Injection molding needle valve hot nozzle system
The injection molding needle valve hot nozzle system is a high-precision injection molding equipment component primarily used for molding multi-cavity molds or large plastic parts. It controls the injection and stopping of the melt through the opening and closing of the needle valve, achieving precise control of the gating system. Compared to traditional open hot nozzles, needle valve hot nozzles can effectively eliminate gate marks, improve the surface quality of plastic parts, and reduce melt solidification and backflow at the gate, thereby improving production efficiency and product consistency. They are widely used in high-end injection molding fields such as automotive parts, medical devices, and precision electronics.
The needle valve hot injection nozzle system mainly consists of the hot injection nozzle body, needle valve, drive device, heating device and temperature control system. The hot injection nozzle body is made of high-strength alloy material and has a melt flow channel inside. Its size and shape are designed according to the structure and material properties of the plastic part to ensure smooth melt flow. The needle valve is installed at the outlet of the hot injection nozzle and its up and down movement is controlled by the drive device to open and close the gate. The head of the needle valve is usually made of wear-resistant materials such as carbide to increase its service life. The drive device is divided into three types: hydraulic drive, pneumatic drive and electric drive. Hydraulic drive can provide greater driving force and is suitable for large needle valve hot injection nozzles with smooth and reliable operation. Pneumatic drive has a simple structure and low cost, and is suitable for small and medium-sized hot injection nozzles. Electric drive has high control accuracy and can achieve stepless speed regulation of the needle valve, which is suitable for occasions with strict control requirements. The heating device usually adopts a wire-wound heating coil or a built-in heating rod, which is evenly wound or installed on the outside of the hot nozzle body to ensure that the melt in the flow channel is always maintained at the set temperature; the temperature control system monitors the temperature of the hot nozzle in real time through a thermocouple and is linked with the heating device to achieve precise temperature control to avoid melt solidification or degradation due to temperature fluctuations.
The working process of the needle valve hot nozzle system is divided into three stages: injection, holding pressure, and cooling. During the injection stage, the drive device drives the needle valve upward to open the gate. Under the action of injection pressure, the melt is injected into the cavity from the hot nozzle runner through the gate. When the cavity is filled to the preset volume, it enters the holding pressure stage. At this time, the needle valve remains open, and the melt continues to replenish the cavity under the action of the holding pressure to compensate for the cooling shrinkage of the melt. After the holding pressure is completed, the drive device drives the needle valve downward to close the gate to prevent the melt from flowing back. At the same time, the cavity enters the cooling stage until the plastic part is solidified and formed. The opening and closing timing of the needle valve must be precisely coordinated with the working cycle of the injection molding machine. Closing too early will result in material shortage of the plastic part, while closing too late will cause defects such as melt backflow and flash at the gate. Therefore, the movement of the needle valve is usually controlled by a position sensor or time relay to ensure its synchronization with the injection molding process.
The advantages of the needle valve hot injection nozzle system are mainly reflected in the following aspects: First, it can effectively eliminate gate marks. When the needle valve is closed, a tiny circular indentation will be formed at the gate, which is much smaller than the mark of the traditional open gate. It is especially suitable for plastic parts with high surface quality requirements, such as automotive interior parts, mobile phone casings, etc.; second, it reduces melt waste. After the needle valve is closed, it can prevent the melt from flowing back, avoid the generation of cold materials at the gate, reduce the generation of waste, shorten the molding cycle, and improve production efficiency; third, it realizes independent control of multiple cavities. In a multi-cavity mold, the needle valve of each hot injection nozzle can control the switching time separately, and adjust it according to the filling situation of each cavity to ensure the quality consistency of the plastic parts in each cavity, and solve the cavity difference problem caused by unbalanced melt flow in the traditional runner system; fourth, it is suitable for a variety of plastic materials, including high-temperature engineering plastics, reinforced plastics, etc. By reasonably selecting the material and heating method of the hot injection nozzle, the molding temperature requirements of different materials can be met.
When using and maintaining a needle-valve hot-nozzle system, the following points should be noted: First, strictly control the nozzle temperature. Different materials require different temperature settings. For example, when processing polycarbonate, the temperature is usually set between 260-300°C, and when processing polyethylene, it is set between 180-220°C. Excessively high temperatures can cause material degradation, while excessively low temperatures can reduce melt fluidity and cause injection difficulties. Second, regularly check the sealing performance of the needle valve. The clearance between the needle valve and the hot-nozzle gate should be maintained between 0.01-0.03mm. If the clearance is too large, melt leakage will cause flash, while if the clearance is too small, the friction of the needle valve movement will increase, affecting its opening and closing flexibility. Third, properly maintain the drive device. Hydraulic or pneumatic drive systems require regular replacement of hydraulic oil or compressed air filters to ensure stable drive pressure. Electric drive systems require regular inspection of the operating status of the motor and transmission components to avoid needle valve malfunction due to sticking. In addition, the hot-nozzle flow channel needs to be cleaned regularly to prevent solidified melt residue from clogging the flow channel, affecting melt flow and molding quality.
