Generally speaking, hot runner systems are divided into
Internal Heating System (COOL ONE）
External Heating Hot Runner System,
including Single Nozzle Hot Runner System (HOT SPRUE BUSHINGS),
Multi-Nozzle Hot Runner System (HOT ONE/GATE-MATE）
and Valve Gate Hot Runner System (POLYVALVE).
The single nozzle hot runner system mainly consists of a single hot nozzle, hot nozzle tip, hot nozzle connecting plate, temperature control system, etc. The plastic mold structure of the single nozzle hot runner system is relatively simple. Molten plastic is injected from the injection molding machine into the hot nozzle connecting plate, reaches the hot nozzle tip through the hot nozzle, and then is injected into the cavity. It is necessary to control the dimensionsd, D, L and adjust the thickness dimension of the hot nozzle connecting plate to make the fixed mold fixing plate press the end face of the hot nozzle connecting plate to control the axial displacement of the hot nozzle, or directly use the hot nozzle of the injection molding machine to press against the end face of the hot nozzle connecting plate to achieve the same purpose. A wire lead groove is set at a suitable position on the fixed mold fixing plate to allow the power cord to be led out from the mold and connected to the terminal block installed on the mold.
The plastic mold structure of the multi-nozzle hot runner system is relatively complex. Molten plastic is injected from the injection molding machine into the hot nozzle connecting plate, flows to the hot nozzle through the runner plate, reaches the hot nozzle tip, and then is injected into the cavity. The hot nozzle of the hot runner system has radial dimensionD matching requirements and axial dimension limiting requirements with the fixed mold plate. The hot nozzle tip has radial dimensiond matching requirements with the fixed mold insert to ensure that molten plastic does not overflow to non-cavity parts, and the hardness of the fixed mold insert is required to be quenched to about50HRC.
The distanceL between the parting surface and the axial positioning surface of the hot nozzle must be strictly controlled. This dimension should be determined according to the actual distanceL′ of the hot nozzle at room temperature plus the actual extension amountΔL of the hot nozzle at the normal working temperature of the mold. To ensure reliable fitting between the hot nozzle and the hot runner plate without deformation of the hot runner plate, an adjusting pad is set above the top of the hot nozzle. Together with the axial positioning surface of the hot nozzle itself, the adjusting pad limits the axial movement of the hot nozzle and effectively controls the possible deformation of the hot runner plate.
At room temperature, a gap of0.025mm is controlled between the adjusting pad, the hot runner plate and the fixed mold fixing plate, so that the adjusting pad is just pressed tightly at the working temperature after the mold is heated. The positioning seat and positioning pin of the hot runner system together control the position of the hot runner plate in the mold. The positioning seat has radial dimensionD2 matching requirements with the fixed mold plate, and the depthh must be accurately controlled. The axial direction of the positioning seat plays the role of supporting the hot runner plate and directly bears the injection pressure of the injection molding machine.
The positioning pin has matching requirements with the hot runner plate fixing plate. Sufficient clearance must be left between the hot runner plate and the mold plate to wrap thermal insulation materials. The hot runner plate and fixing plate must be provided with sufficient wiring grooves to allow the power cord to be led out from the mold and connected to the terminal block installed on the mold. The hot nozzle connecting plate has radial dimensionD1 matching requirements with the fixed mold fixing plate to ensure good cooperation between the injection head of the injection molding machine and the hot nozzle connecting plate on the mold. Near the hot runner plate, the fixed mold plate, hot runner plate fixing plate and fixed mold fixing plate are connected with screws to enhance the rigidity of the hot runner plate.
The valve gate hot runner system has the most complex plastic mold structure. It has the same structure as the ordinary multi-nozzle hot runner system plastic mold, and additionally has a set of valve pin transmission device to control the opening and closing movement of the valve pin. The transmission device is equivalent to a hydraulic cylinder, which is connected with the mold by using the hydraulic device of the injection molding machine to form a hydraulic circuit, realize the opening and closing movement of the valve pin, and control the injection of molten plastic into the cavity.