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Feeding System In Injection Mold

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In addition to the mold base mentioned earlier, another crucial injection mold component is the feeding system.

The feeding system (feed system), also known as the runner system, directs molten plastic from the injection machine’s nozzle into the mold cavity. Its role is to ensure smooth and orderly filling of the cavity and transmit injection pressure to obtain well-structured plastic parts during filling and solidification.

Feeding system in injection molding
Feeding system in injection molding

Generally, molds with conventional feed systems are also referred to as cold runner molds, though rarely explicitly called so.

Components and Functions of the Feeding System

The design of the runner system significantly impacts the appearance, physical properties, dimensional accuracy, and molding cycle of the final product. The feeding system mainly consists of the following structures:

Feed System
Feed System

Sprue: The initial channel where molten plastic is directed from the injection machine’s nozzle. It is responsible for conveying the plastic melt to the runners.

Runner & sub-runner: Transitional channels that guide the melt and distribute it to various gates after receiving it from the sprue.

Gate: Short channels that accelerate the flow of melt into the cavity.

Cold slug well: Stores cold material to prevent it from entering the cavity and affecting the quality of the molded part.

Design Principles of the Feed System

1. Ensure the quality of plastic parts

● Avoid weld marks as much as possible. The presence of weld marks mainly affects the appearance, making the surface of the product poor. The strength will also be poor where weld marks occur.

● Avoid excessive overpacking and insufficient packing pressure. Poor design of the injection system or improper operating conditions can result in excessive packing time or excessive pressure on the molten material in the cavity. Excessive overpacking increases the density of the product, increases internal stress, and leads to flash.

● Avoid issues such as short shot, flash, air trapping, weld lines, traces, jetting, residual stress, warpage, core shift, etc.

● Ensure good appearance properties of the product, facilitate removal of gates during finishing, and ensure that gate marks do not affect the appearance and application of the plastic parts.

Designed mold feed system
Designed mold feed system

2. Production efficiency

Minimize the need for post-processing as much as possible, shorten the molding cycle, and improve production efficiency.

3. Plastic materials

Avoid using flow channels that are too long or too small for plastics with high viscosity or short L/t ratios.

4. Solidification residue removal

● Convenient and reliable solidification residue removal from the feed system.

● Consider appropriate ejection positions to avoid deformation of molded parts when ejected.

5. Cold material

Design appropriate cold slug wells, and overflow grooves to prevent cold material from directly entering the cavity and affecting filling quality.

6. Filling waste:

Minimize and shorten the cross-section and length of the feeding system to reduce plastic usage and mold size.

7. Heat dissipation and pressure drop

● Keep the flow path short and ensure an adequate cross-sectional area.

● Avoid flow path bends and sudden changes in flow direction (use rounded corners to change direction).

● Surface roughness should be low during flow path processing.

● Multi-gating can reduce pressure drop and required injection pressure but may lead to weld line.

8. Achieve simultaneous filling as much as possible

In the case of multiple cavities in one mold, ensure that the molten material entering each cavity can reach simultaneously and that the pressure at the entrance of each cavity is equal.

In Conclusion

The feed system is a critical aspect of injection molds. For more detailed information on the sprue, runner, and gates, please follow the respective hyperlinks in this article. Feel free to contact us at for further technical discussions or if you require mold manufacturing or part production services, visit our injection molding quotation page.

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