[TheForge] rivets: chapter two

[Chuck Robinson]

For what it's worth one of the theories of the cause of the extensive hull 
damage that sank the titanic was that they used defective rivets. The 
mathematical models used to simulate the forces the iceberg would have 
created were insufficient to cause that amount of damage Bob Ballard 
observed.
Analysis of some of the rivets retrieved by Jason supposedly confirmed the 
rivets were not to spec.
Chuck
----- Original Message ----- 
From: "Thomas A. Troszak" <tom at tomtroszak.com>
To: <theforge at mailman.qth.net>
Sent: Friday, March 04, 2005 11:06 PM
Subject: [TheForge] rivets: chapter two


>
> 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
>
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