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All You Need to Know About Injection Molding Gates

Date: 2023-8-16

Injection molding is a widely used manufacturing process for producing plastic parts. One critical aspect of this process is the design and placement of gates, which control the flow of molten plastic into the mold cavity. Understanding the different types of gates and their advantages and disadvantages is essential for achieving high-quality and efficient injection molding.

What is an Injection Molding Gate?

An injection molding gate is the entrance point through which molten plastic enters the mold cavity. It acts as a channel, allowing the plastic to flow and fill the mold. Once the plastic solidifies, the gate is removed, leaving behind the final plastic part.

Importance of Gate Design

The gate design is crucial as it affects the quality, appearance, and functionality of the molded part. A well-designed gate allows for balanced filling, reduces defects, and ensures consistent part dimensions. It also influences cycle time, material consumption, and mold maintenance.

Types of Gates

1. Edge Gates:

Edge gates, also known as tab gates or sprue gates, are the most commonly used gate type in injection molding. They are located on the edge of the part and directly connected to the runner system. Edge gates provide easy removal and minimize gate vestige. However, they may leave visible marks on the part surface.

2. Submarine Gates:

Submarine gates, also called tunnel gates or submarine runners, are located beneath the part surface. They eliminate visible gate marks on the part and are suitable for aesthetic parts. Submarine gates are often used for thick parts or parts with complex geometries. However, they require additional ejection mechanisms and can be challenging to design and control.

3. Direct Gates:

Direct gates, also known as sprue gates or pinpoint gates, are directly connected to the part surface. They offer excellent filling control and minimize material waste. Direct gates are commonly used for small, thin-walled parts or parts with tight dimensional requirements. However, they may leave noticeable gate marks and require more effort for gate removal.

4. Fan Gates:

Fan gates, also called radial gates or fan runners, are designed to distribute the molten plastic evenly into the mold cavity. They are commonly used for larger parts or parts with thin walls to prevent flow imbalances. Fan gates require proper design to ensure uniform filling and avoid part defects.

5. Hot Runner Gates:

Hot runner gates are a more advanced gate type that uses a heated manifold system to keep the plastic molten. They eliminate the need for a runner and reduce material waste. Hot runner gates offer better control over injection parameters, resulting in improved part quality and reduced cycle time. However, they are more expensive and require additional maintenance.



The tube preform shape of bottles preheat process on the production line to the automatic blowing machine. The operation of PET bottle processing by blowing process with the blowing mold.




Factors Influencing Gate Selection

Several factors influence the selection of the appropriate gate type for a specific injection molding project:

1. Part Design: The part’s geometry, wall thickness, and appearance requirements play a significant role in determining the gate type. Complex geometries or aesthetic parts often require submarine or direct gates, while simple parts may use edge gates.

2. Material Properties: The material’s viscosity, flow characteristics, and shrinkage behavior affect gate selection. High viscosity materials may require larger gates to ensure proper flow and filling.

3. Part Size: The size of the molded part influences gate selection. Larger parts typically require fan gates or hot runner gates to achieve balanced filling.

4. Production Volume: The expected production volume and cost considerations can impact gate selection. Hot runner gates may be more suitable for high-volume production runs, while edge gates are cost-effective for low-volume projects.


Injection molding gates are critical elements in the successful manufacturing of plastic parts. The choice of gate type depends on various factors, including part design, material properties, part size, and production volume. Understanding the advantages and disadvantages of different gate types allows manufacturers to optimize the injection molding process, resulting in high-quality parts with minimal defects.

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