Unbalanced multi-cavity mold melt flow solution

In the injection molding process, the resulting melt flow imbalance for many reasons, including changes in temperature caused by the unbalanced flow is particularly difficult to detect and avoid, so as to cause great inconvenience to injection molding. So, what better way to solve it?http://www.prmindustry.com/Abstract...Articles section In a multi-cavity molding process, to make uniform and balanced flow of melt into each cavity is very difficult. Gates of different sizes or flow in the shear mode system is inconsistent and other factors, can lead to imbalance in the flow of melt. But few people know that in the hot runner system, the heat changes the temperature of the gate leading to the flow imbalance particularly troublesome, and not easily diagnosed.
Hot runner temperature changes will not only lead to the same injection cycle occurs within the cavity filling phenomena such as insufficient or flash, it will result in the same cavity in a different injection cycles occur in different situations. For example, in a 4-cavity mold, the first injection cycle may be the case: the second and third chamber in the best quality of the products obtained, and the emergence of the first chamber of insufficient filling phenomenon, the fourth chamber side of the phenomenon appeared in the fly. However, the next injection cycle, filling the cavity mode with the constant changes that may lead to emergence of the first chamber flash phenomenon occur in the fourth cavity filling is insufficient, or each cavity The quality of parts obtained are very good. This imbalance is sometimes very serious, there may be a cavity in the injection cycle to fill only 50%, while the next injection cycle is filled with 100%. This happens even in two-cavity mold are a frequent occurrence. In the actual production applications, regardless of the required injection pressure is high or low, are filling imbalances occur.
A region with another region between the small temperature changes will cause the melt in a few minutes in the process of filling a liquidity imbalance, although sometimes very small temperature change that is necessary in the production .
Temperature changes
Lead to changes in temperature within the hot runner for many reasons. One reason is because the heat caused by the PID controller at the nozzle of the temperature oscillation. With the heater on and off, the actual temperature of each cavity will fluctuate back and forth around the set point, making the injection molding process, the temperature change between the cavity varies. For example, the temperature may rise in the first cavity, and the second cavity of the temperature drop, resulting in the first melt flow more easily into the mold cavity. This phenomenon starts to cool until the first cavity and the second cavity when the heat began to improve, when the melt flow will gradually reach a balance. Trends from long-term changes, temperature changes of this cavity will occur once every few minutes.Another leads to a liquidity imbalance of reason is that the gate at the end of each hot mouth will form a very small solidification embolism (plugs), similar to the material in the course of each injection nozzle formed in the cold material rod (cold slug). In the injection process, the melt flows into the cavity, you must ensure that embolization has been completely cured. However, not all of thrombosis are at the same time completely cured, and the last to complete curing of the mold cavity filling will be finalized, which delayed the filling time and reduces filling pressure, as well as filling or contraction may occur inadequate and so on. However, since the last complete filling of the cavity before the next injection cycle embolization of the shortest, so the injection process, the cavity will be the first to complete the filling and the cavity pressure will increase significantly , resulting in flash phenomenon. It can be seen, the cavity in each injection mold filling pattern during the different changes occur.
Through all the mouth cavity to heat the heat, can effectively reduce the number of embolization, thus ensuring at each injection process, the melt flow is more stable equilibrium. However, this method is not the case for all applications are applicable parts because of quality problems resulting in a variety of reasons.
Solutions
Usually, by changing the temperature controller to regulate the hot runner temperature controller settings, or state, we can solve these problems. However, for processors, this method does not cure in more cases.
In each cavity pressure sensors are installed should be a good solution that will help improve the process accuracy. Obtained through the cavity pressure data analysis, can effectively evaluate the chosen solution applied force, while the injection unit provides closed-loop system obtained from the feedback. At this point, when the cavity pressure reaches the preset value, the injection machine will enter the injection phase. By installing pressure sensors, the user can clearly see the difference between the cavity pressure peak, and even able to observe what each injection mold cavity filling and the first to complete the highest peak pressure.
Typically, the injection machine into the second phase (packing phase) before the first has already begun filling a cavity filling will continue to maintain state. If the first phase of the melt in the injection mold cavity to reach the end of the cavity pressure will peak, and thus lead to flash phenomenon.
In the first lower cavity filled completely before the injection speed, can effectively prevent the peak cavity pressure. When filling up 80% to 90%, beginning the second phase of low filling, which can not guarantee the cavity under high pressure filling. This set a lower filling rate is usually the initial filling rate of 10% to 20%. This low rate of filling the cavity should be kept to the pressure parts in the packing stage to reach the required pressure, then the injection machine into the packing stage. This makes all the cavities of the packing more uniform.
Often, people will assume that the low-speed injection would effectively extend the injection molding cycle. In fact, the result was the opposite. This is due to imbalance of the filling process requires the existence of an adequate dwell time and cooling time, thus ensuring the final cavity is fully filled. Pressure through the use of speed instead of packing, can make the final cavity filling can be completed quickly, but to shorten the injection molding cycle.
This method ensures that each injection, the pressure inside the cavity is more consistent, and thus can not extend the cycle time of cases, access to better quality and consistency of parts.
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         Peter Huang