Re: Plexiglas or whatever

[protek@shreve.net]

Dick,
    These are good figures to know.  I have never researched Lexan's
properties and did not know where Harold got his 250 times figures.  I have
expressed my concern before to Harold but he is confident that the windows
are better than acrylic because he uses Lexan in his firm and really
believes in it.  He also tested a window to a pretty good depth, can't
remember what now, but he tested it to failure.  Of course, as I have said
over and over on here, a single test is not enough.  I don't think he dives
the sub anymore anyway.  Harold, in general, is a good designer.  His sub
"Intrepid" is a very workable design for what he used it for.  Just didn't
like his windows.  
    One other feature of his sub that I would have, and did do, differently
was his ballast tanks.  His design on either side of the conning tower
(Saddle bags) is easy to use and not as tricky as my end ballast tanks.
However, they are not really separate tanks at all but more like 5-sided
boxes welded onto the hull itself to form the 6th side.  His hull is 0.25
inch thick.  The problem with doing this is corrosion.  There are two big
areas of the hull that have NO paint and are just bare metal exposed to the
water.  He told me that when he blows the tanks, crud (rust) blows out of
the bottom of each tank.  I suggested adding an access door on each side to
allow coating the metal hull and inside of the ballast tank.  I have such
an access door on my sub's tanks, and yes, they are painted inside.

Gary Boucher

At 02:45 PM 3/31/99 -0800, you wrote:
>Gary,
>I did a little searching after reading your post and would like to
contribute the
>following to the thread.
>
>"LEXAN" is a registered trademark of the General Electric Company.  It is a
>polycarbonate resin available in a wide variety of grades and
formulations.  I
>counted 21 in the literature I have.  These formulations are designed to
maximize
>properties such as dielectric strength, modulus, moldability, flame
retardancy,
>and high heat capabilities.  The tensile strength for the various LEXAN
>formulations seems to stay around 8,000-9,600psi for most grades but can
go as
>high as 23,000psi when enhanced with 40% glass fiber.  Compressive
strengths are
>around 12,500-14,000psi.  There are different figures for the Tensile,
Flexural,
>and Compressive Modulus' but they are all around 325kpsi to 345kpsi (for
non glass
>re-inforced).
>
>In the ASME-PVHO Safety Standard the term "acrylic" is used for "cast
polymethyl
>methacrylate plastic" and is the only material they allow.  The minimum
tensile
>strength is 9,000psi, minimum compressive strength is 15,000psi, and the
minumum
>modulus (tensile and compressive) is 400kpsi.
>
>According to these numbers, normal general purpose "LEXAN" is actually
weaker than
>acrylic and would not pass the minimums for the standard!  The "250 times"
figure
>your friend quoted probably has to do with the impact resistance compared to
>glass, not the strength!  In one catalog I have they state lexan is about 250
>times as impact resistant as glass, 30 times more than plexiglass.  Again,
this is
>"impact resistance", not strength!  If your friend does not know
specifically what
>he has then he is diving in a window test chamber!  Please let your friend
know
>about these figures so he doesn't end up on the "accident data site".
>
>Sincerely,
>Dick Morrisson
>
>
>protek@shreve.net wrote:
>
>> Ray,
>>     I think you are right on all counts.  Lexan is a trade name for a
>> certain polycarbonate.  They are related to acrylic plastic.  It is used
>> for bullet proof windows.  I know of people using it for viewports, but
>> here is my reasoning why not to use it;  I know of no studies of this
>> material used in viewport designs.  It seems logical, but I just don't know
>> of any solid figures on it.  It is a lot more durable than acrylic and it
>> is far more shatter resistant.  I have heard though that it bends more
>> under stress when used in sub windows.  My friend Harold from Longview
>> Texas used it in his sub.  He has taken it down to 100 feet before and his
>> windows are slightly larger than mine.  He used 0.5 inch thick Lexan.
>> Personally, I think this is too thin for any window at 100 feet.  He
>> reasoned that Lexan is "250 times stronger" than plexiglass so it did not
>> need to be thicker.  I don't agree, but he has made 100+ dives, some to
>> better than 100 feet.  I can see why people want to use it for sub windows.
>>  However, the acrylic figures are there and it is tried and proven.
>>
>> Gary
>>
>> At 11:17 AM 3/31/99 -0800, you wrote:
>> >Hi,
>> >
>> >>From what I can remember is:
>> >
>> >1. Lexan is a trade name for one manufacture's polycarbonate.
>> >
>> >2. Polycarbonates are simular to acrylic but not the same thing.
>> >   Polycarbonates are tougher but more brittle than acrylic. Occasionally
>> >   a piece of polycarbonate being cut would catch in a saw and kick back
>> >   causing some nasty cuts. Vicious stuff to work with even with carbide
>> tipped
>> >   blades.
>> >
>> >3. Because polycarbonate is tougher it is the material used for bullet
>> >   proof (resistant really) glass.
>> >
>> >4. Can polycarbonates for used for view ports? I don't know. I would
consult
>> >   the viewport book.
>> >
>> >Regards,
>> >Ray
>> >
>> >> Okay, here's part  what I didn't know.
>> >>
>> >> >David,
>> >> >    The reason I use, and suggest the use of, acrylic plastics for
windows
>> >> >can easily be summed up. ....The main contender for replacement is
>> >> >polycarbonate (Lexan)....
>> >>
>> >> ...I just always thought of all this stuff as the same -- "Clear
Plastic"
>> >> -- And the different names being trademarks. Duh. I'm not even sure,
but I
>> >> think I recall the guy at the window place saying the stuff he was
putting
>> >> in my windowframes was "lexan." So... this is apparently polycarbonate
>> >> which is not what you're using. Is there a common brand name of acrylic
>> >> thrown around just as carelessly? Is "plexi-glass" (further
bastardized by
>> >> the careless "nucular" crowd into "flexi-glass") something else
entirely?
>> >>
>> >> If what I've got in my trailer is polycarbonate (or, to be on topic,
if I
>> >> use a spare hunk of it in an ambient sub or glass-bottomed boat)...
can I
>> >> polish it in a similar way?
>> >>
>> >>
>> >> ---------
>> >> David
>> >> buchner@wcta.net
>> >> http://customer.wcta.net/buchner
>> >> Osage MN USA
>> >>
>> >>
>> >
>> >
>> >
>
>