Strings When Molding Nylon
By dm123
Published: July 22nd, 2010
Published: July 22nd, 2010
I have always heard about the stringing issues at the runner sprue when molding nylons but until now I have not ran this material. Now we are running more and more of it and yes we are getting the stringing I have heard so much about.
I start out with one string and end up with a birds nest of strings in the bin.
I would like to learn from everyone what they have done or the rules they follow to minimize or eliminate this problem.
Thank you
- Login or register to post comments
Email this page
When I first started to run
When I first started to run nylon, a fellow from DuPont advised me to run a 1" long extended tip nylon nozzle. Put a heater band and TC on the nozzle, I use a spade type and run it very close to the end of the nozzle. If that strings, just keep lowering it until the stringing stops. It stopped stringing for me years ago!
Do you check material
Do you check material moisture? You may have wet material!
I also agree with Bill and Ricks comments.
Thank you for the advise, and
Thank you for the advise, and we pretty much do as has been recomended but I will verify melt temp.
A few pointers to help you.
A few pointers to help you. 1-Use the correct type of nozzle tip, one made for nylon. 2-Use the correct orifice size for the mold. 3-Have the nozzle t/c as close to the tip as possible. 4-Slow/delay screw charging so that the shot size is full 3-5 seconds before the cooling timer expires. 5-There are special tips that normaly stop that last 10% of molds/machines that continue to string when running nylon. Hope this helps, Rick.
Stringing has one universal
Stringing has one universal cause and two modes.
The Universal cause is that when the sprue pulls, the 'solid' sprue is still bonded to a liquid mass. It 'cold extrudes' (no pressure) and you get stringing.
Two modes
#1 the melt is not decompressed enough and there's enough of a pressure head to keep the cold slug (that should be in the machine nozzle) on the sprue, and when it pulls out your get stringing.
Solution #1 - increase your melt decompression.
#2 the material in the nozzle hasn't formed a cold slug.
Solutions #2
A. turn down the nozzle heat.
B. Buy a nozzle tip specifically for nylon - these are designed to form the cold slug.
C. Check your overall melt temp - it's probably too high.
D. Lower your packing pressure.
Hope this helps.
Bill