Nozzle Tip Radius

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.

Nozzle tip is the very end of the injection machine's nozzle, in direct contact with the mold sprue bushing. Every shot of molten material passes through it, and its geometry (orifice and radius) drives pressure drop, closure speed and wear. ## Nozzle tip types - Open (general purpose): no valve, relies on melt freeze to avoid drooling - Pin-gate (positive shut-off): mechanically actuated pin, ideal for PE and PP - Thermal gate: relies on freezing, simple but with drool - Mixing tip: adds downstream mixing for color or additives - Anti-drool: mechanical device that closes at low pressure ## Typical parameters - Orifice: 3 – 12 mm depending on part and resin - Seat radius: standard 12.7 mm (½″) or 19.05 mm (¾″) per SPI standard - Material: nitrided H13 or D2 steel for abrasive resins (PVC, glass-filled) - Service life: 200,000 – 2 million cycles depending on resin and tip material ## Common issues Drooling from excessive temperature or fluid resin, stringing from insufficient temperature, leakage between nozzle and sprue from misalignment or worn radius, and orifice wear with glass-fiber-reinforced resins.

The nozzle tip orifice is the small hole through the nozzle tip that the melt passes through on its way from the nozzle into the mold's sprue. It is the final, narrowest restriction in the injection unit before the plastic enters the tool — so its diameter directly shapes flow, pressure and several common defects. ## Why its size matters - Smaller than the sprue: the orifice must be smaller than the mold's sprue-bushing orifice (and the tip radius slightly smaller than the sprue radius) so the tip seats and seals cleanly — otherwise melt leaks around the seat or the cold sprue can't pull free. - Flow & pressure: a smaller orifice raises shear and pressure drop (more shear heat, can help mixing) but can choke fill on big shots; a larger orifice eases flow but risks drool and slower freeze-off. - Freeze-off & drool: the orifice is often where the melt freezes between shots; sized and temperature-controlled wrong, it gives cold slugs, melt stringing or drooling. ## Selecting it Match the orifice to the shot size and resin: large enough to fill without excessive injection pressure or injection speed, small enough to seal against the sprue and control drool. It is a wear point and a quick service item on the nozzle tip/nozzle adapter — orifices erode and round over time, shifting the process. ## Related terms - See also: nozzle tip, nozzle, sprue, nozzle adapter, melt ## What is the nozzle tip orifice in injection molding? The small hole in the nozzle tip through which molten plastic flows from the nozzle into the mold's sprue; it is the last flow restriction before the mold and must be smaller than the sprue orifice to seal. ## Why must the nozzle orifice be smaller than the sprue? So the tip seats and seals against the sprue bushing without melt leaking around the joint, and so the solidified sprue pulls free cleanly on mold opening; a too-large orifice causes leaks and sprue-sticking. ## How does nozzle tip orifice size affect molding? A smaller orifice raises shear, pressure drop and heat but can restrict fill; a larger one eases flow but risks drool and slow freeze-off — so it is sized to the shot and resin to balance fill, sealing and stringing.

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.