HOME  > Plastic Molding Tutorial  > #026 Basic Varieties of Tunnel Gates
Plastic Molding Tutorial

#026 Basic Varieties of Tunnel Gates

Category : Runner, Gate
January22, 2010

A tunnel gate (submarine gate) is used very frequently as a gate method for a structure that automatically cuts the product and the gate at the time of opening and closing the parting surface.

While the know how of the shape and dimensions, etc., is necessary at the time of the basic design of a tunnel gate, here, the basic varieties in the relationships among the product, the gate, and the runner are explained.

The basic patterns of tunnel gates generally used are shown in the following figure. When these are broadly classified into a movable side and a fixed side with the parting surface in between them, there are four types of combinations of the gate and runner.

image

When the tunnel gate is provided on the fixed side, cutting of the molded product and the gate is done at the time when the parting surface is opened. Therefore, the condition of gate cutting is considered to vary depending on the speed of opening the mold.

On the other hand, when the tunnel gate is provided on the fixed side, the cutting of the molded product and gate is done at the time when the runner ejector pin protrudes from the runner. Therefore, the condition of gate cutting is considered to vary depending on the speed of the protruding runner ejector pin.

When the runner is provided on the fixed side, since it is likely that the runner itself remains on the fixed side, it is necessary to have a structure with a long pin in which case the runner is pulled to the movable side.

When the runner is provided on the movable side, it is necessary to provide an appropriate ejector pin for protruding the runner.

As a special example, there is a structure in which the tunnel gate is provided on a boss shape (formed by fine grinding the ejector pin) located on the movable side, and the plastic is injected from the underside of the top surface of the molded product.

In actuality, depending on the features of the molded product or the characteristics of the plastic, the design of the mold is carried out considering which gate pattern and which runner pattern is most appropriate.

MISUMI USA eCatalog