View Full Version : Kind of confused....
Zephik
10-21-2006, 02:06 PM
Why do they make windshields and windows out of glass? Windshields mainly because of rocks that have been flung at them causing them to crack and break. Why do they not use a different material? Like acrylic or polycarbonate? Arent they, not only clearer than glass, but stronger as well? And even if you wanted to fork out the extra bucks, you could laminate polycarbonate and make it bullet resistant. So whats up with that??
-SF
rosecityracr
10-21-2006, 02:20 PM
i know one things for sure, glass is a heck of a lot easier to clean and keep clean than any type of clear plastic i've ever messed with...i dont know for sure though. my dad's in the auto industry and ive asked him that before and gave me a logical answer but apparently i wasnt paying close enough attention :rolleyes:
GT40_GearHead
10-21-2006, 05:06 PM
the main reason i can think of is sun light and temp variation, two things that lexan, acrylic and polycarbonate hate, leave a piece of acrylic in the sun for a few days and you will see what i mean
tybrenis
10-21-2006, 05:16 PM
For one, acrylic scratches very very easily, even more so with polycarbonate. Glass is also a lot cheaper to produce in that thickness and size, acrylic that size would have to be cast, and they is expensive and hard.
Also, acrylic isn't so great in weathering, it yellows. They do have "outdoor" acrylic now that resists that, but it's very expensive.
Also, acrylic and polycarbonate hold a lot of static electricity and always attract dust and other particles. Acrylic can only be cleaned with special cleaners or just water, for instance something like acid rain or even windshield wiper fluid might weaken it or make it blurry.
Zephik
10-21-2006, 06:09 PM
lol well that explains it.
They need to make chip resistant glass then. Cuz flying rocks are too common!
-SF
Windshields are layered. There is are 2 pieces of shatter-resistant glass sandwiched around a thick piece of some plastic to keep thrown rocks from entering the cab of your car. If the glass didn't chip then it would either stick or go through the windshield. Chipping prevents both. It's rather ingenious really.
CanaBalistic
10-21-2006, 11:34 PM
Laminated windshields are designed for safety, they are moderatly hard from the outside but are designed to let object's (human heads for example) through quite easily from the inside. Another thing is that acrylic tends to shater, flinging rather jaged pieces at high speed through the air. It's also more prone to scratches and hazing.
Slug Toy
10-21-2006, 11:57 PM
ya, have you ever tried snapping a piece of plexi? its hard to do, but when it goes... wow does it go. little bits flying off like high speed razor blades... no kidding. its just asking for trouble.
Very similar to old glass I'm sure.
Windshields are a wonder of science and I'm sure in the next 50 years we will figure out a way to make them do their job better.
Ironcat
10-22-2006, 09:00 PM
I have a friend who used to be an engineer for Ford and he is now an honest to goodness rocket scientist... so I asked him.
There are mainly 2 reasons and you guys have sorta hit on them already.
1: Plastic (acrylic, lexan, plexi, whatever you want) scratches very easily. A lot of mass commuter systems use plastic coated glass windows, if any of you take mass transit, check out the side windows of your local buses and trains... you will see a bajillion little teensy eeensy scratches, and this is from dust and wind and whatnot flying past the window and barely grazing it. Now imagine the scratches and therefore nonivis of front impacts with rust, sand, debris, etc.
2: Glass is ablative protection. This means that is you damage it a very small amount, a very small amount of it will be damaged (ie, chips). Glass will hold, chip, chip, chip, chip, crack, crack more, crack more, etc, giving you time to get it replaced... Plastic will hold, crack, and then shatter.
Razors Edge
10-22-2006, 09:03 PM
I don't know much about windows and plexi and stuff, but when my dads at the track taking his '72 mustang running at like 200 MPH, I don't think hed appreciate have rocks breaking his "Plastic" window at 200 MPH?
If a 5 pound turkey breaks a windshield at 45 MPH (it was on the news like 8 months ago), what about a tiny little rock at 200 MPH, or like 75 MPH on the highway?
simon275
10-23-2006, 01:25 AM
I was driving with my dad and my cousin and a bird hit our wind screen at 110km bounced off and got sucked away by the slip stream very scary but the windscreen was fine.
Zephik
10-23-2006, 07:18 AM
lol that would of scared the inards right out of me! Just driving along and BAM!
My dad had a deer jump out right in front of his truck (I was behind him with my mom) and we were going about 60. I would say he probably nicked his tail. That was the closest call I have ever seen in my entire life. But I am guessing if he did hit it (and somehow the deer got up high enough) the deer would go through the windshield right? Or no?
-SF
Razors Edge
10-23-2006, 06:36 PM
It would. Windshields are only WIND shields. They don't shield you much other then that.
justblair
10-23-2006, 07:43 PM
I'm glad they make them out of glass. About 15 years ago I was driving my parents in my mums car. A artic blew a tyre just in front and to the side of me sending rubber and metal at the screen. I was doing (ahem) 70mph at the time and the window took a fair bit of damage. However the laminate prevented anything hitting the occupants (ie me and my inheritance... cough parents). Other than being hit several times by a hysterical mother I came out with no injury. Its pretty amazing what those screens will take.
Interestingly the side widows are made from a different construction. They are made from safety glass. The glass is stressed at manufacture, so if its hit with a sharp object it the whole glass disintegrates into little cubes. So if you need to get out a car you can strike it with your key and you will have an instant safe aperature to exit through.
i hit a deer, it was an old ford i was driving. the front of the truck actually crumpled around it. the windscreen shattered the rear window hit me in the back of the head. no airbags, the only thing that saved me was my seat belt. completely totaled the truck. i was going 75mph ~120km/hr.
a rock at 75km/hr cracks glass windshields
a bird, let me do some physics.....
200 km/hr -> 55.55m/s
.03=55.55^2/2a
a=-514.3m/s/s
F=ma
F= .5kg X -514.3m/s/s
F=257.15N
divide that by your area
257.15/.094=2375 N/m^2
my physics isnt quite right, didnt take into account the angle of the windscreen, but it would be comparable to having a guy that weighs 280kg sit on it. gives you a rough idea. couldnt find my textbook with all the tables so i could actualy tell you if the glass would sheer or not.
Airbozo
10-24-2006, 07:00 PM
Speaking of deer...
Couple of years ago I was with a bunch of friends riding our motorcycles on Skyline highway (hwy35 in the santa cruz mountains, northern california), about 25 of us. I was towards the end of the pack so did not witness the impact but saw the aftermath. Turns out one of the lead riders drove RIGHT THROUGH a doe at 85+mph(that was the official police estimate. I think they were being kind). His Ducatti was a complete wreck with parts all over the hwy, only the engine was recogniseable. He only suffered a broken arm a fractured leg and a disc problem in his lower back (along with some various bumps and bruises). I say _only_ because there was nothing but the head left of the doe. Complete hamburger on the highway for 100's of feet. He went RIGHT THROUGH IT! I am still amazed that he even lived... Needless to say he still has not gotten back on a bike. He wants to but still has some lower back issues and wife issues (she insists he not ride again).
Hehe good luck with that plastic windscreen on a motorcycle...
Zephik
10-24-2006, 07:06 PM
Wow, that is crazy! :eek:
Is the deer okay? We're they able to save him/her?
-SF
simon275
10-24-2006, 11:06 PM
The mercedes A class cannot be driven in Sweden and Norway as it didnot pass the moose test. Which is will the occupants of the car survive hitting a fully grown male moose at 75km/h ~ 46mph around that speed.
I'm glad they make them out of glass. About 15 years ago I was driving my parents in my mums car. A artic blew a tyre just in front and to the side of me sending rubber and metal at the screen. I was doing (ahem) 70mph at the time and the window took a fair bit of damage. However the laminate prevented anything hitting the occupants (ie me and my inheritance... cough parents). Other than being hit several times by a hysterical mother I came out with no injury. Its pretty amazing what those screens will take.
Interestingly the side widows are made from a different construction. They are made from safety glass. The glass is stressed at manufacture, so if its hit with a sharp object it the whole glass disintegrates into little cubes. So if you need to get out a car you can strike it with your key and you will have an instant safe aperature to exit through.
My parents are rather old and have horror stories from friends in car accidents before modern windshields. So be thankful.
The safety glass is so safe you can put it in your mouth and it won't cut you.
Fantastic stuff, I wish I knew how it was made.
As for the deer question, on rare occasion deer do come through the windshield. The two instances that are consistantly fatal are the antlers or the hooves coming through. More so if the deer is still alive and able to move.
Being impaled by a deer hoof into your chest or abdomen is bad enough, then having the deer buck around struggling to be free is beyond comparison. I can't think of much worse involving a car accident.
simon275
10-25-2006, 01:20 AM
The safety glass is so safe you can put it in your mouth and it won't cut you.
Fantastic stuff, I wish I knew how it was made.
http://en.wikipedia.org/wiki/Safety_glass
"Laminated glass was invented in 1903 by the French chemist Edouard Benedictus, inspired by a laboratory accident. A glass flask had become coated with the plastic cellulose nitrate and when dropped shattered but did not break into pieces. Benedictus fabricated a glass-plastic composite to reduce injuries in car accidents. However, it was not immediately adopted by automobile manufacturers, and the first widespread use of laminated glass was in the eyepieces of gas masks during World War I.
Today, laminated glass is produced by bonding two or more layers of ordinary annealed glass together with a plastic interlayer, usually polyvinyl butyral (PVB). The PVB is sandwiched by the glass which is passed through rollers to expel any air pockets and form the initial bond then heated to around 70 °C in a pressurized oil bath. The tint at the top of some car windshields is in the PVB."
Ironcat
10-25-2006, 02:45 AM
The safety glass is so safe you can put it in your mouth and it won't cut you.
Fantastic stuff, I wish I knew how it was made.
?????????????????????????????????????????????????? ????????
Have you ever been in an accident? Have you ever had to break a window to get something/someone out of a car? Have you ever played in a salvage yard?
Safety glass will cut the hell out of you. Once it shatters it is now a teensy tinesy multi faceted piece of glass. It cuts plenty!
I've never been cut by it. The most I've gotten is scratched without blood. The edges round off and aren't dangerous at all.
Played in a salvage yard? Definitely not. I have better sense than that.
Hooray internet. The world's largest library.
GT40_GearHead
10-25-2006, 06:53 AM
i did had to brake a side window, had to get a friend out of his car, the engine was onfire and the seat-belt was stuck, i had to brake it with my fist,
and i can tell you its hard as a rock
i also had to brake a windshield, a nother friend of mine, lost it in a bend, the car fliped 4 or 5 times and stoped on the left side, the glas had a few crack but i couldn't brake it with my fist, so i had to use my head(i know i know but desperate times call for desperate mesures) he didn't made it :(
Powered by vBulletin® Version 4.2.1 Copyright © 2025 vBulletin Solutions, Inc. All rights reserved.