Thread: Lexan Hood

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I did spend a small furtune on my blown 392 hemi.
all nice aloy parts and its gona look great.
This engine is going in my 1957 imperial.
I don't want to hide this engine under the hood.
Any sugestions for a clear see trough hood.
I an thinking of lexan or epoxy.
Regards
Remco
The Netherlands

Lexan would be good except for the yellowing that occurs when it ages. This effect can be sped up by exposure to UV. Another type of clear resin may give you some longevity.

I had a friend in the early eighties who had a smoke tinted see-through hood on his black 1965 Corvette. It was nice, since you could see the engine, but still had a sense of the cars styling.

Lexan - a polycarbonate trade name - available at Home Depot in various thicknesses works well.

The yellowing bit doesn't seem to happen due to modern Lexan has an Ultraviolet resistant coating on it.
It will be noted on the protective paper so be sure to orient the coating side toward the sun.

I've been running Lexan windwings in my 32 roadster for the last 7-8 years.
No problems except for where some clown dragged his diamond ring across it to check whether it was glass or not.
Other than that, no scratches and all I do for maintenance is wash them when I wash the car.
With for-real car soap fwiw . . . no dishwashing liquid for me . . . unless Sweetie asks me to do the dishes....

I have spent the last two decades in the aircraft transparency business (that's somebody's idea of a snooty way to say "aircraft windows, windshields, and canopies") both in manufacture and overhaul/repair of those parts. I probably can tell you quite a bit more than you really want to hear about Lexan and the acrylics used in airplane and helicopter parts.

If you like, send me a private message with your e-mail address and I'll get back get back to you. We can discuss exactly what you have in mind.

Polycarbonate is wonderful stuff. It's extremely tough and resistant to cracks and crazing (Lexan is polycarbonate). If it has a downside, my experience is that it very susceptible to chemical damage, like maybe paint stripper and other solvents. Also, scratches and other surface damages are very difficult to repair. Acrylic, and particularly "stretched acrylic" might be a better choice. Most airplane windshields that aren't glass are stretched acrylic now.

Incidentally, acrylic doesn't like stripper, either.

As I said, send me an address. I'll be glad to help if I can

Jim

PC is great stuff and as bigun said it scratches really easy. We use PC and ACR to vacuform all of our sign faces. I have been doing this stuff for 10 years now and formed ACR is very tough, doesn't scratch, and is resistant to UV. Duraplex is a wonderfully strong ACR for forming nearly any shape under 3'' deep. sign

Originally posted by Big Tracks
I have spent the last two decades in the aircraft transparency business (that's somebody's idea of a snooty way to say "aircraft windows, windshields, and canopies") both in manufacture and overhaul/repair of those parts. I probably can tell you quite a bit more than you really want to hear about Lexan and the acrylics used in airplane and helicopter parts.

If you like, send me a private message with your e-mail address and I'll get back get back to you. We can discuss exactly what you have in mind.

Polycarbonate is wonderful stuff. It's extremely tough and resistant to cracks and crazing (Lexan is polycarbonate). If it has a downside, my experience is that it very susceptible to chemical damage, like maybe paint stripper and other solvents. Also, scratches and other surface damages are very difficult to repair. Acrylic, and particularly "stretched acrylic" might be a better choice. Most airplane windshields that aren't glass are stretched acrylic now.

Incidentally, acrylic doesn't like stripper, either.

As I said, send me an address. I'll be glad to help if I can

Jim

It's very nice that you've offered to help via email.

I'm sure I'm like many others here on the board and would like to learn more about Lexan as well as the stretched acrylic you spoke of and perhaps where to get it.

Why not post the questions and answers here where we can all learn something?

If you're going to be doing a lot of typing you may as well reach the largest audience possible.

Can I use the original hood as a mold.
How should I prep the mold.
can the stretched acrylic ( have no clu what this should be called in dutch ) be formed the same way as Lexan.
I have read that there is a scratch resistand coating for lexan.
How about scratching of the acrylic.
I don't plan to use paintstripper a lot.
But how about petrol and oil products.
A long long tima ago when I was at school we made boxes out of lexan for electronic components.
We heated the material with a kind of paintstripper heat gun.
Would this work on something as big as a hood .
Or is this better done by a profesional.
Regards
Remco

You will need professional help. A vacuforming press is what you will need to form a piece this big. Look in your area for anyone forming ABS, Lexan, Acrylics. Possibly a large sign manufacturing company.

Well, C9, you’re right, of course. This is, after all, a forum, and two guys B.S.ing doesn’t exactly constitute a forum. I’ll put down some random thoughts pertaining to acrylics and to Remco’s project.

First, m falconstein is right on. Remco needs to call in the pros.

Remco asks if his present hood might be used as a mold. Well …… conceivably, I guess, but we’re not talking fiberglas here. A piece of Lexan or acrylic would have to be really big to make a hood for an Imperial. It would have to be heated to a temperature of 300 degrees (plus or minus) then carefully and expertly placed on, and held to, the hood/mold. Male molds are successfully used in some applications. Cessna Citation windshields are formed on male molds. A sheet of stretched acrylic is hung vertically in an oven and heated at 300 degrees until it reaches the proper state of softness, or flexibility, or “rubberyness”. Whatever. It is then rolled out of the oven and is grabbed by four big dudes wearing asbestos gauntlets who quickly move it to a big sort of mushroom shaped tool that has been covered with a very fine textured felt. They carefully place the sheet on the tool and pull down hard on the corners and hold tension on it for a few moments until the material begins to harden. When the part is cold, they bandsaw it to a rough shape. They then put it into a fixture and use a router to cut it to the exact shape. The system works for them, but to try it for something as large as an Imperial hood could be challenging!

Our friend m falconstein utilizes vacuum molding in his business. This is the best and most used system for items with compound curves. Simple curves, like maybe an airplane cabin window, can be formed on a drum the same size and contour of the window. Usually vacuum is applied to hold the plastic snugly to the drum or tool. A Learjet windshield is a curved flat piece of stretched acrylic, but I’m not sure they use this method.

Stretched acrylic? Well, acrylic sheet comes in two flavors. “As cast” and “stretched”. The stretching process is interesting (at least to me). The acrylic comes in a big slab about six feet square and six inches thick. It is placed horizontally in a machine and pneumatic finger-like clamps are attached every few inches around the perimeter. Then heat is applied and the clamps pull outward and literally stretch the acrylic block until it is the desired thickness.

Why stretch it? During the stretching process the molecules … no, that doesn’t sound right … the polymers, maybe? …. I don’t know, are caused to realign themselves and make the product much stronger than it would be were it not stretched. This way a part, say a window, can be much thinner and therefore much lighter, and at the same time will be stronger than as-cast. Lighter weight is big time important to an airplane company.

Back to Remco’s Chrysler. A piece if cast is much less expensive than a piece of stretched. A hood made of cast would be thicker and heavier, and that ain’t necessarily bad. A man driving an Imperial may not be too concerned about weight, for one thing, and a thin hood would be likely to flex and flap up and down when he drives, because I doubt that he will want to keep the ugly supporting stiffeners that are under his steel hood. The object is to show off his engine under a see-through hood, isn’t it? He might do well to cut the largest tastefully designed holes he can think of in his present hood (without making total scrap of the hood) then firmly installing some thick (half inch or so) Lexan or cast acrylic windows on the inner surface of the hood. That way he could retain some of structural integrity he would lose when he cuts out that reinforcing support metal.

Well, C9, I told Remco I could probably tell him more than he really wanted to hear on this subject, and I’m sure I have done so. I hope everybody doesn’t put me on the “ignore” list because of it.

Jim

Hey Jim, how about some advice on a formable, light weight material for making windshields and sideglass for a chopped car??? I've always used Lexan, is there a better product with a bit more scratch resistance??? Thanks for the offer on the help, appreciate it.

Dave, both materials (Lexan and stretched acrylic) are excellent.

For impact resistance I'd go with the polycarbonate (Lexan). I saw a tape a long time ago demonstrating Lexan's strength in that area. An airplane windshield was very solidly attached to a fixture in an angle similar to the one it would have in a corporate jet type airplane. To simulate a bird strike situation, chickens, like you'd buy at a grocery store, were fired from an air cannon at maybe 300 mph (a guess on my part) directly at the windshield. The windshield bowed way in, it looked like two or three inches, but it didn't shatter or even crack. Lexan is tough material!

But since the liklihood of your encountering a duck flying 300 mph while you are out on a Sunday drive is small, I'd use the stretched acrylic. It is, as m falconstein indicated, more scratch resistant than Lexan. I'm not saying stretched can't be scratched, it can, but when it does get scratched, the damage is much easier to polish out than it would be on Lexan.

I have never worked in either purchasing or sales of these products so I don't know who sells smaller amounts of these products or what they would cost, but my guess would be that a company called "Aircraft Spruce and Specialty Co." would be a very good place to look. They sell just about everything for people who build their own airplanes. I'm sure they have a website.

I have only made one acrylic window for one of my vehicles. The lovely child of one of my former neighbors (I'm certain that's who did it) was given a pellet rifle. He decided to test it by shooting at the drivers side window in a 1970 Dodge 3/4 ton crew cab I owned. I bouight a piece of 0.250 stretched from my employer and made a new one and it worked fine and was still looking new when I sold the truck.

Good luck,

Jim