Molding a clear (Transparent) bowl from PA12, Getting what looks like gate splay or flow marks- Silver lines emanating from the sprue. Any Ideas?

Hi Robert,
Is there a way to post a picture?
Does it appear over time or as soon as the part is ejected?
It's not cracks right?

Hi Robert,
usually, the phenomena that you described occurs when the injection gate design (size too small) does not proportional to the injection pressure (too high) and the polymer melt squirts into the cavity.
possible action towards solution might be (one of them or combination of all):
* increase gate size
* reduce injection pressure
* locate the gate against a wall (if possible)
* add (or increase, if already existing) the "cold- well", this break the melt ad reduce the melt squirt.

the notes listed above are general guidelines to improve the kind of injection phenomena you mentioned . To be more specific, you should upload an image as Eliad suggested.

Best regards,
Igal

Hi Robert,
If it is the cold like spray marks. Perhaps you can check the material contamination and make sure you are processing dried material or reduce injection speed.
If due to high shear. Consider to increase process temperature.

I agree with Igal follow those steps and you should see improvement

It's probably shear splay. Make sure the material is dry, keep your pressures as low as possible. Gate size can be up to 75% of nominal wall.

Please let us know if this helps... For excessive swirl or splay
Make one adjustment at a time; starting with A,B,C etc., and allow time for the change to affect the total process.

A. Decrease the melt temperature

B. Decrease the nozzle temperature

C. Increase the mold temperature

D. Decrease the injection pressure

E. Decrease the injection rate

F. Increase the injection rate

G. Ensure that the resin is dry

H. Increase the venting

I. Decrease the foaming pressure or amount of CFA

J. Check additives or contaminants

K. Check for a heat controller problem

L. Check for water leaking into the mold

M. Increase the size of gate

N. Shorten the mold flow path

Silver streaking in a clear part is usually a heat related problem, Igal Is on a good path as are a few others here as well.
Specifically, if it is truly silver streaks, they are generally caused by shear heat as the material flows.
They generally happen around a gate during injection. Your description indicates you have a sprue gated part, hence, the problem is initiated further upstream. Check to insure the nozzle to sprue relationship is correct, (minimal step in a positive direction), insure you have a true Nylon nozzle tip on the machine and insure there are no edges , burrs etc. in these components that may be acting as a shear riser. Look at the temperature profiles, injection rates, back pressure profiles, etc. to determine if the issue may be lurking there. if the condition persists, look into the screw and screw tip conditions, the culprit could be hiding there as well. Do not be shy about checking moisture, nylons prefer arrid conditions PA-11 needs to be far drier than most manufacturers suggest to avoid these issues, i doubt PA-12 is much different.
Is the screw check assembly correct for PA12? Some materials prefer a ball check rather than the more common ring check and this will impact shear heat.