Our Customers feedback that in the process of using the temperature control box, sometimes it is found that the material of the hot runner leaks. As for why this happens, today we will explain to you why this happens.
In the hot runner system, the molten material of the hot runner system flows into the manifold groove after leakage. In most cases, leaks in hot runner systems are not due to poor design, but due to not operating according to design parameters. Typically, the leak occurs at the seal between the hot nozzle and the manifold. According to the general design specification for a hot runner, there is a steel edge at the hot nozzle, which can ensure that the height of the hot nozzle assembly is less than the actual groove depth on the hot runner plate. This dimensional difference (often referred to as the cold gap) is designed to avoid damage to components due to thermal expansion while the system is at operating temperature. For example, for a 60 mm thick manifold and 40 mm hot nozzle assembly (100 mm overall height), it will typically expand by 0.26 mm when the temperature rises to 230°C. Without a cold gap, thermal expansion tends to cause damage to the edges of the hot nozzle. Therefore, the main reason for hot runner leakage is that there is no effective seal in the cooling state.
In general, to ensure the tightness of the system (hot nozzle and manifold), the system needs to be heated to operating temperature with sufficient force to counteract the injection pressure, thereby preventing the injection pressure from separating the two parts. Generally, inexperienced operators won't wait for the system to reach operating temperature, and worse, they may even forget to turn on the heating system. In this way, the pressure generated on the surface of the cold-gap hot runner cannot prevent material leakage until it reaches the operating temperature.
In addition, material leakage may also occur in the event of overheating. Due to the poor adaptability to thermal expansion of the hot nozzle at the edge of the strip, once the system is overheated and then lowered to the operating temperature, the resulting sealing pressure cannot prevent leakage due to the influence of the steel deformation. In this case, in addition to the system damage caused by material leakage, the hot nozzle is also irreparably damaged due to excessive pressure, so it is necessary to replace the hot nozzle. Since the preload of the hot nozzle and manifold is very important, the dimensional and tolerance requirements provided by the hot runner supplier need to be strictly adhered to effectively prevent material leakage.