1. Working principle
Cold Runner: transports molten plastic from the injection molding machine nozzle to the mold cavity through the channel inside the mold, and the runner system (main channel, splitter and gate) is cooled and solidified simultaneously with the mold cavity. After each injection, the plastic in the runner solidifies to form waste (called "runner waste"), which needs to be separated from the finished product and recycled.
Hot Runner: The runner system keeps the plastic always in molten state through heating elements such as heating rods or heating rings, and only part of the mold cavity is cooled and solidified. The molten plastic enters the mold cavity directly from the injection molding machine nozzle through the heating runner, without cooling runner, so no runner waste is generated.
2. Structure and complexity
The cold runner structure is simple and there is no need for an additional temperature control system. The runner design is directly connected to the mold cavity and relies on the mold to naturally dissipate heat. Suitable for single or multi-cavity molds, but manual or mechanical removal of runner waste.
The hot runner structure is complex and requires integrated heating elements, temperature controllers and thermal insulation layers. The runner system independently controls the temperature and needs to accurately manage thermal balance to prevent plastic degradation or blockage. Usually used in multi-cavity molds or high-precision molding without post-processing and cutting the runner.
3. Material Utilization
The cold runner produces runner waste (about 20% to 40% of the total injection volume) after each molding, which needs to be recycled or discarded, increasing material costs and waste.
Hot runners have no runner waste and the material utilization rate is close to 100%, especially suitable for expensive or high viscosity plastics (such as engineering plastics).
4. The molding cycle,
the cold runner flow channel is cooled simultaneously with the product, resulting in a long molding cycle (you need to wait for the runner to solidify). Multi-cavity molds may be filled unevenly due to different runner lengths.
The hot runner runner is always in a molten state, shortening the cooling time and faster forming cycle. It is easier to achieve uniform filling, especially for complex or thin-walled parts.
5.Cost
The cold runner mold manufacturing cost is low, but long-term material waste and waste disposal costs are high.
The initial investment in hot runners is high (mods and temperature control systems are increased costs), but saves materials and improves efficiency over the long term.
6. Applicable
For small-scale production or prototype development of cold runners in scenarios. Cost-sensitive applications and low-priced materials (such as PP, PE). Don't mind the waste disposal scenario.
Hot runners are mass-produced (such as automobiles, electronic parts). High value-added materials (such as PC, PEEK) or transparent products (avoid runner marks). Products that require high surface quality, accuracy and efficiency.
7. Maintenance and operation
Cold runners is simple to maintain and has low failure rate, but runner waste needs to be cleaned frequently.
The hot runner needs to be regularly maintained for heating elements and temperature control systems to prevent thermal expansion or plastic carbonization from being blocked. High technical requirements for operators.