Cold runner molding

Cold runner molding

How Cold Runner Molds work

Cold runner molding is a method used in injection molding processes where the molten plastic travels from the injection molding machine’s nozzle into the mold cavities via a system of channels, known as runners, which are not heated. Once the molten plastic fills the cavities and cools, it solidifies, forming the desired part. At the same time, the material within the runner system also solidifies.

Components of a Cold Runner System:

1. Process:

This is the main channel where the molten plastic first enters the mold from the machine’s nozzle.

This channel branches out from the sprue, leading the material towards secondary runners or directly to the gates.

These further distribute the plastic from the primary runner to the gates. In multi-cavity molds, they help ensure an even distribution of plastic to each cavity.

These are the final channels that allow the plastic to enter and fill the mold cavities. The design and position of the gates are vital as they influence how the part fills and solidifies.

2. Advantages:

Cold runner systems are straightforward in design and operation, making them easier to set up and maintain.

Suitable for a wide range of polymers without concern for the material’s prolonged heat exposure.

Generally, molds with cold runner systems are less expensive than their hot runner counterparts.


3. Challenges:

Since the plastic in the runners solidifies, it often results in wasted material. However, some of this waste can be minimized by regrinding and reusing the runner material, depending on the polymer and product specifications.

The need for the plastic in the runners to solidify can increase the overall cycle time of the molding process.

Once the parts are ejected, the solidified runners usually need to be manually separated or trimmed off, adding an extra step and potential costs.

The position and design of gates in cold runner systems can sometimes lead to aesthetic imperfections or structural weaknesses at the point where the part meets the gate (known as the “gate mark”).

3. Types of Cold Runner Systems:

This is the simpler of the two designs, where the mold splits into two plates. One plate holds the cavities, and the other holds the sprue and runners.

Here, an additional plate holds the runner system, allowing for more complex runner designs and making it easier to separate the runner system from the parts during ejection.

Cold runner systems are commonly used across a wide range of injection molding applications, including consumer goods, automotive components, and medical devices. They’re especially favorable for short production runs, prototypes, or when working with materials that might degrade with prolonged heat exposure.

4. Summary

In conclusion, cold runner molding is a fundamental method in the injection molding industry, with both advantages and drawbacks. The choice between cold runner and hot runner systems will often depend on production requirements, material characteristics, and budget considerations.

Have Questions about Plastic Injection Molding?

Please contact us, and we shall be happy to answer them!