body/frame stiffening with expanding foam

[71tr]

Anyone ever thought of using expanding foam in either their box-frame members or the body rocker panels? Ford is using this stuff in their truck a-pillar members and i've seen tuners use it in their rockers to stiffen the body. obviously the mechanics of this process might be a little messy and i would be concerned with defeating the evaporative process for trapped moisture. any thoughts?

 

[tony barnhill]

Real good way to ensure your car rusts away! It'll trap moisture...how do I know? Bought a parts car that somebody had done that to in doglegs...there was NO metal left!

 

[LastDeadLast]

I was actually told about this stuff by an engineer friend of mine; He thought it would be perfect for what you suggest. He called it structural foam. The thought that 3M made a version of it, but I was unable to find it on their website... that being said, I'm not sure that the product is something that the typical do-it-yerselfer messes with. I did a quick search on the internet and came back with a quite a few hits, if you decide to pursue this, let me know what you find out.

From what I know it's strong as steel in certain structrual situations and it's waterproof.

 

[Alan_Myers]

Hi,

Nope, never tried it... But I must say it's an interesting thought. I've used self-expanding foam for work around the house, closing up gaps under stucco repair, etc. But never in a car.

Ever see a Saturn that's been in a front end collision? Foam everywhere. I wouldn't be surprised it's used in many cars now, to add rigidity and reduce impact force during collisions, while adding very little weight.

I got a gearbox shipped from the UK that arrived totally encased in the stuff, too. It did a wonderful job keeping a heavy item like that from breaking out of it's cardboard box during shipment. But it made for an awful upacking job!

Giving it a bit of consideration, I think you are wise to worry about problems with evaporation of moisture from inside the foam-filled compartment. Perhaps if some form of rustproofing were done first, before the foam is inserted, there would be less concern about trapped moisture.

Most modern cars undergo a rustproofing process done very early in manufacturing. That's often a dip, I believe. But, probably not zinc plating. (Personally, I'd never dip/zinc plate a TR body or frame. The old saying is that it takes two guys to carry the frame into the plater, four guys to carry it back out. So, I imagine modern car manufacturers do some sort of rust proof dipping other than zinc plating, but I don't know what it is.)

So, what about other forms of rust-proofing? Well, you might need to worry if the foam would work properly in conjunction with Waxoyl or similar. Part of the structural property from the foam, I think, is that it sort of adheres to a surface. Many rustproofings would prevent that, I am guessing.

Another thought, most modern car body panels are lighter gauge, high tensile steel. I was really surprised a few years ago when I pulled a front fender from a Ford Aerostar to replace a radio antenna that the carwash broke. That fender was amazingly light weight, maybe 2-3 lbs. I could acutally pick up and hold that large fender with one finger. 22 gauge and even lighter is not uncommon now, and composites or plasics are sometimes used in cars, too.

So, I guess I'm wondering how much additional support will the foam offer for the 18 gauge body panels and 16 gauge frame materials found in TRs? I really don't know.

Another thought, that expanding foam might warp or deform body panels, if a little too much is injected. At the same time, too little will leave gaps and won't add much rigidity. So, it's a matter of getting just the right amount injected.

I do know that when used in construction, you have to be a little careful around windows and doors. When it expands, too much foam that's got no escape has been known to break windows and warp door frames.

Finally, if you ever need to do a weld repair or similar, that foam is pretty flammable, I'm guessing. Might make a welding job very nasty, maybe even highly toxic. A side issue would be flammability during regular use of the car, how it reacts to common automotive fluids and the properties of the foam in reaction to heat, such as in close proximity to exhaust system.

I don't want to sound like I'm raining on your parade. Just trying to consider the idea and put forth a few concerns. I do think it's an interesting thought. Hopefully some other folks will chime in with their thoughts and experiences.

/ubbthreads/images/graemlins/cheers.gif

 

[TRTEL]

Have to echo everyones concerns regarding corrosion. In an attempt to shave a couple extra pounds of weight many moons ago we cut off the rocker panels on a 3A racecar. Made replacements out of extremely thin aluminum, pop riveted them on and filled the space with a particularly nasty foam available around at that time (released something like cyanogen), but was a perfect solution. Weighed probably a few ounces per side but was absolutely rigid and solid. Until two years later when loading it on a trailer, we mangled one side. Took it off to replace it and found the inner sill just about gone adjacent the foam. Maybe the car had been through two or three wet weekends, I don't remember. And the original condition of the inner sills was very good. Nor do I remember if we did any primer work.
Tom Lains

 

[Banjo]

Another concern would be for any future repairs. Once that stuff is in there, I woulden't want to do any welding on the frame, or where ever that stuff was injected. If it were ever to catch fire, it would be durn near impossible to put out.

 

[aeronca65t]

Someone mentioned "structural foam". That's a different product. More of a hard polymer suitable for injection molding. My toolbox is made from structural foam.

We built sort of a go-cart thing a few years ago and used the expanding insulation foam inside part of the frame to strengthen it...worked good, but this was only a fun project, not something that had to last.

I *might* use this stuff in a "through-away" car, but never in a classic. In fact, if you have any cavities in a unibody car and it is sitting for a period of time, it's best to blow air through them to try to dry the inside out. I have a small fan and I regualarly move it around the racer after a weekend to try to dry out any moisture trapped inside the sills, etc. (I remove the rubber inspection plugs to do this). Airplane guys often leave small 110V fans on inside a plane to reduce mold and corrosion.

 

[CraigFL]

There are three things structural foam can do for you:

1. Make a panel more rigid and resistant to localized denting.

2. Add structural strength to things like frame members.

3. Noise reduction

The first is to just fill the space behind thin membranes(thin aluminum or fiberglass)to give it some resistance to denting when handling/using it.

The second is to actually add mechanical strength to the member. The key here is that the foam itself must either add strength to steel member in some way or the addition of the foam must help to transfer loads from one part of the member to another part that the member wouldn't ordinarily be able to do. Unless the foam is very specialized(like a honeycomb type for example), it probably wouldn't/couldn't be as strong as the steel member and therefore add strength to it. This means, realistically, if you are injecting foam into a frame member, you are probably only going to help in by transferring the loads more effectivly. One of the chief ways a frame member can be weak is in a buckling or torsion type situation. U-channel members are nortoriously weak in torsion because they are not closed sections like square tubes. If you would just fill the "U" in the channel with foam, it would become much stiffer torsionally. But in order to this in the best way, the foam would have to adhere completely and evenly to the surface of the member which would allow the forces to transfer evenly.

Of course even with the worst application, the foam would add some stiffness though ever so slight. And as stated, the liklyhood of rust/corrosion would be great if moisture was able to be trapped.

 

[71tr]

This is a good discussion, thanks everyone for contributing. I think the insulation would add stiffening qualities and reduce torisional forces, but I would be greatly concerned with moisture entrapment. I'm a big believer in keeping the evaporative channels open in these cars to prevent/reduce rust growth. I like the idea of using a fan, how about taking it two steps further and building small fans into the frame and rocker that can be started with the flick of a switch?

 

[Don Elliott]

I had a 1992 Buick Le Sabre and it had this foam in the "A" posts to each side of the windscreen and down to the floor level. It all rusted through. Don't use it.

I restored my TR3A from 1987 to 1990 and have driven it more than 87,000 miles since then. During this time and all those miles, I would guess that the total mileage in the rain was under 4,000 miles. Any rain water or splashing that got into the box sections of the frame soon dried out.

Do you plan a lot of miles ? In the rain ? If not, you don't need much protection for inside the frame providing it's nice and cleanly painted all over the outside of the frame.

Don Elliott, Original Owner, 1958 TR3A

https://www.britishcarforum.com/ubbthreads/photopost/showphoto.php/photo/1919/ppuser/4127

 

[Got_All_4]

I agree with CraigFL. He had the best explanation. Structural foam is one of the products I sell and it is much different then crash and sound deadening foams. It is a closed cell foam and water cannot get into it. Very high strength. You can take a hammer to it and be hard pressed to beat it up. It is primarily used to strengthen door and roof pillars in modern automobiles. Chrysler first can out with it then Ford.

As far as using it in a restoration it would depend on what you need it to do. First of all there is nothing like steel patches or replacing body panels. Don't think of using it as a shortcut to strengthen a rusted panel. You WILL trap moisture and be in bigger trouble down the road. Do it right the first time and you won't have to revisit it. The frames of the car are designed to flex with the handling of the car. By stiffening one area, your transferring the load to another area that possibly may not handle the stress. Now you have two week spots. Also all of the box frames have rust in them and the foam won't get good adhesion and soon separate with the twisting of the frame. Also will probably accelerate the corrosion process .


Possible places to use it would be in a cavity where on the out side panel you may have had to take off a lot of metal there by weakling the panel. It would gain strength and the foam would make it more dent resistant. Door pillars where they mount onto the rockers and only when new panels were used. I would not use any inner panel corrosion protection like a wax or oil spray until after the foam was applied. Remember you need that adhesion for the foam to work.

 

[bobh]

TR3ATR250 Is right about using closed cell foam. Boston Whaler pioneered the use of expanding foam in their boats. They lay up the inner and out hulls (fiberglass) then while they are still wet the halves are brought together. Foam is injected in the space between the hulls. The whole thing is held together under heavy pressure while the foam expands and everything cures. The result is a tremendously strong hull.
Sometime around 1976 BW changed to closed cell foam. I suspect it had to to with the waterproof properties of closed cell. I've read about people restoring old Whalers that had water in the foam.
Open cell foam is like a sponge in that it absorbs water. CLosed cell foam does not. I don't think foam in place packaging foam or Great Stuff is closed cell. If you are serious about using foam I would use only closed cell.
Someone mentioned foam in Saturn cars. Many of todays cars use a foam backing for the bumpers. A hard hit that tears off the plastic overlay and damages the bumper will generally break off chunks of the foam backing. This foam is not the yellow stuff you see in packing or at Home Depot. It's similar to styrofoam but a lot stronger.