Nozzle Temperature

Barrel temperature is the set of heater-band temperatures along the injection barrel, zone by zone, that progressively melt the resin as the screw conveys it forward. It is set from the resin's recommended melt temperature and is the operator's main lever on melt quality. ## The barrel zones A barrel is split into three to five controlled zones (plus the nozzle), driven by the barrel heat bands: - Rear / feed zone: takes in pellets and starts softening — kept coolest to avoid bridging at the throat. - Middle / compression zone(s): where most of the melting and mixing happens. - Front / metering zone: homogenizes the melt to target before the nozzle temperature zone. ## Temperature profiles - Increasing (ramped): coolest at the rear, hottest at the front — the common default. - Flat: similar across zones — used for shear-sensitive resins. - Reverse (declining): hotter rear, cooler front — sometimes used for heat-sensitive resins or to fight drooling. ## Why it matters - Too hot: thermal degradation, drool, discoloration and longer cooling, and it raises residence time risk. - Too cold: unmelted pellets, high screw torque, short shots and accelerated screw/barrel wear. Always verify the actual melt with an air-shot probe — the set point is not the same as the real melt temperature. ## Related terms - See also: barrel, barrel heat bands, melt, nozzle temperature, residence time ## What is barrel temperature in injection molding? It is the zone-by-zone heater setpoints along the barrel that melt the resin, set from the resin's target melt temperature. ## How many barrel zones are there? Typically three to five controlled zones plus the nozzle, from the rear feed zone to the front metering zone. ## What happens if barrel temperature is too high? The melt degrades — discoloration, black specks, drooling and weaker parts — while cooling and residence-time problems grow.

The nozzle is the tip at the front of the barrel that connects the injection unit to the mold and channels the melt into the mold's sprue bushing, keeping it molten on the way through. It is the last metal the plastic touches before the sprue. ## Types of nozzle - General-purpose (open / free-flow): a simple open bore — most common, lowest pressure drop. - Reverse-taper: tapers so the cooled slug pulls back with the sprue; helps stringing on some resins. - Shut-off / valve nozzle: a mechanical or spring valve closes the bore to stop drooling, needed for free-flowing resins (PA, PP) or when the nozzle pulls away between shots. ## How it seats and heats The nozzle tip has a spherical nozzle tip radius and an orifice that must match the sprue bushing for a leak-tight seal. The nozzle has its own heater band, controlled as the nozzle temperature zone, because it is a small thermal mass touching the cool mold each cycle. ## Common problems - Drooling / stringing: nozzle too hot or no shut-off. - Freeze-off / cold slug: nozzle too cold — short shots and a plugged tip. - Flash or leak at the interface: wrong radius or orifice match with the sprue bushing. ## Related terms - See also: injection unit, barrel, sprue, nozzle tip, nozzle temperature ## What is the nozzle in injection molding? It is the tip at the front of the barrel that delivers the melt from the injection unit into the mold's sprue, with its own heater band to keep the plastic molten. ## What are the types of injection nozzles? General-purpose (open), reverse-taper, and shut-off (valve) nozzles, chosen by resin flow behaviour and whether drooling must be prevented. ## Why does a nozzle drool? Because it is too hot or has no shut-off valve, so low-viscosity melt seeps out between shots; a shut-off nozzle or lower nozzle temperature stops it.

A nozzle heat band is the electric heater that clamps around the nozzle and keeps it at its own controlled temperature, separate from the barrel zones. Because the nozzle is the last, narrowest part of the injection unit before the mold and sits against cold steel, it loses heat fast and needs its own dedicated band to hold a stable nozzle temperature. ## What it is and how it works - A band (or coil/ceramic) heater wrapped on the nozzle body, drawing power from the machine controller. - A thermocouple on the nozzle gives feedback so the controller maintains the setpoint as its own heat zone. - It is sized for the nozzle: too little wattage can't keep up, too much overshoots and degrades the melt. ## Why a separate nozzle zone matters - Prevents freeze-off: if the nozzle runs too cold, the melt skins over or solidifies at the nozzle tip, blocking flow and causing short shots or cold slugs. - Prevents drool and degradation: too hot and the resin drools between shots, strings, or thermally degrades — discoloration and splay. - Melt consistency: a steady nozzle temperature keeps the melt entering the mold uniform shot-to-shot, which is why it is tuned independently of barrel temperature. ## Practical notes Set it from the resin's recommended melt range and fine-tune for drool vs freeze-off; watch for a failed band (cold zone, alarms) or a shorted band. Many shops insulate the nozzle to reduce radiant loss and stabilize the zone. ## Related terms - See also: nozzle, nozzle temperature, nozzle tip, barrel, melt ## What is a nozzle heat band? An electric heater band clamped around the injection nozzle that maintains it as a separate temperature zone, so the nozzle stays hot enough to flow but not so hot it drools or degrades the melt. ## Why does the nozzle need its own heater? The nozzle is thin and presses against the cold mold, so it loses heat quickly; a dedicated band with its own thermocouple holds a stable nozzle temperature that the barrel zones alone can't. ## What happens if the nozzle temperature is wrong? Too cold causes freeze-off, cold slugs and short shots; too hot causes drooling, stringing and thermal degradation (discoloration, splay). It is tuned independently to balance these.

Sprue is the main channel of the mold that receives molten plastic directly from the machine nozzle and conducts it to the runner (or directly to the cavity in single-cavity molds). In cold-runner molds it is the first piece of scrap generated each cycle. ## Sprue geometry - Conical shape with 2 – 4° per side (4 – 8° included) for clean ejection - Entry radius equal to or larger than the nozzle radius - Entry diameter: 2 – 6 mm depending on part - Exit diameter: 4 – 12 mm - Length: as short as possible, typically 30 – 80 mm ## Mold types - Standard sprue bushing: hardened-steel insert (H13, P20) bolted to the plate - Hot sprue: heated, eliminating the scrap cone - Direct gate: sprue feeds directly into the cavity, no runner (single cavity) - Cold sprue eliminator: hybrid with extended nozzle ## Sprue extraction In cold-runner molds the sprue must come out with the runner via: - Sprue puller (Z-pin, reverse-taper retention) - Robot with cutter - Gravity drop if mold geometry allows ## Common issues Sprue sticking to the nozzle (insufficient radius or draft), drooling at open, gating of the cone to the stripper plate, and premature wear of the sprue bushing with glass-fiber-reinforced resins.