What are the composition of the plastic injection molding

Although the structure of the mold may vary widely due to the variety and performance of plastics, the shape and structure of plastic products, and the type of injection machine, the basic structure is the same. The mold is mainly composed of pouring system, temperature control system, molding parts and structural parts. Among them, the pouring system and the molded parts are the parts that directly touch the plastic, and change with the plastic and the product. They are the most messy and the largest changes in the plastic mold, and require the highest processing finish and precision.

The plastic injection molding is composed of a movable mold and a fixed mold. The movable mold is installed on the movable template of the plastic injection molding machine, and the fixed mold is installed on the fixed template of the plastic injection molding machine. During plastic injection molding, the movable mold and the fixed mold are closed to form a pouring system and cavity. When the mold is opened, the movable mold and the fixed mold are separated to take out the plastic product. In order to reduce the heavy mold planning and manufacturing workload, most plastic injection moldings use standard mold bases.

Casting system

The pouring system refers to the part of the runner before the plastic enters the cavity from the nozzle, including the main runner, cold slug, runner, and gate.

The pouring system is also called the runner system. It is a set of feed channels that lead the plastic melt from the injection machine nozzle to the cavity. It is generally composed of a main runner, a branch runner, a gate and a cold material cavity. It is directly related to the molding quality and production efficiency of plastic products.

Main runner

It is a passage connecting the nozzle of the plastic injection molding machine to the runner or cavity in the mold. The top of the main runner is concave to connect with the nozzle. The diameter of the inlet of the main runner should be slightly larger than the nozzle diameter (0.8mm) to avoid overflow, and avoid the blocking of the two due to the prohibition of connection. The inlet diameter depends on the size of the product, generally 4-8mm. The diameter of the main runner should expand inward at an angle of 3° to 5° to facilitate the demolding of the runner.

Cold feed hole

It is a cavity at the end of the main runner to trap the cold material that occurs between two injections at the end of the nozzle, and then to avoid the blockage of the runner or gate. If the cold material is mixed into the cavity, internal stress will easily occur in the manufactured product. The diameter of the cold slug hole is about 8-10mm and the depth is 6mm. In order to facilitate demolding, the bottom is often supported by a demolding rod. The top of the demolding rod should be planned into a curved hook shape or a recessed groove, so that the main runner can be pulled out smoothly during demolding.

Shunt

It is the channel connecting the main runner and each cavity in the multi-slot mold. In order to make the molten material fill the cavities at the same speed, the runners should be placed symmetrically and equidistantly on the mold. The shape and size of the cross-section of the runner have an impact on the flow of the plastic melt, the product demolding and the difficulty of mold manufacturing.

If the flow of flat material is used, the flow path with a circular cross-section has the least resistance. However, because the cylindrical runner is smaller than the outer surface, it is unfavorable for cooling of the runner superfluous, and the runner must be opened on the two mold halves, which is laborious and difficult to align.

Gate

It is the channel connecting the main runner (or branch runner) and the cavity. The cross-sectional area of ​​the channel can be the same as the main runner (or branch runner), but it is generally reduced. So it is the smallest cross-sectional area in the entire runner system. The shape and scale of the gate have a great influence on the quality of the product.

Temperature control system

In order to satisfy the mold temperature requirements of the injection process, a temperature adjustment system is required to adjust the mold temperature. For plastic injection moldings for thermoplastics, the cooling system is mainly planned to cool the mold. The common method of mold cooling is to open a cooling water channel in the mold, and use the circulating cooling water to take away the heat of the mold; the heating of the mold can use the cooling water channel hot water or steam, and also install electricity in and around the mold. Heating element.

Molded parts

Molded parts refer to the various parts that constitute the shape of the product, including movable molds, fixed molds and cavities, cores, molding rods, and vents. The molded part consists of a core and a cavity mold. The core forms the inner and outer surface of the product, and the concave mold forms the outer and outer shape of the product. After closing the mold, the core and the cavity constitute the cavity of the mold. According to process and manufacturing requirements, sometimes the core and die are combined by several pieces, sometimes as a whole, and inserts are only used for parts that are easy to damage and difficult to process.

Exhaust vent

It is a trough-shaped air outlet opened in the mold to discharge the original gas and the gas brought in by the molten material. When the melt is injected into the cavity, the air originally stored in the cavity and the gas brought in by the melt must be discharged out of the mold through the exhaust port at the end of the material flow, otherwise the product will have air holes, poor connection, Dissatisfaction with the filling of the mold, and even the accumulated air will burn the product due to high temperature due to compression.