Molding

 A molding consists of a sprue to introduce molten resin, a runner to lead it to cavities, and products. Since obtaining only one product by one shot is very inefficient, a mold is usually designed to have multiple cavities connected with a runner so that many products can be made by one shot.

  

If the length of the runner to each cavity is different in this case, the cavities may not be filled simultaneously, so that dimensions, appearances or properties of the moldings are often different cavity by cavity. Therefore the runner is usually designed so as to have the same length from the sprue to each cavity.

A molding typically consists of three main components: the sprue, the runner, and the cavities where the final products are formed.

- Sprue: The sprue is the channel through which the molten plastic resin is introduced into the mold. It connects the injection unit of the molding machine to the mold cavity system. The molten plastic material flows through the sprue and into the runner system.

- Runner: The runner is a system of channels that distributes the molten plastic from the sprue to multiple cavities within the mold. It ensures that the plastic material reaches each cavity evenly. The runner system can be designed in various configurations, such as a single runner that branches into multiple sub-runners leading to each cavity, or a hot manifold system where each cavity has its own individual runner connected to a central manifold.

- Cavities: The cavities are the hollow spaces within the mold where the molten plastic material takes the shape of the desired final product. The number of cavities in a mold depends on the production requirements and the size of the final product. Multiple cavities allow for the production of multiple products in a single shot, which increases efficiency and productivity.

It is important for the runner to be designed properly to ensure that all the cavities are filled simultaneously and uniformly. If the lengths of the runners leading to each cavity are different, the flow of molten plastic may vary, resulting in differences in dimensions, appearances, or properties of the molded products. To avoid such issues, the runner system is often designed with equal lengths from the sprue to each cavity, ensuring consistent filling of all cavities and maintaining uniformity in the molded parts.

By designing an efficient runner system, manufacturers can optimize the injection molding process and achieve consistent, high-quality molded products.

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