In general, the hot runner system is divided into single-head hot runner system, multi-head hot runner system and valve gate hot runner system. The single-head hot runner system is mainly composed of a single nozzle, nozzle head, nozzle connecting plate, temperature control system, etc.

Single head hot runner system plastic mold structure is simple. The molten plastic is injected into the nozzle connecting plate by the injection molding machine, and then injected into the cavity after reaching the nozzle head through the nozzle. The same purpose can be achieved by controlling dimensions d, D and L and by adjusting the thickness of the nozzle connecting plate to make the fixed die plate press the end face of the nozzle connecting plate and control the axial displacement of the nozzle, or by directly using the injection molding machine nozzle against the end face of the nozzle connecting plate. A lead groove is provided at a suitable position of the fixed die plate, so that the power cord is drawn from the die and connected with the wiring base installed on the die.

Multi-head hot runner system plastic mold structure is more complex. The molten plastic is injected into the nozzle connecting plate by the injection molding machine, flows to the nozzle through the hot runner plate, reaches the nozzle head, and then injected into the cavity. The nozzle of the hot runner system and the fixed template have radial size D1 matching requirements and axial size limit requirements. The nozzle head and the fixed die insert have radial dimension d matching requirements to ensure that the molten plastic does not overflow to the non-cavity part, and the hardness of the fixed die insert is required to be hardened to about 50HRC. The distance L between the parting surface and the axial positioning surface of the hot nozzle must be strictly controlled, and the size should be determined according to the actual distance L' of the nozzle at room temperature plus the actual extension ΔL of the nozzle at the normal operating temperature of the mold. In order to ensure the reliable fit between the nozzle and the hot runner plate and not cause deformation of the hot runner plate, the top of the nozzle is provided with an adjustment pad, which, together with the axial positioning surface of the nozzle itself, limits the movement of the nozzle in the axial direction and effectively controls the possible deformation of the hot runner plate.

At normal temperature, the gap between the adjustment pad and the hot runner plate and the fixed die plate is controlled by 0.025mm so that after the die is heated, the adjustment pad is just pressed when the working temperature is in the state. The positioning seat of the hot runner system and the positioning pin together control the position of the hot runner plate in the mold. The positioning seat and the fixed template have radial size D2 matching requirements, and the depth h must be controlled accurately. 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 machine. The positioning pin and the hot runner plate fixing plate must meet the requirements. There must be enough space between the hot runner plate and the formwork to wrap the insulation material. The hot runner plate and the fixing plate must be provided with sufficient wiring slots to allow the power line to be drawn from the mold and connected to the connector mounted on the mold. There is a radial dimension D1 fit requirement between the nozzle connecting plate and the fixed mold plate, so that the injection head of the injection molding machine can fit well with the nozzle connecting plate on the mold. In the vicinity of the hot runner plate, the fixing plate of the hot runner plate and the fixing plate of the fixed die are connected with screws to enhance the rigidity of the hot runner plate.

Valve gate hot runner system plastic mold structure is the most complex. It has the same structure as the common multi-head hot runner system plastic mold, and there is also a set of valve needle transmission device to control the opening and closing movement of the valve needle. The transmission device is equivalent to a hydraulic cylinder, and the hydraulic device of the injection machine is connected with the mold to form a hydraulic circuit to realize the opening and closing movement of the valve needle and control the molten plastic injection cavity.