Basic Injection moulding processing help needed!

[mayhem77]

Hi there, I have very recently been thrown into world of injection moulding and need help on the processing side. I am a total newbie, so please forgive my ignorance. My boss is quite a stickler on certain aspects of the application and wants me to solve the problems without cost to the company (of course) but I'm thinking I need to make changes. Here are my 2 current issues:

Details:
Machine: 350 ton JSW electric injection moulder
material: HD Polyethylene (Boss is set on using this material)


1st: Cooling times: Calculating Reynolds number? These are the specs I know
pipe diameter - 7/16 inches
water with glycol
pressure - 40 PSI
Flow rate on gauges read - 2.5 gallons per minute

We are having some cooling issues and I'm wondering if my Reynolds number is laminar, transient or turbulent. I know I'm looking for a value over 4000, just not exactly sure IF OR HOW I can calculate it with the specs I have.

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2nd: Hot runner system - Producing no nipple/tit on part

We are using a INCOE hot runner system with NO valve gate.
-Pin is almost flush inside the nozzle and seated very close to mould insert.
-Total cycle time = 23 sec
-Hold time = 15 sec hold time
-Cooling time = 2 sec
Result = I have played with the cooling and hold times and with this combination I get no nipple/tit on the part and it breaks cleanly.

If I drop the hold time to even a fraction under 15 sec I begin to get a molten nipple protruding. I've constantly played with the hold & cooling time and the best I can get is 23 sec. My boss is looking for quite a bit faster cycle time.

- Is a valve gate the only way to go?
- Different pin/insert on the hot runner to prevent tit/nipple?
- Smaller gate? Or will this just increase shearing/heat?
- Any ideas how to achieve more cooling in this area?

Any suggestions on either of these issues would be greatly appreciated.

[brentb]

Turbulent (But why use glycol?

15 sec hold and 2 cool?

What is fill time?

Might have to play with tip height?

KOM

brent

[brentb]

Now tell me how to change Engel clock!

[jonturka]

1- see my post here;

http://www.injectionmoldingonline.com/forum/showthread.php?t=391

2-

[mayhem77]

Turbulent (But why use glycol?

15 sec hold and 2 cool?

What is fill time?

Might have to play with tip height?

KOM

brent


Glycol - antifreeze
15 sec hold and 2 sec cool - For some reason when I reduced the hold time and increased cool time the nipple/tit would be even larger and more pronounced.
Might be tip height - yes I've been researching some more and found different tip heights that are not buried in the nozzle allowing more cooling area near the tip and gate. Might be a solution.

Thanks!

[mayhem77]

ah yes thank you

[rickbatey]

You time between screw completing recovery/decompression and mold open should be around 5 seconds. Any longer or shorter and you'll get the drooling. Tip temp and decompression speed/stroke can help gate vestige. Last point you know, tip height and style might need changing. Placing a dimple under the part, opposite the tip can help with vestige also.

Brent-What controller on the Engel? CC200 is a little different.
Rick.