How to avoid solution leakage in hot runner mold during production?

How to avoid solution leakage in hot runner mold during production?

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 easy to leak. Melting leakage will not only affect the quality of plastic parts, but also seriously damage the mold, resulting in 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 the parts in the hot runner system, there is usually a certain cold gap between the parts when designing and assembling the mold. Only at the specified operating temperature can the thermal expansion of the part completely eliminate the cold gap and seal the leak. Melt leakage caused by improper operation mainly occurs in the following situations:

1. The injection temperature does not reach the specified operating temperature. After the system is heated, the support ring, the hot runner plate and the gate nozzle expand axially, the support ring is pressed on the fixed plate, and a certain hot pressure is generated between the hot runner plate and the nozzle. If the injection is performed at a specific temperature, the hot pressure resulting from thermal expansion is not sufficient to offset the melt pressure, which will separate the nozzle from the hot runner plate and cause melt leakage.

2, the system heating temperature is higher than the operating temperature caused by melt leakage. In this case, because the amount of thermal expansion is too large to produce a large thermal pressure, the system parts will be deformed and melt leakage will occur. On the other hand, when the temperature of the pouring system is reduced to the operating temperature, melt leakage will also occur due to the poor adaptability of the hot nozzle with rigid edge to thermal expansion.

3. Melt leakage caused by improper heating process or uneven temperature control. In the heating process, if the nozzle heating rate is higher than the hot runner plate, the axial thermal expansion of the system components will limit the transverse thermal expansion of the hot runner plate, resulting in the deformation of the hot runner plate and melt leakage. The uneven temperature of parts in the pouring system will lead to uneven expansion of parts, deformation of parts and melt leakage.

To sum up, the operation in accordance with the correct steps and process conditions is the premise of avoiding melt leakage. The general hot runner mold can be operated according to the following steps:

1. Heat the mold to the set temperature. In particular, large molds 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 is divided into two steps: first, "soft start" to eliminate the humidity of the heater; Second, the system is heated to a set temperature at full load. First, 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 the new or cleaned hot runner system, low pressure and slow injection should be used first.

5, after several cycles, if there is no melt leakage phenomenon, then use the set injection process parameters for production