Stringing
At mold opening the gate is still molten, drawing a fine thread from the part to the gate that lands on the part or in the cavity.
Timing: The cooling step did not drop far enough; break-off happens while the melt is still connected.
TECHNOLOGY PRINCIPLES
Technology Principles
The whole runner does not heat and cool. Temperature changes only at the tip and gate, following the molding cycle: heat during filling, hold during packing, cool down in the cooling step, and finish gate solidification before mold opening.
01HEAT LOCATION
Heat is applied only where the tip meets the gate
Heat is applied only at the contact interface between the tip and the mold gate; the middle of the runner is not heated.
The tip is heated and sensed independently, so heat stays close to the gate. The manifold and nozzle body remain on the constant-temperature controller, avoiding repeated heating and cooling of the whole runner.
The thermal inertia of the whole runner is therefore not part of the response. Heating and cooling happen only in the small tip section, which is why it can keep up with an 18-second cycle.
02CYCLE TIMING
In one molding cycle, gate temperature moves in three steps
Temperature setpoints switch across filling, packing and cooling, and gate solidification finishes before mold opening. The example below uses an LCP precision connector with an 18-second cycle.
FILL
Raise to setpoint
320℃
Bring the tip to setpoint before melt enters, so low-viscosity material can fill the part.
PACK
Hold setpoint
320℃
Keep the temperature through packing so local cooling does not stop the flow.
COOL
Drop below freeze
260℃
The gate solidifies before the cavity; the break-off point stays at the tip, not on the part.
OPEN
Set and break
Instant
No cycle-time penalty. The gate is already solid at mold opening, so stringing and drooling have no chance to form.
03GATE DEFECTS
Three defects fail at different steps
All three occur where the tip meets the gate. The same LCP precision connector reference applies: stringing and drooling come from excessive temperature, clogging from insufficient temperature. Once the temperature sequence is right, they are not suppressed by machine tuning; the conditions for them never form.
Drooling
Gate temperature is too high; melt out-of-control at gate after mold opening results in continuous dripping and flash that builds into a slug.
Timing: Solidification is not complete before mold opening, so the gate never forms a seal.
Clogging
Gate temperature is too low, so melt freezes early in the tip channel; the next shot sees a smaller or fully blocked passage.
Timing: The filling step does not heat fast enough, and thin-wall parts are especially exposed.
04CONSTANT vs. FHFC
How it differs from a constant-temperature runner
A constant-temperature runner heats the gate through the nozzle body and holds a nearly fixed temperature, making filling and clean break hard to satisfy at once. FHFC heats and senses the gate independently and switches with the cycle.
| Metric | Constant temperature | FHFC |
|---|---|---|
| From cold start to production | 24 min | 18 min (the gate reaches temperature in the first 3 min) |
| Gate temperature | 285℃ (about 35℃ below setpoint) | 320℃ (at setpoint) |
| Temperature swing per shot | ±20℃ (268–307) | Switches between 320℃ and 260℃ with the cycle; the gate breaks cleanly at mold open |
The 24 min, 285℃ and ±20℃ figures come from on-site measurements on an LCP precision connector project running an 18 s cycle; values vary with material, cavitation and mold structure.
The problem with constant temperature is not controller accuracy. The gate section has no independent heat source; its temperature is transferred, not controlled.
Heat transfer decays, so the gate runs about 35℃ below setpoint. The whole runner is heated together, and each shot still swings by ±20℃.
A fixed temperature means you can only choose one point: the high temperature needed for filling or the low temperature needed for break-off. FHFC separates the two with an additional AM Smart controller dedicated to the gate.
05PARAMETERS
In parameters, only three numbers need to be set
Resin temperature, mold temperature and hot runner temperature are calculated separately. Gate temperature is set by heater power, gate-section heat capacity and cooling time; it cannot be replaced by resin temperature.
Gate temperature
320℃
The cooling step drops to 260℃. Set two points for the material: high temperature for filling and packing, below the freeze point before mold opening.
Heating power
300W / circuit
An independent tip channel reaches temperature in 3 minutes. It does not heat the entire manifold, so heat-up does not hold up the cycle.
Cycle timing
18s(example)
All three values are examples from an LCP precision connector running an 18 s cycle; recalculate when the material or layout changes.
How the principle maps to four products
Choose a series by gating method and gate mark, then return here to check temperature timing and parameters.
SD Series
Flame-retardant and corrosion-resistant resins; transparent and optical components; runner-gate molds
View specificationsTP Series
Precision plastic parts, standard precision molding, direct-gate molding
View specificationsVG Series
High-precision connectors, cosmetic components, mirror-finish molding, gate-mark-free parts
View specificationsPVG Series
PVC and other easily degradable resins, corrosive materials, and specialized engineering plastics
View specifications06ARTICLES
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