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chergui
12-25-2004, 08:57 PM
Is there anyway to restore clouded Lexan? I read that you can apply something called NOVUS No. 1 and 2 to remove/restore the clouded layer. Would it be possible to sand it down first and then apply these chemicals or would sanding scratch it so badly that nothing could save it? Anyone tried this before?

ion barnes
12-26-2004, 01:42 AM
No sanding! Lots of elbow grease and fiberglas cut polish. Same stuff you can get for f/g shower stalls. You might try an electric buffer, but I have not done so. Just elbow grease.

carioca1232001
12-26-2004, 05:00 AM
Is Lexan the same as Polycarbonate ?

Well I have successfully cleaned up the Polycarbonate windows on my boat as follows:

1 )First wash the surface well with warm water and soap;

2 )Use a clean swob with kerosene - no thinners please , or you will wreck the polycarbonate - to wet the surface thoroughly for the next step;

3 )Put some N 2 (N1 is too coarse) polishing paste - sold in paint shops to polish faded car paint - on a swob of cotton fibres (used by mechanics) and "elbow grease" the foggy surface in circular motions, until your elbow gives up;

4 )Top-off the polishing CAREFULLY with a circular polishing pad (made out of successive layers of "jeans" material, stitched together,about 1 cm. thick)attached to an electric drill, until nearly all the polishing N 2 paste disappears.

You should now end up with a clear piece of polycarbonate.

carioca1232001
12-26-2004, 05:20 AM
Addendum:

To 4 ) above..... hold the pad-cum-drill contraption at an angle to the polycarbonate surface , bucking the pad as the drill turns, thereby using the circumference of the pad, plus a portion of the pad surface.

Do not polish spot-on, as the pad boss will ruin the polycarbonate aside from rendering an inferior result.

Should a different soft of buffing pad be used, make sure it is as "aggressive" as the jeans material sort. Foggy polycarbonate needs some mild persuasion before it is restored !

raycon
12-27-2004, 10:42 AM
What are the physical dimensions of the part you're trying to clear?
Look up polycarbonate/lexan methylene(sp?) chloride vapor bath on the web. Locally there is a machine shop or two that perform this service --post machining of engineering prototypes clears the part of machining marks. 104 degrees F ten seconds and you're back to a clear surface. Nasty stuff though call a material supplier(polycarbonate) and talk to there engineering support they'll give you the low down and read the material safety sheet not something you'll want to do in the kitchen.

John Blazy
12-27-2004, 11:16 AM
Yes, Lexan is a brand name for polycarbonate. For bad crazing and deep cloudiness, you MUST sand first. As a plastics supplier, I know what I'm talking about. Key is to sand with the correct grit.

Start off with wet/dry paper (at automotive supply) @ 1000 grit (wet) unless scratch / haze is too deep, then go 800 grit.

Then go 1500 and then buff with the Novus polishes or automotive rubbing compound (essentially the same).

Do a small area first to see if the 1000 grit will do it ok (go through all the steps to polish to see), then do the whole surface.

Use to foam pad (for polishing compound) on a drill, hand polishing is not aggressive enough to remove the 1000 - 1500 grit scratches.

carioca1232001
12-27-2004, 11:22 AM
I had heard about the methyl chloride technique, which requires strict temp/time control etc., prior to restoring polycarbonate as I have outlined above. Twas a tough nut to crack.

Wonder though as to what the machine shops charge for the high-tech solution - just short of buying new polycarbonate to make you feel happy ?

raycon
12-27-2004, 11:41 AM
First time I tried it was over a hot plate with the methylene chloride in a baking pan. Temperature was set to WARM not much temp control --that was 15 years ago still do it the same way for small parts .
Small part being less than a foot in width. Helps having a chemical fume hood.

carioca1232001
12-27-2004, 12:05 PM
Curious to know why the size limitation for the polycarbonate to be restored.

Due to size of baking tin, hot plate and/or fume hood ?

When I heard about this technique, the methyl chloride needed to be par-boiled/boiled in a stoppered beaker over a flame, and a tube with the vapour directed onto the target surface, with no size limitation as far as I recall.

raycon
12-27-2004, 12:21 PM
When the parts were larger I used a local machine shop that specialized in machining plastics they have a commercial vapor bath blower -- used to clean up large extruded sheet where a vent or sheared surface may have caused a surface imperfection.
We used clear polycarbonate for housing prototypes so the mechanism inside could be seen. The housing were often small (surgical hand tools) no need to go larger. A lot of our saftey shields on machinery are polycarbonate and are as large as 4'x8' 1/2" thick -- these we send out once every few years. When you're doing large surface areas you have to be patient to not create runs in the material--stand off distance from the vapor bath controls this.
I don't like to use methylene chloride in general so thats one of my self imposed limitations not so much size but it does the job.

carioca1232001
12-27-2004, 12:40 PM
I read you now. No wonder you are able to do it at home ;)

I still stand a very good chance of ruining the lot, if I choose this route. :D

Frank Wentzel
12-27-2004, 01:05 PM
For anyone who is tempted to try the methylene chloride routeplease make sure you have a very good fume extraction system and use a proper chemical vapor respirator - supplied air is the best way to go. MC is one of the highest toxicity solvents commercially available. Very easy to screw up your liver with it.

/// Frank ///

raycon
12-27-2004, 01:33 PM
I do it in a shop environment never at home nor would I try it at home. Like Franks said its nasty stuff.

carioca1232001
12-27-2004, 01:51 PM
I imagined that it would be a toxic substance, say like polyurethane paint fumes - but never that toxic as Frank has correctly made out to be.

For the record, innocent-looking ethylene glycol knackers your kidneys permanently if ingested, amongst other nasty things it does.

In the interests of all, we should exercise some caution on this Forum about proposing schemes that have catches to them - the unsuspecting ones amongst us may otherwise run the risk of endangering their lives.

Some time ago there was a helpful fellow giving me inside knowledge on how to brew my own red (or white) lead, but the "please dont do this and that" tipped me off that it could be a near deadly thing to do.

chergui
12-28-2004, 01:03 PM
Hi all. The Lexan windows are about 14" wide by 8" high. My boat is 15 yrs old so it is starting to cloud over. There are no crazes and I can still see through the window, it's not that bad. The only reason I'm doing it is because the window is leaking and I need to take it out to rebed it. I think I'll avoid the methyl chloride techique and try John's suggestion.

Jon

[ 12-28-2004, 01:22 PM: Message edited by: chergui ]

Paulyboy
01-04-2005, 11:28 AM
You can use plastic polish sold for people who need to clean the rear window in convertible top applications. These are all available at automotive paint supply houses or larger auto parts stores. You can also use metal polish, such as Flitz, and use a buffer wheel with a small hand held drill. I've used both on Lincoln towncar headlights, which are polycarbonate (most auto manufacturers use polycarbonate as opposed to glass for their headlights) with good results. The metal polish is a shade more aggressive than the plastic polish, which is used more for fogged up or hazy plastic.

cbob
01-04-2005, 08:17 PM
cher, My windows are about the same size, eight of them. The first 20 years were a light blue plexiglass, replaced for chemical damage, age and leakage, the next ten years was a bronze tinted plexiglass, changed for leakage and windows letting in light should be clear, IMHO, so went in with Lexan, amazingly strong and tough, used in error 5200 and in five years these suckers were leaking and embarrasingly crazed, and power polishing adjacent to bright work was a royal pain, and not lasting, dunno why? I learned later that some lexans have one side that should face the elements, the outside? anyway , I bit the bullet and put in tempered glass on Sikaflex, and have been very happy since. These are installed from inside, not the best way, and the only caution is that plastic will take some bend, glass, well you know. It's worth a thought. Or, if youre taking them out anyway, think about some new lexan, proper side out, on something good for this application, not 5200 type stickum/bedding. cbob

chergui
01-06-2005, 10:29 PM
I'm waiting for the rain to stop for a bit until I start Maybe I'll practice on my car headlights, now those are bad. Speaking of sealants, I searched the forum here but still couldn't get a clear answer of what to use. I chose BoatLife Life Seal because they say it is good for Lexan to wood. Has anyone used this before for sealing windows?

Bruce Hooke
01-06-2005, 11:22 PM
I had good luck cleaning up crazed Plexiglass with Soft Scrub. However, the crazing did come back within a year. I don't know if Soft Scrub would work on Lexan but it sure would be easy to try!