What are the components of the injection mold

The injection mold consists of a moving mold and a fixed mold. The moving mold is installed on the movable template of the injection molding machine, and the fixed mold is installed on the fixed template of the injection molding machine. During injection molding, the movable mold and the fixed mold are closed to form the gating system and the cavity, and the movable mold and the fixed mold are separated to take out the plastic product when the mold is opened. In order to reduce the heavy workload of mold design and manufacturing, most injection molds use standard mold bases.

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Gating system
The gating system refers to the part of the runner before the plastic enters the cavity from the nozzle, including the main runner, cold material cavity, runner and gate. The gating system, also known as the runner system, is a set of feed channels that guide the plastic melt from the nozzle of the injection machine to the cavity. It usually consists of a main channel, a runner, a gate and a cold cavity. It is directly related to the molding quality and production efficiency of plastic products.

The sprue is a channel in the mold that connects the nozzle of the injection molding machine to the runner or cavity. The top of the sprue is concave to connect with the nozzle. The inlet diameter of the main channel should be slightly larger than the nozzle diameter (0.8mm) to avoid overflow and prevent the two from being blocked due to inaccurate connection. The inlet diameter depends on the size of the product, generally 4-8mm. The diameter of the sprue should expand inward at an angle of 3° to 5° to facilitate the demoulding of the excess in the flow path.

Cold slug hole It is a cavity at the end of the sprue to catch the cold slug generated between two injections at the end of the nozzle, so as to prevent the blockage of the runner or gate. Once the cold material is mixed into the cavity, internal stress is easily generated in the manufactured product. The diameter of the cold slug hole is about 8-10mm, and the depth is 6mm. In order to facilitate demoulding, its bottom is often borne by a demoulding rod. The top of the demoulding rod should be designed as a zigzag hook or a sunken groove, so that the main channel can be pulled out smoothly when demoulding.

Runner It is the channel connecting the sprue and each cavity in the multi-slot mold. In order to make the molten material fill each cavity at an equal speed, the arrangement of the runners on the mold should be symmetrical and equidistant. The shape and size of the cross-section of the runner have an impact on the flow of the plastic melt, the ease of product demoulding and mold manufacturing.
If the flow of the same amount of material is concerned, the flow channel with a circular cross-section has the least resistance. But because the specific surface of the cylindrical runner is small, it is unfavorable to the cooling of the debris in the runner, and the runner must be opened on the two halves of the mold, which is labor-intensive and difficult to align.
Therefore, trapezoidal or semicircular cross-section runners are often used, and they are opened on half of the mold with ejector pins. The surface of the runner must be polished to reduce flow resistance and provide faster filling speed. The size of the runner depends on the type of plastic, the size and thickness of the product. For most thermoplastics, the cross-sectional width of the runner does not exceed 8m, the extra-large one can reach 10-12m, and the extra-small one can reach 2-3m. Under the premise of meeting the needs, the cross-sectional area should be reduced as much as possible to increase the debris in the shunt channel and prolong the cooling time.

gate
It is a channel connecting the main channel (or runner) and the cavity. The cross-sectional area of the channel can be equal to that of the main channel (or branch channel), but it is usually reduced. So it is the part with the smallest cross-sectional area in the entire runner system. The shape and size of the gate have a great influence on the quality of the product.