The runner balance design of injection mold plays an extremely critical role in ensuring the uniformity of injection molding, and directly affects the quality and production efficiency of plastic products.
First of all, one of the basic methods of runner balance design is to use a combination of equal-section runners and adjustment devices. In the early stage of mold design, the cross-sectional shape and size of the main runner and the branch runner should be kept consistent as much as possible, such as the common circular or trapezoidal cross-section, so as to ensure that the initial flow resistance of the plastic melt in each runner is similar. However, due to the complexity of the mold structure and the actual processing error, it is difficult to achieve complete balance only by equal-section runners. Therefore, an adjustable throttle valve or adjustment block will be set in the runner system. During the mold trial process, by fine-tuning these adjustment devices, the melt flow rate of different runners is changed, so as to achieve the synchronization of filling each cavity. For example, for a multi-cavity mold, if a cavity is filled before other cavities, the flow rate of the corresponding runner of the cavity can be appropriately reduced to make the plastic melt more evenly distributed to each cavity.
Secondly, the length design of the runner is also an important consideration for runner balance. Reasonably plan the runner length, and try to make the runner length from the main channel to each cavity equal or similar. Longer runners will increase the flow resistance and pressure loss of the melt, resulting in difficulty in filling the cavity that first passes through the long runner. By optimizing the mold layout, shortening the total runner length and balancing the length of each branch runner, the uneven injection caused by the difference in runner length can be effectively reduced. For example, when designing an array multi-cavity mold, a central symmetrical layout is adopted to minimize the distance difference from each cavity to the main channel, and with appropriate runner section design, the uniformity of injection molding can be significantly improved.
Furthermore, the use of computer simulation technology for runner balance design is an important means of modern injection mold design. With the help of professional injection mold simulation software, such as Moldflow, virtual injection analysis can be performed on different runner design schemes before the actual manufacture of the mold. The software can accurately predict the flow behavior of plastic melt in the runner system, including parameters such as pressure distribution, temperature change, and filling time. According to the simulation results, the problem of runner imbalance can be intuitively found, and the runner size, shape or layout can be adjusted in time. This design method based on simulation analysis can not only improve the accuracy and efficiency of runner balance design, but also reduce the number of mold trials and reduce production costs.
The runner balance design of injection mold effectively ensures the uniformity of injection molding by comprehensively using equal-section runners and adjustment devices, optimizing runner lengths, and using computer simulation technology. This is of irreplaceable importance for the production of high-quality, dimensionally stable and good-looking plastic products. It also helps to improve the stability and economy of the injection molding production process and promote the technological progress and development of the injection molding industry.
