Nozzle VS Drooling/Stringing effects

[Wiseco]

I'm working on a hot runner prototype for our injection-blow molding process and now I must find a way to make nozzles that will not drool or at least, that will reduce it. And we cannot use shutoff nozzle.

With my experience, I saw that if the nozzle have an angle gate, it tend to reduce drooling. But why? I know that the melt flows from the inside to the outside like rolling but how can an angle gate make less drooling?

Here is an image to show what I'm talking about :

 

[lorelei5607]

First Question:
Are you molding Nylon ?

Note
You may want to check the reverse tapper nozzle design (it will help with drool and stringing)

Also you may want to develop your Temperature of Melt vs Viscosity curve for the most otimum Fill Time and Melt Temperature

You may want to check the length of your tips (hot runner) -

 

[wgknestrick]

It is probably PP he is working with. That material is notorious in IBM for this problem.

 

[Wiseco]

I'm molding Styrene. Yeah I know the reverse taper trick but my question is why. Why a reverse taper reduce drooling/stringing effects?

 

[patprimmer]

You can run the nozzle cooler and get a clean break without risking blocking the nozzle as the solidified material can be pushed out of the taper by the next shot.

For materials with a tendency to string, very accurate temperature control of the nozzle, with voltage up down (not on off) or PID type controllers.



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.

 

[Pud]

Styrene stringing? Too cool..

Where is the pic in original post? Might help..


Cheers

Harry

 

[Wiseco]

Yep, Styrene. A crystal 4.0 of melt flow grade.
Here is a link for the pic.

http://www.cnczone.com/forums/attachment.php?attachmentid=41175&d=1185219195

 

[Pud]

Have to register to view image - no thanks. Try a free site eg tinypic.

Cheers

Harry