1. Melting temperature

Melt temperature is very important in the injection molding process. Melt temperature can be measured at the injection molding machine nozzle or roughly estimated using the air jet method. The temperature setting at the barrel depends on the melting temperature of the plastic melt, screw speed, back pressure, shot size and injection cycle. If the operator is inexperienced in processing a particular plastic, the test should be started at the lowest temperature setting allowed. In order to accurately control the melting temperature, the barrel is generally divided into multiple heating zones, and each heating zone can be set to different temperatures. If the injection time is long or the operation is at high temperature, the temperature of the first zone should be set to a lower value, which will prevent premature melting and shunting of the plastic. Before injection starts, make sure the hydraulic oil, hopper closure, mold and shot cylinder are all at the correct set temperature.

2. Injection pressure

Injection pressure is the pressure that promotes the flow of the plastic melt and can be measured with sensors located on nozzles or hydraulic equipment. It has no fixed value, and the more difficult it is to melt-fill the mold, the injection pressure should increase accordingly.

The injection pressure can be divided into several stages. In the filling stage of an injection cycle, the first stage pressure and the second stage pressure may require high pressure to maintain a high injection speed. The pressure can be turned down after the melt has filled the mold. However, when injecting some semi-crystalline thermoplastics (such as PA and POM), due to the sudden change of pressure, the internal structure of the product will undergo adverse changes, so sometimes it is not necessary to use stage pressure.

3. Clamping pressure

In order to resist the injection pressure, the mold must maintain a certain pressure during clamping, but the clamping pressure should not be too large, otherwise the equipment may operate under high pressure for a long time, which may cause damage to the mold and equipment. When calculating the clamping pressure, the projected area of the plastic product should be considered, and a suitable pressure value should be calculated accordingly. The projected area of the injection molded part is the largest area seen from the direction in which the clamping force is applied. However, if the height of the injection molded part is large, the side wall area must also be taken into account.

4. Back pressure

Although the use of high back pressure is conducive to the uniform dispersion of fillers such as pigments and the melting of plastics, it also prolongs the return time of the screw, which will cause loss of fibers in the fiber-reinforced plastics. The setting of the back pressure should not be too high, and under no circumstances should it exceed 20% of the injection pressure (maximum rating) of the injection molding machine.

5. Injection speed

When injecting thin-walled products, a high injection rate must be used so that the mold can be completely filled when the melt from the gate is not solidified. However, the injection speed should not be too high, and a stepped injection speed can be used to avoid defects such as melt injection or trapped air.