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Old Rivets

CPSONE

Well Known Member
I've read that heads may split and other problems might come from using rivets that are too old. Anyone know how old is too old? I bought an un-started (no rivetting done) -7 emp kit that's from 2005. Should I get a new full set of empennage rivets?
 
No problem with old rivets! Drive 'em!

This has been brought up over time. I have rivets in my shop that are over 25 years old. They are fine.
 
Try 'em

...if they work, great. If they crack or don't drive right, pitch 'em and buy some new ones. I had some that are ~5 years old go bad. My brother (RV-6A sloooowww builder) has lots that are still good after 15 years. He also ran into some that were bad, too, though.

Good luck.
 
HUH???

So if rivets go bad in 5 to 10 years does that mean we have to replace our airplane in 5-10 years? If an old rivet can't handle the pressure of being driven I doubt it could safely handle the G loads these planes are designed for.:rolleyes: Go with Mel's advice...he's the one that would know.
Unless they have been stored in salt water I wouldn't worry about it at all.
 
So if rivets go bad in 5 to 10 years does that mean we have to replace our airplane in 5-10 years? If an old rivet can't handle the pressure of being driven I doubt it could safely handle the G loads these planes are designed for.:rolleyes: Go with Mel's advice...he's the one that would know.
Unless they have been stored in salt water I wouldn't worry about it at all.

Aaron,

I think the issue is rivets get hard when driven but sometimes they get hard before being driven and are difficult to set and may crack. Why that happens but I don't.

I bought a ton of old rivets from the Boeing Surplus Store in Seattle once and many of them were so hard they were useless. There's nothing more frustrating than trying to drive an old hard rivet. But I've never heard of RV rivets going hard before being driven.

I also read somewhere that heating old hard rivets will make them soft again, but that doesn't seem worth the effort considering how cheap they are new.
 
Aaron,

I think the issue is rivets get hard when driven but sometimes they get hard before being driven and are difficult to set and may crack. Why that happens but I don't.

I bought a ton of old rivets from the Boeing Surplus Store in Seattle once and many of them were so hard they were useless. There's nothing more frustrating than trying to drive an old hard rivet. But I've never heard of RV rivets going hard before being driven.

I also read somewhere that heating old hard rivets will make them soft again, but that doesn't seem worth the effort considering how cheap they are new.

Is it possible that the old rivets had a composition problem and that is why they were in the surplus store? I have a hard time believing that an aluminum rivet will actually harden over time unless it is subjected to some sort of environmental stress...correct me if I'm wrong.
 
The rivets are made to a Mil-Spec. If they had an "expiration date" then every batch would be required to be marked with the date of manufacture - just like some Mil-Spec hoses.

The Mil-Spec has no mention of dates, so the rivets are not date limited...

http://www.everyspec.com/MIL-SPECS/MIL+SPECS+(MIL-R)/download.php?spec=MIL-R-5674F.008075.PDF

Added

The Boeing surplus rivets may have been surplus because they did not meet the specifications.

I did like visiting that store....:)
 
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Rivets don't go bad over time. If they are stored in a corrosive environment, they can, like if an aluminum rivet was exposed to ammonia stored in a closet, for instance, but just time will not do it.

The Boeing surplus rivets were probably made of some material that behaves differently than you expected it to, like a rivet that was intended to be driven while hot or something. If they had a batch of known bad fasteners, I doubt they would have resold them.

Tim
 
AD rivets

The rivets supplied with the RV kits are AN426AD and AN470AD rivets. AD is identified with a single dimple in the head and are made from 2117-T3 aluminum alloy. These rivets are the most widely used for manufacturing and maintenance of modern aircraft. These rivets require no heat treating and are often referred to as "field" rivets.

However, AN426D and AN470D rivets are made from 2017 aluminum alloy which is extremely hard, and are identified with a raised dot on the head. Because they are so hard, they must be heat treated (annealed) before use. After heat treatment, the rivets are kept in a freezer (so called "ice box rivets") until they are driven. After they are driven and warm up they gradually attain the pre heat treatment hardness. These rivets are susceptible to cracking if driven prior to heat treating.

I suspect this is what you are referring to, so if you buy surplus rivets be careful to only buy the AD alloy not the D alloy.
 
Depends on the type of rivets

There are a couple of different alloys used to make aircraft rivets, and they have different part numbers.

Our normal AN-470-AD and AN-426-AD rivets are made from 2117 aluminum and are already age-hardened to a certain extent. They should not normally get harder with more age, so they don't have a shelf-life.

There are some rivets, often called "refrigerator rivets" that are in a solution-treated state (soft) and will age-harden over time at room temperature, so they are stored cold. These are the type of rivets that will get too hard to drive over time if not stored correctly, and the shop-formed head may crack when driven.

There is a procedure for re-solution-treating these rivets to rejuvenate them, making them softer so you can drive them.

I think that you would typically find these rivets in larger sizes, and in the aerospace industry where higher strength would be called for, so it is plausible that you would find some of these in a Boeing supply stock - although if they were not being stored cold, they probably were surplus.

To AARVIG, who asked if old rivets crack, does that mean they would go bad on the airplane, the answer is no, just the opposite! These rivets are getting stronger over time, not weaker. But by getting harder, they are less formable, and so the tails may crack, or the heads crack if yout try to buck them. But a soft rivet, bucked, then age-hardened, gets stronger and better.

Age-hardening aluminum, normally done by heat treatments, but most age-hardening alloys continue to 'age' and gain strength for a period of time even at room temperature. This is cool. For big airplanes that have thick, complex-shaped wing skins, you get a fresh slab of aluminum, machine it and form it into your wing skins (usually rolling, sometimes even shot-peening to form compound curves), drill the holes, put the wing together, and then, as it moves its way up the assembly line, over weeks and weeks, the wing skins are getting stronger as the aluminum age-hardens.
 
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Problem rivets diagram

I posted the question after reading page 5-25 (Problem Rivets) of the Rv-7 builder manual. I'd never thought of rivet age being a concern as there is no shelf life as another poster stated. Bottom row 4th rivet from the right is showing a cracked manufactured head and the possible reasons below are "Rivet too hard (too old) when formed, replace"
Thanks for the insight.
 
Old rivets.. No such thing

I've been working on large airliner aircraft for 20 yrs now and this is the first I've herd of OLD RIVETS.

What is the part number of the rivet you suspect is OLD.

The only rivets that age harden are heat treated "DD" rivets, they harden to full strength within 1-3 days of being driven or after heat treatment, they have to be driven within 40min after heat treating, to prolong this time they are kept in dry ice after heat treating, all rivets work harden when they are driven, and RV's are built with AD rivets, a medium soft rivet so it might be the riveter who is causing the rivets to crack by not forming the tails properly or chopping the heads with the rivet snap.

An over driven rivet is always stronger than an under driven rivet because of the work hardening effect. A properly driven rivet tail should be 1.5 the Dia of the shank, and half the shank dia high.

D rivets are not heat treated, these are the most common rivet used in construction of large pressurised airliners, the DD rivet with the raised dashed do have to be heat treated.

I did a quick search for rivet head markings, this is a good link to describe the different types of rivets and there applications http://www.mlevel3.com/BCIT/rivetID.htm

Or even Wikipedia has a good run down on aircraft rivets http://en.wikipedia.org/wiki/Rivet
 
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Old rivets.. yes such thing (proof)

I've been working on large airliner aircraft for 20 yrs now and this is the first I've herd of OLD RIVETS.

What is the part number of the rivet you suspect is OLD.

Mine were AN470AD4-5.

The only rivets that age harden are heat treated "DD" rivets, they harden to full strength within 1-3 days of being driven or after heat treatment, they have to be driven within 40min after heat treating, to prolong this time they are kept in dry ice after heat treating, all rivets work harden when they are driven, and RV's are built with AD rivets, a medium soft rivet so it might be the riveter who is causing the rivets to crack by not forming the tails properly or chopping the heads with the rivet snap.

Not in my case. I was squeezing, not driving the rivets. Same squeezer settings were used for both the old and new rivets with drastically different results as shown below.

When working on riveting my center section to the fuselage side skins, I originally started with the remnants of the batch of rivets from the wings. Using the squeezer, nearly every rivet was cracked like so:

crackedrivet1.jpg

(note: the misshapen shop head is an effect, not a cause)

or

20090509-10-tn.jpg


I drilled them out and switched to a newer batch of rivets (the same size), and squeezed them without further problems.

Here's a comparison of one of the old rivets (that happened not to crack) to one of the new ones:

Old:
20090509-08-tn.jpg


New:
20090509-09-tn.jpg


Note that the old batch of rivets performed just fine when I was assembling the wing, so they clearly became harder in the intervening time period. You could hear the difference when operating the squeezer.

If I had kept them, I would have been glad to send a few to the naysayers so they could see for themselves, but I didn't want them in my shop, so I threw them out. Sorry.

One's absence of observing a phenomena doesn't mean that phenomena does not exist.
 
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Old rivets

Hi Mike,

Looking at your photo's, the first photo shows the rivet tail (shop head) hasn't formed central to the shank, you can see the witness mark isn't in the centre of the tail, this shouldn't normally cause cracking, clearly there is something else going on with these rivets.

Also the second photo shows a rough surface of the formed tail, this also isn't normal, the 3rd photo shows what I would consider s normal surface finish and properly formed tail.

I don't think there is any difference between riveting and squeezing rivets, they still work harden when they are forming the tail so this also shouldn't cause cracking.

In all my years of riveting, Monel rivets and Alloy rivets the only rivet's I've seen that have cracked were DD rivets that had been left too long after heat treating. I would never have guesses that AD rivets would crack, all I can suggest is your rivet batch might have been a dud batch, over heat treated during production maybe, I'm no metallurgist, AD rivets shouldn't crack and normally they don't age harden as in this case. If I hadn't see the photo's I wouldn't think it were possible for AD rivets to crack.
 
I've had both new and old rivets that were bad. I think the issue is less likely due to age and probably poor heat treatment or possible storage conditions. I tossed a new batch of rivets from ACS after I had issues with cracking. I also have rivets in my kit that are from the early 90s that set perfectly.
 
But what about MIL-R-47196A?

Mike, take a look at MIL-SPEC R-47196A (since renamed to NASM47196). That spec appears to indicate that the cracks you got are perfectly acceptable, since they are on the edge of the shop head. The spec allows for cracks outside of the area that is concentric with and 1.10 times the nominal shank diameter, non-intersecting cracks, and up to four cracks on a single shop head! (See 4.2.1.k.)

I have a number of rivets on my project with cracks, some very similar to yours, and couldn't for the life of me figure out what causes them (I didn't think to try brand new rivets -- the rivets I used were about two years old). Even squeezed rivets that otherwise looked perfect would get cracks in the shop head sometimes. This spec put my mind at ease (a little!). "If it's good enough for the military and NASA...."

I'd be interested in the opinions of those much more knowledgeable than I regarding this observation.

[Edit: Slight elaboration and changed "OK" to "acceptable."]
 
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Mike, take a look at MIL-SPEC R-47196A (since renamed to NASM47196).

<snip>

I'd be interested in the opinions of those much more knowledgeable than I regarding this observation.

Shannon, thanks for the spec. Based on that, some of the rivets that were cracked would have been acceptable. I still would have drilled them out and replaced them however since I'm a bit of a perfectionist.

I was trained as an aircraft structures mechanic in the US Navy, but didn't have that much practical experience prior to my RV-7A since I served in the reserves for 6 years rather than active duty. I don't recall my Navy instructors saying anything about cracked rivets...but that was > 20 years ago, so who knows.

Interestingly, the cracked rivets squeezed quite a bit differently than usual. My squeezer technique is to feather the valve so it slowly approaches the rivet. Once the ram makes contact with the rivet tail and I'm assured my alignment is good, I trigger the valve to give full pressure. Usually this results in a nice smooth action to squeeze the tail. But on these rivets, once I applied full pressure the squeezer would hesitate for perhaps 1/4 second, then BAM! It would rather violently squeeze the rivet.

I recall thinking after the fact that it would have been nice if I had been bright enough to realize this clue and stop work before getting all dozen rivets squeezed on the right side of the fuselage. Then I wouldn't have had to drill out nearly as many. At least I didn't do both sides with these rivets. Sigh.
 
I know exactly what you mean. I experience the same with my pneumatic squeezer. For certain lengths of rivets, it's as though the squeezer can't quite get the leverage it can with other lengths of rivets. So, for some lengths, a squeeze of the trigger causes the squeezer to smoothly squeeze the rivet. For other lengths, it tries, but pauses momentarily, then finishes the squeeze at a faster speed than usual. I'll get a tiny little puff of smoke or dust from the rivet, and yes, sometimes the shop head has a slightly rough surface, as shown in one of your pictures.

At times, my squeezer simply can't squeeze the rivet completely in one operation. To deal with this, I have found two solutions: (1) adjust the squeezer to squeeze the rivet only part-way; once I do that it squeezes easily in two operations, with an adjustment in-between. (2) crank up the air pressure to the squeezer a little. I normally set it at 90 PSI but my gauge is at the tank and there's some 50' of hose and couple 3/8" and 1/4" fittings between it and the squeezer, so the squeezer may be seeing less. Nevertheless, I keep it at 90 PSI at the compressor and those few times when the squeezer can't quite get the "umph" I know I can temporarily crank up the pressure to 100 PSI or so and that takes care of it. (I know, I really should put a pressure gauge at the squeezer itself and adjust it for 90 PSI there.)

These little "gotchas" are frequent enough for me that I just figured it's the way it is. The MIL SPEC reinforced that belief. But now I'm wondering...

My shop is an old drafty outbuilding. The temperature in there varies between the teen's and low 20's in the winter to the 90's or even over 100 F in the summer. (The humidity also varies widely, although I have a dehumidifier running to try to keep it down during the 8 months of rainy weather!) Are rivets intended to be stored long-term at "room temperature" before they're set? If I kept all my rivets in the [climate-controlled] house and only brought them out to the shop on days that I'm riveting, would I not get these cracks, puffs of dust/smoke, or difficulties with the pneumatic squeezer at times?
 
Hard Rivets

Hi Shannon,

From your description it sounds like the rivets are harder than what they should be for AD Rivets. I'm guessing your squeezing 1/8th rivets. For the squeezer to hesitate then slam the tail down sounds like it is struggling then as the air pressure builds up it finally get's the tail down. The puff of smoke is probably the anodised finish being disturbed as the tail is set.

There must be some dodgy batches out there for this to be happening so frequently. Are they VAN's supplied rivets?? If so maybe VAN's need to change rivet suppliers.

As I wrote in my earlier post, I have never seen an AD rivet crack, until this thread I didn't think it was possible, I am guessing the cracking rivets haven't been manufactured properly and they have been incorrectly heat treated.

Happy building,
 
Yup. From Van's. 1/8th inch (AN470AD4). Hmmm... I guess next time it happens I'll stop, buy some "fresh" rivets, and see if there's a difference.
 
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Old Rivets Update

Thanks for all the great feedback. Thought I'd give an update of the old rivets situation.
Squeezed a bunch of 6 year old rivets in my VS rear spar. Pneumatic squeezer had trouble setting some of them they were so hard. About half of them cracked (even perfectly set ones) and they all had a pebbly finish around the shop head. Drilled them all out, ordered all new rivets (complete emp set) from Van's and installed the new rivets last night with no problems. The new rivets seemed much softer and had a much smoother texture around the shop head. Must have to do with how they were stored, perhaps in a hot garage or?. They were all in plastic zip lock bags which should be a good thing.
I got this emp kit used but almost untouched although 6 years old...

VS almost done! just one side of the skin to rivet on and the rear spar assembly! First component of my second emp kit. (its exciting for me anyway, finally some progress...) :)

So beware of old rivets...
 
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