The main channels, runners and gates serve to transport the plastic melt from the nozzle of the injection molding machine to the various cavities. The pouring system condensate can be pulverized and reused. This is true, but despite this, the presence of the condensate means that the productivity of the injection molding machine is reduced because the material of the casting system must also be in the barrel of the injection molding machine. Plasticized. For smaller plastic parts, the pouring system can account for 50 or more of the actual shot volume.
Mainstream road
The mainstream can be seen as a continuation of the passage of the nozzle in the mold. In a single cavity mold, the gate of the main runner directly to the plastic part is called a sprue.
The productivity of a single cavity injection mold is usually determined by the cooling time of the main channel. In addition to providing adequate cooling to the main channel bushing, the small diameter of the feed port on the main channel bushing should be as small as possible and fill the cavity as appropriate.
However, there is no universally applicable law because the filling of the cavity depends on many factors. The main channel should have a draft angle of 1.5. The large draft angle makes the main channel easy to escape from the main channel bushing, but when the main channel is long, it will lead to a larger diameter, and therefore requires a relatively long cooling time. The outlet diameter of the nozzle of the injection molding machine should be 0.5 mm smaller than the small diameter of the main channel bushing, so that no groove is formed at the top end of the main flow channel to prevent the outflow of the main flow aggregate.
Split runner
In a multi-cavity mold, the plastic melt must be injected into each cavity through a split runner provided on the mold parting surface. The basic rules applicable to the main flow also apply to the cross section of the runner. There is also an additional factor that must be considered. The cross-section of the runner is also a function of its length, since it can be assumed that the increase in pressure loss in the runner is at least proportional to the length of the runner.
In most cases, the pressure loss will be greater because the cross section is reduced by the solidification of the plastic melt along the flow channel wall, and the further the distance from the main flow path, the greater the pressure loss. In addition, the main channel and the runner system mean the loss of raw materials and the amount of plasticization of the injection molding machine, so the runner should be designed as short as possible, and the cross section should be as small as possible. The length of the runner is determined by the number of cavities in the mold and the geometry of the cavities.
Splitter cross section shape
Since the surface area of the circular cross-section runner is small, the heat loss with respect to the cross-sectional area of the split runner is small, so a split runner with a circular cross section should be used as much as possible. Due to the solidification of the melt at the center of the circular section runner, the plastic melt can flow a long distance along the center of the circular section runner under the pressure of the holding pressure. Thus the gate (the section between the runner and the cavity) should be designed such that the melt enters the cavity through the gate from the center of the runner of the circular or rectangular section.
At the small section of the flow path, the steel around the gate is locally heated due to the flow friction of the plastic melt, so that under the action of the holding pressure, the melt can continue for a longer period of time before the gate solidifies. Inject into the cavity to complement the cavity.
When there must be movement between the smooth surface and the runner, the splitter of the circular section cannot be used. In this case, a splitter of a semi-circular groove can be used. The advantage of this shape is that it is only necessary to machine the runner on one side of the template. However, when the semicircular groove shunt has the same radius of curvature and the diameter of the male cross-section runner, the semi-circular groove shunt accommodates more than 12.5 more material than the circular shunt.
