[TheForge] NJMT (was: rivets: chapter two)

Mon Mar 7 12:22:34 EST 2005

I don't think I would like to be around a boiler that someone made who had
no prior experience.  We had a bad boiler explosion in the next county about
3-4 years ago that killed several and injured several more.  Because of
that, Ohio has really put the clamps on pressure vessel repair and
operation.

Last night I watched a steam locomotive show that showed the railroad shop
is Strasburg, PA.  They noted that this shop was fully licensed and does
boiler repairs.  See here:
  http://www.strasburgrailroad.com/mechshop_overview.aspx

Walt

-----Original Message-----
From: theforge-bounces at mailman.qth.net
[mailto:theforge-bounces at mailman.qth.net] On Behalf Of Bruce Freeman
Sent: Monday, March 07, 2005 9:21 AM
To: theforge at mailman.qth.net
Subject: [TheForge] NJMT (was: rivets: chapter two)

Tom,

You seem to know a fair amount about riveting boilers.  Happens I know some
folks looking for info on that subject.  A fellow down a the Pine Creek
Railroad (NJ Museum of Transportation) needs to rivet up a boiler for a
locomotive they're rebuilding.  He has some references on proper rivetting,
but expressed an interest in some more.  Know any good ones?

One reference I have noted that the rivet head should be made with a
continuous, straight-on use of the (power) header.  This is not how they did
it in a demo I watched.  Rather, they headed down, then rotated the tool
around the rivet head to make a bead on the edge that they could later
caulk.  What's your take on the proper procedure?

Bruce
NJ

>>> tom at tomtroszak.com 3/5/2005 12:06:36 AM >>>

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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