Design of injection mold threads

The threads on the injection mold are divided into two forms: internal thread and external thread, and the thread profile of injection molded products usually has six types: standard thread, rectangular thread, trapezoidal thread, zigzag thread, arc thread and V-shaped thread, as shown in the figure. Different tooth profiles can be selected for different applications, such as serrated threads for high strength requirements. For the commonly used packaging bottle and cap threads, the multi-head arc thread is commonly used, which can make the cap tighten within one or two turns.

Because the strength of the plastic mold is not very high compared to the metal, and the plastic is usually soft, the thread on the plastic part should be selected with a larger screw size. When the thread diameter is small, it is not advisable to use fine threads, otherwise it will be difficult to obtain the ideal strength with the shrinkage of the plastic threads. You can usually choose from the table below.

1. Follow the basic design principles:

Avoid threads with a pitch of less than 0.75 mm, as well as threads with a maximum usable thread of 5 mm.

Prevents the formation of long threads directly due to plastic shrinkage to prevent deformation of the pitch.

Make sure that the tolerance is greater than the plastic shrinkage of the thread.

If the inner and outer threads match, the gap should be controlled between 0.1~0.4 mm.

The screw teeth should not extend to the end of the product, and a polishing rod of about 0.8mm should be installed to facilitate injection mold processing and extend thread life.

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