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Suhas
15th November 2011, 03:01 PM
Have any of you encountered a material that needs a LONG drying time? Which one?
I was teaching a class a few months ago and one of the attendees mentioned a material that comes dry in bags and must be processed once the bag is open. If you leave it on the shelf and it picks up moisture, there is no way it can be dried. Any experience with this?
Thanks,
Suhas

pjhall
15th November 2011, 08:40 PM
No experience with the material your speaking of Suhas, but my "Drying Nemesis" is TPU Dow Isoplast 2530 and 2531. We keep a minimum of 12 hr dry time. Dried air shot hoppers loaders are a MUST.

rickbatey
15th November 2011, 09:27 PM
Ran some High Tech Polyurethanes once: 12-14 hours at 260°F with -40°F Dewpoint. I can say that we tried to cheat the numbers (hours), and ended up with garbage!

brentb
16th November 2011, 01:51 AM
Rick, and Suhas,

I think the guy at the seminar mentioned that he thought the resin was a PU.

Nylon and nylon regrind sitting can be nasty to dry, especially if has been sitting open all (damp) summer in a warehouse. It can take days to dry.

As a young molder, (3rd shift tech), I stayed on 1st to set and start a mold. The regrind was as I mentioned, WET nylon. Upon each injection, water would gush out of the mold and the parts (throw away spacer sticks) that were about 14" long and had a wall of about 0.070" would break into pieces upon ejection. I told the "experts" that the material was wet they didn't believe me, and pulled the mold and sent it to the Tool Room 3 times to " find the crack".
Finally I said that we should shoot the mold in PP. Result: No water gushing out!
In those days, nylon came in big 5 gallon cans and one ran out all the resin after opening the can. This gushing resin was regrind from years of runners.
Dryers in those days mostly consisted of hot air ovens.
The importance of drying the resins was yet to be discovered or at least emphasized. Heck turbulent water flow wasn't really known then. People would have portable chillers running sub-freezing glycol mixes through their molds with ice building on the lines, in an effort to get faster PP and PE cycles!

Keep on Molding!

brent

Suhas
16th November 2011, 03:47 PM
That is interesting info Brent about the past. It will be interesting to do a study on the drying of regrind. I have often heard that the regrind poses a special problem. I think that the water that you see there is probably also some other volatiles and such.
I am going to try hard to find the material I asked about, I think Rick is right that it is a PU.
Suhas

pjhall
16th November 2011, 08:17 PM
Dow Isoplast comes in vacuum sealed multiple lined (foil, on the inside) bags. I've never tried to cycle right out of the bag because I'm prety sure I know what the outcome would be.

rickbatey
16th November 2011, 10:55 PM
It was either from Dupont, Bayer, or BASF I think. I can't find some of the old process sheets from that job, but I remember us searching out for the absolute BEST drier to put the resin into! I know it was a PUR, with glass and mineral filler in it!

brentb
16th November 2011, 11:22 PM
That is interesting info Brent about the past. It will be interesting to do a study on the drying of regrind. I have often heard that the regrind poses a special problem. I think that the water that you see there is probably also some other volatiles and such.
I am going to try hard to find the material I asked about, I think Rick is right that it is a PU.
Suhas

Are referring to the regrind (volatiles)?

Zehrmldr
17th November 2011, 11:18 PM
Wow, Never a material that can not be re-dried. I deal with alot of nylon 6 and glass fill nylon. But 4 hours and it's up and running.

brentb
18th November 2011, 01:06 AM
The very wet regrind eventually dried, remember that this was in the days of hot air oven dryers
We do lost weight analysis, not just drying until mold-able, and have had some extensive dry times.

Keep on molding!

brent