Injection hot injection nozzle outlet groove
The wire groove of an injection molding hot runner nozzle is a critical structure in the hot runner system, housing and protecting the heater wire and thermocouple wires. Its design directly impacts the nozzle’s temperature control accuracy, wire life, and assembly and maintenance efficiency. The groove must ensure safe routing of wires within a limited space (the nozzle diameter is typically 10-30 mm) while also avoiding impacting the nozzle’s heating uniformity and melt flow path. Scientifically designing the groove’s size, shape, location, and protective measures is crucial to ensuring the nozzle’s long-term stable operation.
The dimensions of the wire trough must match the wire specifications. The trough width should be 0.5-1mm larger than the wire bundle diameter, and the trough depth should be 1-1.2 times the bundle diameter to ensure smooth insertion of the wires without pinching. For example, a wire bundle consisting of a 0.5mm diameter heater wire (1mm diameter with insulation) and a 0.3mm diameter thermocouple wire (0.8mm diameter with insulation) has a total diameter of approximately 1.5mm. The trough width should be 2-2.5mm and the depth should be 1.5-1.8mm. The trough length should cover the wire path from the heating element to the terminal block, and corners should be rounded (R ≥ 1mm) to prevent abrasion of the wire insulation caused by right angles. For hot-dip nozzles with multiple wire bundles (such as nozzles with independent heating sections), separate troughs are required to separate wires with different functions (such as the main heater wire, auxiliary heater wire, and thermocouple wire), with spacing ≥ 1mm to prevent interference or short circuits.
The location of the wire trough must balance thermal uniformity and wire heat dissipation. It should avoid the hot nozzle’s melt channel (distance ≥5mm) and areas with dense heating elements (distance ≥3mm) to prevent accelerated wire aging due to localized high temperatures. The wire trough is typically located at the side or end of the hot nozzle, extending along the nozzle’s axis. For side-gated hot nozzles, the wire trough should be away from the gate (distance ≥8mm) to prevent high temperatures at the gate from affecting the wires. For example, in a needle-valve hot nozzle with a melt channel diameter of 6mm and a heating element located 3mm outside the channel, the wire trough is positioned at a 90-degree angle to the side of the heating element, 8mm away from the channel. This avoids high-temperature areas without compromising nozzle strength. The outlet of the wire trough should be located close to the terminal block to minimize exposed wire length and reduce the risk of damage. A wire grommet (made of high-temperature-resistant silicone rubber, temperature resistance ≥200°C) should be installed at the outlet.
The protective structure of the cable trough is crucial for ensuring the lifespan of the conductors. The trough must be filled with a high-temperature-resistant insulating material (such as thermally conductive silicone rubber with a temperature resistance of ≥ 250 °C and a thermal conductivity of ≥ 1.0W/(m・K) ). This material completely encases the conductors, providing stability, insulation, and thermal conductivity, preventing vibration wear and localized overheating. Filling must be performed to ensure that no air bubbles are present, as these air pockets can easily cause the conductor temperature to rise due to thermal insulation. For cable troughs exposed near mold cooling channels, an insulating layer (such as mica sheets, 0.2-0.5mm thick ) should be added to prevent brittle insulation caused by sudden temperature drops. For example, a hot-dip nozzle’s cable trough, located near a 10mm diameter cooling channel, employs a 0.3mm thick mica sheet to maintain a stable temperature within the trough at 120-150 °C, preventing wire aging from temperature fluctuations between 60 and 180°C.
The machining accuracy of the cable trough affects assembly quality. The roughness of both sides of the trough must be ≤ Ra1.6μm to avoid scratching the wire insulation. The straightness of the trough must be ≤ 0.1mm/m to ensure smooth wire routing. Wire-cut EDM (accuracy ±0.01mm) is the preferred machining method. For deep troughs (depth > 10mm), wire-cut EDM is used to ensure wall verticality (≤0.02mm/100mm). For example, a 20mm diameter hot-dip nozzle with a 12mm deep and 2mm wide trough can achieve a wall verticality of 0.01mm/100mm and a roughness of Ra0.8μm. After laying, the wires are free of noticeable bending or squeezing. During assembly, the trough must be cleaned of oil and burrs. Then, the wire bundle must be placed evenly using specialized tools. Finally, the insulation material must be slowly injected. After curing, an insulation resistance test (≥500MΩ) is performed to ensure compliance.
Cable troughs must be easily accessible for maintenance and repair, and the design should consider the possibility of wire replacement. For easily damaged heating wires, removable terminal blocks can be installed at the ends of the troughs to avoid disassembling the hot-dip nozzle for wire replacement. During daily production, the cable trough seal should be inspected every 5,000 molds. Any cracks in the insulation material or exposed wires should be repaired or replaced promptly. For example, a hot-dip nozzle on one production line experienced insulation resistance drop below 50 MΩ due to a failed trough seal, allowing cooling water vapor to enter. By refilling with thermally conductive silicone rubber and replacing the deteriorated wires, the insulation resistance returned to above 2000 MΩ. Regularly monitor the temperature of the cable trough area with an infrared thermometer. If localized overheating (exceeding the wire’s upper temperature limit by 10°C) is detected, investigate whether the heating element is misaligned or the insulation material is deteriorating, and address the issue promptly to prevent wire burnout.
