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Classification of hot runner systems

Date：2024-09-09 Hits：296

Classification of hot runner systems


Generally speaking, hot runner system is divided into single head hot runner system, multi-head hot runner system and valve gate hot runner system. Single head hot runner system mainly consists of single nozzle, nozzle head, nozzle connecting plate, temperature control system and so on.


 


Single-head hot runner system plastic mould structure is relatively simple. The molten plastic is injected from the injection moulding machine into the nozzle connecting plate, and then injected into the cavity after reaching the nozzle head through the nozzle. It is necessary to control the dimensions d, D, L and the axial displacement of the nozzle by adjusting the thickness dimensions of the nozzle connecting plate, so that the fixed mould fixing plate presses against the end face of the nozzle connecting plate, or directly using the injection moulding machine nozzle to press against the end face of the nozzle connecting plate, which can also achieve the same purpose. Set a lead slot at a suitable position of the fixed mould fixing plate to allow the power cable to be led from inside the mould to connect with the terminal block mounted on the mould.


 


Multi-head hot runner system plastic moulds are more complex in structure. The molten plastic is injected from the injection moulding machine into the nozzle connecting plate, flows through the hot runner plate to the nozzle and then reaches the nozzle head and is injected into the cavity. The nozzles of the hot runner system have a radial dimension D1 fit with the stator plate and an axial dimension limit. The nozzle head and the fixed mould insert have radial dimension D to ensure that the molten plastic does not overflow into non-cavity parts, and the hardness of the fixed mould insert is required to be hardened to about 50 HRC. The distance L between the parting surface and the axial positioning surface of the hot nozzle must be strictly controlled, and this dimension 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 working temperature of the mould. In order to ensure that the nozzle and the hot runner plate fit reliably, so as not to produce deformation of the hot runner plate, there is an adjusting pad above the top of the nozzle, which, together with the axial positioning surface of the nozzle itself, restricts the movement of the nozzle in the axial direction and effectively controls the possible deformation of the hot runner plate. At room temperature, a gap of 0.025 mm is controlled between the adjustment pad and the hot runner plate and the fixed mould plate so that the adjustment pad is properly pressed at operating temperature after the mould has been heated. The hot runner system's locating seat and locating pin together control the position of the hot runner plate in the mould. The locating seat and the fixed template have radial dimension D2 to match the requirements, and the depth h must be controlled accurately, the axial direction of the locating seat plays the role of supporting the hot runner plate, which is directly subjected to the injection pressure of the injection machine. Positioning pin and hot runner plate fixed plate have matching requirements. There must be enough space between the hot runner plate and the template to wrap the heat insulation material. The hot runner plate and the fixing plate must be provided with sufficient wiring slots to allow the power cable to lead from inside the mould to connect with the terminal block mounted on the mould. There is a radial dimension D1 fit requirement between the nozzle connection plate and the fixed plate of the fixed mould so that the injection head of the injection moulding machine fits well with the nozzle connection plate on the mould. Near the hot runner plate, the fixed plate, hot runner plate fixing plate and fixed mould fixing plate are connected with screws to enhance the rigidity of the hot runner plate.


 


Valve gate hot runner system plastic mould structure is the most complicated. It has the same structure with the ordinary multi-head hot runner system plastic mould, in addition, there is also 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, using the hydraulic device of the injection machine connected to the mould, forming a hydraulic circuit to achieve the opening and closing movement of the valve needle, to control the molten state of the plastic injected into the cavity.


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