Nozzle Tip Orifice

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 radius is the spherical radius machined on the end of the machine nozzle. It must match the concave radius of the sprue bushing in the mold so the two seat together leak-tight when the nozzle contacts the mold. ## Standard radii The two most common (SPI) standards are 1/2″ (12.7 mm) and 3/4″ (19.05 mm). The nozzle radius and the sprue-bushing radius must belong to the same family — a 1/2″ nozzle does not seal in a 3/4″ bushing. ## The matching rule Two classic rules keep the interface tight: - Radius: the nozzle tip radius should be about 1/16″ (1.5 mm) smaller than the sprue-bushing seat radius, so contact happens on the inner ring and seals fully. - Orifice: the nozzle orifice should be about 0.5–1 mm smaller than the sprue-bushing entry hole, so the cooled sprue pulls cleanly without an undercut. ## Why it matters A mismatch leaves a gap at the interface: material drools or flashes there, the sprue sticks, cold slugs form, and you lose the thermal seal. Correct radius matching is part of basic nozzle-to-mold setup and prevents a whole class of sprue defects. ## What radius should the nozzle tip be? Match it to the mold: use the same standard family (1/2″ or 3/4″) as the sprue bushing, with the nozzle radius about 1/16″ (1.5 mm) smaller than the bushing seat radius for a tight seal. ## How do you match the nozzle to the sprue bushing? Keep the radius about 1.5 mm smaller and the nozzle orifice about 0.5–1 mm smaller than the sprue bushing. This seals the contact and lets the sprue release without an undercut.

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.