Injection molding is a widely used manufacturing process that produces plastic parts by injecting molten material into a mold. The process involves melting the plastic material, injecting it into the mold under high pressure, cooling it down, and then releasing the finished part. A crucial element of this process is the gate, which plays an essential role in controlling the flow of molten plastic into the mold cavity. This comprehensive guide will explore the different types of gates in injection molding, their meanings, advantages, and disadvantages.
Types of Gates in Injection Molding: A Comprehensive Guide
2025-08-13
Gates are small openings in the mold through which the molten plastic flows into the mold cavity. They act as a valve, controlling the flow of material and ensuring that the cavity is filled evenly and completely. Gates vary in shape, size, and location, depending on the specific requirements of the molded part. The type of gate used can have a significant impact on the part's quality, appearance, and overall production cost. In this guide, we will discuss the following types of gates:
1. Edge Gate
Meaning: The edge gate is the simplest and most commonly used type of gate. It is located on the parting line of the mold, allowing the plastic material to flow directly into the mold cavity.
Advantages:
Easy to design and machine.
Suitable for a wide range of part geometries.
Low cost.
Disadvantages:
May require manual removal of the gate vestige.
Potential for uneven flow, leading to part defects.
Not suitable for very thick or large parts.
2. Submarine/Sub Gate
Meaning: The submarine gate, also known as a sub gate, is located below the parting line of the mold. It allows the molten plastic to flow into the mold cavity from the side or bottom.
Advantages:
Automatic separation of the gate from the part during ejection.
Reduced labor costs.
Suitable for high-production runs.
Disadvantages:
More challenging to design and machine.
May leave a small vestige on the part.
Limited to thin-walled parts.
3. Tunnel Gate
Meaning: Tunnel gates are similar to submarine gates, but they extend into the mold cavity from the side, creating a tunnel-like path for the molten plastic.
Advantages:
Automatic gate separation during ejection.
Reduced labor costs.
Can be used for thicker parts than submarine gates.
Disadvantages:
More difficult to design and machine.
May leave a small vestige on the part.
Not suitable for very large or complex parts.
4. Fan Gate
Meaning: The fan gate is a variation of the edge gate, with a widened opening that distributes the molten plastic more evenly across the mold cavity.
Advantages:
Improved flow and filling of the mold cavity.
Reduced risk of part defects.
Suitable for large, flat parts.
Disadvantages:
May require manual removal of the gate vestige.
Increased design and machining complexity.
Not suitable for very thick parts.
5. Sprue Gate
Meaning: The sprue gate is a simple, straight channel that connects the nozzle of the injection molding machine to the mold cavity. It is typically used for single-cavity molds.
Advantages:
Easy to design and machine.
Low cost.
Disadvantages:
May require manual removal of the sprue.
Not suitable for multi-cavity molds.
Limited to simple part geometries.
6. Tab Gate
Meaning: The tab gate is a variation of the edge gate that connects to the molded part via a small tab. This allows for easy removal of the gate vestige after molding.
Advantages:
Easy separation of the gate vestige.
Suitable for a wide range of part geometries.
Disadvantages:
Increased design and machining complexity.
May require manual removal of the gate vestige.
Not suitable for very large parts.
7. Ring Gate
Meaning: The ring gate is a circular gate that surrounds the core of the mold, allowing for even distribution of the molten plastic around the core.
Advantages:
Improved flow and filling of the mold cavity.
Reduced risk of part defects.
Suitable for parts with a central core, such as caps and closures.
Disadvantages:
Increased design and machining complexity.
May require manual removal of the gate vestige.
Not suitable for very large or complex parts.
8. Diaphragm Gate
Meaning: It is actually an umbrella gate with a vertex angle of 180°, which is used for cylindrical plastic products with large inner holes, or plastic products with larger rectangular inner holes, and the gate is on the entire periphery of the inner hole.
Advantages:
1) The speed at which the melt enters the cavity is basically the same, so there are generally no weld marks on the plastic parts, and the appearance is beautiful.
2) The gate is located on the inner surface of the product, which is relatively hidden, does not affect the appearance of the product, and has no fusion line.
3) Due to the large cross-sectional area of the gate, the injection speed is low, the force on the core is uniform, and the molding quality is high.
4) The melt enters the melting cavity from one end, and fills the cavity evenly and smoothly, so that the gas is discharged in sequence and the exhaust is good.
Disadvantages:
1) Since the gate has a large cross-sectional area and is located inside the product, the traces after removal are large and there are many wastes.
2) The gate aggregate is difficult to remove by conventional methods, and it is often removed by punching. Therefore, the convenience of punching should be considered when selecting its location.
Conclusion
The variety of gate types in injection molding allows for the production of a wide range of plastic parts with different geometries and requirements. Understanding the advantages and limitations of each gate type is crucial to achieving the desired part quality and performance. By carefully selecting the appropriate gate type for your application, you can ensure efficient and cost-effective production while maintaining high-quality standards.
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