MOLD - hot runner

Runner refers to the flow channel from the end of the runner to the gate. The form and size of the runner are often affected by factors such as plastic molding characteristics, the size and shape of the runner, the number of mold cavities and customer needs, so there is no fixed form, but the design of the runner should consider the following issues:

1 The cross-sectional shape of the runner, including circle, semicircle, square, rectangle and trapezoid, etc. When other parameters remain unchanged, the larger the perimeter of the runner section, the larger the contact area between the melt and the mold, and the greater the heat loss; on the other hand, the larger the runner section area, the smaller the pressure drop. The efficiency of the full circle section is the highest. Although the efficiency of the square section is also high, it is inconvenient in processing and demoulding, followed by the trapezoidal section. In actual production, circular or approximately circular and trapezoidal cross-sections are the most common.

The processing cost of the circular runner is high, and it is often used in hot runner molds, because it is more troublesome to slot two templates, and it is not suitable for various molds. For example, there is a relatively sliding two-plate mold on the parting surface. In this case, it is better to use a semicircular or trapezoidal section. Although the efficiency of the semi-circular section is low, its processing is simple. In the case that the length of the runner is not too long, the trapezoidal section has the advantage of being more efficient, and it is only processed on one plate of the mold, and if the size is designed Ingenious, it can achieve the same effect as the circular runner. The bottom and side walls should be smoothly connected by rounded corners, preferably semi-circular at the bottom. The side wall should be inclined at about 5° to facilitate ejection. Trapezoidal runners are commonly used in three-plate molds, which are left on a certain setting plate for demoulding when the mold is opened, so trapezoidal cross-section is the most commonly used runner form.

2. Runner arrangement

In multi-cavity molding, the cavity layout determines the design of the runner. From the perspective of runner balance, the flow distance from each cavity to the runner should be equal, and it is also conducive to gate balance. If the number of cavities is 2 The power of , the cavity layout is easier to achieve balance.