Are all car roof materials similar? 4

[tffy]

Hello everyone!

I am developing a product which uses magnets to attach to the roof of cars. I am aware that some cars use aluminum or fiberglass in their construction - that's easy to test for. Ignoring this, the question that I have is - is there any information to help me be sure that all cars in the US (and hopefully foreign) market are sufficiently magnetic-attractive?

All the cars I've tested thus far (with a magnet attached to a scale) have shown a sufficient degree of attraction, yet some differences are noticeable. I imagine that this is mainly caused by the variations in thicknesses and types of steel used. Not surprisingly, fancier and older cars seem to do better.

What worries me is - how can I be sure that there isn't some outlier that is drastically lower in magnetic attraction (thinner/some different strange metal) than what I've seen (on about 40 different cars) thus far without testing every car out there?

Is there a typical steel that is used or is there an average gauge thickness? I imagine that in the quest to save money, there are some other limits that manufacturers must heed...but these I do not know.

Thanks a bunch!

 

[patprimmer]

The amount of body filler used either by repairers or the OEM will have an influence.

Regards
Pat
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[tffy]

Thanks, Pat. That definitely would have a major effect - luckily roof repairs/patches seem to be quite uncommon and the usual encounters thus far have been with clean sheets of bent steel.

 

[GregLocock]

The thickness of the general run of the roof panel will be 0.9-1.5mm I'd guess. The material will be nothing special, I can't see HSLA being used, as stiffness and oil-canning are the issues. So, except for the occasional snow powered oddball, I think you can assume a not veyr fancy grade of steel will cover >95% of the market.

Cheers

Greg Locock


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[KENAT]

Beside the Al & Fiber glass vehicles, how much variation is there in the paint and related finishes? Would this impact results?

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[MikeHalloran]

Vinyl roof covering, now fortunately out of style, will interfere with a magnet's attraction to a steel roof.

... as will extreme curvature, e.g. associated with pressed-in ridges and bumps found on the roofs of many SUVs.

... as will presence of a glass or plastic panel/ sunroof/ moonroof.


Other issues arise:
- How do you prevent the magnet from scratching the paint?
- How do you remove the magnet without scratching the paint?



Mike Halloran
Pembroke Pines, FL, USA

 

[tffy]

Thank you, guys!

Thanks for the info, Greg. I guess I was just wondering if there are any specific "guidelines" or "rules of thumb" that are used for body/roof design that I'm not aware of... or any suggestions that the manufacturers have been reducing panel thicknesses as of late. If not, all of that is good to hear.

What's a "snow powered oddball," if I may ask?

Paint would certainly impact the results - and maybe that is already responsible for a bit of what I'm seeing - with magnetic attraction, every thou of separation from the metal matters.

Thanks, Mike. Yes, the instruction manual for this product specifically states that it is not designed for uneven surfaces/any non-metal interference. Scratches to roof are prevented by a combination of a thin (<5 thou) covering and a compressible "foam" surface surrounding the magnet(s).

Thanks everyone! If there's more info on the subject, would love to hear!

 

[GregLocock]

De Lorean -stainless steel panels.

Cheers

Greg Locock


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[BrianPetersen]

The exceptions are likely sufficiently rare so as not to present too much trouble. The DeLorean also had gull-wing doors that would preclude anything being attached to the roof, even if you *could* get it to stick.

Won't work on Corvette (fiberglass), late model Audi A8 (aluminum), original Honda Insight (aluminum), some of the old 1970's and 1980's T-top cars (glass), anything with a vinyl roof, or any convertible, and it could get interesting if someone puts something on one of those newfangled folding-roof convertibles and then presses the button.

 

[CoryPad]

Steel roof panel thickness for current automobiles should be 0.7 mm to 1.5 mm, and the steel would be a low-strength grade such as the 5 defined in SAE J2329 Categorization and Properties of Low Carbon Automotive Sheet Steels or maybe a dent-resistant type according to SAE J2340 Categorization and Properties of Dent Resistant, High Strength, and Ultra High Strength Automotive Sheet Steel. That should cover > 95 % of the vehicles produced today.