vacuum line clogging

[PravinP]

Hello Everyone:

I work for a plastic compounder. We compound Nylon 6 and Nylon 66. While running a compounding extruder, we experience a lot of clogging in vacuum vent line. This problem is not due to raw materials as we tried different feed stocks as problem occured everytime. I had experienced clogging of vacuum line after running for a long time. But now we have clogging within 2-3 hours. Any remedies?

Thanks.
Pravin

 

[sos2]

do you have filters on your loaders

 

[patprimmer]

It might be clogging with free monomer, or a volatile in your additive package.

The monomer in nylon 6 is caprolactum. It is a white solid that can be dissolved in water.

The monomers for 6.6 are hexamethylenediamine and adipic acid. I don't know their physical form from memory, but I think hexamethylene diamine should be a waxy solid. Both should be water soluble.

Does the material causing the blockage wash of in water.

Do you specify monomer content or very low molecular weight component in your raw material spec.

Regards
pat

 

[Soupcat]

Have you tried putting a solenoid valve with a pulsing circuit on the line and pulsing the air periodically to avoid clog?

Kieran

http://www.moulddesigner.com

 

[maiweb]

sorry I found your post only now, but if your problem still exists, here are my suggestions:

Probably the cause for clogging comes from the monomer (like pat already explained):
You´ll need a very well designed vacuum line (short, straight, easy to dismantle, electrical tracing (slightly higher than melting point of caprolactam, which is 68°C) can be very helpful, use stainless steel, inside diameter of this vacuum line should be carefully adapted to the gas flow/volume (which is depending on machine throuput and monomer content in basic polymer and processing temperature and residence time and screw design > all of this you´ll need to check too!), rather chose a smaller diameter to get higher gas velocity to get some kind of self cleaning effect.

Also check if vacuum is set right. Probably between 700 and 900 mbar is more than enough. Check again if the hole system is tight and there is no air leakage inside.

Last not least you can add some nitrogen continuously to the vacuum connection at the machine to further increase gas velocity in the vacuum line (do never ever add air! because of the oxidation/degradation of the polymer).

Best wishes for 2004,
maiweb