Material Drooling

[Viju vj]

We are Facing material Drooling in hot sprue mould while Moulding with nylon 66.
Pls suggest an opinion

[nemanja]

Hi,

Few questions:
-Is material dry?
-Value of back preassure?
-How big decompression is and is it before or after dosing?
-Temperature on nozzle tip (real vaue)?
-Do you have shut off nozzle on machine or not and if you do is it active or not?

[Bryan E]

Agree with all the questions from nemanja, just wanted to mention there are nozzle tips designed specifically for nylon that will help. Making sure the material is dry is top of the list, But keep in mind Nylon 66 can be over-dried when dried for extended periods of time. Nozzle and barrel temperature are equally important. You can download some very good processing guides for all grades and types of nylon from Dupont plastics website.

[Viju vj]

1. Material is 4 Hour pre heated
Moisture is .04
2.Back pressure. 40 Bar
3.5 mm
4.Value is 320deg
5.No shut off Nozzle

[nemanja]

Hi,

If you are able try 6h pre-drying on higer temperature. Depends from material it is posible that needed longer time to dry (had this case in my production).
I assume temperature is in celsius, so try also to reduce to 290-300deg. One thing that helped me is higer temperature in middle of barrel and lower on tip (5 zones from rear to tip; 290->300->310->305->295).
Maybie to increase decompression (but that also depends from tool venting).

In any case my solving "algoritam" for this problem is:
1. Reduce nozzle temp to min possible (dont pay atention to drooling);
2. Increase decompresion to point that drooling stops
3. Check parts and process to see if i have problem with traped air
4. Try to fix it with clamping force and adjusting parametes to put air out
5. If step 4 is not possible to do or dont fix problem, i start to play a bit with dosing parametes (back preassure, dosing speed, decompression speed).

Depends from product and use of product, you should be werry cafefull when changing parametes not to affect dimensions of part, trapped air, voids.....
All my products have high requests for tolerances and overall quality of mold, so im always checking this after any change of parameters or mold.
Please post test and resaults to see if we going in right direction.

[Airwinghma]

Greetings;

Great questions above, I have a few more.

Does your material have enough resonance time in the dryer hopper? The material needs to have 4 hrs of dry time in the hopper.
What is your hourly throughput of material?
What is the size of your hopper?
If your 4 hour throughput exceeds your hopper size , that could be an issue.

Have you checked your dewpoint, with a stand alone device, lately?
Does your process start up fine the start drooling after a few hours?

Thanks

Scott