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Author
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Topic: Would like to convert from PVC to PET
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phayward
Junior Member
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posted 09-20-2002 01:30 PM
   
Extruding PVC regrind for tubing. I would like to switch to PET regrind.
Bekum S50 extruder. HP 15-25 variable speed. Top screw RPM 100.
Need 50 Lbs per hour. 2"OD 33" Oal screw fligths. I want want to make pipe to
50mm and then up to 160mm. Please advise if PET needs to be treated before in enters the extruder.
I understand that in addition to the drying and recrystalling of it, some post extrusion treatment is needed to get the proper strength (to avoid brittleness). Any comments on this? Is it possible to give me a very brief description of the complete process (flow diagram) that you have in mind in order to extrude pipe, for example:
Regrind material -> Dry -> recrystalize -> ????? -> ????? -> ?????? -> ?????
Also, apart from the screw design, what else need to be looked at to convert the extrusion process from ridgid PVC to PET. If possible, give some ballpark figures for budget purposes.
I would appreciate any advise you can give me.IP: Logged |
TomBlack
Moderator
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posted 09-20-2002 03:30 PM
Indeed PET regrind needs to be crystallized and dried
prior to processing. Without crystallization, the
regrind will not flow uniformly into the extruder
causing surging, or worse, bridging. Pre-drying is
recommended to prevent degradation, however, depending
on the quality standards of the end product, a vented
extruder may be all that is necessary (most processors,
crystallize, dry and vent the barrel).The design will need to be much more aggressive to
achieve the higher melting temperature of PET (as
opposed to the PVC you may be used to) and should include a
mixer as well. IP: Logged |
Steve H
Moderator
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posted 09-20-2002 04:07 PM
I would avoid using the vented barrel route to produce anything made of Apet- check out the single screw forum(barrel heating) for the reason why.To adequetly dry Apet, you are talking 4-6 hours residence time (not 4- 6 hours total) at 150C. So you are talking serious dollars for desicant dryers etc. Probably you'll want to regear the reducer on your extruder to give you 0-150 RPM, what LD ratio is the barrel on your present extruder. If you choose to go for barrel venting, you'll need at least 28 LD and really 30-32 would be better. You'll probably need a few more HP too. As Tom has said, a new screw will be on your shopping list too. Try talking to an Eastman rep- get some copies of their processing guides for Apet- the dies you're using for PVC may need rebuilding for Apet also, (this is the case with sheet and I suspect it would be so with pipe/tube). How are you cooling your PVC tube? this is probably another part of the setup you'll have to re-engineer. Damm its not getting better, is it  Steve H
[This message has been edited by Steve H (edited 09-20-2002).]
[This message has been edited by Steve H (edited 09-20-2002).] IP: Logged |
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