Injection molding process

Plastic injection molding process parameter 1:Temperature and pressure

Plastic injection molding process parameter 1:Temperature and pressure

The setting of plastic injection parameters generally depends on five main conditions: temperature, pressure, speed, time, and measurement.

This article mainly describes the temperature and pressure of injection molding process.

Injection Molding Temperature

Generally, the heating temperature of the feed tube is mostly divided into three sections. The temperature of the front section is lower, and the temperature of the middle and rear sections is higher. The temperature difference of each section is about 5 ~ 10℃. Suppose the temperature in the front section is too high. In that case, the plasticizer melts too early, and the resin supply will produce an uneven phenomenon (because part of the melted particles will form chunks in the feed part of the screw). Nozzle temperature does not need special attention because it directly contacts the mold and affects the forming cycle.

In addition, should pay special attention to the impact of the environmental temperature on the shrinkage of the forming parts. In addition, environmental humidity will also affect the quality of finished products.

Injection Molding Pressure

Generally, the heating temperature of the feed tube is mostly divided into three sections. The temperature of the front section is lower, and the temperature of the middle and rear sections is higher. The temperature difference of each section is about 5 ~ 10℃. Suppose the temperature in the front section is too high. In that case, the plasticizer melts too early, and the resin supply will produce an uneven phenomenon (because part of the melted particles will form chunks in the feed part of the screw). Nozzle temperature does not need special attention because it directly contacts the mold and affects the forming cycle.

In addition, should pay special attention to the impact of the environmental temperature on the shrinkage of the forming parts. In addition, environmental humidity will also affect the quality of finished products.

1.Injection pressure

The engineer should take injection pressure into account the fluidity of the injection molding material, shrinkage, and the physical properties of the formed product.  The setting of injection pressure should generally be high rather than low. In practice, it can be set as the highest first and then be appropriately lowered according to the filling time after all other parameters are stopped.

2.Holding pressure

Cavity sol compression formed a great internal pressure, the internal pressure will be reduced because of the temperature, but in the gate has not yet condensed and sealed before, it still has the ability to sol extrusion cavity, so must continue to give appropriate pressure resistance to it, this is called maintaining pressure, referred to as pressure.

The pressure should be maintained with the gradual solidification of molten plastic caused by the reduction of internal pressure and gradually reduced. Insufficient pressure holding or holding time will form undersize or sag; Too much pressure holding results in over-saturation and residual stress.

3.Back pressure

As the screw rotates and the plastic pushes forward in the sequence, the function of back-pressure is to maintain the speed at which the guide screw does not retreat from the reaction force.

The back-pressure is too high, and the screw back time is prolonged, the shear force of the material is also increased, easy to make the material overheat; Back-pressure is too low, which will make the material mixing, and measurement accuracy is reduced, but also easy to feed into more air so that the shape of the product silver strip appearance.

General back pressure to 5 ~ 15Kg/cm2 is appropriate.

Increasing the back pressure can increase the work done by the screw on the molten resin, eliminate the unmelted plastic particles, increase the density and uniformity of the material in the feed tube, reduce injection pressure and warpage, and other problems.

Most notably, back pressure is applied to raise tube temperature.

Back-pressure is too large, easy to decompose the plastic with high heat sensitivity; A “runny nose” may occur for plastics with low viscosity.

If the back-pressure is too low, the finished product may have bubbles.

4.Suck-back, Decompression

The end of the screw backsliding, the front end of the barrel (nozzle part) accumulated molten material is still in the state of back compression, appropriate to make the screw in no back-pressure and no backsliding conditions, can make the compressed molten material to be relieved, without dripping from the nozzle part, this is called pressure relief.

5.Clamping force

In general, the projection area of the finished product in the direction of the switching die is calculated based on the external dimension of the finished product.

Support die force = projection area (cm2) of the finished product in the direction of the switch die × mold hole number × mold pressure (kg/cm2).

Mold pressure will vary with raw materials, generally raw materials (350 ~ 400kg/cm2).

The clamping force of the machine should be greater than the supporting force, and for the sake of insurance, the clamping force of the machine should be greater than the supporting force of more than 1.2 times.

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