Composite fiberglass/foam panel build question
- Thread starter Jonturgeon
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The XPS foam used for panel manufacturing appears to be the same as the hardware store material, only with an added planing process to acheive better tolerance (I can attest to the thicknesses of hardware foam being approximate and variable) and a better gluing surface since the cells on the outer surface are cut. If the thickness variability doesn't bother you, you can acheive a similar gluing surface by sanding. IMO the dog brush is much better than sanding as a surface prep, but you could do both easily enough.
OC panel foam: http://commercial.owenscorning.com/assets/0/144/172/174/3ebc8d51-67ac-4c49-a251-7db4d8f20fc9.pdf
OC hardware foam: http://www.foamular.com/assets/0/144/172/174/98cf58e1-c3d2-4b6c-beb5-2063215bea18.pdf
Boat builders don't use XPS because it is too weak for optimized strength/weight hulls. They use foams >5 lb/ft^3, while XPS ranges from 1.15 lb/ft^3 for 15 psi and 2.2 lb/ft^3 for 60 psi. But panels made for vehicles do not need to withstand repeated pounding of waves.
In my testing the foam core is definitely the weak link in flexural failure, but I don't see that as an issue. Skins need to be "overbuilt" (much stronger than needed for optimal flexural strength/weight) to resist impacts and denting, and panel thickness is primarily determined by the degree of insulation desired. I can jump up and down (hard) on a 6"x36" 2" thick wall sample (supported at the ends) without it breaking.
OC panel foam: http://commercial.owenscorning.com/assets/0/144/172/174/3ebc8d51-67ac-4c49-a251-7db4d8f20fc9.pdf
OC hardware foam: http://www.foamular.com/assets/0/144/172/174/98cf58e1-c3d2-4b6c-beb5-2063215bea18.pdf
Boat builders don't use XPS because it is too weak for optimized strength/weight hulls. They use foams >5 lb/ft^3, while XPS ranges from 1.15 lb/ft^3 for 15 psi and 2.2 lb/ft^3 for 60 psi. But panels made for vehicles do not need to withstand repeated pounding of waves.
In my testing the foam core is definitely the weak link in flexural failure, but I don't see that as an issue. Skins need to be "overbuilt" (much stronger than needed for optimal flexural strength/weight) to resist impacts and denting, and panel thickness is primarily determined by the degree of insulation desired. I can jump up and down (hard) on a 6"x36" 2" thick wall sample (supported at the ends) without it breaking.
Cool!
How much does that adhesive cost?
Does it work better than epoxy? The stuff I've been using is Ebond brand and seems to work well. <$30/gal, about $40/gal including 2k mile shipping. You aren't using as much though, so price isn't such a big deal.
A potential issue with moisture cure is that there really isn't any way for moisture to get in. I used PL Premium on foam/plywood and it was fine, but you are gluing two waterproof materials.
Maybe ask the foam manufacturers what they suggest?
For adhesion tests I'd suggest making narrow samples and peeling them apart. I'm pretty sure a properly prepped foam surface will stick a lot better than "raw".
How much does that adhesive cost?
Does it work better than epoxy? The stuff I've been using is Ebond brand and seems to work well. <$30/gal, about $40/gal including 2k mile shipping. You aren't using as much though, so price isn't such a big deal.
A potential issue with moisture cure is that there really isn't any way for moisture to get in. I used PL Premium on foam/plywood and it was fine, but you are gluing two waterproof materials.
Maybe ask the foam manufacturers what they suggest?
For adhesion tests I'd suggest making narrow samples and peeling them apart. I'm pretty sure a properly prepped foam surface will stick a lot better than "raw".
I agree with what IdaSho is saying, epoxy is very easy and available, but the other thing to consider is the time required for epoxy vs polys. 1-2 hr clamp time for poly vs 12-24 for epoxy. The easiest set up for small shop is vacuum bagging for either adhesive. The invest can be rather small even for large panels. Pumps are often available used for reasonable, and you just need a large flat table and plastic sheeting. Especially if your only doing 6 panels for one box, durability isnt as important. Wood working and boat forums are full of advice, some of it even good!
My best answer is contact some of the larger suppliers for adhesives and talk to their tech. Most chemical companies have so many types its easy to get lost and they dont advertise all their offerings. Tell them the type of panels and the foam and they can make a recommendation. FRP and XPS is a very common lay up even in the US so there are plenty of options. The only problem is they are accustomed to dealing with production volumes using 450G totes so it might take a little talking and waiting to get smaller amounts. Henkel/Loctite is a great place to start, HB Fuller is another. Your regional distributors are another great resource.
My best answer is contact some of the larger suppliers for adhesives and talk to their tech. Most chemical companies have so many types its easy to get lost and they dont advertise all their offerings. Tell them the type of panels and the foam and they can make a recommendation. FRP and XPS is a very common lay up even in the US so there are plenty of options. The only problem is they are accustomed to dealing with production volumes using 450G totes so it might take a little talking and waiting to get smaller amounts. Henkel/Loctite is a great place to start, HB Fuller is another. Your regional distributors are another great resource.
A possible alternative for skins would be phenolic resin and FG sheets made by Durasip. http://www.durasip.com/products.html
As I recall they were a little over $1/sq ft plus shipping. You'd need to paint/finish them, but they are affordable.
As I recall they were a little over $1/sq ft plus shipping. You'd need to paint/finish them, but they are affordable.
I called Epic Resins and told them what I was doing and that is what they sent me. I've done quite a bit of testing and adhesion is great. Destructive testing showed the foam failing and no urethane failure. The test panels were incredibly rigid and took a lot of abuse.
Keep in mind the samples below had zero surface prep on the foam.
Keep in mind the samples below had zero surface prep on the foam.