Subject: Reflective Surface Needed

From: [email-masked]
Date: Mon, 3 Apr 1995 15:36:48 UTC

From: tcupp (Terry Cupp)

  I am in the process of making a 10' parabolic mirror out of an old satilite
  dish.  I have found some reflective silver plastic which works well for a
  while, however after a few months the sun fades and cracks this material. 
  Does anyone know of a flexable material that would hold up to the sun for a
  longer period of time.  I live in Las Vegas so the material will be exposed
  to alot of summer dry heat.

Aluminum foil, shiny side up?  Then you just need to worry about finding a
suitable adhesive.

Stainless Steel Auto Body 'repair'/trim tape?

Jim Baranski                     ! Note:  I use the Anon Server to Post because
Norwich, CT                      ! I don't have a Posting Host. So I include my
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From: Cyberberus <[email-masked]>
Date: Mon, 3 Apr 1995 20:41:02 GMT

>   to alot of summer dry heat.

  Check out the reflective mylar sold at indoor garden places.  It *is*
humidity sensitive but I found that if you sandwich it between 2 pieces
of plastic (I use 1/16 LEXAN on sun side and 1/16 plexiglas on back) and
seal the edges that it holds up quite nicely, at least here in Michigan.
I use a V channel of this with black plastic pipe as a passive hydroponic
solution heater in the winter.

Re: Reflective Surface Needed                                                R

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From: Robin van Spaandonk <[email-masked]>
Date: Wed, 5 Apr 1995 08:20:18 GMT

>Date:    Mon, 3 Apr 1995 13:33:42 -0700
>From:    Cyberberus <[email-masked]>
>Subject: Re: Reflective Surface Needed
>
>[snip]
>Re: Reflective Surface Needed

If this sandwich layer were simply suspended between two supports
that were slightly too narrow, wouldn't it form a nice curved trough
to concentrate the suns rays? (And cheap at that!). If not strong
enough, then either make it narrower, or use thicker plexiglass.
For that matter, there ought to be a market for aluminized
plexiglass, i.s.o. mylar. This should enable very cheap solar thermal
power.

Regards,

Robin van Spaandonk <[email-masked]>
Re: Reflective Surface Needed

---

From: Cyberberus <[email-masked]>
Date: Wed, 5 Apr 1995 09:35:31 GMT

<original msgs follow>

  Unfortunately Lexan does not bend and still maintain its transparency,
it tends to form cloud lines and/or hairline stress fractures, for curves
you generally have to buy it pre-formed.
  Plexiglas will bend to a certain extent but its transparency value,
well .. it sucks .. the stuff eats light.

        Form                    reflective%     Note
        Reflective mylar        95%             As is, perfectly smooth.
        reflective mylar        93%             normal home installation.
        mylar backed Lexan      91%
        mylar backed plexiglas  82%

  The reason I use plexiglas as the back of the sandwich is because it's a
*cheap* way to weatherproof the mylar ... since you have to use the
ultraviolet-resistent/transparent form of Lexan (or replace it every year)
the cost of using it on both sides of the sandwich drives the total cost
up to the point where it's no longer a savings except in the *real long*
run. The only reason I could afford it at all was it was "scrap" (ie
miscut sizes) and it wasn't cheap.
  BTW: if anyone plans on using this sandwich a couple pieces of advice.
1)  Buy the 2 mil mylar, its actually more than double the cost but the
  added thickness make the surface smoother which increases reflectivity
  by 1-2% ... and its easier to handle ... less chance of wrinkles.
2)  *Don't* use adhesives except on the very edge, it *will* cause wrinkles.
3)  When you seal the edges make sure you clamp the whole piece as firmly
  as possible to exclude as much air as possible.

Have fun!