Screws for Aluminium?

[vyv_cox]

In fitting an aluminiun box to an alumiiun bracket I would use alumiium pop rivets the size would depend on the load involved but 5 mm should be OK in most applications.

If tapping into aluminium use a coarse thread so the thread has a higher shear load

I have fitted nylon folding steps to my mast using M6 ss set screws tapping into my 6 mm thick mast

Yes, aluminium pop rivets would probably be best from a corrosion point of view. It is worth knowing that there are two (at least) grades of aluminium that may be used for them. The first is pure aluminium, soft, not very strong but easy to install. The second is an aluminium alloy, stronger and more resistant to corrosion, with the advantage here that it might be more noble than the material it is fixing.

It can be quite difficult to locate the alloy version as most suppliers seem unaware of what they are selling. RS stocked the better version when I last looked but no doubt there are others.

 

[Muddy32]

+1 for Duralac, my tin has lasted for 3 years, and is still 70% full.

 

[IanCC]

You cannot be serious

The same way you protect a bolt or stud in a windlass. You dip the rivet, or stud, in the goo and then apply as normal. I think you will find your SS pop rivets use 'goo' but Seldom wipe the surface clean after attachment - its more professional. If you use Duralac as your goo you don't need to worry about not coating the rivet correctly - the stuff gets everywhere

Jonathan

Mmm but if pop rivets clearance is half a mm of diameter, ie quarter mm around edge, not much is going through the hole.
When I removed the ss 'bits' on my boom, can't remember why, corrosion was rampant. Lots of yellow stuff there as well. Wonder what it was.

 

[Stemar]

Rivnuts are also good for thin masts, allowing removal. But you have to buy the kit and they do not pull the part in tight (they leave a small gap).

There's a rivnut kit in Lidl at the moment. Around £25, so not dear, and I've always found their tools to be decent quality.

 

[Snowgoose-1]

There's a rivnut kit in Lidl at the moment. Around £25, so not dear, and I've always found their tools to be decent quality.

I have just purchased some Parkside boxer shorts from my local LIDl.

I'm expecting high performance that will hold one in comfortably .

 

[Neeves]

Mmm but if pop rivets clearance is half a mm of diameter, ie quarter mm around edge, not much is going through the hole.
When I removed the ss 'bits' on my boom, can't remember why, corrosion was rampant. Lots of yellow stuff there as well. Wonder what it was.

Actually quite a lot goes through the hole and when you tighten it up you can see the Tefgel or Duralac squeezing out from under the 'exterior' ring, and the same will be going on inside. Duralac 'sets' and the resultant set product has low solubility in water, even under pressure, and should be visible when you remove the rivet.

But if you don't think its effective you are quite entitled to ignore the stuff, and its reputation over decades to inhibit corrosion, and you will not then find it 'messy'. It will be so easy to instal devices - just hope you never need to remove them. But scepticism is healthy, and stating your scepticism is even more healthy. Questioning what has become lore or cant can lead to new ideas - so follow your beliefs and lets us know in a few years time.

If you don't use a corrosion inhibitor, Tefgel is an alternative, you might find that your experience with your boom was typical, capable of removing components with ease - commonly unprotected components are seized solid - read any windlass service thread, sea change has a series of them active currently.

Jonathan

edit. I have no financial interest I either Duralac nor Tefgel, nor any other corrosion inhibitor. I confess I have not tested either, so I don't know the difference between use and non use. My experience is all based on use, they work. I have helped remove windlass where no corrosion inhibitor was used (and the windlass had to be cut out). But I accept I had no 'control' half the bolts coated, half not etc etc - so my personal conclusions are lacking in any serious technical comparison.

Its still a free world, insurance companies have not mandated use of corrosion inhibitors - do your own research, draw your own conclusions

But report back, with photos.

J

 

[IanCC]

Actually quite a lot goes through the hole and when you tighten it up you can see the Tefgel or Duralac squeezing out from under the 'exterior' ring, and the same will be going on inside. Duralac 'sets' and the resultant set product has low solubility in water, even under pressure, and should be visible when you remove the rivet.

But if you don't think its effective you are quite entitled to ignore the stuff, and its reputation over decades to inhibit corrosion, and you will not then find it 'messy'. It will be so easy to instal devices - just hope you never need to remove them. But scepticism is healthy, and stating your scepticism is even more healthy. Questioning what has become lore or cant can lead to new ideas - so follow your beliefs and lets us know in a few years time.

If you don't use a corrosion inhibitor, Tefgel is an alternative, you might find that your experience with your boom was typical, capable of removing components with ease - commonly unprotected components are seized solid - read any windlass service thread, sea change has a series of them active currently.

Jonathan

edit. I have no financial interest I either Duralac nor Tefgel, nor any other corrosion inhibitor. I confess I have not tested either, so I don't know the difference between use and non use. My experience is all based on use, they work. I have helped remove windlass where no corrosion inhibitor was used (and the windlass had to be cut out). But I accept I had no 'control' half the bolts coated, half not etc etc - so my personal conclusions are lacking in any serious technical comparison.

Its still a free world, insurance companies have not mandated use of corrosion inhibitors - do your own research, draw your own conclusions

But report back, with photos.

J

Ha ha, i was a bit shocked by my boom. I cleaned it all up and used tefgel. Re pop rivets, my fear is the pressure squeezes it all out, so going monel.

 

[Neeves]

Ha ha, i was a bit shocked by my boom. I cleaned it all up and used tefgel. Re pop rivets, my fear is the pressure squeezes it all out, so going monel.

My guess is the ingredients are around 10 -15 micron in particle size and you will never squeeze the active ingredients to a point where they are even close to one layer thick. On a micron scale the hole you drill will not be circular nor a perfect 'tube', will have 20 micron scratches -

but Monel is good.

The idea of worrying that Monel are expensive - again - they cannot be serious.

Jonathan

 

[IanCC]

My guess is the ingredients are around 10 -15 micron in particle size and you will never squeeze the active ingredients to a point where they are even close to one layer thick. On a micron scale the hole you drill will not be circular nor a perfect 'tube', will have 20 micron scratches -

but Monel is good.

The idea of worrying that Monel are expensive - again - they cannot be serious.

Jonathan

A boatyard, no names, told me "silicone is as good as anything".

 

[vyv_cox]

Ha ha, i was a bit shocked by my boom. I cleaned it all up and used tefgel. Re pop rivets, my fear is the pressure squeezes it all out, so going monel.

Duralac has a long and successful history of corrosion inhibition for pop riveted joints in airframes. Widely used for decades worldwide. The problem is not the metal of the rivet but the galvanic couple between it and the sheet metal. The chemistry of Duralac contributes to reducing the corrosive action, plus it is a sealant. Tefgel simply fills the gaps and keeps water out.

 

[rogerthebodger]

Duralac is a barium chromate,

Barium chromate - Wikipedia

for full details

When I was building my last boat, I used Duralac extensively when fitting my aluminium tow rails, Mast/boom fittings, main sheet traveler and jib tracks when fitting to steel deck and stainless-steel fittings on mast and boom,

I purchased a 500ml tim from the manufacturer in Birmingham when I visited my hometown some time ago

 

[Neeves]

Duralac is a barium chromate,

Barium chromate - Wikipedia

for full details

When I was building my last boat, I used Duralac extensively when fitting my aluminium tow rails, Mast/boom fittings, main sheet traveler and jib tracks when fitting to steel deck and stainless-steel fittings on mast and boom,

I purchased a 500ml tim from the manufacturer in Birmingham when I visited my hometown some time ago

Yellow Duraac contains chromic chemicals which I think are carcinogenic. The chrome containing chemicals, barium chromate, were replaced and a new formulation is available. I believe that in some jurisdictions yellow, the original formulation, is still available alongside green and in other jurisdictions only the green formulation is now available. You use so little Duralac that a tin can be willed to younger members of the family and it will be yellow. The stuff in the tubes did not last so long, the tubes were not sufficiently robust to out last the contents and you may find when you replace you will only be offered green Duralac.

I believe, but have no proof, that green Duralac is as good as the original yellow.

Google has chapter and verse but I could find no robust information on a comparison of the green vs yellow formulations. Just unsupported statements saying that green was the equal of the yellow. But I could find no negative statements on the use of Green Duralac. I found the lack of a comparison 'odd' its the 'go to' remedy - the only product, apart from grease , (Tufgel) and I would have thought a perfect project for the likes of PBO. As mentioned Duralac is used extensively in aeronautics but there is no comparison in that industry (that I could find) either.

Jonathan

 

[thinwater]

A few things for the pile:

• Aluminum rivets are much weaker (read the specs--there are many materials and also types, and the strength varies 50% even within 316 SS. All SS bolts are more or less the same strnegth (same grade steel, same dimensions), but there are self-sealing, high-strength, flat head and many other sorts of rivets. Read the specs.
• Duralac is barely available in the US, same with other chromate products.

Hazardous ingredients:
BARIUM CHROMATE
EINECS CAS PBT / WEL CLP Classification Percent
233-660-5 10294-40-3 - Acute Tox. 4: H302; Acute Tox. 4: H332 10-30%
2-BUTANONE OXIME
202-496-6 96-29-7 - Carc. 2: H351; Acute Tox. 4: H312; Eye
Dam. 1: H318; Skin Sens. 1: H317

• Yes, rivets corrode. When they do, they take seconds to drill out. Machine screws, on the other hand, are an invention of the devil when they seize and you can move the fastener. If they are anything other than hex head you probably can't get a really good grip on them. Drilling out an SS screw is aluminum isn't easy; if it wanders a bit, the drill slides into the aluminum and snaps. I have a couple of screws I would like to remove (1992 F-24) but I don't think I ever will. I have feeder I would like to replace. On the other hand, I relocated some riveted hardware on the boom; it took less than 30 seconds each to drill off the head and punch them through. Never a problem. On the other hand, the screws on my PDQ were all anti-seized, and I don't recall any big battles. Just sayin'.

I mostly use machine screws. Only rivets when it is very thin and the size works. Up the mast, rivets can be a lot easier to work with; tapping a swaying mast sucks.

I did a bunch of strength testing once for a mag. If like size, strength is not very different and it can go either way. Really. Designed properly, it won't matter.

 

[Neeves]

Duralac Green (contains no (known) carcinogens (but that's what they said of talc).

If Americans did not use, or it is difficult to buy, Duralac - what did they use instead. Duralac of either colour was always mentioned on almost every thread in YBW where corrosion was an issue - but primarily stainless in aluminium, windlass or pop rivets. Tefgel has come on the scene recently, Duralac has been around for decades. Tefgel just resists water (until it doesn't) - Duralac once applied dries out, is sparingly soluble in water (if at all) and lasts the life of the rivet, machine screw, stud.

You know if Duralac has been used, you cannot miss it - its messy and gets everywhere.

Duralac, what's not to like?

Jonathan

Llewellyn Ryland - Duralac Green - Anti Corrosive Jointing Compound

 

[Neeves]

I believe Airbus machine wings from a billet of 7075 aluminium. I still note that the wings are full of rivets (I assume they are rivets) but maybe they are not machined from a billet . I might assume the rivets in an aluminium wing machined from the 7075 alloy would also be 7075. The 7075 alloy (and other aluminium alloys with Lithium) have a high tensile strength, can be around 600 mpA, but low yield, less than 10%.

I assume if you had a 7075 wing and used 7075 rivets (or fasteners) corrosion would not be an issue (as the metals are the same).

Oddly the 7075 alloy is reported to have a poor resistance to corrosion in a salt spray test - I had an aluminium Excel anchor with a 7075 shank - after 10 years it demonstrated no corrosion, at all. 7075 shank secured in a pocket in the fluke, also aluminium but I don't think 7075, and retained by stainless bolts, machine screws. The shackle and the chain were both alloy steel with a high tensile strength. The bow roller was aluminium, alloy unknown but I'd guess 5083, with a polymer roller retained with a big stainless bolt.

Maybe salt spray tests are not the panacea, sometimes mentioned.

Jonathan.

 

[thinwater]

Duralac Green (contains no (known) carcinogens (but that's what they said of talc).

If Americans did not use, or it is difficult to buy, Duralac - what did they use instead. Duralac of either colour was always mentioned on almost every thread in YBW where corrosion was an issue - but primarily stainless in aluminium, windlass or pop rivets. Tefgel has come on the scene recently, Duralac has been around for decades. Tefgel just resists water (until it doesn't) - Duralac once applied dries out, is sparingly soluble in water (if at all) and lasts the life of the rivet, machine screw, stud.

You know if Duralac has been used, you cannot miss it - its messy and gets everywhere.

Duralac, what's not to like?

Jonathan

Llewellyn Ryland - Duralac Green - Anti Corrosive Jointing Compound

Agreed. Duralac green is more common and is used. And there are other marine anti-seize products that are quite good. Locktite LB 8023 is excellent. The aircraft guys sell Duralac and many similar products, but not so much marine sources.

 

[Sandro]

Interesting, William. I would not have considered using an electric drill.
.

Many years ago for tapping many M4 holes in steel sheet panels for electric equipment I used a Bosch tapper. It's a slow turning hand drill with a junction and turning CW until yuou push the tap and automatically reversing when you pull.
When I bought it I expected that the probably increase in tap breaking would be compensed by the reduced production time.
Well, I was pleasantly surprised realizing that the tap breaking rate dropped greatly versus hand tapping.