By Raj.M
Published: February 28th, 2013

Hello everyone in the forum,
We have problems with processing HIPS (white) using shut off  valve hot runner system.
It's a new Mold, equiped with shut off Valve hot runner Nozzle.
The gate opening is 4.8mm dia.
Part weight: 700 gm
There is dimple opposite the gate.
The mold has been tried out several times but the flow mark around the gate area (say 30 to45 mm away from the gate) still exists. The process setting has been tried in different setings, with low to high step injection, increasing the Nozzle temperature, using MTC in cavity but still could not get rid off from the flow marks.
 All your inputs will be highly appreciated.
Thanks, Raj

How much air psi you using?

How much air psi you using? May be too low to force the nozzle to close completely. Also the entire drop may be growing into the cavity too much when hot and may need to be ground flush at running temp.

The pin is pneumatic

The pin is pneumatic actuated, seals off after pack & hold on period. There are cooling lines near the gate (both sides of the Nozzle).

The gate is 4.8mm that is

The gate is 4.8mm that is into the cavity plate. The Nozzle flow channel is 6mm to wards the TIP.

One last thought: 700 g

One last thought: 700 g through 4.8 mm valve gate pin might be too much. You may need a larger drop and pin size.

I would suggest doing a short

I would suggest doing a short shot study to look at the flow paths. You should also look at your cooling lines, you've described what happens with a cooler section on the mold.

How are you actuating the

How are you actuating the valve gate? I think either it's not closing completely, the pin is not sealing off when closed, or your too hot ( temp or no/poor cooling around valve gate). Also when do you close the valve gate? Pack and hold time?

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