Blind rivets for mast - stainless steel or monel?

[transmitterdan]

Originally Posted by deblen

If installing aluminum item to aluminum mast :
Aluminum Rivet w/Aluminum Mandrel

This is the right answer to the OP question.

Monel is almost the same as stainless steel on the galvanic series. Monel will cause the erosion of the aluminum pretty much the same as stainless steel does. There was a famous case of a monel clad boat that corroded itself into almost falling apart. The inside of the boat was steel with monel cladding. The theory was that monel doesn't corrode. That theory is right. But the steel and monel make a pretty good battery and the steel dissolved away pretty quickly. The monel did not corrode but there was no steel structure left.

[a64pilot]

I think I remember reading about that, it was a long time ago?

[transmitterdan]

Originally Posted by a64pilot

I think I remember reading about that, it was a long time ago?

As I recall it was more than 100 years ago.

[Omatako]

Originally Posted by Alan Mighty

* punch out the cores;

* count the cores as you retrieve them and hunt for the missing until found

Whilst not contesting the added strength theory postulated by Guy (although I could), I'm more interested in how you would retrieve and count the cores when you've just knocked them into the mast.

On my boat (keel stepped) that would be next to impossible meaning I would end up with a festering pile of mild steel cores causing galvanic mayhem in the base of the mast.

Unless of course you intend the rig to be pulled each time you install accessories?

[model 10]

[QUOTE=Omatako;2166498]Whilst not contesting the added strength theory postulated by Guy (although I could),

In shear you could not. I didn't "postulate" squat. A modern aircraft is held together with a ton of structural blind fasteners and none, (got that?) none, have the stem punched out.
If you have corrosion problems get a different rivet, don't punch out the stem.

[CarinaPDX]

I have a stainless trysail track which I riveted to the mast with monel rivets. I don't remember if I gooped them or not. Anyway, corrosion and loss of paint occurs around the rivets and eventually extends out from the track (over decades). There seems to be no problem between monel and stainless but of course the aluminum is a problem as always. I am thinking about refastening the track, putting something insulating (tape?) between the track and mast and using lots of goop.

Any ideas?

Greg

[Reefmagnet]

Wow, lots of responses but i'm still scratching my head on the use of monel rivets. If it helps, I spent near 100 bucks yesterday on Tefgel and Duralac to use mostly for reattaching all the stuff back onto my mast. I'm not too keen to use aluminium rivets on a mast step, as my girth isn't getting any smaller and I just feel more comfortable using a higher tensile material. I should note that aside from some blanking plates, every other fastener is either a stainless screw or rivet. These actually haven't caused too much issue with corrosion over the (many) years, but were coated in something like duralac when originally installed.

Out of interest, The main corrosion when I stripped my mast was under some of the bigger fittings like the spreader and boom brackets. Not overly significant though thanks to a painted surface and a barrier between the mast and stainless steel. One eye opener was to observe that the unpainted cast aluminium winch mounts were very close to being destroyed by electrolysis where they where in contact with the base of the winch with, apparently, no barrier of any sort applied on original installation.

[artisanmach]

check out this link
http://www.gsa.gov/portal/content/113038

[wsmurdoch]

Originally Posted by Russ

Real answer is the insulate dissimilar metals with Tef- Gel. Russ

I hear this frequently said, but I have measured the resistance between a Tef-Gel coated stainless steel rivet set into a Tef-Gel filled hole in my boom with a VOM meter. The resistance is too low to measure (much less than one Ohm).

The stainless steel rivet and the aluminum boom are in electrical contact.

[artisanmach]

I used to work on some Navy assemblies that were installed in a pretty harsh environment. We always installed rivets "wet" meaning they were dipped in zink chromate primer as they were being installed. I used this process last year on my mast.

[model 10]

Originally Posted by wsmurdoch

The resistance is too low to measure (much less than one Ohm).

You need to use a Megohmmeter to measure that.

[Kokanee]

Originally Posted by transmitterdan

There was a famous case of a monel clad boat that corroded itself into almost falling apart. The inside of the boat was steel with monel cladding. The theory was that monel doesn't corrode. That theory is right. But the steel and monel make a pretty good battery and the steel dissolved away pretty quickly. The monel did not corrode but there was no steel structure left.

Here's the link to the newpaper report:
https://news.google.com/newspapers?n...,4714005&hl=en

Whether you use monel or stainless, they need to be protected from direct contact with tefgel or similar, and checked for corrosion on a regular basis. I use stainless just because rivets are cheaper and easier to find. Use aluminum for low stress fittings.

[bglad]

I would avoid Monel. It is an alloy of nickel and copper. Copper is very hard on aluminum. Stainless has crevice corrosion issues but is not too hard on aluminum. Aluminum suffers poultice corrosion if gaps are left between it and mounted hardware.

Some perspective. Bronze alloys are not supposed to be connected directly to aluminum tanks. Copper used in bronze alloys corrodes tanks. Stainless is used between the bronze and aluminum since it gets along ok with both.

These comments are experience based but not specifically with attaching hardware to spars.

Originally Posted by Reefmagnet

Wow, lots of responses but i'm still scratching my head on the use of monel rivets. If it helps, I spent near 100 bucks yesterday on Tefgel and Duralac to use mostly for reattaching all the stuff back onto my mast. I'm not too keen to use aluminium rivets on a mast step, as my girth isn't getting any smaller and I just feel more comfortable using a higher tensile material. I should note that aside from some blanking plates, every other fastener is either a stainless screw or rivet. These actually haven't caused too much issue with corrosion over the (many) years, but were coated in something like duralac when originally installed.

Out of interest, The main corrosion when I stripped my mast was under some of the bigger fittings like the spreader and boom brackets. Not overly significant though thanks to a painted surface and a barrier between the mast and stainless steel. One eye opener was to observe that the unpainted cast aluminium winch mounts were very close to being destroyed by electrolysis where they where in contact with the base of the winch with, apparently, no barrier of any sort applied on original installation.

[Jim Cate]

Originally Posted by Kokanee

Here's the link to the newpaper report:
https://news.google.com/newspapers?n...,4714005&hl=en

Whether you use monel or stainless, they need to be protected from direct contact with tefgel or similar, and checked for corrosion on a regular basis. I use stainless just because rivets are cheaper and easier to find. Use aluminum for low stress fittings.

But Tefgel, as reported above, does not prevent direct electrical and physical contact. And BTW, one does not use a Megohm meter to measure low resistance circuits!

I believe that in most cases,, the role of the Tefgel or other compound is to exclude salt water intrusion into the joint, thus eliminating the electrolyte and preventing corrosion. I have had pretty good results in threaded joints using a variety of materials: lanolin, anti-seize of several types, silicone sealant, polyurethane sealant, Tefgel and Duralac. When applied correctly, they have all worked well enough to keep the joints from locking up. My experience with rivets is not sufficient to comment, but I suspect that it would be similar.

Jim

[transmitterdan]

Lots of bad info in this thread. You are right to worry about strength of the rivet. Aluminum rivets can support a significant load. Check the ratings of the rivet and use a decent pop rivet tool. Make sure the rivet is pressed all the way in when drawing out the mandrel. Make sure the rivet is the proper length and neither too long or too short.

The mandrel is not a significant source of strength in a pop rivet. The rivet should pull the two parts together with enough force that the resulting friction holds them in place. Thus it's important to use the right length rivet for the thickness of the joint. The joint must not slip else the rivet might shear off. If the joint is loose something is wrong.

Aircraft rivets retain their mandrels but they are not "pop" rivets. So not the same thing at all.