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Old 01-24-2008, 12:19 AM   #29
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Curvature issues....?

Dwightdi -

Saw your post and thought I'd add this question to the mix.

Are any of the types of "poly" you described more, or less, amenable to bending? Reason I ask, I have a front rock guard that need replacing, but it is a wing section ie it has a bend to it. Would REALLY like to see to this repair/replace myself..... but.....

Is there one or another, poly/ lexan/ other, that is better, preferable, or simply 'best' when it comes to replacement of these wing/bent units?

Just wonderin'

Thanks!

Axel
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Old 01-24-2008, 08:48 AM   #30
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There are two kinds of acrylic. The one they used was a thermal plastic and could be heat formed at about 250-290 F. It does not need to be dried before you heat it. It can be bent with a heat shrink gun or a paint peeler type hot air gun or radiant heat source. Polycarbonate should be dried before you try and heat it too high. It absorbs water in normal conditions and will bubble up if you try to heat it too fast. If you get it dry, you can bend it successfully when it reaches about 350 F. You can evaluate the amount of stress in either PC or acrylic by using a polarized light source on one side and an other Polaroid filter to look through from the other side. Rainbows indicate the severity of the stress. Slump heating, in which the material losses enough strength to simple relax and fall to contact a wood mold give the least stress. A little gentle encouragment usually is not too bad. A cold bend with result in high stress in PC and will crack acrylic. By the way, some sheets Acrylic also comes as thermal set grade material and will not lose strength when heated and so can not be formed.
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Old 02-29-2008, 11:01 PM   #31
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Question Window Question

Dwightdi,

I've got a '49 Spartan Mansion I'll need to do curved window replacement on. It still has the original (I assume) acrylic in place but is badly star marked and crazed. Most of the Spartanizers seem intent on Polycarb but unless they use enough thickness (requiring heat bending) the windows tend to blow/pop out on them. I would probably use Polycarb too if I could but in my research I too found that drying is required to stress relieve/ bubble prevention. I'm familiar with resin drying (I work with PET injection molding and stretch blowmolding at the bottling plant where I work), but wonder if you could give me some info on Sheet material drying. Is this something that could be "homebrewed"? I work in maintenance and have the tech skills to build apparatus or a heating oven but I don't know anything about reqd. temp/ dewpoint, time to dry etc. Is this feasible and or worthwhile, or should I stick with Acrylic/ Plexi that doesn't require drying to heat bend? ...I guess 59 years is pretty good for the original windows. Also, what should I look for in fade/ UV protection. Any books on the subject you know of?

Thanks, Brad
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Old 02-29-2008, 11:22 PM   #32
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Try this

When I was restoring my old Fighters I had a canopy maker in LA make several plexiglass/acrylic canopys for me. He made a plaster form and heated the material over the form in a large oven affair. There are several places where you can still have that done and I am sure your windows would not be a problem.
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Old 03-01-2008, 12:12 AM   #33
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I've never heat formed anything this large before but interestingly enuf I too was thinking of a plaster form cast from the inside surface of the original. Did your source use any coating/covering over the plaster or just on the bare surface? I seem to remember reading once of laying felt or flannel over the forming surface to protect the plastic from damage.
I have access to heating elements from several machines where I work so the oven shouldn't be too much trouble. I also have a buddy who has done Plexy/ acrylic forming as a resource but he does'nt have any background in Lexan/Polycarb drying if I were to go that route.
The more I mull this over the more I'm thinking Plexy may be the cheapest, easiest route to take.

Thanks for your info,

Brad
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Old 03-01-2008, 08:43 AM   #34
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mold covering

Yes, the plaster mold form was covered with a felt or cotton cloth.
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Old 03-01-2008, 09:02 AM   #35
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GE owned and produced Lexan until recently. They had some very good Tech literature which might be available off the web. Sarbic recently bought the name, business, and people from GE. I have not done business with them yet. Drying proceedures and vac forming used to be in their literature. You need to be about 220 F to get effective drying. You need to be about 100 F higher temps to do the vac forming. From memory, I think it was about 350F. Acrylic would be easier to do and half the money but can be fairly easily broken by flying rocks. Spartans were never intended to be really road machines like the Airstreams and so did not need to be as resistant to abuse.
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Old 03-01-2008, 11:23 AM   #36
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As the story goes the USAF exported their canopy chicken cannon to Canada or Britain so they could check their latest NATO design and completely destroyed several of their best designs - As you can imagine it took some long-distance trouble shooting over velocities and mounting etc. and it was by deduction from a description of how messy a raw chicken can be that it dawned on the other end of the line "Oh gawd - you mean we should thaw the bloody birds!...

Mar-guard scratch resistant lexan is great stuff and comes in some 20% tints, but the lexans and polycarbonates etc. with scratch resistant coatings will not heat form without stripling the coatings into zebra stripes.

Rain-X does a great job reducing hazing - crazing - sand blasting - UV damage on polycarbonate. Be generous so it can fill the pores and dry slowly in the pits and scratches, use a couple of coats.
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Old 03-01-2008, 11:27 PM   #37
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As to drying Lexan/ polycarb....... Is the drying done with dehumidified (over a desicant bed)air or just by heated air only. The dryers we use for resin drying are hoppers which have dehumidified and heated air blowing thru them. I didn't know whether the desicant was required for lexan or not. Anyone know???
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Old 10-31-2010, 04:10 PM   #38
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Originally Posted by Melody Ranch View Post
Hey....if you have a star crack showing...its not Lexan. It won't do that.
Also, when you get the new Lexan be sure its SR (scratch Resistant). If your in the Dallas area go to ABS Plastics....I have to check that name if your interested. They will cut to size, and have many tints of color and thickness selections.
Hi, I'm a newbie with a 66' Caravan to renovate. After much research I am suspecting those metal covers on the outside front window is called a rock guard? We can order it from vintage trailer supply or ____? Is this place in Dallas put in new windows or rock guards or both? We are 3 hrs from Dallas.
We need one window (plexiglass?) reinstalled, it was caulked (?) messily in place.

Jerri
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Old 11-01-2010, 04:13 AM   #39
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The original curved windows in a 66 were actually glass. Some people were putting Plexiglas in as replacements, when the originals got broke. I was at an auction yesterday that had a unit for sale that had two Plexiglas windows. Recently, a restoring supplier has developed a glass source for "similar to the original" glass windows. They are a bit pricey but you choose. I have had a Lexan window in the side of my 63 for 25 years. It is now getting yellow and foggy.
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Old 11-01-2010, 06:48 AM   #40
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Bill Lear made the same frozen chicken mistake when testing the windscreen on the LR23. He originally wanted to sit in the cockpit during the test as a demonstration of his confidence. Fortunately the engineers were able to convince him otherwise.
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