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Gloss Plastic Could Eliminate Auto Painting
customs writes "There is a new plastic out from GE that covers plastic surfaces with a really good sheen. It's more resistant to scratches and random chemicals compared to conventional paint. It's actually a .5 mm polymer called Sollx; the Segway was the first semi-mass-produced product to use it, it has slender two tone fenders. Kinda cool. Auto painting is the industries largest manufacturing expense, and this could be what they're looking for...as soon as the price comes down."
Regardless what the submitter says, the article says that car manufacturers aren't looking at it because plastic is 3x more expensive than galvanized steal.
When plastic comes down in price, then it will be here. The thing that I don't like about this is it seems that it has to be in place during the molding process. This would mean that if you were to ever scratch it, or something along those lines, you'd have to replace the entire piece. Unless they developed a patch kit for it, which seems like the patch would be weaker than the rest of the area because it wasn't present in the mold...
Of course, a plastic fender with this on it would probably be cheap because they have already reduced the cost of plastic below that of steal. The thermochromatic aspect of it would be cool though, but I'd prefer it to be uniform. I wouldn't want the rest of the car to be black and my hood to be red... that would just look weird.
Dacels Jewelers can't be trusted.
I got out of graduate school in 1999 and found myself in the market for a new car. I didn't shop around, I thought I knew what I wanted -- a new 2000 Saturn SC2, black. I found that dream car sitting on the lot, and bought it (well, a bank helped me).
So, here I am, 4 years later, the not-so-proud owner of a blackberry (purple in bright sunlight, black at night) Saturn, having learned so much about the downfalls of plastic. I'll never buy another Saturn. If I had it to do over again, I wouldn't have bought a Saturn in the first place. The sales pitch says this: when you get into an accident, plastic body panels are much easier to replace than metal ones. They don't say that every little ding and scrape you get (ever park next to an SUV that doesn't have enough repsect for drivers of smaller cars that they open their doors until they hit the next car over? Ever find a shopping cart resting against your car?) will leave you with a white mark. In a white car, that may not be bad, but when this car is all newly washed and shiney, it's got ugly white scratches on the sides and rear fender. For some reason, metal cars don't seem to have this problem as much.
Gloss plastic. In practice, does this mean that it'll stick as well as paint does to my plastic Saturn? Or will it have the staying power of paint on metal? I don't care about the press articles on it, I want to know what the field tests say in the hands of real people.
Well, not to belabor an obvious point, but you wax plastic with. . . wax. Just as you do paint, wooden furniture, unpainted metal, every kind of flooring material you can think of (including plastics) and a host of other products and materials.
And for the same reasons. It adds a sacrificial layer that erodes instead of the base material. Prevents oxidation.Provides a smoother surface (racing cars are waxed for this reason, the aero drag of a waxed car is measurably lower than an unwaxed one), and as result, entirely coincidentally, gives a glossy sheen that some people find attractive.
People already wax plastic all the time. Hell, I wax my Lexan R/C car bodies. Makes 'em look great.
KFG
Second, metal is stronger than plastics, up until you get into carbon fiber or similar carbon or aramid composites, which aren't plastics. They're composites. Even FRP (Fiber-reinforced plastic) which is somewhat common for air dams and such, it's floppy. You could make it hard but then it would be brittle.
Something that people tend to forget about cars is that unibody cars are a monocoque or semi-monocoque design. Most unibody cars are actually half monocoque, with a unibody rear, and then frame rails and underfenders just sort of sitting out in front of the car beyond that. The entire back skin of a unibody car is load-bearing, which is why it's a monocoque design. Stresses from spirited driving are transferred into the roof. This is why convertibles are floppy and require additional reinforcement.
There are some full-monocoque cars, like the older Opel GT. They don't really HAVE a classic frame, they're just built up where the suspension equipment bolts on. Of course the new classic example (since no one seems to know what an Opel GT is any more) is the McLaren F1, which everyone has heard of. That, however, is a carbon fiber full-monocoque design.
So metal is stronger than plastic, necessary in the car's design, and it will in almost every case look different than plastic even after painting. Plastic and metal require different primers, and the texture of the primer on a different material changes the way the car looks when it is painted. It can also be a challenge to get a primer for plastic and a primer for metal which won't interact differently with the paint you lay on top of it.
If you want a prime (oh I kill me) example of this phenomenon, examine a Pontiac Fiero. The Saturns with plastic doors aren't old enough to really see a color change, but of course that is due to fading which this stuff is supposed to not do. The Fieros, however, are painted with different paints depending on whether you're painting plastic or metal. It becomes very noticable on them as they age.
The final and perhaps most compelling reason to use metal is that it has the best failure mode out of all available materials. Plastic tends to shatter when you put enough force into the same part of it all at once. Steel, on the other hand, first work hardens when you flex it, making it stronger in the bent place. If you bend it beyond its elastic limit, anyway. If you continue to stress it it will distress (Crack) and then tear. However, with sheet steel, it mostly causes other areas to deform instead of tearing.
With steel, there is no damage which cannot be repaired. Pieces too badly damaged to straighten can be replaced to or near original specifications by removing a relatively small piece and fabricating a new piece of steel to fill the hole. This is true of any steel part of the car, from the body to the unibody to the frame. Plastic, on the other hand, usually has to be cured into a shape. Plastic bumper covers can be repaired (with some difficulty) but they are not load-bearing. They're just dressing. The only load they ever have to bear is atmospheric.
I should not have to remind you that this tendency to work-harden when pushed past the elastic limit and excellent failure mode is the technology behind "crumple zones" in cars. We know about how the stress is going to be transferred into other parts of the steel. Even cars which DO have plastic parts on the outside have metal parts right under them to deal with crashes. The upgraded version of crumple zone technology is used in NASCAR racing, and it's carbon fiber honeycombs built to fail in a predictable way, just like the crumple zones in a normal car - except of course the cells are smaller and more predictable. The bumpers are also upwards of $2000, which makes them impractical for street use.
Steel is cheap and good and can be easily repaired out in the real world. Plastics may make it possible, but they also possibly make repairs a big pain in the ass. You have to consider the difficulty of repair as well as initial construction.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
I don't know what Lexan is,
Lexan is a bullet resistant plastic, similar to bullet proof glass but lighter, easier to mold, and more resistant to penetration. A few years ago, I made a skateboard out of the stuff just to have a clear skateboard. Now, it weighed in excess of 25 lbs. and was completely impractical but it looked good, and couldn't be shattered. I agree with you, the people who come up with these materials deserve to be compenstated fairly for their effort and hard work.
"...we dont care about the economics; we just want to be able to hack great stuff."
The impact of a crash is absorbed by the frame, not the metal panelling.
Not entirely true. Crumple zones are designed to absorb the energy of an impact rather than transmit it to the passengers.
This design was taken from high performance race cars (like Indy and F1, not so much NASCAR) where the cars appear to disintegrate upon impact.
Dispersion of energy is one of the best protections a passenger can have. This is what an airbag does. The energy of the impact gets disapated into the air filled bag of large volume.
So, a rigid frame may help handling, but it does not help accidents from causing bodily damage.
You might be interested to know that the windshield ends up absorbing/transferring to the roof up to 40% of the forces in a collision. This is the real reason it is illegal to drive around with a cracked windshield, not visual issues. If it were a visual issue, it would be illegal to drive around with a dirty windshield.
You can build your sacrificial crumple zones inside the body (in the front, the part of the body which the fenders are bolted to are called underfenders) but then you're just going to add weight. The fact that the skin of the car is load-bearing and part of the crumple zone just means that you don't need to add as much crap specifically and ONLY for the purpose of crash absorption under the body.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"