It is the channel connecting the main channel 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 shunts on the mold should be symmetrical and equidistant. The shape and size of the shunt cross-section have an impact on the flow of the plastic melt, product demolding, and ease of mold manufacturing.
If the flow of the same amount of material is used, the resistance of the runner with a circular cross section is the smallest. However, because the cylindrical flow channel has a smaller specific surface, it is unfavorable for the cooling of the debris in the flow channel, and this flow channel must be opened on the two mold halves.
Therefore, it is often used a trapezoidal or semicircular cross-section shunt, and it is opened on the half of the mold with a release rod. The surface of the runner must be polished to reduce the flow resistance and provide a faster filling speed. The size of the flow channel 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 8m, the extra large can reach 10-12m, and the extra small 2-3m. Under the premise of satisfying the needs, the cross-sectional area should be reduced as much as possible in order to increase the shunts and increase the cooling time.
