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12 metre

Epoxy/aluminum long term bonding

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Probably a thread on this already, but can't find one - so here goes...

Most literature indicates epoxy will create a satisfactory bond to properly prepared aluminum.

By the same token, the general consensus on internet forums is “yes it will bond – but not for very  long”.  Mainly because even epoxy has a degree of permeability allowing oxidation of the aluminum surface.  On the other hand, there are others who point out epoxy is used on aluminum aircraft wings.  One fairly well known Kiwi said they applied epoxy/carbon tows (suitably isolated)  to alloy masts and they were fine after 20 years

 Unfortunately, most of this info appears to be anecdotal or opinion.

What little scientific literature I’ve stumbled across with regards to longevity indicates the degree of degradation appears dependent on the following:

  • Type of aluminum alloy (6061 alloys are among the more corrosion resistant)
  • Ambient temperature & humidity (3 months at 53C had noticeable degradation – 23 C was minimal).  This is probably obvious since higher temps tend to speed up chemical reactions and higher humidity would allow more moisture to pass.
  • Salt (5% salt spray caused complete degradation of some alloys within 3 months).

I can see why the bond would degrade in underwater applications, but wonder if the same holds true in a cool ocean air environment. 

The reason I am asking about this is that I am looking for ways to reinforce an aluminum mast  with carbon/epoxy rather than resorting to struts and stays.   Wishful thinking on my part I suspect, but who knows?  

Particularly helpful would be if you can point me toward any useful scientific literature on the subject.

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Edit:

Reinforce is not the term I should have used since the existing aluminum section is strong enough on it's own.

Stiffen would be the correct term so I'm not overly concerned if the bond failed.  I would just prefer that it did not.

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It's not a good idea. The modulus of elasticity of carbon and aluminum is so different that the stiff carbon wants to take all the bending load first, and it does, until it cracks. Then you are back to the plain aluminum.

See 1979  Fastnet-  OD34 rudder stocks. They did exactly what you propose (wrapped aluminum rudder stocks in CF). Failed 1,2,3...

Oh, you should also isolate any carbon touching aluminum with a layer of E-glass too. Otherwise the aluminum gets eaten.

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I bet Zonker is 100% correct there. However it does bond well. My boom was made all pretty with epoxy+filler patches on holes and other insults. No special prep. Grind and fill. 10 years later all is good.

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1 hour ago, Zonker said:

It's not a good idea. The modulus of elasticity of carbon and aluminum is so different that the stiff carbon wants to take all the bending load first, and it does, until it cracks. Then you are back to the plain aluminum.

See 1979  Fastnet-  OD34 rudder stocks. They did exactly what you propose (wrapped aluminum rudder stocks in CF). Failed 1,2,3...

Oh, you should also isolate any carbon touching aluminum with a layer of E-glass too. Otherwise the aluminum gets eaten.

This!!!

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1 hour ago, Zonker said:

It's not a good idea. The modulus of elasticity of carbon and aluminum is so different that the stiff carbon wants to take all the bending load first, and it does, until it cracks. Then you are back to the plain aluminum.

See 1979  Fastnet-  OD34 rudder stocks. They did exactly what you propose (wrapped aluminum rudder stocks in CF). Failed 1,2,3...

Oh, you should also isolate any carbon touching aluminum with a layer of E-glass too. Otherwise the aluminum gets eaten.

I believe that UD carbon would take the majority of the load since it's E is roughly 2x that of Al (135 GPa vs 70 Gpa) - but not all of the load.  However if one used standard 0/90 CF, the E is almost identical to Al according to this site: http://www.performance-composites.com/carbonfibre/mechanicalproperties_2.asp . The section won't be as stiff as one using UD CF, but it will likely be similar to sleeving with Al (as Duncan mentions). 

So why not just sleeve it?  I'm also relocating the halyard sheave box and would rather not leave the open wound from pulling the old one out.  So in that area, the CF actually would be more for reinforcement than stiffness. 

It goes without saying the CF needs to be isolated from the Al using something like E-Glass.

I feel the biggest problem with carbon laminated over another material is when people lay it over E-glass under the assumption the strength and stiffness of the two materials are additive.   I managed to convince a guy who was proposing to do exactly that that it was not a good idea.

As I mentioned in my original post, I doubt it would do much harm if the CF peeled away since the underlying original structure is adequate (barring open the sheave box area).

Going back to my original question, (which was more about bond longevity than the mis-matched properties of CF and Al) El Boracho seems to have come closest to answering the question.

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3 hours ago, Zonker said:

It's not a good idea. The modulus of elasticity of carbon and aluminum is so different that the stiff carbon wants to take all the bending load first, and it does, until it cracks. Then you are back to the plain aluminum.

See 1979  Fastnet-  OD34 rudder stocks. They did exactly what you propose (wrapped aluminum rudder stocks in CF). Failed 1,2,3...

Oh, you should also isolate any carbon touching aluminum with a layer of E-glass too. Otherwise the aluminum gets eaten.

otherwise the aluminum gets eaten with the addition of salt water.

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OK - if you do use a 0/90 then cool if the moduluses are similar.

I did a bit of this repairing a 60m aluminum catamaran cruise ship cracked bulkhead/bottom structure. We fixed the crack as a temporary measure because drydocking was very costly and would mess up the schedule.... Anyway the research papers I read suggested that with proper prep the bond will be good for a few years at least. But I wouldn't count on it for 20 years. So maybe somewhere between 2 and 20 years :)

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3 hours ago, Zonker said:

OK - if you do use a 0/90 then cool if the moduluses are similar.

I did a bit of this repairing a 60m aluminum catamaran cruise ship cracked bulkhead/bottom structure. We fixed the crack as a temporary measure because drydocking was very costly and would mess up the schedule.... Anyway the research papers I read suggested that with proper prep the bond will be good for a few years at least. But I wouldn't count on it for 20 years. So maybe somewhere between 2 and 20 years :)

I realize you're half joking when you say 2-20 years, but assuming the research I found is correct - the degradation rate appears highly dependent on the temp and humidity; I would expect variability among different climates.  So hot and humid places like Florida or the Caribbean would yield a much shorter shelf life than somewhere in PNW.  Like Vancouver which has an annual average temperature of 11C and is way less humid.

I would be disappointed if I only got 2 years out of it, pleased if I got 5-10 years out of it - and ecstatic if I got over 10.  Would want to keep a watchful eye on it though

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I assume you are strengthening a topmast section to run masthead chutes? If so probably easier to just suck it up and whack a set of jumpers on, or set them up a cathedral system. Just did this a week ago with carbon spreaders, weighed 1800 grams, and stiffened up the mast perfectly. Was a carbon mast though. 

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7 hours ago, Alcatraz5768 said:

I assume you are strengthening a topmast section to run masthead chutes? 

It's related - but it's not the reason.

Building me a FrankenDash - it's a popular pastime in PNW (how's that for an alliteration)

Lots of alterations planned - too many to list here.

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What about sanding the alloy, then painting with an etch primer then laminating over that. 

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Sanding the alu with the resin was and is a technique that seems to help, just a question if you’re happy to get the laminate on there and Vac bagged. 

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In the ski/snowboard industry we used a very thin acid etched rubber foil between dissimilar materials such as hardened steel edges and the epoxy glass laminate. I have always felt it would have a place for applications just like this both as an isolator and to introduce a slightly flexible interface between materials with dissimilar stiffness. This is the job it does very well in snowboards that have to endure much more abuse than anything i have seen in the marine industry. I have in fact used an epoxy/ s glass external sleeve to repair an otherwise unrepairable mast that has worked very well for probably 8 years and counting.

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4 minutes ago, Steve said:

In the ski/snowboard industry we used a very thin acid etched rubber foil between dissimilar materials such as hardened steel edges and the epoxy glass laminate. I have always felt it would have a place for applications just like this both as an isolator and to introduce a slightly flexible interface between materials with dissimilar stiffness. This is the job it does very well in snowboards that have to endure much more abuse than anything i have seen in the marine industry. I have in fact used an epoxy/ s glass external sleeve to repair an otherwise unrepairable mast that has worked very well for probably 8 years and counting.

Have you got any links? Sounds interesting. 

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5 minutes ago, mad said:

Have you got any links? Sounds interesting. 

No, its been a long time since iv'e used it but try googling VDS rubber foil, its very thin, maybe .010" We used to buy it at 12"wide from Snowtech in Seattle. Don't know if they still exist as that was in the 1990's. let us know what you find. It was a European product and made all the difference as to whether a snowboard lasted or not. My son still rides boards we built 25 years ago. Without the foil you would be lucky to get through a season without edge delam.

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3 minutes ago, Steve said:

No, its been a long time since iv'e used it but try googling VDS rubber foil, its very thin, maybe .010" We used to buy it at 12"wide from Snowtech in Seattle. Don't know if they still exist as that was in the 1990's. let us know what you find. It was a European product and made all the difference as to whether a snowboard lasted or not. My son still rides boards we built 25 years ago. Without the foil you would be lucky to get through a season without edge delam.

Thanks, I’ll have a search around and post anything interesting. 

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Interestingly West System used to sell a nasty acid etch kit to bond to aluminum. Now they find that G-Flex works just fine on it's own (better than 105 + acid etch).

But G-flex is too flexible as a laminating resin. But as a base layer (bond e-glass with G-flex, let cure) then use carbon + regular laminating resin it would probably work very well.

In the PNW yes I think you'd get >2 years. 5 is probably a reasonable guess, 10 if you are lucky.

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On 10/27/2018 at 8:21 PM, Zonker said:

Interestingly West System used to sell a nasty acid etch kit to bond to aluminum.

 

Still very much recommended in the aluminum bonding world. Chromate conversion -  the kits are often known as Alodine or Iridite. 

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Just to throw out yet another consideration, aluminum and carbon fiber have very different coefficients of thermal expansion (CTE). Aluminum expands quite a lot and carbon fiber actually has a negative CTE.

The effect of this is that for every temperature other than what I'll call the neutral temperature the two materials produce shear stress across the bond. The neutral temperature may be the temperature the materials were at when bonded or higher is using an aggressive cure. If you get really carried away and prestress the CF you might not have a real-world neutral temperature.

The effect is aggravated by length of bond and yearly temperature extremes.

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15 hours ago, ibanezplayer said:

Alodine

That's what I was trying to remember! Thanks.

14 hours ago, Feisty! said:

The effect of this is that for every temperature other than what I'll call the neutral temperature the two materials produce shear stress across the bond.

He just needs to apply some heat tracing tape to inside the mast so the bond area stays the same temperature all year long...

Sure you don't want to rivet some thicker strips of aluminum to the topmast ?

 

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14 minutes ago, Zonker said:

That's what I was trying to remember! Thanks.

He just needs to apply some heat tracing tape to inside the mast so the bond area stays the same temperature all year long...

Sure you don't want to rivet some thicker strips of aluminum to the topmast ?

 

This, just do it old school. 

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On 10/27/2018 at 5:53 PM, Steve said:

In the ski/snowboard industry we used a very thin acid etched rubber foil between dissimilar materials such as hardened steel edges and the epoxy glass laminate. I have always felt it would have a place for applications just like this both as an isolator and to introduce a slightly flexible interface between materials with dissimilar stiffness. This is the job it does very well in snowboards that have to endure much more abuse than anything i have seen in the marine industry. I have in fact used an epoxy/ s glass external sleeve to repair an otherwise unrepairable mast that has worked very well for probably 8 years and counting.

Curious about the mast repair. Was this an aluminum mast? I have a section that is pretty banged up with a sizeable dent down low, plan has been to take it to the dump but maybe laminating an external sleeve would work as a spare mast in a pinch...

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5 hours ago, samc99us said:

Curious about the mast repair. Was this an aluminum mast? I have a section that is pretty banged up with a sizeable dent down low, plan has been to take it to the dump but maybe laminating an external sleeve would work as a spare mast in a pinch...

Yes, it was /is a tall fractional alluminum  rig on an old one tonner. The thing was sleeved in a traditional manner up to a point above the gooseneck presumably from new with a lot of fasteners and there were quite a few cracks caused by the fasteners. A new rig was out of the question based on cost as it would cost more than the boat was worth. So we laid up a glass sleeve around the area using uni and double bias with epoxy and it has proven itself to be a practical repair and is still going strong after 8-10 years so far. If we had not done this the entire boat would have been scrapped.

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FWIW When I bought my boat around 2005 it had a quarter sized hole corroded right through the boom where a bronze shackle had been in contact with the alu.  I wire brushed the crater, filled and faired over with MarineTex.    It currently shows no sign of failure or loss of adhesion, although it is only just filling a hole.  My expectation at the time was it would only last a few years and my surface prep was minimal at best.

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