1. Melting temperature

Melting temperature is very important in injection molding process. The melting temperature can be measured at the nozzle of the injection molding machine or roughly estimated using the air injection method. The temperature setting at the barrel depends on the melting temperature of the plastic melt, screw speed, back pressure, injection volume and injection cycle. If the operator has no experience working with a particular plastic, the test should begin with the minimum temperature setting allowed. In order to facilitate precise control of melting temperature, the cylinder is generally divided into a number of heating zones, each heating zone can be set at different temperatures. If the injection is prolonged or operated at high temperatures, set the temperature in Zone 1 to a lower value. This will prevent premature melting and shunt of the plastic. Before injection, ensure that the hydraulic fluid, hopper sealer, mold and shooting cylinder are at the correct set temperature.

2. Injection pressure

Injection pressure is the pressure that causes a plastic melt to flow and can be measured by a sensor located in a nozzle or hydraulic equipment. It has no fixed value, and the more difficult the melt filling mold, the injection pressure should increase accordingly.

Injection pressure can be divided into several stages. In the filling phase of an injection cycle, the first stage pressure and the second stage pressure may require the use of high pressure to maintain a high injection rate. The pressure can be lowered after the melt has filled the mold. However, in the injection of some semi-crystalline thermoplastics (such as PA and POM), due to sudden changes in pressure, will make the internal structure of the product adverse changes, so sometimes do not need to use stage pressure.

3. Clamping pressure

In order to combat injection pressure, the mold must maintain a certain pressure during mold locking, but the mold locking pressure should not be too large, otherwise the equipment under high pressure operation for a long time, may cause damage to the mold and equipment. When calculating the clamping pressure, the projection area of plastic products should be taken into account and an appropriate pressure value should be calculated accordingly. The projected area of the molded part is the largest area seen from the direction of the clamping force. But if the height of the injection parts is large, then the side wall area must also be taken into account.

4. Back pressure

Although the high back pressure is beneficial to the dispersion of fillers such as color material and plastic melting, it also prolongates the return time of screw, which will cause the loss of fibers in fiber reinforced plastics. The setting of back pressure should not be too high, in any case can not exceed the injection molding machine injection pressure (maximum quota) 20%.

5. Injection speed

When injection molding thin-walled products, a high rate of fire must be used so that the mold is fully filled before the melt from the gate is solidified. However, the injection speed should not be too high. Step injection speed can be used to avoid defects such as melt injection or trapped gas.