TL;DR
Gate drool and stringing are nearly always caused by a gate temperature too high or insufficient decompression at end of shot. Lower the gate zone temperature by 5 C increments before adjusting decompression.
What you might see
- plastic strand attached to the gate area on ejected parts
- drool visible at the gate when the mold opens
- gate vestige longer than specification
- part weight inconsistency correlating with drool events
Likely causes
Gate zone temperature above the optimal narrow processing window for the material
Insufficient decompression (suck-back) at end of injection allowing residual melt pressure to drool
Worn gate tip seal allowing melt to leak around the gate
Valve gate not closing fully or check valve on valve-gate pin worn
Required tools
- Digital caliper for gate vestige length measurement
- TempMaster setpoint adjustment capability
- Injection press decompression parameter access
- Gate tip insert wrench (mold-specific)
Safety first
- Adjusting hot runner temperature while the mold is closed requires monitoring for material degradation. Do not hold gate zones at reduced temperatures for longer than 20 minutes without purging.
- Gate area and ejected parts are hot. Use heat-resistant gloves when handling parts immediately from the mold.
Procedure
- 1
Reduce the gate zone setpoint by 5 C and run 10 cycles. Inspect the gate area on ejected parts and in the open mold.[1]
- 2
Continue reducing gate temperature in 5 C increments until drool reduces, or until part quality degrades from cold gates (freeze-off or splay).
- 3
On the injection press, increase the decompression (suck-back) distance by 2 mm increments. Monitor for air introduction in the runner.[1]
- 4
If the gate uses a valve gate pin, inspect the pin for wear or damage. A worn valve gate pin will not seal against the gate seat.
- 5
Inspect the gate tip area on the mold for erosion or damage at the gate insert seat.
- 6
If both temperature reduction and decompression adjustments fail to eliminate drool, pull the gate tip insert and inspect the sealing surface for erosion or contamination.
Sources
Mold-Masters (Milacron) Mold-Masters TempMaster Hot Runner Controller / System general technical documentation, Mold-Masters (Milacron)
Mold-Masters TempMaster documentation, gate temperature optimization and drool control procedures (general)
More guides for Mold-Masters (Milacron) Mold-Masters TempMaster
How to fix thermocouple drift on a Mold-Masters TempMaster hot runner system
A thermocouple that reads persistently above or below actual melt temperature will cause out-of-specification parts. Verify with a reference thermocouple before replacing the suspect sensor.
How to diagnose a hot runner zone not heating on a Mold-Masters TempMaster controller
A zone that fails to heat is usually a failed heater element, open thermocouple, or blown fuse on the TempMaster output card. Check the fuse first before testing heater resistance.
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