drooling nylon

[shoobaka1]

why does nylon tend to drool? Is it do to crystallinity? Does an amorphous nylon drool less?

 

[patprimmer]

The question you ask is a bit bigger that i think you expect, but basically, nylon normally has a low melt viscosity and a very sudden transition from solid to liquid. Amorphous nylons tend to be less sudden.

Also nylon is hygroscopic, and if it has absorbed much water, then the outguessing as the water boils off will force some material out the nozzle as drool. If it is moisture causing the drool, the drool will spit and bubble with gas (steam) discharging from the melt.

Bottom line answer.

Ensure the granules are dry.
Ensure the nozzle heater is in good condition, is in good contact with the nozzle (good clean smooth mating surface).
Ensure the heater is very close to the tip of the nozzle.
Use a variable voltage controller to the nozzle, NOT AN ON OFF cycling type controller. DME controllers or even domestic light dimmer switches all work OK.

The temperature fluctuation during reaction times with on off type controllers is enough to cause drool then freeze then drool then freeze cycles to be set up.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
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[ornerynorsk]

you can also use a shut-off nozzle to control the drool. This does restrict flow somewhat.

 

[dwightdixon]

Make sure you are using a nylon type nozzle, it helps. Crystaline nylon is naturally low in viscosity. Millions of pounds of nylon have been run for 60 years, so this is a managable problem.

 

[tables]

This sounds like a heat issue not a material.

I would ask how you are controlling your heat dissipation to the sprue. If you have to much contact from sprue to mold or not enough this can cause the sprue to freeze, drool and many other symptoms.

Some presses have the ability to vacuum the nozzle to prevent drool. I am not really clear on this, but can check with my molding floor to verify.

Cheers


Terry Ables
Micro Plastics Inc.

http://www.microplastics.com

 

[patprimmer]

It is both a heat and material issue as normally the material nylon has a very sudden transition from solid to a relatively free flowing liquid, and therefore, is exceptionally sensitive to very small changes in temperature at the nozzle, therefore the temperature needs to be very accurately and consistently controlled, buy techniques I previously described.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.