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drying moisture out of lexan
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barndog
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Joined: 15 Apr 2012
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Location: eureka,ca

PostPosted: Wed Jan 09, 2013 11:13 am    Post subject: drying moisture out of lexan Reply with quote

hey guys ive been looking for the info on drying lexan im useing .040 to make r/c car prototypes and i was wondering how to bake it can you steer me in the right direction.i have been doing petg but they dont hold up for testing.thank you!
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spektr
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Joined: 07 Jan 2008
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PostPosted: Thu Jan 10, 2013 11:44 am    Post subject: Reply with quote

The secret here is the masking film. If the film is not hygroscopic, drying of 040 material is not necessary.
I've never had to dry any rolled material in those thicknesses. Individual sheet material might be different, but running 1 sheet should give you the answer. Be careful to understand that you can overtemp 040 easily and that decomposition bubbling can be mistaken for moisture damage. Decomp damage also turns the clear sheet white, somewhat like PETG does. Dust on the mold can also show up as a bubble on the inside of the part where it mated to a male mold. (assuming a male rc car mold).

If you actually have to dry the sheets, 180 f overnight in an oven was good enough for my 1/4 inch thick windshield blanks, so I'd do that since its simple to set up and walk away.......
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barndog
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PostPosted: Mon Jan 14, 2013 12:26 am    Post subject: Reply with quote

great thank you i will look into that and order some up to try out i have heard of guys drying it in a plywood box is this a good method also.
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glenn201
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Joined: 06 Apr 2013
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Location: Brazil IN

PostPosted: Sun Apr 07, 2013 8:35 am    Post subject: Reply with quote

spektr wrote:
The secret here is the masking film. If the film is not hygroscopic, drying of 040 material is not necessary.
I've never had to dry any rolled material in those thicknesses. Individual sheet material might be different, but running 1 sheet should give you the answer. Be careful to understand that you can overtemp 040 easily and that decomposition bubbling can be mistaken for moisture damage. Decomp damage also turns the clear sheet white, somewhat like PETG does. Dust on the mold can also show up as a bubble on the inside of the part where it mated to a male mold. (assuming a male rc car mold).

If you actually have to dry the sheets, 180 f overnight in an oven was good enough for my 1/4 inch thick windshield blanks, so I'd do that since its simple to set up and walk away.......

I would like to see your oven Im making 1/5 scale rc car bodys out 1/8 inch
lexan I need to make something to dry it in
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jdougn
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PostPosted: Mon Apr 08, 2013 8:42 am    Post subject: Reply with quote

I had to dry some ABS that had too high a moisture content. Not much to see but a plywood box with a door. I used "disc limit switches" that turn off at the desired temp but are cheap on Ebay, as in a few bucks a piece. Then some left over nichrome wire and hardibacker for the heat source but using a standard baseboard heater would've been easier.

Made the box big enough to keep the plastic 5-6" away from the heat source plus used a circulating fan inside the box. Spaced the plastic sheets so air would easily circulate between the sheets. After 4-6 hours the plastic molded perfectly instead of blowing up!
dn
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glenn201
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Joined: 06 Apr 2013
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Location: Brazil IN

PostPosted: Mon Apr 08, 2013 6:25 pm    Post subject: Reply with quote

jdougn wrote:
I had to dry some ABS that had too high a moisture content. Not much to see but a plywood box with a door. I used "disc limit switches" that turn off at the desired temp but are cheap on Ebay, as in a few bucks a piece. Then some left over nichrome wire and hardibacker for the heat source but using a standard baseboard heater would've been easier.

Made the box big enough to keep the plastic 5-6" away from the heat source plus used a circulating fan inside the box. Spaced the plastic sheets so air would easily circulate between the sheets. After 4-6 hours the plastic molded perfectly instead of blowing up!
dn


here is what im trying to make i got heat set up to run all the time how can i wire in a fan to come on at like 150 an go off at 140 would like any help you can give me


Thank you
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jdougn
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PostPosted: Mon Apr 08, 2013 7:18 pm    Post subject: Reply with quote

Quote:
here is what im trying to make i got heat set up to run all the time how can i wire in a fan to come on at like 150 an go off at 140 would like any help you can give me Thank you


My experience here is a bit limited. The disc thermometers tend to have a wider range of operating temps. The ones that I used come on around 140 and go off around 110-115 but there are others. The disc thermometers wire straight in but you general can't adjust the temp range.

Lots of other inexpensive options exist depending on what you want to do and how much you can spend. Here's a couple more possibilities found on ebay:
http://www.ebay.com/itm/110V-Digital-Temperature-Controller-Thermostat-WH9002A-Control-Accuracy-BLACK-/251257460321?rt=nc&_trksid=p2047675.m1851&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D163%26meid%3D6828997516924791925%26pid%3D100005%26prg%3D1088%26rk%3D2%26sd%3D200903804018%26
http://www.ebay.com/itm/STC-1000-Digital-Temperature-Controller-Thermostat-With-Sensor-Probe-2M-Cable-US-/200903804018?pt=LH_DefaultDomain_0&hash=item2ec6ccc472
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glenn201
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Joined: 06 Apr 2013
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Location: Brazil IN

PostPosted: Tue Apr 09, 2013 4:31 pm    Post subject: Reply with quote

thanks a lot i think that could do it
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RobL
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Joined: 19 Jun 2013
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Location: Indiana

PostPosted: Fri Jun 21, 2013 12:07 pm    Post subject: Reply with quote

Quote:
Be careful to understand that you can overtemp 040 easily and that decomposition bubbling can be mistaken for moisture damage.


I think I experienced this with my couple of test runs, as I had long heat times.

Good info to have regarding the polycarb masking vs. hygroscopic issues.
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RobL
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PostPosted: Thu Jun 27, 2013 10:03 pm    Post subject: Perhaps I was incorrect before.... Reply with quote

So, I re-cobbled my heater system, ( pics in my thread,) and in a 90 second heat cycle, I got these bubbles.




I did leave the protective mask on the top side of the lexan, as it's typically left on to help protect overspray during painting ( rc car body,) and it was easy to remove, didn't seem melted...which leads me to ignorantly believe that this is what moisture soaked lexan looks like?

I could see them forming when the lexan was heating, so they were there before they came in contact with the mold, to rule out dust, etc.

thank you,

Rob
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Last edited by RobL on Thu Jun 27, 2013 10:27 pm; edited 1 time in total
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jdougn
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PostPosted: Thu Jun 27, 2013 10:14 pm    Post subject: Reply with quote

According to Spektr's post decomposition bubbles from overheating also turn the sheet white. What is your analysis on this?
dn
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RobL
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PostPosted: Sun Jun 30, 2013 9:31 pm    Post subject: Reply with quote

I came across the video below which shows what the white discoloration looks like. At the 6:00 min mark, they've removed their lexan (?) and you can see bubbling and the discolored sections.


That's one hell of a heater they have! Shocked


http://www.youtube.com/watch?v=cseFvsFj2sk


So, at least for my pic, it's just moisture. Time to construct a drying apparatus.
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spektr
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PostPosted: Tue Jul 09, 2013 2:15 pm    Post subject: Reply with quote

YOU DO NOT NEED TO DRY .040
YOU ARE LOOKING AT CLASSIC DECOMPOSITION BUBBLES.
REMEMBER THE HEAT TRIANGLE.... WATTS/DISTANCE/TIME.
ADJUST THE PARAMETERS AND YOU WILL GET THERE.
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RobL
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PostPosted: Tue Jul 09, 2013 5:44 pm    Post subject: Reply with quote

Quote:
YOU DO NOT NEED TO DRY .040
YOU ARE LOOKING AT CLASSIC DECOMPOSITION BUBBLES.
REMEMBER THE HEAT TRIANGLE.... WATTS/DISTANCE/TIME.
ADJUST THE PARAMETERS AND YOU WILL GET THERE


This is awful news, as I've nearly completed my "oven." Not much money has been spent, but the time...oh, the time.....lol.

Anyway, thanks spektr, I ignorantly thought I would see the "white" symptom when decomp was happening, good to hear that the bubbles are kinda' the first stage of improper heating.

Perhaps my heater distance is too large, so I end up cooking my material in order to get the right droop. So, I'll have to give it some thought, but my initial thought is to decrease the distance from the heaters.

Once again, thanks spektr, now off to figure it out....
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spektr
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PostPosted: Wed Jul 10, 2013 12:06 pm    Post subject: Reply with quote

I still can't seem to get people to get away from droop as a primary indicator of sheet temp... get yourself an infared heat gun and run it by the numbers.. additionally, i can almost gaurantee that you have sheet temps all over the map doing a part that large. pm me your phone number..
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