Headlight Restoration

[AKnowles]

My litronic headlights that i bought form eBay arrived, but then needed two things:

1) An amberectomy. Completed that with a butane powered soldering iron with a wedge shapped cutter. Pretty easy. Took less than 45 minutes form start to finish.

2) Restoration of the headlights. Some wear and tear due to age, but the rest is somehting else again. It is not pitting, but appears to be an overspray of some type. When I rub my finger over it I can feel it. Here's a picture of the light with a close up of the overspray.



Close up of area with overspray. It's the white curved area. There is also overspray or pitting like this on the bottom and left hand edge too where the blinker is located..



Here's what is looks like aftyer hitting it with a pneumatic orbital sander with 400 grit sandpaper. All wet sanded. FWIW: I tried it with the manual method first. No joy. There was a coating on it in some palces that could not be cut through without a LOT of effort and sanding that was not possible with the sponge sanding block provided.



Close up of overspray area.



Also, for those with an interest, the restoration kit is by mequires. I bought it because I did not want to use electric power tools, but I had no idea this was going to be so difficult to cut through the gunk on it.

Tomorrow I will wet sand it with 600, 1000, then 3000 and start the polishing with the Plastix polishing compound. I'll post pics of the finished results then. As it is taking so long to restore the headlights, I'll probably have to wait until next week to actually install them. Oh well, on the good side I guess that leaves me time to buy some silver turn signal lights and my clear side markers should be in by then too.

[nieuwhzn]

i don't think that's overspray. I had the same thing when I bought my Boxster. No idea what is causing, local differences in the plastic? Used a 3-step headlight restorer kit from Turtle, came out fine. I only see some slight pitting still. If I ever have time I'll just sand off a bit more a re-polish.

[AKnowles]

This is what it loks like after polishing and adding the UV protectant ...




Overspray (?) area ...



I'm on to the next one now. FWIW, there is still some plastic crazing. Meaning, if you look closely at the plastic you can see a puzzle type pattern in the plastic. It does not appear to be on the surface though. I do wish I could get to the interior just to wipe it down too though.

[Chard]

awesome, looks WAY better than when you started.

[woodsman]

It's probably a primer with a catalyst ( a hardener), a high quality product that someone used carelessly. Either way your approach makes sense. I can't tell from the picture of the finished lens whether it's clear now. Are you happy with it?

[particlewave]

Originally Posted by AKnowles

there is still some plastic crazing. Meaning, if you look closely at the plastic you can see a puzzle type pattern in the plastic. It does not appear to be on the surface though. I do wish I could get to the interior just to wipe it down too though.

FYI: crazing in polymers is perfectly normal and though it may not be pretty, it actually makes it stronger. The "cracks" are just that; micro fissures. Does not affect the integrity of the polymer, just looks weird

[woodsman]

Originally Posted by particlewave

FYI: crazing in polymers is perfectly normal and though it may not be pretty, it actually makes it stronger. The "cracks" are just that; micro fissures. Does not affect the integrity of the polymer, just looks weird

so are these fissures only on the surface? and, what do you do to get rid of them?

[particlewave]

They are internal and there is no way to get rid of them, other than having new lenses made.

Polymer crazing(from Wikipedia)

Crazing occurs in polymers, because the material is held together by a combination of weaker Van der Waals forces and stronger covalent bonds. Sufficient local stress overcomes the Van der Waals force, allowing a narrow gap. Once the slack is taken out of backbone chain, covalent bonds holding the chain together hinder further widening of the gap. The gaps in a craze are microscopic in size. Crazes can be seen because light reflects off the surfaces of the gaps. The gaps are bridged by fine filament called fibrils, which are molecules of the stretched backbone chain. The fibrils are only a few nanometers in diameter, and cannot be seen with a light microscope, but are visible with an electron microscope.

A craze is different from a crack in that it cannot be felt on the surface and it can continue to support a load. Furthermore, the process of craze growth prior to cracking absorbs fracture energy and effectively increases the fracture toughness of a polymer. The initial energy absorption per square meter in a craze region has been found to be up to several hundred times that of the uncrazed region, but quickly decreases and levels off. Crazes form at highly stressed regions associated with scratches, flaws, stress concentrations and molecular inhomogeneities. Crazes generally propagate perpendicular to the applied tension. Crazing occurs mostly in amorphous, brittle polymers like polystyrene (PS), acrylic (PMMA), and polycarbonate; it is typified by a whitening of the crazed region. The white colour is caused by light-scattering from the crazes.

[woodsman]

holy chit ! That's detailed and complex Particlewave thanks

[Kenny Boxster]

That "pitting / overspray" is probably caused by a very strong solvent getting on the plastic lenses, and judging from the pattern like it came out of a spray can. I caused that same over-spray by getting carb & choke cleaner on the lens. Nasty stuff, had to sand and polish the lens for quite a while.

[AKnowles]

Keeny, I suppose it is possible, but the same pattern was on both lenses. In fact, I need to resand the passer side one as I didn't sand it enough to give it the same clear elns effect as the drivers side. The good news on both though is the cleaning seems to be holding up quite well.

My only problem to date is alignment. The passenger side is poiting too close to the center. When I adjust it the adjuster nut only moves it so far to teh outside and then it starts to move back inside. I think I need to adjust the tray at this point to fix the alignment issue.

PS: Thanks for all the information on this subject. I had no idea about the crazing either.