What is a needle valve hot runner system
For the current injection hot runner technology, the hot runner system is mainly divided into open type and needle type. Each has its own advantages. Different types of hot runners are selected according to different needs of the manufacturer. We know many advantages of the hot runner system, open and needle. The most intuitive and sure difference between a valved hot runner is the price, so what are the advantages and value of the needle valve?
Performance
Valve needle hot nozzle, good color change performance, suitable for most plastics, good flow performance, very fine gate marks. 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.
2 types
This type of hot runner system has many advantages that are not available with hot tip and cast runner systems. If the gate switching time can be controlled artificially, the gate is smooth and flat, and the technical field of hot runner technology can be expanded.
Since the valve gate is closed by the mechanical action of the valve needle and is not limited by the plastic cooling time at the gate, the valve gate runner system can sometimes greatly shorten the molding cycle of the plastic part. The gate size can also be made larger, which is good for processing shear sensitive plastics. The valve gate method can process small parts of several grams and can process large parts of several kilograms. Various engineering plastics can be processed to produce parts using valve gates. If there are multiple cavities of different sizes in a set of molds, such as the valve type runner system, the switching time of each gate can be controlled to realize the separate adjustment and control of the flow of each cavity. This is especially important for a multi-cavity mold with a large difference in shape and size. Also for high productivity, molds with multiple layers of facets are only achieved by using a valved hot runner system.
3 action device
The mechanical action of the valve needle can be controlled by hydraulic oil or compressed gas. The hydraulic needle method is effective and accurate. However, it is possible to soil plastic parts during the production process. Therefore, in the production of medical plastic products, it must be produced by compressed gas control methods to ensure the cleaning of the products. In addition, the use of the valve needle control device increases the height of the mold set and the overall mold. Consideration should be given to mold design and injection molding machine selection. A cooling water channel is also required on the formwork on which the valve needle control unit is mounted.
4 considerations
As with the hot-tip and cast-in-place hot runner system applications, if the temperature control of the valve gate is not good, it will cause serious production difficulties. For example, if the temperature at the gate is too high, the plastic may stick to the valve needle when the mold is opened. Conversely, if the temperature at the gate is too low, the gate plastic is too cold, making it difficult to close the valve needle. Valve gate hot runner molds are more expensive than hot tip and cast sleeve hot runner molds. If the valve-type hot runner system and the valve needle control device are not designed and manufactured well, problems such as a flow dead angle after the valve needle or a flashing phenomenon on the sliding mating surface between the valve needle and other parts may occur. In addition, if the valve needle is not made well, the closing operation is improperly controlled, and there are serious consequences of damaging the gate. Therefore, the valve hot runner system has many advantages that are not available in the other two types of hot runner systems, but also increases the complexity of the mold.
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