The pouring system in the hot runner mold is always in a high temperature state during use. Under the action of high temperature and high pressure, the plastic melt in the hot runner system is prone to leakage. Melting leakage not only affects the quality of plastic components, but also seriously damages molds, leading to production failure. Incorrect operation process is one of the main reasons for melt leakage during mold production. In order to compensate for the thermal expansion of parts in the hot runner system, there is usually a certain cold gap between the parts during the design and assembly of the mold. Only at the specified working temperature can the thermal expansion of the parts completely eliminate cold gaps and seal leaks. The melt leakage caused by improper operation mainly occurs in the following situations:
1. The injection temperature did not reach the specified operating temperature. After the system is heated, the support ring, hot runner plate, and gate nozzle expand axially, and the support ring presses against the fixed plate, generating a certain amount of thermal pressure between the hot runner plate and the nozzle. If injection is carried out at a specific temperature, the hot pressure generated by thermal expansion is not sufficient to offset the melt pressure, which will cause the nozzle to separate from the hot runner plate and lead to melt leakage..
2. Melt leakage caused by system heating temperature exceeding operating temperature. In this case, excessive thermal expansion can generate significant thermal pressure, causing deformation of system components and resulting in melt leakage. On the other hand, when the temperature of the pouring system decreases to the operating temperature, melt leakage may also occur due to the poor adaptability of the rigid edge hot nozzle to thermal expansion.
3. Melt leakage caused by improper heating process or uneven temperature control. During the heating process, if the nozzle heating rate is higher than that of the hot runner plate, the axial thermal expansion of the system components will limit the lateral thermal expansion of the hot runner plate, resulting in deformation and melt leakage of the hot runner plate. Uneven temperature of parts in the pouring system can lead to uneven expansion, deformation, and melt leakage.

In summary, following the correct steps and process conditions is a prerequisite for avoiding melt leakage. A typical hot runner mold can be operated according to the following steps:
1. Heat the mold to the set temperature. Especially for large molds, they are heated before injection and then cooled during injection.
2. Heat the injection machine barrel to the set temperature.
3. Heat the hot runner system to set the temperature. Generally speaking, it consists of two steps: first, "soft start" to eliminate the humidity of the heater; Secondly, the system heats up to the set temperature at full load. Firstly, the nozzle temperature can be heated to 2/3 of the hot runner plate temperature, and then the nozzle temperature can be heated to the set temperature after the hot runner plate temperature reaches the design temperature.
4. For new or cleaned hot runner systems, low-pressure slow injection should be used first.
5. If there is no melt leakage after several cycles, use the set injection process parameters for production