Stringing Issue with SAN Kostil

Hi

I am new to this Forum, so I am sorry if similar postings have already been made and answered.

However, I would be grateful for any comments/suggestions anyone can give me to solve a problem using SAN Kostil (Styrene). We make a clear circular cosmetic grade lid which is made using a 6 cavity tool and picked off using a Robot which sends it through a Hot Foil Printer. We find that we get a small build up of 'string' (that appears a little like Candy Floss) which accumulates and sticks to the robot head, it then gets caught when the tool closes and gets dragged into the mould. Obviously we have a cleaning program, but this does not guarantee that every moulding is perfect which the customer expects!

We have also set up a Vision system and Packing system to check and then layer pack the products. Unfortunately, whilst the Vision system is excellent at picking up faults within the print it is not able to detect the stringing and so these products end up being packed.

I am not particularly technical regards the moulding process, but since everyone is telling me this cannot be prevented, want to do my own research to prove one way or the other.

If anyone can help or require any further information to provide assistance it would be much appreciated.

Many Thanks

Colin

Colin,
Yes you can control and eliminate the stringing. First we need more info on the mold and machine settings. Mold- I take it this is a hot tip mold without valve gates? It could be the tip heat settings are too high, low, or manifold settings wrong. Nozzle PID set wrong. Too low/high nozzle heaters. Other causes are not enough cooling in the mold, too high mold (steel) temp, gate style wrong for resin or even too large an oriface (diameter). Wrong nozzle tip, style, oriface or wrong nozzle body. Nozzle temp too high.
Process- melt temp too high. Decompression too fast, slow, too short stroke. Screw recovery finished too soon before cooling time expires.
Rick.