www.TK560.com

[onedge30]

Just saw mention of this in the PETG thread -

And have been meaning to ask more about this process? Drying the ABS before you use it to vac form?

How is this done?

Jeff

[AlterEgos]

Indeed!!! That knowledge would be very useful for many people here.
_________________
-John

[drcrash]

There are two basic ways to dry ABS. (Or polycarbonate, which often needs drying, or other plastics like acrylic and PETG that sometimes do.)

One way is to bake it in a low oven for a while. This thermoforming and troubleshooting guide

http://www.spartech.com/plastics/vfmanual.pdf

says that for ABS, the oven should be 180-200 degrees and the recommended drying times are:

4 hours for .040
5 hours for .060
6 hours for .090
8 hours for .125
12 hours for .187
16 hours for .250
24 hours for .375

For polycarbonate the usual recommended temperature is 250 degrees for these drying times:

20 minutes for .020
45 minutes for .030
1 hour for .040
2 hours for .060
4 hours for .090
8 hours for .125
14 hours for .187
24 hours for .250

Some people think it's bad to get it that hot, though, and recommend drying it at a somewhat lower heat (not much above the boiling point of water) to avoid micro-bubbles forming when the moisture heats up, and damaging the plastic.

The other way is to keep it warm in a "hot box" (basically a very low oven, about 130 degrees or something like that (???)) for a day or two.

You can make a hot box out of plywood with a regular incandescent light bulb or two in the bottom for heat. (A light bulb puts out more heat than light.)

I used to have a link to a nice article about this, with construction diagrams for the hot box, but the link seems to be broken now.
_________________
Paul (a.k.a. Dr. Crash)

Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com

[onedge30]

Hmmm, very interesting.

So, let me get this right - there is a moisture content in manufacturing these plastic sheets?

Jeff

[onedge30]

And a second thought - what are the signs, when vac forming ABS, that tell it needs to be dried?

How does the plastic act when dry compared to not dry?

Jeff

[harley guy]

in the past year i have pulled about 250-300 sheets of 1/8 abs . i have had only 3 sheets that acted strange. they melted inconsistant and orange peeled. i dont know if they need drying or what. didnt really care since it was only 3 sheets out of 250-300 sheets. i wouldnt worry about it til the numbers change to 50/100 sheets. if i baked that many sheets it would of took to much time and money for only 3 sheets

[onedge30]

Ah, so this is a low occurrence issue. Hmmm. Thanks for the info.

Harley Guy, where are you located - to see if the general location may affect the plastic.

And that is a ton of ABS! What is your normal use? Are you a commercial vac form business?

Thanks,

Jeff

[cod]

I read somewhere that the most problematic plastics for drying issues are polycarbonate and acrylic. Acrylic seems like it will bubble easily if it has absorbed water. Absorbing water can happen just by the plastic laying around for yrs, with or without protective packaging.
_________________
<.o'>

[sethb6025]

Orange peel can also be the result of over-heating. I think if you keep your plastic in a temperature controlled area you shouldn't have a problem.

[in2plastic]

Polycarbonate and ABS are hydroscopic materials which will pull moisture from the air. The amount they draw depends on the relative humidity of surrounding air. Wet" material issues typically occur in the summer months when it is very humid.
"Drying" the material is a quick fix to remove this moisture - warm, dry air is circulated through material. This also requires sheets to be seperated on a rack system.

A "Hot Box" storage facility will not accomplish anything if the humidity inside it is high.

What you really need is a sealed area for material storage with a good dehumidifyer.

Wet material will bubble and blister the surface of the sheet. Orange peel effect may be the result of surface moisture on the sheet - (slight condensation) I would need more info.

[Mattax]

So, would you recommend a basement storage closet with a dehumidifier?

I have a storage room that I can place these sheets into. When I do finally get around to ordering the sheets will be aprox 26x26 inches. So they will store nicely. However, I doublt seriously that I can store all 1000 pounds in there.

Anyone know how much .090 ABS weighs on a 4x8 foot sheet?

Could I store want I wanted for immeadiate use in the closet and the rest wherever and then rotate them into the closet a considerable amount of time prior to usage?
_________________
Mattax
TK487
Garrison Tyranus

[drcrash]