1. By controlling the opening time of the gate, the cavity can be filled smoothly and the melt flow can be balanced to eliminate welding marks.
Injection molding of large injection molded parts usually requires two or more hot gates to fill it. For ordinary hot-gating systems, the gate opens at the same time as the injection begins. Such a way of feeding glue inevitably has fusion defects, that is, when the two melt forwards meet, because the two melts cannot be completely melted into one body, and a fusion mark is formed, the reaction is generally called a welding mark on the product surface. . Although it can be improved by increasing the melt temperature, increasing the holding pressure, and adjusting the injection molding process parameters, the actual improvement is limited. The valve-valve hot runner technology is used to construct the pouring system, which can realize the program control of the opening and closing of each valve gate, and also control the valve needle to open when the first melt just flows through the second valve gate. Open the second gate. At this time, you can open or close the first gate as needed, and continue until all gates are opened and the cavity is filled, so that the melt is completely fused to obtain a product without welding marks.
2. The products obtained by this technology will not have residual gate marks. Therefore, it can be applied to injection molded parts with high surface quality requirements.
Sometimes the reason for using the valve gate is because the valve gate has a smooth trace on the part, which is only equivalent to the trace left by a ejector pin, so it is compared with the latent gate and other types of hot runner end marks Much smaller.
3. More effective control of the holding pressure and forming cycle.
The needle valve hot runner can use a larger diameter gate, which can accelerate the flow of the melt in the mold cavity, thereby shortening the forming cycle of the part and better holding pressure.
4. Effectively reduce the internal stress of the product and improve the stability of the product.
As mentioned earlier in the hot runner of Zhongshan Automobile Mould, in the traditional hot casting system, the two melt flow fronts will form a weld mark after the convergence. The result will not only affect the appearance of the product, but also easily generate large residual internal stresses inside the product. . This stress concentration will reduce the strength of the product. If valve gate control technology is used to control the melt feeding sequence, the direct intersection of the melt flow front can be effectively avoided, thereby avoiding the occurrence of stress concentration and improving the stability of the product.
In addition, the use of a needle valve type hot nozzle can also prevent the occurrence of back suction and wire drawing (drawing) when the mold is opened. Needle-valve hot runner system structure and principle. The needle movement of the needle-valve hot runner can be controlled by spring, and it can also be controlled by air pressure or hydraulic pressure. Its structure is various.
For large injection molded parts like car bumpers, we usually use timing needle valve hot runners. Its stability is better, and the opening and closing time control of the gate is also more reliable.
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