m_kiel

West system + fillers for maximum strengh bonding of CF parts

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Hi everyone,

I am looking for some advice on how to use the West System Epoxy for maximum strenght bonding of a carbon fibre hound fitting to a carbon fibre mast. The fit of the two parts is good, with the maximum gap width less than 1mm. Cleaning and surface preparation with 120 grit is clear to me. However, I was unable to find out which filler and which consistency would be ideal for this purpose. I was planing to use the 404 High Density in a two step bonding process and normally use the fast hardener. I also have access to microfibers. 

To get an idea of the task at hand, here is a picture of the hound fitting, mast diameter is a little under 40mm.

Thanks and best regards
m2rhf__21396.1399276731.jpg?c=2&imbypass

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Hello Kiel, I'm not the world's expert on this, but I think that you are on the right track. Using a toughened epoxy (such as G-Flex) has some advantages, but it's probably not a good idea for your application. To me, the challenge is in surface preparation. Sanding well and then sanding again with fresh paper is good, but removing the dust is the challenge. Unless you have medical acetone and contaminate-free cotton, I think that just rubbing the surfaces hard with clean cotton is the best. That combined with priming the surfaces before filler is added. I would get the parts warm and prime by rubbing the thin epoxy into the surfaces with a gloved fingertip. I would add some Colloidal Silica to the High-Density filler, but keep the mix fairly thin to keep the epoxy content high. Can you use gravity to keep the part in place while curing? Post curing will add a lot to the strength. This can be done in your case with just a droplight and incandescent bulb. Not too hot though, especially not for the first few hours.

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I'd look at the bonding area and typical epoxy bond strength values versus the max loads expected on the part before going through hoops to maximize bond strength. I'm guessing by eye that you've got ~60 sq cm of bonding area. That's about 9 sq in. Gflex is rated for roughly 2500 psi tensile. 

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     If it is true that GFLex is 2500 lbs that makes me reconsider the old story I heard about how 3M 5200 got its name. I was told even before the product came to market that it had tested to 5200 psi in shear strength and the marketing types were coming up with all sorts of clever trade names but one engineer just said, 'Let's make it simple and call it 5200!'.

    I know that stuff is damned near impossible to break the bond (without heat or special solvents) but have a hard time believing that GFlex would only rate about half that. I wonder what Plexus is rated for comparison.

    I'd go with what Russell says, his epoxy work is wondrous and he doesn't like to beat his chest but I'll do it for him here:

https://www.pinterest.com/source/ptwatercraft.com/

m_k, Nice fitting but what is the size of the mast and what sort of loads do you anticipate? I'm right in the middle of designing a rig and need a similar hound for my jib stay.

 

Edited by Rasputin22
I can't shut up!

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48 minutes ago, Russell Brown said:

 Unless you have medical acetone and contaminate-free cotton, I think that just rubbing the surfaces hard with clean cotton is the best.

When I clean a surface for bonding (not CF ever, yet) I wipe it with clean cotton rags and regular acetone then a final wipe with clean cotton and alcohol.

Do you see a benefit from using medical acetone (which until now I had never even heard of) over that process.

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That  a moth mast tang?

Gurit 345 has better shear strength than 340, is quite rubbery and challenging to mix well, but get it warm and its good, also ideal thickness for secondary bonding straight out of the tube.

Its tougened with rubber particles or something like that so doesn't pick up shock like neat or filled conventional epoxies which are relatively brittle even if postcured.

- Like Russel (who is a guru!) says, way to get all of the secondary bond shear strength is in surface prep, and rubbing the surfaces with the glue before adding the majority of the glue and clamping if app / necessary. Make sure if its a big part (unike this one) you have holes drilled in such that you can ensure that all air escapes and you get glue issuing from all edges.

Get a tube of that 345 and a gun you will need it for mothing! I believe West do a similar product .

 

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    This whole discussion reminds me of working for Bill Seemann of C-Flex and SCRIMP fame (and fortune!). His main business at the time was producing C-Flex fiberglass planking but he had a boat/fab/R&D shop across the street from the main warehouse. Great place for an aspiring boatbuilder/designer like myself to learn the nitty gritty of the composites business and Bill was a great mentor. He went to compete with ACADIA on the ill fated Fastnet race and while away the guy who ran the C-Flex machine in the warehouse went on a good old New Orleans bender and a weeks worth of C-Flex production was way too saturated to bend and edge set the way it was supposed to when building a one off hull or plug. Bill had a fit when he got home and spent the next couple of months trying to figure a way to use that bad batch. He dreamed up the C-Flex Sheathing System which was to laminate a layer of funky C-Flex at right angles (more or less) to a aging wooden boats planking. By the time we had perfected the process, we had used up the funky stuff but the project carried on on its own momentum using prime product. There was a big world wide composites convention coming to town and Bill had us shop grunts build a typical plank on frame panel of a wooden boat full size and then to the sheathing process in a cut away fashion that demonstrated perfectly the concept. Layer by layer you could see the bare planking, then the bonding matrix (3M 5200), the C-Flex planking dry and then saturated, and then the matt/roving, and finally the fairing, primer, and finished paint. It really was a nice 'look at us' sort of thing which meant a lot to Bill in the composite trade. The day the show opened, Bill decided that we should put a water line, bottom paint and boot top on it so we hustled to get that done and the exhibit loaded and delivered to our booth at the convention center downtown.

    We rolled up in the company truck and rolled the thing in and took it to the booth where Bill was all in his finest suit and tie anxiously awaiting his display. My buddy and I were still in our shop clothes reeking of polyester and paint and covered with dust and dust masks still pushed back on our heads. He was appalled that we hadn't cleaned up and made ourselves presentable before showing ourselves in public and told us to put the thing down and get lost! Like he wasn't running a sweat shop...

    We were a bit miffed at his embarrassment but heading back down the exhibition hall saw a kiosk with videos running and headsets to listen to the product description and specs. The company specialized in 'filled composites' and made a wide variety of injection molded stuff like light sockets, insulators, and just about anything you could imagine. They had parts as handouts and my compadre and I put each put on headsets and listened to a very good presentation of how a variety of fillers could be used to create properties such as heat resistance, strength, and di-electric values. Colloidial silica, talc, mica platelets, milled fibers, micro-spheres, micro-balloons and such were standard in our shop practices but we had never really delved into just why each additive to polyester or epoxy modified the mix in the way that it did. I was about to go get Bill and tell him to be sure to come watch the show but about then I noticed a guy in a suit standing just behind up as if awaiting a turn at the headphones. I turned and offered him my headpiece but he smiled and told us he was the salesman for that company and was curious about our rapt interest in what to anyone else would be a really boring subject.

    The vid was just starting to loop over again and the salesman made an odd statement, 'You guys look like you know more about this sort of thing than most in here' and nodded to our dusty coveralls and respirator masks still hung around our necks. He then added, 'Are you familiar with colliodial hydrochloride compounds' or something like that and barely pulled a vial out of his pocket and showed it to me with a smile on his face. I thought it might be another powdered additive to their gadgets, but my friend caught on right away and we ambled over to a couch in a lounge area. He had a lot of product brochures and samples laid out and this was obviously his 'sales desk' but when he started chopping out lines of coke on the table and handed over a rolled up bill I was shocked. My buddy huffed up the longest line and approved of the whole sales pitch and we talked at length about our shop and New Orleans night spots and had a fine time with our new best friend. 

    Along the way he imparted on us a thorough understanding of how the physical geometry of all the various fillers contribute to the resultant properties of a resin matrix. 

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3 hours ago, DRDNA said:

Don't forget clamping pressure with West products for a good adhesion!

 

Uhh, no. You don't really need to clamp epoxies. For best results you want a thin bond line but nothing like old Resorcinol glues that needed clamping pressure.

3 hours ago, Daniel Holman said:

Gurit 345

Yes, the rubber toughened epoxies are usually the go-to for bonding jobs like this.  Spabond 345 says lap shear on steel is about 37 MPa on steel / 5400 psi. That is pretty strong.

 

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3 hours ago, Rasputin22 said:

  The vid was just starting to loop over again and the salesman made an odd statement, 'You guys look like you know more about this sort of thing than most in here' and nodded to our dusty coveralls and respirator masks still hung around our necks. He then added, 'Are you familiar with colliodial hydrochloride compounds' or something like that and barely pulled a vial out of his pocket and showed it to me with a smile on his face. I thought it might be another powdered additive to their gadgets, but my friend caught on right away and we ambled over to a couch in a lounge area. He had a lot of product brochures and samples laid out and this was obviously his 'sales desk' but when he started chopping out lines of coke on the table and handed over a rolled up bill I was shocked. My buddy huffed up the longest line and approved of the whole sales pitch and we talked at length about our shop and New Orleans night spots and had a fine time with our new best friend. 

    Along the way he imparted on us a thorough understanding of how the physical geometry of all the various fillers contribute to the resultant properties of a resin matrix. 

I never had any seminars like that - about anything. :angry:

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    Yes, it was an odd encounter and I'm glad my boss didn't walk by and witness our little business conference. If we had been dressed for the occasion no one would have though anything of it but I admit us worker bee garb really stood out at the time. The first day was winding down and I think the general attendance had already been lubed well at the many bar setups all over the concourse. If I had smart I would have called some hookers!

    I finally recalled the odd description of the blow when he first brought it up. 'Chelated Alkaloids' I had to google it but it is a pretty apt codeword. I got the impression that the saleman had one of the company chemists doing the formulation, clean as you could imagine.

    Like the old expression, 'Better Living Through Chemistry'

Image result for Better Living Through Chemistry

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The West guys typically recommend 80 grit abrasion. This does three things it increases the surface area. It removes any dodgy debris and it increases the overall glueline. Conventional woodworking glues like PVA like thin glue lines. The epoxies do not. The mottled surface when you take off peel ply is a very good surface. Clean and that texture ensures plenty of epoxy.

You've got really stiff brittle carbon/epoxy part bonded to the same thing. I would go for a similar hard resin. Like a good epoxy high density filler or a methylacrylate like Plexus.

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Hi everyone,

thanks for the extensive input.
 

23 hours ago, IStream said:

I'd look at the bonding area and typical epoxy bond strength values versus the max loads expected on the part before going through hoops to maximize bond strength. I'm guessing by eye that you've got ~60 sq cm of bonding area. That's about 9 sq in. Gflex is rated for roughly 2500 psi tensile. 

 

23 hours ago, Rasputin22 said:

m_k, Nice fitting but what is the size of the mast and what sort of loads do you anticipate? I'm right in the middle of designing a rig and need a similar hound for my jib stay.

 

As you correctly guessed it is the forestay tang for a moth. Mast diameter should be around 35 mm at the attachment point. I can only estimate maximum loads, however they will be well under 500 kg as that is a ballpark estimate for the breaking load of the forestay itself. In any way I am way below any critical loads and will follow the recommendations for a good surface preparation. Thanks for getting me on the right track and best regards!

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Loctite Hysol E-120HP or EA-9462. The former is specifically for composite to composite bonds, the latter is a more general purpose adhesive but also works just fine for composite to composite bonding and has a high tensile shear strength (4100 psi vs. 4300 for the E-120HP). A pretty good comparison of their products here: http://www.henkel-adhesives.com/com/content_data/172023_lt4809_structural_brochure.pdf

If I were to use my own epoxy mix in this application, I personally wouldn't use West Systems which softens (pretty drastically) in the heat. I had some length discussions on this regarding the vang strop on top of a 505 boom, basically in the heat the epoxy softened and allowed the strop to slide between the boom and the carbon part intended to hold the strop in location.  Anyway, I would use MGS and the West 404 filler, or just order some Hysol.

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21 hours ago, Zonker said:

Uhh, no. You don't really need to clamp epoxies. For best results you want a thin bond line but nothing like old Resorcinol glues that needed clamping pressure.

Yes, the rubber toughened epoxies are usually the go-to for bonding jobs like this.  Spabond 345 says lap shear on steel is about 37 MPa on steel / 5400 psi. That is pretty strong.

 

so, Epoxyworks, and other west systems instructions that say to apply some clamping pressure to insure mating of surfaces are incorrect??  I'll keep bagging and clamping surfaces anyway.

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5 minutes ago, DRDNA said:

so, Epoxyworks, and other west systems instructions that say to apply some clamping pressure to insure mating of surfaces are incorrect??  I'll keep bagging and clamping surfaces anyway.

For a secondary bond , If you clamp the joint, it  will be resin starved and weak .

gentle pressure to hold the component in place and achieve 100 percent  epoxy substrate  contact is all that is needed

when you vacume bag a laminate stack you are compacting the fibres and generating 100 percent resin fiber contact .

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I guess my definition of clamping is different- I only use enough pressure to barely squeeze out material 

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Personally, I would use a simple 105/205 or 206 (depending on ambient temperatures), not G-Flex.

Strongest filler is 403

Scuff to 80 grit is perfect.  Epoxy needs a "tooth" for a good adhesion.

Not sure about that guy that said "never wipe with acetone".  Probably because he's "never worked with epoxy"....

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Not sure about that guy that said "never wipe with acetone".  Probably because he's "never worked with epoxy"....

If you say so it must be true then.  Or maybe instead of being a asshat you could ask why I said that and you'd find out epoxy is all I work in.   I've got carbon epoxy curing near my right now on like the 30th rudder I've built....   all epoxy/foam/carbon.  I've worked directly with epoxy resin developers who always stressed "Don't do a final wipe with acetone!".   

So go ahead and don't listed to West Systems who say don't use after the initial cleaning:  https://www.westsystem.com/instruction-2/epoxy-basics/surface-preparation/.

Or another from West Systems that says don't use it at all:  "We are all familiar with solvents like acetone, lacquer thinnerand proprietary mixtures like DuPont Prep-Sol that are made to remove specific contaminates. Most solvents of this type will remove organic contaminates such as oil, grease, wax, etc. So wiping a surface with an organic solvent may seem like a great idea. However, the solvents are also capable of dissolving contaminates from rags and depositing them on the work surface. This is not good. "   https://www.jamestowndistributors.com/userportal/document.do?docId=372&title=Avoiding+surface+contamination+-+West+System

Or I guess we shouldn't listen to System Three then?:  "Don't use acetone or similar solvents for this. Much acetone sold today is reclaimed and may have impurities that interfere with secondary bonding by leaving a film of residue on the surface."  https://www.jamestowndistributors.com/userportal/document.do?docId=223

Tons of info. out there if you search:    "Epoxy surfaces shouldn't be cleaned with solvents before application of subsequent coats of anything. The appropriate approuch is to wash the surfaces with a slightly alkaline (soap) rinse. Next the surface is "toothed" to an appropriate grit and finally "tacked off" to remove dust and other surface contaminants, left from the teething process. The washing and toothing process can be combined if desired, using proper procedures. A common method is, to use a ScotchBrite pad to tooth up the surface as you wash it down, killing two birds with one stone.
Slower evaporating solvents, such as spirits or mill oil on metals isn't to clean the surface as much as to slow the oxidation rate, before protective coatings can be applied. Single part polyurethanes are compatible with these solvents, so not a contamination issue. Acetone flashes too fast as mentioned, for contaminates to be removed, usually just smearing it around and leaving a haze instead."

So I guess I'll just keep listening to all of the manufacturers and experts with their dissemination of false information.    Your mileage may vary if your an asshat.

 

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Just don't try and wipe your asshole with Acetone! 

 

    Seriously, I would think that if one were doing any sort of secondary bonding Plexus would be a good solution. There is a reason they use that stuff to bond decks to hulls even on large boats.  That Moth mast and the very nicely molded hound would have plenty of bonding area and Russ's suggestions would be just fine. 

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11 hours ago, thereefgeek said:

Personally, I would use a simple 105/205 or 206 (depending on ambient temperatures), not G-Flex.

Strongest filler is 403

Scuff to 80 grit is perfect.  Epoxy needs a "tooth" for a good adhesion.

Not sure about that guy that said "never wipe with acetone".  Probably because he's "never worked with epoxy"....

Be alert....Acetone can contaminate the surface by disolving whatever substance that may be in the rag.

i dont often see composite workers  or painters use solvent .

Painters often use  alcohol for contaminate removal  

when possible use only detergent and water 

water gives a clear visual indication of contaminates when is sheets off the surface 

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I would personally use west pro-set toughened epoxy - much stronger than standard west (consumer) epoxy

Alternatively Plexus - but choose the right version

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Personally I do a final wipe with alcohol when working with epoxy. Its easier than doing a spray rinse for small parts/indoors work and I personally haven't had an issue with a failed bond due to alcohol. Surface prep issues (using too fine a grit, definitely don't go above 150, 80 grit is good, 120 is okay), poor clamping, poor epoxy choice, humidity saturated material etc. but not a failure due to alcohol. Alcohol has been used as a thinner with epoxies before-not the best idea for structural applications, but if trying to get a deep penetration into wood its not the worst idea. Point is it evaporates more quickly than water, usually doesn't damage the rag and leave behind nastiness, and if there is any on the surface it can evaporate through epoxy. One should also keep in mind that West Systems is intended for use with wood based applications and as such their instructions are generally geared to surface prep on wood. Obviously their long build manual has other suggestions.

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Kind of curious if ammonia could be used to clean the surface.  It does a great of cleaning gunk around the house (better than alcohol IMO) and amines are derived from ammonia (apparently ammonia can can be used to cure epoxy - it just doesn't do it as well as amines).  I have little knowledge of chemistry, so perhaps this idea is ludicrous  IDK.   A table I found on line indicates epoxy is resistant to isopropyl alcohol and ammonia - acetone not so much as mentioned above. 

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