Question

4) What are some considerations when designing with tunnel gating?

Answer 1

When a tunnel gate is provided on the fixed half, the molded product is cut off from the gate at the time of opening the parting surface. Therefore, the condition of cutting the gate is considered to vary depending on the speed of opening the mold. On the other hand, when a tunnel gate is provided on the fixed half, the molded product is cut off from the gate at the time that the runner ejector pin ejects the runner Therefore, the condition of cutting the gate is considered to vary depending on the speed of projecting the runner ejector pin. When the runner is provided on the fixed half, since it is likely that the runner itself remains on the fixed half, a structure that pulls the runner to the fixed side such as a lock pin will be required. When the runner is provided on the moving half, it is necessary to provide an appropriate ejector pin for ejecting the runner As a special example, there is also a structure in which a tunnel gate is provided on a boss shape (crafted by scraping the ejector pin) on the moving half, and the plastic is injected from the underside of the top surface of the molded product. In actuality, the mold design is carried out by considering which gate pattern and runner pattern is appropriate based on the features of the molded product and on the properties of the plastic. When the specifications require that traces of gate should not remain on the side surface and top surface of the molded product, it will be necessary to provide the gate on the bottom surface of the molded product. The curved tunnel gate structure is used very rarely as a technique for such situations.