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Gating system
Apr 27, 2018

Gating system


The gating system refers to the part of the flow path before the plastic enters the cavity from the nozzle, including the main channel, the cold material hole, the runner and the gate.


The gating system, also known as the runner system, is a set of feed channels that direct the plastic melt from the nozzle of the injector to the cavity, usually consisting of a main flow channel, a runner, a gate, and a cold pocket. It is directly related to the molding quality and production efficiency of plastic products.


Mainstream road


It is a section of the mold that connects the injection nozzle of the injection molding machine to the runner or cavity. The top of the main flow channel is concave for engagement with the nozzle. The main channel inlet diameter should be slightly larger than the nozzle diameter (0.8mm) to avoid spiking and prevent the two from being blocked due to inaccurate convergence. The diameter of the inlet depends on the size of the product, usually 4-8mm. The diameter of the main flow path should be enlarged inwards at an angle of 3° to 5° to facilitate the stripping of runners.


Cold material hole


It is a hole located at the end of the main channel to trap the cold material produced between the two shots at the tip of the nozzle to prevent clogging of the runner or gate. If the cold material is mixed into the cavity, the internal stress is likely to occur in the manufactured product. The cold material hole has a diameter of about 8-10mm and a depth of 6mm. In order to facilitate demoulding, the bottom is often borne by the stripper. The top of the stripping rod should be designed as a zigzag hook or a depressed groove so that the strip can be smoothly pulled out during demoulding.


Split channel


It is the channel connecting the main channel and each cavity in the multi-slot die. In order to make the molten material fill the cavity at equal speed, the arrangement of the runners on the mold should be symmetrical and equidistantly distributed. The shape and size of the runner section affect the flow of the plastic melt, the release of the product and the ease of mold making. If an equal amount of flow is used, the flow path resistance with a circular cross section is minimized. However, due to the small specific surface area of the cylindrical flow passage, it is unfavorable for the cooling of the diversion channel material, and this diversion passage must be opened on the two mold halves, which is labor-consuming and difficult to align. Therefore, trapezoidal or semi-circular cross-section runners are often used, and they are opened on half of the mold with a stripper rod. The runner surface must be polished to reduce the flow resistance to provide a faster filling rate. 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 runners does not exceed 8mm, extra large up to 10-12mm, extra small 2-3mm. To meet the needs of the premise should be reduced cross-sectional area as much as possible to increase the shunt material and extend the cooling time.


Gate


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


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