| Author |
Message |
Bogie (24.161.206.58)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 12, 2003 - 4:05 am: | |
Have huge wraparound windshield with several large cracks complements of many trucks. Am considering Lexan or same as aircraft material for new windshield at about 1/3 the cost. Any opinions????thanks Bogie |
Ace (24.28.44.126)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 12, 2003 - 9:18 am: | |
You will probably find that Lexan requires much more maitenence and if you let it go you will end up with many scratches that are not worth the money saved in replacing with Lexan, especially for a winshield! Other areas may be ok but I wouldn't recommend it for the windshield!
My opinion of course!
Ace |
Jeff (Jeff) (68.10.101.219)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 12, 2003 - 9:25 am: | |
As far as I know, the windshield HAS TO BE DOT approved glass. Several years ago, Tidewater Rapid Transit (Hampton Roads Transportation today) in Norfolk, Virginia received several buses that did not have DOT approved glass and all brand new buses were dead lined by the VA State Police until all of them had the proper glass installed. I do not believe Lexan is an approved front windshield on vehicles. May be OK on airplanes but not anything on our roads. Check with your DMV and State Police before you invest any money.
Jeff
"Take Another Road" <-- Jimmy Buffett
Rustless not Busless in Buckroe
1988 TMC RTS-06
da Bubba |
jason (24.107.116.157)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 12, 2003 - 12:10 pm: | |
My father flies a hawker 1000 business jet and you have to take real good care of those windshields. If you wipe it down while it is dry, you will surely scratch it. It is almost like having two pieces of plastic put together. If one side cracks you will still want to replace the windshield though. |
DaveD (64.235.198.76)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 12, 2003 - 6:29 pm: | |
Buse may be different, but for most cars, the windshield is a structural part of the vehicle. What kind of bus do you have? MCI windshields are relatively cheap and can be obtained from MCI as well as other sources. GM and Eagle may be harder to get.
FWIW
Dave Dulmage
(MC-8) |
Paul Tillmann (152.163.188.227)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 12, 2003 - 6:44 pm: | |
I may be wrong, but I don't think windshield wipers can be used on Lexan. The least bit of dirt, wet or dry, will scratch Lexan. And, as others have said, I don't believe they are DOT approved.
Paul
MCI MC-5C
T6H 5308A |
Mike Stabler (Docdezl) (64.255.109.218)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 12, 2003 - 9:49 pm: | |
I think the problem is going to be in its flexability. That big slab of glass gets pushed in at speed and the corners leak. UPS trucks that use straight wiper blades don't work in the center of the blade. The driver told us we were nuts,until he pushed out on the glass with his finger! Wala the wiper started working.
smoke,rattle&,stink.....dcodezl |
OAE Palmer (216.39.187.88)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 13, 2003 - 12:12 am: | |
#1...Lexan®, although "bullet proof" does shatter if not mounted exactly correctly.
#2...Lexan® although clear to the human eye, is actually like a large clear alka-seltzer in that it continues to off-gas over 1-5 or more years. (Put a stick-on decal on some and watch the bubbles form over time on the backside!)
#3 Lexan® is actually softer(scratches ez) than Plexi-glas®, which is what is used in aircraft winshields and side windows. HOWEVER the price of a 1/8th inch sq.ft. of commercial grade plex® is about$1.40 whareas aircraft grade is as much as $55.00 per sq. ft. The cadnium content affect the price as well as the casting of the sheet.
#4...You CANNOT use Lexan® OR Plexi-Glas® for a windshield on any vehicle EXCEPT a MOTORCYCLE on any state or federal road that I am aware of...you must have SAFETY GLASS.... BTW windshield glass and side window glass are completely different!
#5...A clear coating can be applied to Plex® (but NOT Lexan®) that makes it so scratch resistant that you can rub steel wool on it w/o a detectable trace! The application is about $2.50 a sq.ft. and done to whole sheets only.
thats my 2cents worth.... |
Steve 80 Crown Atomic (205.188.209.11)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 13, 2003 - 2:08 am: | |
I plan to replace all my bus windows and windshields with optical grade lexan. I’ve only done basic research, but do know there are at least a dozen different grades, with quite a variance in strengths, surface hardness, and aging properties. You can buy a specific grade of Lexan that is optically clear as glass, is extremely scratch-resistant, and has a 10 year warranty against crazing/cracking/yellowing.
I don’t know what kind of design your plastic manufacturer is offering, but I suspect it is similar to those used in small general aviation aircraft, that use single layers of acrylic or polycarbonate plastic. This does scratch easily (waxing and polishing is the solution) and bug splatters can be very difficult to remove if baked on for days. Constant flexing and intense heat can create crazing after a few years.
Most windshields on the next bigger size of aircraft (turboprops and bizjets) are laminations of glass and plastic. The glass is on the outside and is scratch resistant. The strong inner plastic prevents birds and broken glass from entering the cockpit. Many bizjet pilots are concerned about scratches. But their concern is mainly for the fantastically expensive coatings applied to the windshield after it has been manufactured. These coatings repel rain, reduce glare, etc and are easily ruined when cleaned with ordinary household products. Cleaning is usually done with demineralized water and an ultra-clean cloth. Most coatings cannot be reapplied in the field, as our aircraft washer discovered after he cleaned a windshield with a heated pressure washer, a $28,000 mistake. These windshields often suffer from various degrees of delamination but I suspect this is due to the temperature extremes and pressurization cycles. I doubt delamination would be a problem for a factory made auto windshield, of an established design, properly installed. Some of the older bizjets, with windshields made of layered plastics also suffer from an opaque fungus that grows as water seeps between the layers. The only solution is replacement.
My experience in windshield/window R&R is several automobiles and a few dozen aircraft, including bizjets. I don’t recall any of them being “structural”, assuming a definition of “structural”as something that supports more than it’s own weight and/or transfer loads from one member to another. The windshield/window frames actually transferred the loads, the glass was mainly designed to withstand air pressures and provide some crash protection. My Crown factory windshields and windows are all set into channels with rubber and adhesives keeping them in place, definitely not structural, but I don’t have a lot of experience with other makes of buses.
I suspect the absence of “D.O.T. approved” windshield markings could cause significant problems during a safety inspection by police, your insurance rep, or DMV officials. How those easily duplicated markings get onto your custom fabricated windshield is none of my business.
There are thousands of vehicles on our roads with bullet-proof windshields/windows that ARE D.O.T. approved. Your local armored car company may provide some leads to manufacturers. In the military, I was associated with armored 18-wheelers used to transport “Priority-A” resources across the nation. These vehicles were standard Freightliners with armor added. The windshields used two flat panels of Lexan set into heavy 2-inch steel channels, one of the few features (besides gunports) that differentiated them from regular Freightliners. These panels ought to be pretty close to the size needed for a bus windshield. You might start an internet search with “Department of Energy” “Transportation Safeguards Division”, “Safe Secure Transport”. The prices ought to be quite impressive though.
Weight and installation refit may become problems if you use a bullet-resistant or bullet proof thickness of Lexan. Bullet-resistant starts around 3/8". I have a 3/4" thick Lexan window, about 18x24 inches. It is easily 5-8 times heavier than a similar size of 3/16" thick sheet glass. I’ve beat it with a hammer and it doesn’t show any obvious impact marks.
Different thermal expansion may be another problem to overcome. My internet research of a year ago indicated lexan would expand about four times more than glass, but if your windshield isn’t a structural member and is mainly sitting in place, this expansion might be easy to compensate for.
BTW, I did experiment with “bullet-proof” windows removed from a bank’s drive-up teller windows. I spent two years watching a vacant bank, and when the wrecking company finally arrived, I got the windows for a small donation to the foreman’s personal retirement fund. Unfortunately, these windows were made of 5 sheets of regular glass with thin sheets of plastic sandwiched between. A 4ft x 5ft section weighed about 200lbs. The surface scratched as easily as regular household glass. At the rifle range, a variety of calibers failed to fully penetrate the panel, but most shattered fist-sized craters into the 3rd and 4th layers of glass. Worthless for my bus applications.
When discussing this topic awhile back, a fellow busnut ((Tom, I think) offered another interesting solution. He lived in Florida and new building codes created in the wake of hurricanes, required construction companies to used windows capable of withstanding debris hurled at hurricane speeds. The contractors were using a new window film that added this strength to regular window glass. I haven’t researched this alternative, and don’t know of it’s scratch-resistant capabilities, but it might be an inexpensive and easy way to prevent rock damage to standard bus glass.
Let us know what you do, myself and others are working similar problems.
Steve ‘80 Crown Atomic |
jmaxwell (66.42.92.16)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 13, 2003 - 12:00 pm: | |
I would be willing to bet that Lexan is available DOT approved for windshields. However, cost would probably render it un-feasible. 7 yrs. ago I bought some 7/16" DOT approved panels from LA Rapid Transit @ $50.00 ea (New cost was $840.00 ea), so-called bullet proof, 44" x 58". They were DOT approved for side windows and are DOT stamped (The stamp does not indicate what the approval is for; just a spec # stamped into them which would probably pass the inspection of any cop I ever knew). Ended up not using them due to the co-efficient of expansion which renders them difficult to seal (Genuine DuPont, 7/16", 4'x8' sheet will expand 1" and 2.1" respectively in 100 degree temp difference. So, with cost and expansion in mind, it may not be a good choice in the long run, plus the crazing/checking/scratching that has been mentioned. As to bullet proof: Just for the hell of it, I fired off 6 rounds from a 45 Long Colt at one of them. Nothing more than six dimples where the bullets hit; set it aside; 2 yrs. later found it laying in a pile of about 20 pieces. |
ED-NJ (67.85.224.113)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 13, 2003 - 9:56 pm: | |
Harley Davidson uses lexan. but if you use a squeegee on it it will scratch. |
OAE Palmer (216.39.186.168)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 13, 2003 - 10:39 pm: | |
FWIW....When I was in the biz, my Lexan came from GE the inventors of the stuff, like most everyone elses did.
There are dozens of manufacturers of "polycarbonate" the industry term for Lexan, Scheffield is among the leaders.
There are balistics grades of polycarb as well as multi laminated versions, some with glass that ARE DOT approved...at about $200.00 a sq.ft. (who here is going to spend that kind of money?)(better yet who here needs that kind of security?)
Polycarbs are fine for side windows, if you like looking thru expensive haze eventually.
(remember YOU have to clean it AND take MORE care of it than you ever would with glass, are you gonna carry the special cleaner and ALL cotton rags with you along with scratch remover)
As I stated before, polycarb is SOFT....try to buff a scratch to crystal clarity and what you get is more distortion...acrylic (plexi-glas)was made to be buffed clear in the field and is why it is used in F-16 canopies as it has been in most fighters since the late 40's. But also remember that your windshield is hit dozens of times a minute by micro particles that bounce of HARD GLASS, but imbed and impress plastics because they are SOFT.
BTW did you know the viscosity of lexan is LESS than plex?
Polycarbs also absorb water unlike acrylics, thats why we use to have to dry the sheet in a vertical oven for 8 hrs @ 150deg. before fabrication or thermalforming.
It bows in heat and gets brittle in the bitter cold.
one last item....
while cutting a 6ft by 8ft panel of 3/8ths inch polycarb on a flat panel saw with a 10hp motor and a 14in. blade, the polycarb fractured into 4 pcs.
one left a 3inch gash in my arm...
one was kicked by the saw across the 30ft shop, sailing between 2 other employees 6ft apart and THRU a metal garage door, leaving a gash 3x 16.
the 2 largest pcs stayed on the saw table.
Frankly I am suprised nobody has started promoting the virtues of PETG, another CLEARER material thats even cheaper than plex !
It has 60% of polycarbs properities and you can't polish scratches out of it either! |
Alan Heaberlin (66.159.218.185)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 14, 2003 - 9:36 pm: | |
I worked for many years as a glazing contractor with a large windshield trade. The only acceptable glass replacement according to DOT and NHTSA is classified AS-1. This is 2 optically clear polished layers with a 7/32" plastic lamination. In the USA this is the ONLY acceptable type of windshield material.
For a time I had a small grey market car importing operation. My largest expense was replacing European bulb type headlights and taking the tempered glass windshields out and replacing with AS-1 glass.
Lexan or other polycarbonate material will not stand up to windshield service because the UV stabilizing materials added to the mix makes the plastic soft, without it the material will craze in a couple of months of sunshine. I have seen 1-1/2" Lexgard (Lexan/glass combo) used in custom bullet-proof applications but require a special DOT waiver waiver to be legal. This material will cost around $100/sq.ft. which is much more that even the largest stock windshield. Check with your local limo builder.
The reason that DOT and NHTSA want laminated products used for windshields is that it keeps the occupants inside the vehicle in case of a collision. I won't argue if that's the best solution, but that is the way it is. |
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