Hot injection nozzle specifications and parameters
The hot injection nozzle (also known as the hot nozzle) is a key component in the hot runner system that connects the hot runner plate and the cavity. Its specifications and parameters directly affect the melt delivery efficiency, plastic part quality, and mold compatibility, and must be accurately selected based on the type of plastic, plastic part structure, and molding requirements. The core function of the hot injection nozzle is to stably deliver the molten plastic in the hot runner plate to the cavity while maintaining the melt temperature and pressure. Its specifications mainly include structural form, diameter size, heating power, and applicable materials. Different parameter combinations correspond to different application scenarios. For example, when producing miniature electronic connectors, a fine-mouthed hot injection nozzle with a diameter of 0.8mm is required; when producing large car bumpers, a large-flow hot injection nozzle with a diameter of 12mm is required to meet the needs of fast filling.
The structure of a hot-dip nozzle is the most fundamental specification parameter, determining its applicability and performance characteristics. Open-type hot-dip nozzles (also known as free-flow nozzles) feature a simple structure, consisting of a nozzle body, a heating coil, and a sprue bushing. The gate is directly connected to the mold cavity, making them low-cost and easy to maintain. They are suitable for small and medium-sized parts with low surface quality requirements (such as toy parts). However, they can produce noticeable gate marks (1-3mm in diameter) and are prone to drooling. Valve-type hot-dip nozzles use a needle valve to control the gate opening and closing. The needle valve is actuated by a pneumatic or hydraulic cylinder, enabling precise control of filling time and gate sealing. They are suitable for parts requiring high surface quality (such as appliance housings). Gate marks can be controlled to within 0.3mm, but their structure is complex, and response time must be ≤0.1 second to avoid affecting the molding cycle. Specialized hot-dip nozzles are also available, including pointed nozzles (tip diameter ≤1mm, suitable for thin-walled parts), eccentric nozzles (nozzle axis offset from mounting axis, suitable for molds with limited space), and extended nozzles (nozzle length ≥50mm, suitable for deep-cavity parts).
Orifice size is a key parameter for hot-dip nozzles, directly affecting melt flow and filling speed. It primarily includes the nozzle outlet diameter and runner diameter. The outlet diameter (also known as the gate diameter) is selected based on part thickness and material fluidity. Plastics with good fluidity (such as PE) can use a small diameter (0.8-2mm), while plastics with poor fluidity (such as PC) require a large diameter (2-5mm). For thin-walled parts (thickness ≤ 1mm), the outlet diameter is typically 1.5-2 times the part thickness to ensure smooth filling. The runner diameter refers to the diameter of the melt channel within the hot-dip nozzle and is calculated based on the shot size per mold. The formula is: runner diameter (mm) = (shot size (g) / material density (g/cm³) / flow length (cm)) ^ 0.4 × 1.2. For example, for a PP part with a shot size of 50g (density 0.9g/cm³) and a flow length of 10cm, the runner diameter is approximately 3.5mm. A flow channel diameter that is too small will result in excessive pressure loss, while a flow channel diameter that is too large will increase the melt residence time and easily cause degradation.
Heating parameters determine the temperature control capability of a hot-dip nozzle, including heating power, heating method, and temperature control accuracy. Heating power is calculated based on the nozzle’s surface area and is typically 8-15W/cm². Small nozzles (length ≤ 50mm) require 20-50W, while large nozzles (length ≥ 100mm) require 100-300W. Insufficient power can cause the melt to cool, while excessive power can lead to localized overheating. Heating methods include external and internal heating. External heating (heating coils wrapped around the outside of the nozzle) offers low cost and ease of replacement, but suffers from poor heating uniformity. Internal heating (heating rods inserted into the nozzle) provides uniform heating (temperature differential ≤ 2°C) and is suitable for heat-sensitive materials, but is difficult to maintain. Temperature control accuracy is determined by the thermocouple’s position and the performance of the thermostat. High-quality hot-dip nozzles utilize armored thermocouples (response time ≤ 1 second) and, when combined with a PID thermostat, can achieve control accuracy of ±0.5°C, preventing temperature fluctuations that can cause changes in melt properties.
The material and installation parameters of a hot-dip nozzle affect its service life and mold compatibility. The nozzle body material must be heat-resistant (≥300°C), wear-resistant, and thermally conductive. Pre-hardened steel (such as H13) is used for standard plastics, while wear-resistant steel (such as STAVAX) or tungsten carbide (50-100μm thick) spray-coated is recommended for glass fiber-reinforced plastics. A service life of over one million mold cycles is expected. The nozzle length is determined by mold thickness. Standard lengths include 30mm, 50mm, 80mm, and 120mm, and custom lengths are available. During installation, ensure that the nozzle tip is flush with the cavity floor, with an error of ≤0.1mm, to avoid affecting part dimensions. Mounting thread sizes are typically M16×1.5 or M20×1.5, and must match the threaded holes in the hot runner plate. Tightening torque is determined based on the thread size (e.g., 50-60N · m for an M20 thread ) to ensure a secure seal and prevent damage to the threads.
Performance parameters are comprehensive indicators for evaluating the suitability of hot-dip nozzles, including maximum operating pressure, flow coefficient, and thermal expansion. The maximum operating pressure reflects the nozzle’s ability to withstand melt pressure. Standard hot-dip nozzles range from 150-200 MPa, while high-pressure hot-dip nozzles can reach up to 300 MPa, making them suitable for engineering plastics with high filling pressures (such as PBT with 30% glass fiber). The flow coefficient (Cv value) indicates the melt’s flow rate. A higher Cv value indicates lower flow resistance. It typically ranges from 0.5 to 2.0. When selecting a nozzle, ensure that the Cv value meets the melt flow requirements (calculated by the formula: flow rate = Cv value × √pressure difference). Thermal expansion requires clearance during installation. This is calculated based on nozzle length and operating temperature. For example, for a 100mm nozzle operating at 250°C, the thermal expansion is approximately 100 × (250 – 25) × 12 × 10⁻⁶ , which is approximately 0.27mm . Therefore, the installation clearance should be set to 0.3-0.4mm to prevent mold deformation caused by thermal expansion. For example, a hot runner mold for producing nylon cable ties uses a hot injection nozzle with a Cv value of 1.2 and a maximum working pressure of 200MPa . At an injection pressure of 150MPa , it can deliver 8g of melt per second , meeting the needs of high-speed molding.
