Structural foam to stiffen our cars

70vert

70vert

New Member
Dec 31, 2004
722
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Bay Area, CA
#1
Hey all,
I was just tipped off to this stuff by a guy who should be on our forums. Apparently it is used by BMW and Mercedes and some GM cars to fill and stiffen hollow frame members - makes them more dense. It also was used in the last Tour de France by at least one rider looking to stiffen his light titanium bike.
Here is a link to one company that makes it but of course sells it on a large scale:

http://www.cymat.com/pdf/FAQs.pdf

This stuff might be the Holy Grail of Stiffness, or at least help out. It could be used in torque boxes, hollow subframe connectors, frame members needing stiffness, you name it. Anybody have any thoughts? Anybody know where to get a kit of this stuff?

signed,
the mad mustang scientist
 
#3
i've seriously considered doing this very thing, but i think you would need to have really clean metal inside those pieces otherwise you'd have a real rust mess on your hands, most likely, but i could be wrong.
 
#4
I really like the idea. If you had the car apart, some of this material could be added. I would guess that the foam would be machined to size, and then inserted with some sort of epoxy surrounding it? Otherwise you'd have clearance all around the foam and it could hardly stiffen the body then. It would just rattle around annoyingly.

Bnickel's point is good. I would think you would want a good layer of paint on the metal it was going into. I wonder what welding/assembly would do to this stuff? Aluminum and epoxy melt way before steel, so would you create big voids in the foam while welding the Mustang chassis back together?

Fun to think about! :)
 
#5
clearance in the foam

the way the guy was describing it after talking to a BMW body shop, they just spray it in there. Maybe inside rocker panels on a Mustang, for example. One would think it just expands to fill the space after some kind of reaction occurs, although I am sure you would want to understand the properties of it before beginning. Nothing like a face full of aluminized foam to start your day off wrong! :rlaugh: or better yet, foam expands, has nowhere to go, and breaks the welds of whatever you're working on.

I'm not sure it would have to be epoxied in to work and not rattle around. If it more or less fills up the frame member - why I happen to have an inner rocker panel photo here:

Image-514CB85FF9BA11D9.jpg


it would act as an internal stiffening sleeve, more or less distributing flex along the whole frame member and vice versa.

Try this experiment: get an empty toilet paper roll tube and then stuff it full of toilet paper or even newspaper. Umm, might want to use the paper from a new roll. ;-) Try to bend it from the ends. Stiffer, right? even though there are voids in between the paper and the walls.
 
#7
bnickel said:
this kind of foam is the same kind of thing you can buy at home depot or wherever, that expanding/structural/insulating foam in the aerosol cans.
Click to expand...

Yep and that stuff soaks in water like you wouldn't believe. From the website provided, it mentions using a diamond tip blade to cut the stuff so i would think that this stuff has to be cut to shape and then the frame rails are molded around it, although i don't get the statement they make about filling box rail frames. Maybe they sell two different products, the aluminum foam and expandable foam. I've heard horror stories of people spraying the home depot type expanding foam in their frame rails. It was like filling their frame rails with a huge sponge and rusted out very quickly. If this foam was near impermeable and didn't hold water then it would also prevent rust as it would form an air tight barrier between the metal and the filler foam. Interesting to hear if anyone has used this on their car.
 
#8
Some links

Here is an article on Sport Compact Car using it on a 300zx.

http://www.sportcompactcarweb.com/projectcars/0006scc_proj300zx/

and here is where to order:

http://foamseal.com/auto_after_ordering.htm

I understand the rust concern if moisture is allowed to get in there and gets trapped there, but what if there is existing surface rust inside but the car is kept dry? Would water vapor in air condense and get trapped?

sounds like something at least that could be put in a hollow subframe connector . . .
 
#9
70vert said:
Here is an article on Sport Compact Car using it on a 300zx.

http://www.sportcompactcarweb.com/projectcars/0006scc_proj300zx/

and here is where to order:

http://foamseal.com/auto_after_ordering.htm

I understand the rust concern if moisture is allowed to get in there and gets trapped there, but what if there is existing surface rust inside but the car is kept dry? Would water vapor in air condense and get trapped?

sounds like something at least that could be put in a hollow subframe connector . . .
Click to expand...
That's a polyurethane foam, but the other stuff mentioned was an aluminum foam. Now I can see where polyurethane would be a lot easier to inject and work with in general. The aluminum foam appeared to be available in big sheets only - to be machined later to fit the application. Possibly that could be injected too, but that would have to be more problematic - I'd think you'd have to have the car apart so that plastic parts wouldn't melt when the hot aluminum foam was injected. Aluminum foam would have to be much more effective in stiffening a car, also. I'm sure poly would help though, especially with regards to NVH.

One thing about polyurethane foam - it may be closed cell, but I'd still expect that it would absorb moisture. Almost every type of plastic will absorb moisture.
 
#10
OK, so we've established

that the stuff sportcompactcar was using was NOT aluminum foam, but nor do I think it is the Home Depot stuff. It seems like the aluminized is for OEM, the autoseal is for aftermarket. I could be wrong, but I'm not sure that car companies would recommend a product that would rust out frames quickly, and that they would recommend it for repairs.

The autoseal link mentions it as something that reduces infiltration from air, water, and dust. I don't think this stuff acts as a sponge, but I wonder about condensation and rust in voids that you can't see.

If the rust question can be answered, why not use it? I know that the rocker panels in a convertible could benefit from an internal stiffening sleeve, as would any hollow frame element that is likely to flex. It would seem to me that it's not going to help you if your sheet metal is what's flexing - the flex is going to happen at the weak link in the chain.

You would also want to make sure there are no cables running inside that frame member, or else like the article says, it will be entombed forever.
 
#11
Well it looks like 70vert has it all figured out already, just pull the rails off and use copious amounts of grease to coat the inner frame rails… :D

What would be the rate at which they would rust? Would it be within a year or within 10 years or 15-20 years? I know that really depends on the locale but what about sealing the rails off so that there are no pin prick holes or anything like that?
 
#13
like i said my only concern is existing rust already present in the structure of the car, regardless of whether or not the foam keeps out water/moisture. i have always been under the impression that once rust starts it's almost impossible to stop, however i have also seen really old cars with surface rust all over that actually preserved the body/structure because there wasn't anywhere for else fo the rust to fester. so if the surface rust isn't an issue i'm all for it, but if it will help the rust to grow then forget it.
 
#15
I've seen this stuff and it is impressively strong. It is NOT the same stuff (Great stuff) you find at HomeDepot and do not try using it. The HD stuff is not a 2-part mix and will not cure. It's also flammable and soaks up water like a sponge.

I'm unsure of the rust issues as well but I think it would actually slow or even stop existing rust. This is my main concern also. It is a closed cell foam and although it degrades in sunlight, moisture or oil will not effect it. Its dense, and brittle but you could park on a brick size chunk of it. It's also made to turn into dust under a heavy impact (a wreck).

I've already ordered a can of it and will try it on my lawnmower hood. It has a inside structure sort of like a car hood and flexes a little when I open it from the side. I may even measure before and after to see how it goes.
 
#16
Long ago (about 20 years now - dang I'm gettin old) I made a spot welded steel box the size of a brick with one hole in it. I injected poyurethane foam into it as a crude experiment to see how strong the expanding foam is. The result: The 20Ga. (0.036) steel box bulged and broke half the welds. I think it took the foam somewhere in the neighborhood of 24 hours to reach its maximum cured size. I realize this isn't exactly the same material, but the moral of the story is probably the same: "Know exactly how big your cavity is and how much uncured material is needed to fill it in a cured state, and have plenty of holes for excess material to expand through." I would expect poor results (panel distortion or inadequate fill) on thin steel such as body panels.
 
#17
thanks for the experiment

interesting to see how it works on hollow body panels. I can see the concern for thin metal and we'll see how it behaves with that. With an inner rocker, for example, it seems like material could expand along the length of it - with two holes, you could shoot it in one end, see how far out it expanded and get up to just where your hole is, then fill the middle up to your original hole, then move to the other hole and get the other end, and then fill the middle and end alternately until you fill your second hole.

Remember that with the 1 minute curing time, you have to work relatively fast.

It will be really important to see how much this stuff expands and in what direction - does it expand to where there's open space (good) or will it push out against the box it is filling too? (bad)
 
#18
OK, I finally tried this stuff on my lawnmower hood. Platonic Solid was right. It worked and worked well but it did expand and distort the top of the hood a little. It pushed the thin sheet metal up and you can see where the spot welds are strained. It's defiantly more solid. Before, I had to lift the hood by stratling the mower and push up on both sides. Now, I can lift it with one hand from one side. In all it feels and sounds more solid.

Cleanup is a bisnitch! Before it's cured, acetone will clean it up. After its cured, I haven't found anything yet that will desolve it.

I also tried to burn it with a microtorch, It won't light. It just sort of turned brown and smoked a little.

I put a chunk of it in used motor oil, weighted it down with a brick, and let it sit for three days, then cut it in half. It didn't soak up any oil. The inside is just as clean as new and it didn't seem to effect the outside.


After all of that, my personal opinion is that it would work great as long as it's not used on thinnish sheet metal. Rocker panels, torque boxes, seat pans etc would be fine. Drill a few holes every threeish feet (it expands quick then stops and starts curing). Make sure the inside of whatever you are working on is clean and dry. I would also use a heat gun or do it on a hot dry day to make sure you don't trap moisture. Use LOTS of painter tape and cover everything, then cut holes for the excess to expand through. Expect to use the can only once and have acetone and plenty of drop cloths and rags handy. It cuts fairly easily but sands better. If its done on a striped car you could sand the excess off then just paint over it.

I think it would be worth it and I may give it a go next year when it warms up again on my rockers and seatpans.

Chris
 
#19
before you go putting it in your frame rails go spray a piece of metal then weld that piece to something.

See if the foam will melt or catch fire when exposed to alot of heat.

My main worry would be that the car would be welded together, but the foam would smolder for a few weeks until bursting into a flaming ball of foam pony.
 
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