Polycarbonate Windows Lexan

[Geo]

Hi all,

I am getting ready for warm weather and plan to replace the rear quarter windows and windshield with polycarbonate Lexan.  A few questions may be odd, but I’m new to polycarbonate windows.  Looking through the rule book section 3.U.  How does using polycarbonate apply to 5.E.3 Grand Touring Sport “the stock windshield may not be removed or lowered”?

I would like the joint to be watertight.  Can I glue it in or is bolting the only way?  If glued in using a flexible product made for glass windshields then the joint will be watertight.  If bolted in then what is suggested to seal the joint?

I plan to use three windshield supports on the inside from the top of the windshield to the bottom, NASCAR style.  Any thoughts on placement?  One in the middle.  Then move towards the curve, with the curve being strong, placing another right in front of me inboard of the curve on the flatter center section of the windshield.  And the matching third on the passenger side.

How about placing the windshield retaining tabs at the point I have the internal braces?  This will allow me to bolt through the outer retaining tabs, body and then inner support brace.  Making a sandwich, with the Lexan as part of the sandwich or left out? 

I think the roof rails (4.X) will be too far outboard to meet the windshield supports allowing a combination of roof rail and retaining tab.  No holes have been drilled yet.

Thanks for your thoughts.

Geo

[Milwaukee Midget]

I'll add to Geo's question - how does one put a curve in Lexan or Poly?  I've never been down this road. 

I guess I'm fortunate with a windshield frame that is completely removable and can be disassembled.

[38Chevy454]

I'll add to Geo's question - how does one put a curve in Lexan or Poly?  I've never been down this road. 

I guess I'm fortunate with a windshield frame that is completely removable and can be disassembled.

As for putting a bend in the plastic, it works for one direction by just doing it room temp, but for compound curve you need to form the plastic.  I used to run lexan windows in my drag car (70 Camaro) and the fornt windshield was close enough just bent one direction, even though factory had slight compound curve.  It was attached with screws along the edges and then factory window trim over the screws to look nicer.

Hi all,

I am getting ready for warm weather and plan to replace the rear quarter windows and windshield with polycarbonate Lexan.  A few questions may be odd, but I’m new to polycarbonate windows.  Looking through the rule book section 3.U.  How does using polycarbonate apply to 5.E.3 Grand Touring Sport “the stock windshield may not be removed or lowered”?

I would like the joint to be watertight.  Can I glue it in or is bolting the only way?  If glued in using a flexible product made for glass windshields then the joint will be watertight.  If bolted in then what is suggested to seal the joint?

I plan to use three windshield supports on the inside from the top of the windshield to the bottom, NASCAR style.  Any thoughts on placement?  One in the middle.  Then move towards the curve, with the curve being strong, placing another right in front of me inboard of the curve on the flatter center section of the windshield.  And the matching third on the passenger side.

How about placing the windshield retaining tabs at the point I have the internal braces?  This will allow me to bolt through the outer retaining tabs, body and then inner support brace.  Making a sandwich, with the Lexan as part of the sandwich or left out? 

I think the roof rails (4.X) will be too far outboard to meet the windshield supports allowing a combination of roof rail and retaining tab.  No holes have been drilled yet.

Thanks for your thoughts.

Geo

Geo, you can use the stock rubber gasket if you make the plastic the same size as the glass you removed.  Gluing in you need to have something hold it in place while it cures.  If you have to bend it, as in above question, it will want to spring back.  You would need some screws or other mechanical means of holding it in place.

Plastic scratches easier of course and will not work for defrost in a cold weather driver.  I realize you are referring to a warm weather race car though.

Not having a rule book in front of me right now, I would guess the windshield not removed or lowered means it has to be full factory size and height in place on the vehicle.  Just out of curiousity, why do you want to not use a glass windshield?

[Geo]

Thanks for the ideas and check on my plans.  The factory windshield glass and quarter windows are glued in as is the metal trim with a thin plastic trim edge.  The door glass is clamped at the bottom to guide rollers and does not have a guide channel or frame above the door metal.  Only the rear window has a rubber gasket.

My fear is to have a door window glass break and my racing be over for the week.  I also need vents and would rather not break the factory coatings on the metal.  So a plastic window would be less likely to break and easy to add a vent to.  There are some inexpensive Lexan windows from race teams available that can be trimmed to fit.  

Gluing in you need to have something hold it in place while it cures.  If you have to bend it, as in above question, it will want to spring back.  You would need some screws or other mechanical means of holding it in place.

I need to remove all the glass to finish welding and paint the cage.  It would be a good time to install plastic.  I have been on some airplane forums reading about attaching canopies.

The car will not be driven in cold weather.  Although I would love to keep the AC for cold weather inside the car for the first year while we sort out the car and ourselves.  

Anyone know the forming temp of polycarbonate?

Geo

[hitz]

It's around 270 deg.F

harv

[doug odom]

Be careful here. You can not just heat up lexan and bend it. First you need to raise the temperature slowly for a long period of time to remove the moisture in the Lexan. If you just heat it up you will get bubbles in it from the trapped moisture. You can find on-line the correct way to to this I believe it was from DuPont or who ever the manufacture is.

[Geo]

Adding info as I find it for others who may be interested.

The contractors who do most of out LEXAN guards & such have a series of long, straight rods that resemble electric oven heater elements. They simply lay the LEXAN on the element, turn it on, and wait for it to bend right on the line from gravity. Don't know what temp they use, but a few scraps would probably get you very close.

THERMAL PROPERTIES:
Melting point : 310° F
Heat deflection at 66 psi (ASTM D 648) : 285° F
Heat deflection at 264 psi (ASTM D 648) : 270° F
Maximum serving temperature for short term : 275° F
Maximum serving temperature for long term : 240° F

Polycarbonate sheet must be dried before thermoforming because polycarbonate absorbs moisture at a high rate. Trapped moisture forms vapor above 250°F, and the vapor expansion creates bubbles in the sheet. Sheets of polycarbonate should be placed in a dehumidifying air circulating oven for predrying with approximately 1" separation between sheets. Oven temperature should be 250°F and monitored with controls. Recommended predrying time periods are shown below. A note of caution-polycarbonate sheet begins absorbing moisture immediately upon removal from the predrying oven. The rate of absorption is dependent upon the ambient dew point. For this reason, it is crucial to transfer the sheet directly to the forming machine as quickly as possible.

Gauge
   
Drying Time (Hours)
.093" 4
.125" 6
.187" 14
.250" 24

San Diego Plastics, Inc.
http://www.sdplastics.com/polycarb.html

TAP Plastics
http://www.tapplastics.com/shop/category.php?bid=11&

Port Plastics
http://www.portplastics.com/architect/page22.html

http://www.trivalleyautoglass.com/custom_cut_glass.cfm

sign manufacturers

2005 X? spoke with a polycarbonate representative from GE (the company that manufactures Lexan) and they have all sorts of experts who will help you with this project. In fact, a person included on my conference call was a thermoforming expert.

One very unhappy boatbuilder I know had to replace all of his installed windows because he cleaned up a bit of caulking around the windows with some acetone.

Geo

[saltfever]

Excellent post, Geo. Thanks for sharing the research and all the links. Please keep us informed on your progress.

Why three braces? NASCAR bumper cars are assuming they will be plowing through flying debris from crashes and need the bracing for impact resistance. NHRA 300+ MPH funny cars only have one brace in the middle. I guess it would be based on your planed speed though.

Can you give a source of some of these used racing windows.  Thanks.

[krusty]

    "NHRA 300+ MPH funny cars only have one brace in the middle."    And they're only seeing 300 for < 0.1 sec. I would guess that they'd trade the weight for the short time of distortion. On a Cup windshield, especially on  Daytona and Talledega cars, the windshields have extra bracing (usually located based on wind tunnel visuals) to minimize distortion which adds drag.