So, whenever I see a structure made out of steel, they are bazillions of little bumps on the surface, where we’ve been told the pieces have been riveted together by Big Strong Men. Presumably, this is much more efficient than welding the entire thing. But what the hell is a rivet, anyway? What’s under those little bumps? Bolts? How is the connection made?
A rivet (in this case) is like a bolt with no threads and a rounded head. It’s heated up, inserted in the pre-drilled hole, and bucked (held in place) by one ironworker while another ironworker peens (mushrooms) the protruding shank on the other end.
You end up with a shaft with two heads on either end holding everything together.
The only time I have riveted anything was back in metal shop so bear with me.
A simple description of a rivet is A metal bolt or pin having a head on one end, and then hammered on the plain end so as to form a second head, usually done while hot so it can be formed…
there are rivet guns that can do this with smaller scale rivet for binding sheetmetal, etc. Not like the ones on buildings you see.
hope this helps
-S
BTW, riveting is much less “efficient”. One of the reasons it is so rare nowadays. Often, riveting ain’t possible at all as means of joining metal parts, e.g., pipes.
I realize you can’t rivet pipes, but the History Channel said that if you are building, say, a bridge or a skyscraper, riveting the beams was much faster and just as good as welding.
It was on TV, so it must be true.
I don’t know if it’s more efficient or not. Ships used to be riveted – apparently some rivets failed on the RMS Titanic --but now they’re welded. OTOH, aircraft tend to still have rivets. Could be the metal. Ships are steel and aircraft tend to be aluminum.
There are also pop-rivets. These have a shank with what looks like the head of a finishing nail on top. This head keeps a flanged sleeve from coming off. The shank is put into a riveter and the head and sleeve are inserted into a hole. The riveter draws the shank into it, which squashes the sleeve so that the two pieces of metal are held metween this flattened part and the flange. When the riviet is as tight as it can get, the shank is automatically cut off.
I DEMAND A RECOUNT!
Crap. Not sure how that happened. That last post was supposed to be the OP of a MPSIMS thread.
peace and friedo, I won’t get into the whole “efficiency” question, but from what I’ve seen of skyscraper building sites, rivets (which are, indeed, an extinct breed) have been supplanted, not by welding, but by big, fat, easy-to-install nuts&bolts.
This is not surprising when you know how rivets/bolts work in skyscraper construction. They do not “stitch” the girders together with the strength of their own shanks; instead they “squeeze” them together so tightly that friction keeps the girders from slipping past each other.
My guess is that it would take a lot more time to make a welded joint that’s as strong as a rivetted/bolted one.
I’ve heard that rivets allow a structure to flex a little, but this doesn’t seem to ring true–a rivet should completely fill the holes in the pieces, which wouldn’t allow much flex.
Johnny L.A., you know aircraft better than I do. Aren’t the frames usually welded, with the skin panels riveted on to allow inspections?
It all depends on the aircraft, of course. Originally they had wooden frames that were glued together and then covered with cloth. Then came welded steel tubing. These had “formers” (peices that form the cross section) attached to them, and usually wood or aluminum “stringers” (longitudinal pieces that join the formers) where needed that were then covered with cloth. One popular method of construction (for example, on the Piper “Cub”) was to have a welded steel fuselage and wooden wings. Later, the welded steel structures were covered with aluminum. This allowed for a very strong structure, such as in the WWII fighters. The problem with steel is that it’s heavy. If you look inside of a WWII bomber, for example, you won’t see a welded steel structure. THey had a semi-monocoque construction, where the “formers” (BTW: This is what they were called when I was building balsa models. I don’t know if they are actually called that in full-size aircraft, hence the quotation marks.) were made of aluminum rings and were joined by aluminum “stringers”. When covered with an aluminum skin, this provided a strong, lightweight, rigid structure.
There was a boom in the building of light civilian aircraft after the war. It was expected that the pilots who fought for us would want to continue flying when they got home. Many light (“General Aviation” or “GA”) aircraft were built and there was a glut on the market. With such competition, many manufacturers went out of business. Now, the military are more concerned about performance than they are efficiency. A single-seat North American P-51 “Mustang” had a huge Rolls-Royce “Merlin” engine pumping out 2,000 horsepower. Just the thing for flying around at 450mph and getting the upper hand against the enemy. But not so good if you want to fly the family around and have to pay for your own fuel. GA aircraft had to have engines that sipped fuel rathter than ones that gulp it. Less power meant that the airframe had to be lighter. There were two construction methods that were prevalent after the war: Steel tube, and semi-monocoque. Piper kept to the tried and true tube-and-cloth method, continuing their popular J-3 “Cub” and bringing out new aircraft like the “Tri-Pacer”. Cessna built aluminum fuselages with cloth-covered wings on their 120 model, but later retrofit those with aluminum wings. Beechcraft introduced their all-metal “Bonanza”, and North American built the all-metal “Navion”. All of these aircraft used much less power than the big radials that were in vogue before the war. (There were a few radials out there though, such as the Cessna 190/195.) Rather, the new GA aircraft used engines from about 65 hp to 300 hp. Transport aircraft still used big radial engines, but were all-metal to save weight for passengers and cargo.
Eventually, the “rag wings” (cloth covered wings and welded steel fuselages) gave way to the all-aluminum semi-monocoque designs which required much less meintenance. Virtually all aircraft today are made of riveted aluminum. (See? I did mention rivets!) There are some exceptions, of course. Bellanca still uses the welded fuselage and wooden wings. There are several “glass” (composite) designs flying, and many people build their own aircraft; choosing “rag wing” designs for ease of construction or nostalgia.
What about military aircraft? I don’t know about their construction. But I’ve seen many of them up close, and they have a goodly number of flush rivets in them. No doubt much of their critical structures are welded, but the riveter’s job is, for now I think, secure.
One thing about flexibility. Airframes are built to flex, otherwise they would shake themselves apart. Ever see a Boeing B-52 on the ground and in the air? On the ground the wings droop. While flying, they have a nice upward sweep. The wingtips actually flex something like 18 feet! Flexing reduces the stresses on the airframe.
Here are some of the prime benefits of rivets w.r.t. airplane construction (off the top of my little head):
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Very strong pop-rivets are often used on aircraft in tight places where access to the back of the piece is restricted or impossible.
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Rivets do not self-loosen, like a bolt will. True, there are many locking mechanisms for bolts, but in general the rivet is simpler.
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A rivet weighs less and takes up less space than a bolt, or a bolt and nut arrangement does. This is a factor on an airplane when you are talking about thousands of fasteners on the structure.
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Their low profile heads lend themselves well to not interfering with the aerodynamics of the craft.
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If you want to take a panels off, you drill out the rivets. You do not need access to the back of the piece, which is often impossible to achieve.
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The exotic materials used in aircraft are can be and are frequently welded, but it is more difficult and expensive to do so relative to welding steel alloys. Or using rivets.
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Rivets will not propagate a crack, like a weld can. This is very important in aircraft.
As far as buildings and bridges - rivets are used for one reason - expense. They are cheaper than threaded fasteners, and faster to install.
If there are any crew chiefs here at SDMB, they will be able to correct any mistakes I may have made. The following is an informed, but inexpert opinion.
[/quote]
As an electronic warfare systems specialist, I worked on F-4s, F-16s, and B-52s. Although removable panels were attached to the airframe with screws and locknuts (actually, locking nutplates – a nut held in place by rivets), I think most of the load-bearing panels were riveted. Some were fastened with a type of removable blind fastener that I can’t remember the name of (help?).
Aircraft require fasteners that will not loosen on their own. This is because[list=1][li]Aircraft vibrate in flight.[/li]
[li]A lot.[/li]
[li]If something falls off at 30,000 feet, you can’t just pull over, walk back, and pick it up.[/li]
[li]Loose objects of any sort can jam controls, short out wires, abrade and/or damage insulation and hoses, or otherwise cause all sorts of potentially catastrophic damage.[/list=1]Everything that could possibly come loose on an aircraft is either riveted, fastened with locking fasteners, safety-wired in place, etc. To do otherwise would be to invite disaster.[/li]
In the 1930s, there was an entrepreneur in southern California who had the brilliant idea that aircraft would be much less expensive if they were assembled with sheet-metal screws. He got some backers and built a prototype. It made one maiden flight. It rained screws during the whole flight (but did not crash). The plane wasn’t flown after that, but I think the company made some of its investment back by selling (or renting) the plane to movie companies when the script calls for an airliner in the background. It (and a model used for the flying scenes) appears in at least one early WW II movie where is is used as a makeshift bomber to destroy a bridge by dropping bombs fabricated from gas cans (or some such). It resembled the DC-3 (twin radial engines, low-mounted wing, etc.), but it had a biplane horizontal stabilizer and three vertical stabilizers – the tail resembled a two-cell box kite.
~~Baloo
[sub]I sure hope I addressed the OP, but I just had to share that bit about the “screwy” plane.[/sub]
Another reason that rivets hold well is that they pull together and tighten up the connection as they cool and contract. At least, that’s what I tell my students. I hope I’m right. Also - apropos of nothing, but I’m going public with this anyway - my dad riveted airplane wings during the war. There.
So what’s the deal with the home built aircraft having all the screw slots lined up the same way?
The “problem” with riveting is that you need a greater overlap of metal sheets for the join. Hence a ship made from a riveted hull is much heavier than one made to the same dimentions with a welded hull. Ergo they are heavier, slower, require larger engines, burn more fuel etc.
IIRC, Germany exploited this when rearming because the imposed limits were based on deadweight tonnes.
Today we can weld big pieces that were impossible to weld 75 or 150 years ago and, even if they could be welded, riveting was much cheaper.
Nuts and bolts were much more expensive than rivets so rivets were the logical choice.
During the construction of the Golden gate bridge in San Francisco the procedure for riveting a box beam was:
They worked in teams. One man inside the beam (were he could hardly move). The rivet was heated red hot in a furnace and dropped into a pipe that landed in a cup by the man inside the beam. he took it with tongs and placed it in the hole and backed it. Immediately another man on the other side would finish the rivet with a pneumatic hammer. They had to work very fast or the rivet would cool down.
Psychological, mainly. Having the slots lined up with the airflow should reduce drag, but I’m sure you’d never notice. Essentially all airframe fasteners are flush-headed anyway (flat across the top, with a conical head seating in a recessed conical hole).
[QUOTE]
Originally posted by Baloo ***
Some were fastened with a type of removable blind fastener that I can’t remember the name of (help?). [/QUOTE{/**
Cleco, maybe? A Cleco, named for its manufacturer, fits into a pre-drilled hole to hold a sheet-metal panel onto the frame. With the panel held in place, they can be replaced one by one with the real rivets. If you’re asking about removable aircraft fasteners, you might be thinking of Camlocs.
As has been stated above, aircraft use rivets whenever maintainability allows because they’re lighter than bolts as well as less expensive, and they cannot vibrate loose. They do not provide any clamping load if installed cold, as they are on aircraft, but carry shear loads just fine. Since the friction load from a “clamped” rivet joint is so variable and hard to quantify, typical engineering practice is not to take credit for it at all in stress calculations, but depend on the rivets’ shear strength exclusively.
Re building practices, a practicing civil engineer could answer this one better, but I’m sure that bolts are a less expensive and safer way to go these days. A riveting team required a guy to cook the rivets (on a stove a few hundred feet in the air), then toss them to a catcher/bucker, and a riveter (watch old Three Stooges movies for a good example). Bolting can be done single-handed using a modern design that can be torqued from the shank end, with a wrench that torques the nut and bolt against each other from the same side of the joint. Metallurgy is so much advanced from the early stages of high-rise construction that these bolts provide a more-reliable joint than a riveted kind, even with fewer fasteners. It’s worth mentioning that a rivet needs to be made from a fairly soft grade of metal or the head cannot be formed.
Welded joints are less reliable if done under field conditions, mainly due to difficult access, and require more-expensive grades of worker. Also, as has been noted, a crack can propagate from one member to the next across a welded joint but not a riveted one. That’s partly why so many Liberty ships sank without warning in WW2, when they cracked in half while sailing in cold waters, with welded hulls made of cheap steel that went brittle when cold (ref. Titanic, too). A riveted ship is slower because of its greater weight, but also because of the drag created by the protruding rivet heads.