In most cases, material leakage in the hot runner system is not caused by poor design, but rather by failure to operate according to design parameters. Usually, leakage occurs at the sealing point between the hot nozzle and the splitter plate. According to the design specifications of general hot runner, there is a steel edge at the hot nozzle, which ensures that the height of the hot nozzle component is less than the actual groove depth on the hot runner plate. The reason for designing this dimensional difference (usually referred to as cold gap) is to avoid damaging components due to thermal expansion when the system is at operating temperature. For example, for a 60mm thick splitter plate and a 40mm hot nozzle assembly (with a total height of 100mm), when the temperature rises to an operating temperature of 230 ℃, it usually expands by 0.26mm. If there is no cold gap, thermal expansion often causes damage to the edge of the hot nozzle. Therefore, the lack of effective sealing under cooling conditions is the main cause of material leakage in the hot runner

Usually, in order to ensure the sealing of the system (hot nozzle and splitter plate), it is necessary to heat the system to operating temperature so that the force generated by it is sufficient to offset the injection pressure, thereby preventing the injection pressure from pushing the two components apart. Generally, inexperienced operators may not wait for the system to reach operating temperature, and even worse, they may forget to turn on the heating system. In this way, the pressure generated on the surface of a hot runner with cold gaps cannot prevent material leakage before reaching its operating temperature.

In addition, material leakage may also occur under excessive heating. Due to the poor adaptability of the hot nozzle with steel edges to thermal expansion, when the system is overheated and once it is lowered to operating temperature, the sealing pressure generated by the deformation of the steel cannot prevent leakage. In this case, in addition to causing system damage due to material leakage, it can also cause irreparable damage to the hot nozzle due to excessive pressure, requiring replacement of the hot nozzle.

Due to the crucial preload of the hot nozzle and splitter plate, it is necessary to strictly comply with the size and tolerance requirements provided by the hot runner supplier in order to effectively prevent material leakage in the system. Therefore, for mold manufacturers, all hot nozzle component heights and groove dimensions should be carefully checked according to the drawing requirements of the hot runner supplier. If there are any issues, they should also communicate with the hot runner supplier in a timely manner.