Injection cold runner

A cold runner in an injection mold is a channel designed to guide molten plastic from the injection machine nozzle to the mold cavity. The following is a detailed description of its design:

Definition
During the injection molding process, a cold runner is the channel that guides molten plastic from the injection machine nozzle into the mold cavity. Unlike hot runner systems, after each injection, the plastic in the cold runner cools and solidifies, forming "cold slug." This cold slug is pushed or pulled out when the mold is opened, typically separating it from the molded product and becoming waste.

Features
Simple Structure: Cold runner molds have a relatively simple structure, lacking complex heating elements and temperature control systems, resulting in lower design and manufacturing costs.
Easy Maintenance: Since heating and temperature control are not required, cold runner molds are relatively easy to maintain and service, making them suitable for small injection molding companies.
Material Waste: Cold slug waste is generated with each molding cycle, which can be a significant problem for large-scale production.
Longer Molding Cycles: Because the plastic in the runners needs to cool and solidify, the molding cycle is relatively long, resulting in lower production efficiency. Application Scenarios
Small-Batch Production: For small production batches and a wide variety of products, cold runner molds are an economical and practical choice due to their low cost and flexibility.
Frequent Mold Changes: In production environments where frequent mold changes are required, the easy installation and removal of cold runner molds can significantly improve production efficiency.
Insensitive to Material Waste: For lower-value products or where material costs are relatively low, material waste is less of a concern with cold runner molds.
Design Key Points
Runner Dimension Design: Runner dimensions should be designed based on factors such as plastic flowability, injection pressure, and molding cycle to ensure smooth plastic filling of the mold cavity while minimizing the generation of cold slugs.
Cold Slug Well Design: The cold runner well is the part of the cold runner system that collects cold slugs. Its design should facilitate their discharge and removal to prevent them from affecting the molded product.
Cooling System Design: Although cold runners do not require heating, a sound cooling system design is still crucial for improving molding efficiency and ensuring product quality. The cooling system should be able to cool the mold evenly and quickly to shorten the molding cycle. Comparison with Hot Runners

Comparison Items Cold Runner Hot Runner
Structural Complexity Simple Complex
Manufacturing Cost Low High
Maintenance Difficulty Easy Difficult
Material Utilization Low (with cold material waste) High (without cold material waste)
Molding Cycle Long Short
Applicable Scenarios Small-batch production, frequent mold changes, low sensitivity to material waste Large-batch production, high-demand products, and emphasis on material utilization