SS Pulled Rivet Substitute

[whee]

Anyone substitute solid rivets for the SS pulled rivets used to attach the aluminum formers and sills? I'm curious to know if anyone has and if they upsized the rivets?

[S Lathrop]

I have not done the final assembly so what I am planning might not be optimal.

My experience with SS rivets in other applications has not been good. As such I never use them.

I plan to use Avex rivets (available from Wicks) and a structural adhesive. I have done this for years on an application where I am relying on the integrity of the joint for structural strength. The Avex rivet is a not nearly the strength of a Cherry Max but is generally the next best option in pull rivets. The adhesive will bring the installation to Cherry Max or solid rivet performance.

[whee]

Thanks, I'll check out Avex rivets. I want to use solid rivets but there are a few places I'll have to use a pulled rivet.

[SteveF]

Monel solid rivets are a little bit harder to buck than AD rivets, but they aren't too bad. I use monel rivets when I'm working on stainless sheet metal.
Don't forget to put a barrier of some kind (i.e. primer, ppg/pro-seal, etc) on the rivet before you put it in the hole to prevent/minimize galvanic corrosion.

[Mark Goldberg]

I believe stainless rivets have more strength than aluminum rivets. But I could be wrong. Mark

[S Lathrop]

I believe stainless rivets have more strength than aluminum rivets. But I could be wrong. Mark

Mark,

Stainless rivets are a lot stronger than other types of pull rivets. What I hate is when the rivets loosen slightly. Then you really have an issue removing the rivet. They don't expand and lock into the hole as a an aluminum rivet. And I don't think the clamping force is all that good.

My opinion is based on my experience over decades of working on race cars.

Where Bob called for SS rivets, I went to a larger Avex rivet.

[whee]

I tried looking the shear strength up but was too lazy to calculate anything. What I found is that a single 1/8" SS pulled rivet has a specified shear strength of 420lbs. A single AN470A-4 rivet has a 350lbs shear strength. I couldn't find a spec for the AN470AD-4 rivet which is what I wanted to use but since the alloy used on the AD rivet has a shear strength that is three times that of the A rivet alloy (30ksi vs 10ksi) I figured the shear strength of a AN470AD-4 rivet far exceeded the shear strength of an 1/8" SS pulled rivet.

[jim.mclaughlin924]

I think the 350 lbs shear is for the AD rivet, about 26000 psi

[whee]

You could be right Jim. I didn't calculated anything, I just looked up the material strengths so I knew overall properties then googled shear strength for the specific rivet sizes. Can't trust anything you read on the internet. I should probably calculate the shear strength since I'm about half way through riveting on my formers and sills with AN470AD rivets.

[Bcone1381]

Whee, how are you dealing with dissimilar metals with the Aluminum AN470 rivet and the steel fuselage tabs that the formers and sills are attaching to?

[whee]

Brooks, I'm not dealing with it. SS into steel isn't any better than aluminum into steel. Both don't like each other and will corrode. Lucky for me I live in a desert so moisture isn't around to compound the issue.

[SteveF]

Whee, how are you dealing with dissimilar metals with the Aluminum AN470 rivet and the steel fuselage tabs that the formers and sills are attaching to?

@Bcone1381 the way I usually treat dissimilar metals to prevent galvanic corrosion is by coating the rivet and rivet hole with epoxy polyamide primer and then installing the rivet while it's still wet. Alternatively, in certain places, I'll use proseal to install the rivets wet instead of primer.
In the places where dissimilar structures make contact, I also prime both surfaces with the epoxy polyamide primer and let the paint dry overnight or ~24 hours before I assemble them.
I've seen galvanic corrosion in real life and it is much more destructive than I used to think it was.

[fairchild]

Observation about cherry max ss rivets---
I dont know if any of you have experienced this but I have enough that i dont trust them much.....
Seems like most time I try to install a cherry-max into aluminum...... after it is set --- it usually seems loose in the hole. Thats NOT good. That means its NO GOOD.
Here is my theory- I have a suspicion that the cherry max rivets metal - after being set and work hardening from the upset- that the metal no longer has any elasticity.
What I wonder about- is that as you pull the stem and the body is swelling--- it gradually increases the outward pressure on the hole in the aluminum skin. I feel like
it is causing the skin to expand through its elastic range and and into the range where it yields and no longer exerts a counter force on the rivet shank. All most like a
mis-match between the compressibility's of the 2 materials ( the now work-hardened SS and the more delicate aluminum skin) I should think an aluminum AD rivet
when being set --- pushes out on the skin as it expands and the skin pushes back (successfully) with a counterforce which allows for the shop head diameter and the
hole size to become different. If the SS cherry max applies so much force on the hole that the hole expands.... seems like you dont really have a fastener anymore.
I just never seemed to like the things....... anyone else notice them being often loose after setting ?
Tim

[svyolo]

SS or steel fasteners into aluminum is OK for many non-aircraft applications. Not sure about aircraft. Aluminum fasteners in any steel will turn to white powder in a few short months. I did that once about 35 years ago. If I remember right the engineering concept is called "current density". The tiny aluminum fastener acting as a sacrificial anode for the big sheet, vs the big aluminum sheet protecting a little tiny fastener. Steel fasteners in aluminum form a tiny protective oxide below the head and threads.

Drilling out a SS rivet in light aluminum sheet could get unpleasant very very quickly.

[svyolo]

I have rebuilt a half dozen 20-30 year old aluminum sailboat masts used in saltwater. All had SS bolts and some had some rivets. I had to grind off the heads of most of the rivets. All the bolts came out, but not without a fight. About half needed aerokroil/heat/impact tool to get them out. 10% needed all 3. But they all came out. 70% of holes/threads were reusable. I cleaned the threads with a tap, and used a new fastener. 30% I went with a fastener 1 size bigger.