The plastic mold is mainly composed of three parts: pouring system, molding parts and structural parts. Among them, the gating system and the molding parts are the parts that are in direct contact with the plastic, and change with the plastic and the product. They are the most complex and changeable parts of the plastic mold and require the highest processing finish and precision.
The plastic mold gating system refers to the part of the runner before the plastic enters the cavity from the nozzle, including the main runner, the cold material cavity, the runner and the gate. Molded parts refer to various parts that make up the shape of the product, including movable molds, fixed molds and cavities, cores, molding rods, and exhaust ports.
1. Mainstream
It is a passage in the mold that connects the nozzle of the injection machine to the runner or cavity. The top of the sprue is concave for engagement with the nozzle.
The inlet diameter of the main channel should be slightly larger than the diameter of the nozzle (0.8mm) to avoid overflow and prevent the two from being blocked due to inaccurate connection.
The diameter of the inlet depends on the size of the product, generally 4-8mm. The diameter of the sprue should be expanded inward at an angle of 3° to 5° to facilitate the release of the runner debris.
2. Cold material hole
It is a cavity at the end of the main channel to capture the cold material generated between two injections at the end of the nozzle, thereby preventing the blockage of the runner or gate. If the cold material is mixed into the cavity, internal stress is easily generated in the manufactured product.
The diameter of the cold material hole is about 8-10mm, and the depth is 6mm. In order to facilitate demoulding, the bottom is often borne by the demoulding rod. The top of the demoulding rod should be designed as a zigzag hook or a sunken groove, so that the sprue can be pulled out smoothly when demoulding.
Third, the shunt
It is the channel connecting the main channel and each cavity in the multi-slot mold. In order to make the melt fill each cavity at the same speed, the arrangement of the runners on the mold should be symmetrical and equidistant. The shape and size of the runner section have an impact on the flow of the plastic melt, the demolding of the product and the ease of mold manufacturing.
If the flow of the same amount of material is considered, the flow channel resistance of the circular section is the smallest. However, because the specific surface of the cylindrical runner is small, it is unfavorable for the cooling of the superfluous material of the runner, and the runner must be opened on the two halves of the mold, which is labor-intensive and easy to align.
Post time: Aug-24-2022