Aluminum Vacuum Deposition on Thermoplastic

Maybe you can use one of those rescue blankets, found in ABC rescue kits.

They are made of 12uM mylar plastic coated with very reflective aluminium.

Jonas in Malmoe, Sweden

One way is to fix a Garware or 3M Sun control film over a chamber ensuring it is leak tight. Evacuate the chamber to get the desired curvature. A circular chamber will give a spherical mirror and a rectangular one a cylindrical mirror.

Rather than vacuum deposition, have you looked into electroless plating? It can be done on plastics, and may be cheaper. Typically, the plating is Ni or chrome, which may be better choices for a mirror anyway.

If you use aluminum, you will want the supplier of the aluminum deposition to coat the surface afterward with a clear finish like acrylic. That will keep the aluminum from being damaged and prevent it from oxidizing later, which would make it lose its shine.

Hello,

Am I correct in assuming that you're trying to build "solar troughs" to help concentrate the sun's rays onto a solar thermal collection tube? I am currently building such devices for my own solar project.....

Have you investigated adhering a metallized mylar plastic film to a PVC pipe cut longitudinally in half? There are several suppliers of said film located in Ebay where the rolls of film are relatively inexpensive. Please note that not all mylar films are created equally. You'll have to check the percentage of reflectance for each product. Some are down around 90% whereas some of the much better ones are up around 97-98% reflectance.

Good luck, and please, have a great sunny day!!!!

Interesting project CM

What do you think the life expectancy of the film [or PVC] will be?

I had pondered doing a slightly larger version using construction similar to skate ramps, thin masonite bent over cut 1 inch plywood forms.

we were going to preheat used vegetable oil for biodiesel production, we had gotten fairly impressive results just string out 1" black drip tubing on the ground here in sunny cali...

we were arguing about whether the increase in efficiency was worth the added expense of fabricating such a tunnel

we had anticipated using cheap 2" black iron pipe, plastic would limit which part(s) of the process we could run through it.

the project never hit the top of the list before the company went belly up..

Hello Garthh:

In response to your posed question: I do know that some of the premium metallized mylar films are UV stabilized. From what I have read so far, and I'm still in the research stage so-to-speak here, that the films will start to degrade possibly 5 to 7 years after being placed into service. I guess it all depends on the environment that they're exposed to while in service. Here in upstate NY we get a tremendous amount of Snow and freezing rain during the winter, and a good amount of rain the rest of the year, although we don't get the amount of sun like you'd get in CA, so it's really hard to say exactly how long the films will last without long term testing. I surmise that probably the weak link in the whole shabang will be the adhesive used to adhere the film to the PVC pipe trough.

Looks to me like the first dozen years will be trial and error testing until I eventually get everything right! ***LOL***

Have a great sunny day! It's beginning to snow here this AM......the first of the winter....and the Old Farmer's Almanac says it'll be a long hard and cold one at that! ***YUK***

I am not aware of Noida, but in Mumbai I have tried this. Acrylic gives very good results and after aluminium deposition, is as good as any mirror. The deposition is 4 microns. This is good for a solar reflector.

The best results are with Polycarbonate, the reflectivity is far better than any other plastic. However, polycarbonate is almost double the cost of Acrylic sheets

In Mumbai, I paid only Rs. 15 per square foot for the deposition.

Rajesh

We used a zinc coated steel easy to be moulded into curvature and used an aluminium foil to wrap over it, they just perfectly got cold-welded.