Plastic injection molding

The essential for Injection Molding Stability - Gate

                                                 igbt insert molding



The fourth factor that increases flow resistance: the gate or runner is too small.


What are gates and runners?

Let's review what was mentioned in the previous video "Plastic Injection Molding Principles", the raw material will enter the mold through the material tube, and the product will be formed in the mold. The first place where the raw material enters the mold is the "bushing", the passage in the "bushing" is a part of the "runner", and the entrance where the raw material passes through the runner before entering the finished product is the "gate".
When the cross-sectional area of ​​the gate is smaller, the space for plastic to flow is smaller, and flow resistance will be generated at this time. For example, when vehicles are going on a national highway, if the gate is too small, it will be easy to jam and the traffic flow will not be smooth. Therefore, if the gate can be large, it should not be too small.

Generally speaking, the runners are divided into semicircular, circular, trapezoidal and modified trapezoidal, among which the design of circular and modified trapezoidal is better.

In contrast, the circular flow channel allows the plastic to retain a larger flow space after the skin layer is formed, while the semicircular flow space appears narrower.


In order to reduce flow resistance, the bigger the runner and gate, the better?

When designing the mold, the size of the runner and gate is not as big as possible. The size of the runner is just right, because the raw material in the runner is the so-called unused material. Therefore, when the runner is thicker, the weight of the material is heavier. When these material can not be recycled, the raw material Loss and cost will increase. In addition, the disadvantage of the large gate is that the separation of the finished product and the head often requires manual trimming, and it is not easy to achieve automatic separation of the head, and it is easy to cause uneven trimming and require secondary trimming, which takes longer man-hours.

Finally, special attention should be paid to the mold design. The R angle and hole diameter of the mold liner need to be slightly larger than the size of the nozzle of the barrel, so as not to increase additional flow resistance. In actual production, it is also necessary to pay special attention to the nozzle of the material tube, whether there is any damage, which will cause the problem that the aperture is too small.


Further understanding for the essential for plastic injection molding stability

This is just a partial overview of plastic injection molding. Are they the right knowldge for you? Not sure how to apply them to your

next project? Just contact our technical experts and we can offer helpful advice about how to get the best results from its processes. 

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