posted February 29, 2004 07:28 PM               

Crystalization is usually performed in concert with drying in an agitated dryer.

Putting amorphous pellets in a standard dryer will results in one giant pellet.

Melting point 495F
Melt temp and barrel temps 520-540F

A vacuum vented extruder is prefered.

30 - 36:1 L/D with vent.

PET melt tends to stick to metal.

Screw plastication is generally easy and the melt is tolerant of a lot of conditions provided it is dry first. Keep the residence time on the low side.

These answers are a general as your question. If you need more specific information ask more specific questions....

posted February 29, 2004 10:23 PM               

What are you looking to extrude with Apet? Have you already got the equipment (including drying equipment).

posted March 05, 2004 11:23 AM               

If not what modifications should I do?

Concerning PET drying ,what´s the behavior
of PET in a place with 85 % moisture,ie,

posted March 05, 2004 09:07 PM               

I don't think you are in good shape.

The extruder seems too short and will have trouble providing a stable pressure. You likely need something like 20:1 or more. Vacuum vented (30:1)would be better.

For extruion profiles you will need a high viscosity grade of PET, which is even more sensitive to moisture.

Successful running of PET requires an air tight connection from the dryer to the extruder, or storage under pressurized nitrogen.

Many processors trying to move from PVC to engineering resins have problems. PET is probably one of the most difficult engineering resins to work with.

I would recommend looking at PETG. It is specifically recommended for processing on PVC equipment. My personal expereince indicateds that it is much easier to handle and more forgiving. Still it needs to be dried to below 0.04% moisture. As stated a vacuum vented extruder is rocommended because the process will be more tolerant of variable moisture content.

Check these web sites on PETG;
http://www.scudc.scu.edu/cmdoc/dg_doc/develop/material/resins/a4000014.htm http://www.custombottle.com/guideto.htm#PET

posted March 06, 2004 01:44 PM               

I agree with Tom, you'll need to look at obtaining another extruder, with an L/D greater than 27L/D. Have a look at vacuum dryers (they're new to the market, so not available second hand) to dry the material.

Steve

------------------
Steve Hodgson