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Dongguan HongS Jingyan Hot Runner Technology Co., Ltd.
Shenzhen HongS Hot Runner Technology Co., Ltd.
Jiangxi HongS Mould Co., Ltd.

TEL86-0769-81908761

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AddressPeasant Industrial Zone, Tianwei, Fenggang Town, Dongguan City, Guangdong Province

Company news HOME >> News >> Company news

What is a hot runner - the third chapter
Issuing Time:2018-09-01

structure


Hot runner systems generally consist of hot nozzles, manifolds, temperature control boxes and accessories. Hot nozzles generally include two types: open hot nozzles and needle valve hot nozzles. Since the form of the hot nozzle directly determines the selection of the hot runner system and the manufacture of the mold, the hot runner system is often divided into an open hot runner system and a needle valve hot runner system. The manifold is used in a multi-cavity or multi-point feed, single point feed but level offset. The material is usually P20 or H13. The manifold is generally divided into two categories, standard and non-standard. The structure is mainly determined by the distribution of the cavity on the mold, the nozzle arrangement and the gate position. The temperature control box includes the main unit, cables, connectors, and wiring male and female sockets. Hot runner accessories typically include: heaters and thermocouples, runner seals, connectors, and junction boxes.


Taxonomy


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


The single-head hot runner system plastic mold structure is relatively simple. The molten state plastic is injected into the nozzle connecting plate from the injection molding machine, and after reaching the nozzle head through the nozzle, it is injected into the cavity. It is necessary to control the dimensions d, D, L and by adjusting the thickness dimension of the nozzle connecting plate, so that the fixed mold fixing plate presses the end surface of the nozzle connecting plate, controls the axial displacement of the nozzle, or directly uses the nozzle of the injection molding machine to abut the nozzle connecting plate. The end face can also achieve the same purpose. A lead slot is provided at a suitable position of the fixed mold fixing plate, and the power cord is taken out from the mold and connected to the terminal block mounted on the mold.


The plastic mold structure of the multi-head hot runner system is more complicated. The molten plastic is injected into the nozzle connecting plate by the injection molding machine, flows through the hot runner plate to the nozzle, reaches the nozzle head, and is injected into the cavity. The nozzles and fixed plates of the hot runner system have radial dimension D1 matching requirements and axial dimensional limit requirements. The nozzle head and the fixed mold insert have a radial dimension d matching requirement to ensure that the molten plastic does not overflow to the non-cavity portion, and the hardness of the fixed mold insert is required to be hardened by about 50HRC. The distance L between the parting surface and the axial positioning surface of the hot nozzle must be strictly controlled. The size should be determined according to the actual distance L' of the nozzle at the normal temperature state plus the actual extension amount ΔL of the nozzle at the normal working temperature of the mold. In order to ensure that the nozzle and the hot runner plate are reliably attached without deforming the hot runner plate, an adjusting pad is arranged above the top of the nozzle, and the adjusting pad together with the axial positioning surface of the nozzle limits the axial movement of the nozzle. And the deformation that may occur in the hot runner plate is effectively controlled. In the normal temperature state, the gap between the adjusting pad and the hot runner plate and the fixed plate fixing plate is controlled to be 0.025 mm so that the mold is heated, and the adjusting pad is just pressed at the working temperature state. The locating seat of the hot runner system and the locating pin together control the position of the hot runner plate in the mold. The positioning seat and the fixed template have the radial dimension D2, and the depth h must be controlled accurately. The axial direction of the positioning seat acts to support the hot runner plate and directly withstand the injection pressure of the injection machine. The positioning pin has a matching requirement with the hot runner plate fixing plate. There must be sufficient clearance between the hot runner plate and the formwork to wrap the insulation. The hot runner plate and the fixed plate must have sufficient wiring slots for the power cord to be drawn from the mold to the terminal block mounted on the mold. There is a radial dimension D1 matching requirement between the nozzle connecting plate and the fixed mold fixing plate, so that the injection head of the injection molding machine cooperates well with the nozzle connecting plate on the mold. In the vicinity of the hot runner plate, the fixed plate, the hot runner plate fixing plate, and the fixed mold fixing plate are screwed together 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 plastic mold of the ordinary multi-head hot runner system, and an additional valve needle transmission device controls the opening and closing movement of the valve needle. The transmission device is equivalent to a hydraulic cylinder, which is connected with the mold by the hydraulic device of the injection machine to form a hydraulic circuit, realizes the opening and closing movement of the valve needle, and controls the molten plastic injection into the cavity.


Design procedure


First, determine the position of the inlet according to the structure of the plastic part and the requirements for use. As long as the plastic structure allows, the nozzle and nozzle tip do not interfere with the forming structure within the fixed mold insert, and the feed port of the hot runner system can be placed anywhere in the plastic part. Feed port locations for conventional plastic injection molding are typically selected empirically. For large and complex shaped plastic parts, the position of the injection-molded inlet can be simulated by computer aided analysis (CAE) to simulate the flow of molten plastic in the cavity, analyze the cooling effect of various parts of the mold, and determine the ideal feed. Mouth position.


Second, the nozzle tip form of the hot runner system is determined. The use of plastic materials and products is a key factor in the choice of nozzle tip form. The production volume of the plastic parts and the manufacturing cost of the mold are also important factors in selecting the nozzle tip form.


Third, the number of cavities per mold is determined according to the production batch of the plastic part and the tonnage of the injection equipment.


Fourth, the number of nozzles is determined by the determined position of the feed port and the number of cavities per die. If a product is formed and one or more inlets are selected, a single-head hot runner system is used as long as one nozzle; if a product is formed, one or more cavities or one or more cavities are selected. For the mouth, multiple nozzles are required, that is, a multi-head hot runner system is used, except for a mold structure having a cross flow passage.


Fifth, the size of the radial dimension of the nozzle is determined according to the weight of the plastic part and the number of nozzles. The same type of nozzle has a plurality of size series, which respectively meet the plastic forming requirements in different weight ranges.


Sixth, the size of the mold structure is determined according to the structure of the plastic part, and then the standard length series size of the nozzle is selected according to the thickness dimension of the fixed mold insert and the fixed template, and finally the thickness dimension of the fixed template and other dimensions related to the hot runner system are trimmed.


Seventh, the shape of the hot runner fixing plate is determined according to the shape of the hot runner plate, the power line lead groove is arranged on the plate, and a sufficient cooling water loop is designed in the vicinity of the hot runner plate, the nozzle and the nozzle head.


Eighth, complete the design drawing of the plastic mold of the hot runner system.


Ninth, the mature hot runner system must take into account the degree of cooperation between the hot runner system and the plastic mold, that is, the design of the hot mold half. The hot mold half refers to the precision hot runner system that the professional hot runner manufacturer processes for the customer. It has the characteristics of simple and convenient maintenance, high precision, fast processing, etc.. Reduce the injection pressure and clamping force.