only reason that hot rivets are riveted hot is because they 
have to be deformed so severely to create a decent sized head, as it 
takes about three diameters of rivet to form a full half round head. it 
just would not be possible to upset this much material cold by hand, 
especially when balancing on a scaffold.

Those babies are sticking WAY out when you start, and you really have 
to hold your jaw right to keep the head centered. I draw chalk marks 
perpendicularly across the plate through the center of each hole, so 
that I can keep the heads centered more easily.

I hope you don't think I'm being nit-picky, because I'm not. I'm simply 
trying to be as clear in explaining my understanding of the things that 
I do. I enjoy discussing engineering things with you. There may be 
others lurking out there with more riveting experience than I who can 
explain this better, and if so, please chime in.

Tom Troszak