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Roughly, what temp does kit plastic warp at ?


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I know it's too general of a question but I just need a rough idea of what temp your basic AMT/MPC/Revell etc kit plastic will start to warp and deform at. I found someone with a bunch of unopened kits they want to sell but they have been in a steel shed for a few years. The seller said they were covered in storage boxes and will not let anyone open the kits individualy to check ? I have'nt seen them yet to see the condition of the boxes so I thought I'de ask before I take the drive.

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The temperature at which plastic warps and takes a permanent shape is called the "glass transition temperature", or Tg.

For common "polystyrene" that kits are made from, this occurs at about 100 deg. C, or 212 deg. F.

The exact temperature depends on the exact plastic formulation.

If there's been any weight on the boxes, the contents may have also "cold-flowed", and could be warped even if the temperatures were lower than 100 C.

Edited by Ace-Garageguy
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I know that plastic will warp at a bit less than boiling temperature. I also know you can bend plastic at hot tap water temperature--what's that, 160 degrees?--but it takes quite a bit of effort. So the critical temp is somewhere in between there.

Do you think temps in the steel shed got over 160*?

I've left kits in the trunk of my car for several years, with summer days well over 100*. No damage whatsoever.

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Beyond the bodies warping it has been my personal misfortune to have the tires melt into the bodies and ruin the decals. At best the kits might give you some parts, but I wouldn't give a dime for any of them unless you can see what's inside.

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I've become very wary of sealed kits, ever since I got burned on one years ago-------and this was long before eBay. This was back in the mid '80's and the kit was the "Golden Classics" issue of the '53 Studebaker Starliner. I had ordered it through an ad that was posted in (back then) SAE. The kit arrived at my place, factory sealed and all, but when I opened it------much to my surprise and chagrin, the body was very badly warped! To the point that it was unbuildable. :( So that was $20 down the drain, and the kit's body ended up being practice for paint.

I see stuff that I'd like on eBay right now, but don't want to touch it as the kit's never been opened. No pics on what's inside?.........then probably no sale from me.

Just sayin' that if he's reluctant to show anything in the boxes........well as they say "Caveat Emptor"!

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Yeah Skip, I've heard of those scams too on eBay and it's sad. To me, kits are meant to be built, not just collected and never opened------I don't see the purpose in that. Now of course for those of us that have more kits than we'll ever build..............weeell that's another story! :D

At least the ones I have are NOT sealed and, the full contents can be seen if I ever decide to sell any of 'em.

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I had kits stored in our attic back on LI for many years. It got HOT up in that attic- sweating-as-soon-as-I-got-up-there HOT. I guess maybe just south of 120F on a hot summer day (when else would one go up in an attic?). None of those kits have any damage whatsoever.

Me too--same exact story. You are also correct in your comments about vinyl tires eating into styrene and decals over time. Some kind of chemical leeches out it with age.

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Thanks guys. As fate worked in my favor the seller called me to let me know she had sold them. I never got a chance to see them. Someone found them for me at a yard sale and got her number. She lived about an hour from me or I would have just drove over there. I tried to get picks but the lady wasn't willing to. The phone pic my friend sent me sucked but it really didn't look like I missed much.

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As a child I learned that they will melt in a closed car while sitting on the dash.... :-(

I learned the same thing with a Monogram T-28 in the back window of a '59 Chevy on a hot August day in North Carolina. :(

But the interior of a car (especially one with a lot of glass, like a '59 Chevy) can and will get a LOT hotter than the trunk of that same car (or a windowless steel shed). As I said, not that long ago I had a half-dozen kits in the trunk of my car for two or three years, including many hot summer days, and when I finally took them out they were all fine, no damage at all.

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-Just to confuse the issue further.. I left two kits by the same manufacturer (Revell) in my car in Phoenix in July. It got to at least 150F in the closed-up vehicle..

One kit destroyed, the other ..nuttin'.. Just fine.

So, ???

Exactly. As I said in post #2...

"The temperature at which plastic warps and takes a permanent shape is called the "glass transition temperature", or Tg.

For common "polystyrene" that kits are made from, this occurs at about 100 deg. C, or 212 deg. F. "Polystyrene" is a generic term encompassing a wide variety of specific formulations.

The exact temperature depends on the exact plastic formulation."

Here, I should elaborate. The cheapening of the polystyrene used in kits to save a few pennies has caused these seeming inconsistencies in kit-plastic behavior. Add that to the fact that different runs of kits may be made with different batches of plastic with different specs, and you get even more inconsistencies.

This is also reflected in the varied kit-plastic sensitivity to solvents in paints these days...paints and primers that wouldn't harm an old Johan kit, for example, will horribly craze and ruin some of the recent Revell offerings.

Edited by Ace-Garageguy
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Speaking of sealed kits. A few years back at NNL East I picked out a sealed kit to buy and the vendor got an uneasy look on his face. He tells me that he thinks that one kit 'May have' been resealed. He doesn't want to tick me off since I send out the show' vendor invites. I buy the kit anyway and when I later opened it, sure enough there are parts off trees and optional tires are missing. Yea I knew this clown was wrapping kits! Another buyer may have never been told and could've kept it in his mint sealed kit collection. I can imagine some sealed kits are just boxes of spruce!

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Oddly enough I've had the opposite problem selling kits recently. People are SO accustomed to every kit being sealed on the shelf that when I resell the stuff I import I get uncomfortable looks because none of it is shrink wrapped. Much like Revell AG using those little tape circles to seal their boxes, Japanese kits are 99.98% unsealed when you import them over. Had a guy insist I must have done SOMETHING to Model Kit XYZ because it wasn't sealed and it was "too cheap". Insisted that every foreign kit he's ever seen has been shrink wrapped.

Well yeah, MRC and other Distributors seal them HERE after they arrive from Japan. How did you think they got their logo beneath the shrink wrap in the 1st place? Black Magik?!?! As for too cheap...well I'm importing DIRECTLY from Japan, don't worry I'm making my profit sir.

Edited by niteowl7710
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