What is the difference between hot runner and semi hot runner?

1, Differences in working principles
Hot runner system: The core of a hot runner mold lies in its heating system, which can continuously heat and maintain the plastic in the flow channel in a molten state until it is injected into the mold cavity. This means that the plastic in the channel will not cool and solidify throughout the entire injection molding cycle, thus avoiding the common waste problem in cold channel molds. The hot runner system ensures uniform flow of plastic in the channel by precisely controlling the temperature, pressure, and flow rate of the plastic, thereby improving the molding accuracy and surface quality of the product.
Semi hot runner system: Unlike hot runner systems, semi hot runner molds only use a heating system in some of the runners, while the other part adopts a traditional cold runner design. Specifically, semi hot runner molds usually have heating elements installed at the main or branch channels to maintain the molten state of the plastic in these areas, while cold runner designs are used near the sprue near the mold cavity. This design aims to reduce waste while also retaining some flexibility to adapt to different production needs.
2, Differences in structural characteristics
Hot runner system: The structure of the hot runner mold is relatively complex, including multiple components such as the hot nozzle, splitter plate, and temperature control box. These components require precise machining and assembly to ensure the uniformity and stability of the heating system. At the same time, the hot runner mold also needs to be equipped with a specialized temperature control system to monitor and adjust the temperature inside the runner in real time, ensuring the melting state of the plastic.
Semi hot runner system: In comparison, the structure of semi hot runner molds is relatively simple. It combines the characteristics of hot and cold channels, and achieves plastic flow control through local heating and cooling. This design makes the manufacturing and maintenance of semi hot runner molds more convenient, while also reducing costs. However, due to only a portion of the flow channels being heated, semi hot runner molds may not be as effective in reducing waste as fully hot runner molds.
3, Comparison of application advantages and limitations
Application advantages:
Hot runner system: significantly improves material utilization and production efficiency, reduces waste and manual cleaning costs. Meanwhile, due to the molten state of plastic in the flow channel, it is beneficial to improve the molding accuracy and surface quality of the product. In addition, hot runner molds are also suitable for the production of multi cavity molds and injection molded parts with complex structures.
Semi hot runner system: while maintaining a certain material utilization rate and production efficiency, it reduces the complexity and manufacturing cost of the mold. Semi hot runner molds are suitable for scenarios where material utilization is not particularly high, but there is a desire to reduce waste and shorten production cycles.
limitations:
Hot runner system: The initial investment cost is high, and there are high technical requirements for mold manufacturing and maintenance. In addition, due to the continuous heating required by the hot runner system, the energy consumption is relatively high.
Semi hot runner system: Its effectiveness in reducing waste may not be as significant as that of full hot runner molds. Meanwhile, due to the use of cold runner design in some flow channels, defects such as burrs or sprue marks may occur at the sprue, affecting the appearance quality of the product.