If you wish to post a question, please click here.
 
TOPIC: Hot Runner Valve Gate - Flow Line Issues
 

Submitted: January, 2002

I have a Hot Runner valve gate mold running a thick part out of unfilled polypro. The gate is directly into the thickest section of the part. The problem is that without anything for the melt to hit opposite the gate we are getting all sorts of flow lines. What suggestions do you have? Most here feel we need to open up the gate more as it is currently about .120" running into a 7/8th" wall section.

Assuming that the injection unit is capable of filling the part in less than 1 second and that venting is proper, this sounds like a perfect application for a vacuum. Refer to the Mold-Vac information found at www.caeservices.com, or call 1-630-761-9898, where an application engineer will be able to assist you.

This mold should be vented everywhere possible. If not, you may want to start by correcting that situation; vents should be .0007/.0010" dp with .040-.045" land and as wide as possible, relieved to .050" deep once past the vent land area and out to atmosphere.

You may also increase the temp of the mold and melt by 50-100 (F) degrees to allow the material to remain molten as the thick wall is filled. Gate may need to be increased also: .200" diameter would be a good starting point, with provision to go to .300" if necessary.

As you know, increasing the gate size on a valve is a big job, so you should probably do everything you can to get it working with the gate you have. Focus on venting and fast fill.