We know that the main runner, runner and gate function to deliver the plastic melt from the injection molding machine nozzle to each cavity. It is true that the casting system condensate can be crushed and reused, but nevertheless, The presence of condensate means a reduction in the productivity of the injection molding machine since part of the material in the casting system must also be plasticized in the barrel of the injection molding machine and in the case of smaller plastics the pouring system condensate may account for the actual Injection volume of 50 or more.
Mainstream Road
The mainstream can be seen as a continuation of the nozzle channel in the mold.In the single-cavity mold, the main runner leads directly to the plastic parts of the gate called sprue.
The productivity of a single cavity injection mold is usually dictated by the cooling time of the main runner.In addition to providing adequate cooling of the main runner bushing, the minimum diameter of the feed opening in the main runner bushing should be as small as possible and timely Full of cavities.
However, there is no universally applicable law here, because the filling of the cavity is dependent on many factors. The main runner should have a draft of 1.5 · The larger the draft, the main runner can be removed from the main runner lining Easy to get out, but when the main channel is longer, it will lead to its larger diameter, and therefore require a longer cooling time. Injection molding machine nozzle outlet diameter than the minimum diameter of the main channel bushing 0.5mm, so that the main channel The top will not form a groove impede the main runner condensate prolapse.
Shunt
In multi-cavity molds, the plastic melt must be injected into the cavities through runners located on the parting surface of the mold. The basic rules applicable to the main runner also apply to the cross-section of the runner. There is an additional factor It must be borne in mind that the cross-sectional area of the shunt is also a function of its length because it can be assumed that the increase in pressure loss in the shunt is at least proportional to the length of the shunt.
In most cases, the pressure loss will be greater because the cross-section decreases due to the solidification of the plastic melt along the runner wall and the greater the pressure loss from the main runner, the main runner and runner system mean Loss of raw materials and waste of plasticizing the amount of injection molding machine, so the shunt should be designed as short as possible, the cross-section should be as small as possible.Sink shunt length is determined by the number of mold cavity and geometry of each cavity .
Shunt cross-sectional shape
Because the circular cross-section of the minimum surface area of the shunt, the relative cross-sectional area of the shunt heat loss is minimal, it should be possible to use circular cross-section of the shunt due to the circular cross-section of the center of the last melt channel material curing, Under pressure, the plastic melt can flow a maximum distance along the center of the circular cross-section of the runner so that the gate (section between the runner and the cavity) should be so designed that the melt consists of a circular or rectangular section The center of the runner enters the cavity through the gate.
At the minimum cross-section of the runner, the molten steel flows locally around the gate due to the flow friction of the plastic melt, thus allowing the melt to continue for a longer period of time before the gate solidifies under the effect of the packing pressure Into the cavity, in order to play the role of feeding.
When there is a need to move between the smooth surface and the runner, it is not possible to use a runner with a circular cross section. In this case, a semicircular groove may be used as the runner. The advantage of this shape is that only the However, when the radius of curvature of the semicircular groove flow passage is the same as the diameter of the partial flow passage of the male cross-section, the diameter of the semi-circular groove flow passage accommodates more than 12.5 parts of the diameter of the circular flow passage.