Urethane foam frame stiffener

[Dave]

I was over at zcar.com and some one

mentioned using urethane foam to firm

up the Z. They were using it in the rocker

panels. Has any one over here heard of or

done such a thing? I am putting in a S&W

8 point roll bar but any thing extra can't

hurt. I hear that some of the new cars use

this method.

 

Dave...

[Guest Anonymous]

Hey Dave, my thinking on this is that it can't hurt. I've read that the luxury car manufactures initially used foam to quiet there cars but discovered big differences in the chassis stiffness. I purchased foam at the hardware store & plan on using it in all my interior hollow areas. I have heard that it can absorb water so I'm not going to us it in my frame rails or any where else it would be exposed to the elements even though I live in Az.

Glenn

[Drax240z]

I was the one that mentioned this on zcar.com... There is an article in Sport Compact Car magazine on this very topic, (last months issue) its suggested reading! They say that the household/hardware foam isn't sufficient because it cures in air... and there are places it may end up where it blocks itself in so that it can't cure, since it can't get air.

 

I'd suggest doing a little more research before running out and buying household foam and squirting it into the crevaces of your car... I'm sure it would be a bitch to get it out if there was some kind of problem...

 

 

 

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Drax240z

1973 240z - L28TURBO transplant on the way!

http://members.xoom.com/r_lewis/datsun.html

[pparaska]

Hardware store foam in a can has no structural benefit. The shear strength of that stuff is like cotton candy. Find out what the car manufactures use and use that if you are interested. Also, the bond to the steel of the car needs to be strong as well, or you aren't helping stiffness at all. Not to be snotty, but this is the educated opinion of an mechanical engineer that has designed things with foam core.

 

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Pete Paraska - 73 540Z - Marathon Z Project - pparaska@tidalwave.net">pparaska@tidalwave.net -

[DennisK]

Pete,

I am not an engineer, however I have pro status as a golf club repairman. When metal woods came out, they were hollow and had a tendency to collapse inward in the face area. We put expandable foam in and the problem stopped. It was explained to me that pressure was equalized in and out, that gave more strength. I don't know if this would apply, as the clubhead is completely enclosed. What do you think?

[Owen]

I mentioned this a couple of months ago on

another post. It's used a lot in the rally

scene on race cars. It sounds like a cheap

good idea on a race car but I have doubts

about it on a street car.

The original rubber or whatever it was on

my Z, in between the panels, etc, seem to

be the culprit for much of my rust problems.

I think it soaked up moisture over the years

and caused the rust, this was the case in

my rocker end-panels.

A rollcage and maybe some extra points welded

in should be good enough.

Owen

 

 

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http://www.homestead.com/s30z/index.html

[BLKMGK]

Been thinking about this too since I spied the article in Sport Compact car. I'd like to know the cost and if it absorbs water or not. If I were to use it anywhere I'd start with the rockers in hopes of keeping water out and sealing it all up. If they're using it on Lexi and whatnot it ought to be pretty good but I'd really like to have a warm fuzzy on the water thing first. Maybe put a plastic bag in first?

[Guest Anonymous]

Well, if you re-read the SCC article, you will notice the stuff that they used is supposed to be waterproof and closed celled... so I assume as long as you use stuff similar to what they have you should be okay.

 

But I guess it would still be possible for water or water vapor to be trapped in some areas if you are not very thorough and don't pack that stuff in tight enough.

[Guest Anonymous]

Pete, I do appreciate the opinion of well educated individuals. I will not be using the stuff I bought at the hardware store. Dave e-mailed me info on an aircraft product that uses two parts for the chemical reaction. I guy I work with has some experience with boats thinks this is some good stuff. He said when cured its hard but floats. He did warn that a little goes a long way & if you use to much it will split whatever your filling with it.

Psyence, What product was used in the article your refering to?

Glenn

 

[This message has been edited by Glenn Richelsoph (edited June 22, 2000).]

[Guest Anonymous]

I believe that it was called Foam-Seal or something like that. Aparrently that specific product is the one recommended by the national car repair association to be used for repairs on vehicles that come with urethane foam from the facotry (like the Infinity Q45). They sell a range of foams that range from 1-2 lbs/cubif foot up to 10 lbs/cubic foot. The light stuff stiffens up the applied areas 30-40% while the really heavy stuff can stiffen up areas up to 300%.

[pparaska]

If the auto manufacturers have a product you can source, I'd feel safe - as long as you can be sure it will bond to what you are filling. If it doesn't bond well, first, you get no structural benefit because it won't carry shear from one side to there, and second, it will leave a place for water to sit against the steel.

 

But if you've had the rockers replaced and know the surface to be a good bonding surface (like an epoxy primer), I'd say using the OE sourced stuff is fine. If you're concerned there might be something (like rust, cheap primer, oil or wax based weatherproofing) to keep a good bond from happening, I'd leave it out, as it wouldn't help the stiffness.

 

Cored structures usually use the core to transfer shear from one side of the filled member (the bottom of the rocker box for example) to the opposite side (the top or the rocker box). Bad bond = no shear transfer = no stiffening. (Of course, there are varying degrees of bond, and therefore stiffness).

 

The cored structures I have experience with are sandwich panels, and things built out of sandwich panel techniques. That stuff was built from premade foam sheets and woven fiberglass and carbon / resin skins. Very stiff indeed, for the weight.

 

As for why the golf club works better, is exactly as you thought, Dennis. The club head is closed and loaded normal to the club face. You filled it with foam which created pressure inside to counter the outer pressure, but you also put something with some structural stiffness in compression behind it also. The difference is that the rocker box needs stiffness in bending and depends on the foam for shear transfer to be effective, and the club head sees normal forces. (shear is easily understood if you take a piece of tape , stick it to a table on one end, and pull on it sideways on the other end - the adhesive is transfering shear from the tape's backing to the table.) Totally different application, in terms of the loading conditions.

 

Oops, sorry for the engineering lesson. That was worth 3 CREs, if you are still awake .

 

[This message has been edited by pparaska (edited June 22, 2000).]

[DennisK]

Nnggluh! Yea, sure I'm awake! Reminds me of college! Just kidding, what you say makes perfect sense, as applied to automotive. The foam is also how the rear tub is sealed to the body on the VR and other GTO types.