Injection Molding Learning

1. Rotating speed of the screw

The rotational speed of the screw significantly affects the degree of stability of the injection molding process and the amount of heat acting on the plastic. The faster the screw rotates, the higher the temperature. When the screw rotates at a high speed, the friction (shear) energy delivered to the plastic increases the plasticizing efficiency, but at the same time increases the unevenness of the melt temperature.

Due to the importance of the surface speed of the screw, the screw rotation speed of the large injection molding machine should be smaller than that of the smaller injection molding machine, because the shear heat generated by the large screw is much higher than that of the small screw at the same rotation speed. Due to the difference in plastics, the speed at which the screw rotates is also different.

2. Injection amount

The evaluation of the syringe press is usually based on the amount of PS that can be injected per injection and may be measured in ounces or grams. Another sorting system is based on the volume of melt that the injection molding machine can inject.

3. Plasticizing ability

The evaluation of the injection molding machine is usually based on the amount of PS (in pounds and kilograms) that can uniformly melt the amount of PS in one hour or the temperature of the uniform melt, which is called plasticizing ability.

4. Plasticization capacity estimate

To determine if the product can maintain high quality throughout the production process, a simple formula for yield and plasticizing capacity can be used, as follows: t = (total injection shot g X3600) ÷ (plastic injection molding machine kg/h X 1000)

t is the lowest cycle time. If the cycle time of the mold is lower than the t value, the injection molding machine cannot fully plasticize the plastic to achieve a uniform melt viscosity, so the injection molded parts often have deviations. In particular, when paying attention to the quality of injection molded thin walls or precision tolerances, the amount of shot and the amount of plasticization must match each other.

5. Shooting tank retention time

The decomposition of plastic is based on temperature and time. For example, a plastic will decompose after being exposed to high temperatures for a period of time; however, in a lower temperature environment, it will take longer to decompose. Therefore, the residence time of plastic in the shooting tank is very important.

The actual residence time can be determined experimentally. The method is to measure the time required for the colored plastic to pass through the shooting tank. The following formula can be roughly calculated: t=(the nominal volume of the shooting tank g X cycle time S)÷ Quantity g X300)

It is worth noting that some plastics have a longer residence time in the shooting tank than is required for calculation because they can coalesce in the shooting tank.

6. Calculate residence time and importance

As a general rule, the residence time of a plastic on a particular injection molding machine should be calculated. Especially when a large injection molding machine uses a small amount of shot material, the plastic is easily decomposed, which is not detectable from observation. If the residence time is short, the plastic will not be plasticized evenly; the retention time will be attenuated by the plastic properties. Therefore, it is necessary to maintain the same residence time.

Method: Ensure that the plastic input into the injection molding machine has a stable composition, consistent size and shape. If there is any abnormality or loss of the parts of the injection molding machine, it must be reported to the maintenance department.

7. Shooting tank temperature environment

It should be noted that the melt temperature is important and any shot cylinder temperature used is only indicative. If you have not experienced the processing of a particular plastic, start with the lowest setting. Usually the temperature in the first zone is set to the lowest value to prevent premature melting and blocking of the plastic in the feed port.

The temperature in the other zones then gradually increases until the nozzle is reached, and the temperature at the tip of the nozzle tends to be slightly lower to prevent dripping. The mold is also heated and cooled. Due to the size relationship of many molds, the mold is also distinguished, but unless otherwise stated, the zones should be set to the same size.