The principle of hot runner
Hot runner technology is the use of heating devices in injection molds to keep the plastic melt in the flow channel in a molten state throughout the injection molding process. This technology places heating rods and heating rings near or at the center of the flow channel, so that the entire flow channel from the outlet of the injection molding machine barrel to the gate is in a high temperature state, thereby avoiding the problem of removing the flow channel after cooling and solidification in traditional molds. After shutdown, as the plastic in the flow channel still remains molten, it only needs to be heated to the desired temperature when restarted, greatly simplifying the operation process and improving production efficiency.
Classification of hot runners
Hot runner systems are mainly divided into two categories based on their design and application: open type and needle valve type.
Open hot runner:
The open hot runner structure is relatively simple, mainly composed of injection nozzle, splitter plate, hot nozzle, temperature control box, and accessories. This system is suitable for micro semi hot runner, with a simple structure, low maintenance cost, good stability, and low failure rate. It is widely used in high-precision molds abroad. However, due to the direct contact between the open hot runner and the product surface, problems such as wire drawing and leakage may sometimes occur, affecting the surface quality of the product.
Needle valve hot runner:
The needle valve hot runner system is more complex, including injection nozzle, splitter plate, hot nozzle, temperature control box and other components, as well as control elements such as cylinder or oil cylinder, valve needle, etc. This system controls the injection of molten plastic through the opening and closing of valve needles, with higher control accuracy and flexibility, and is suitable for adiabatic flow channels. However, its design is complex, with high limitations on materials, and the cost is relatively high.
Advantages of hot runner
Shortening the molding cycle: Due to the fact that hot runner molds do not need to wait for the cooling and solidification of the runner and sprue, the molding cycle can be significantly shortened, sometimes even to less than 5 seconds.
Save raw materials: In pure hot runner molds, there is no cold runner system, so there is no production waste, which is particularly important for projects with expensive plastic prices.
Improving product quality: Hot runner molds can ensure precise temperature control of plastic melt in the flow channel system, allowing plastic to flow into each mold cavity in a more uniform and consistent state, thereby improving product quality consistency.
Reduce waste: As the hot runner system can reduce residual stress and deformation at the gate, the waste rate is greatly reduced.
Beneficial for production automation: After the hot runner mold is formed, the parts do not need to trim the gate or recycle the cold runner, which is conducive to achieving production automation.
Disadvantages of hot runner
Although hot runner tools have many advantages, they also have some drawbacks:
Cost increase: The high price of hot runner components may lead to a significant increase in the cost of hot runner molds. For projects with smaller output, the proportion of mold costs is higher, which may not be economically cost-effective.
High equipment requirements: Hot runner molds require precision machining machinery as a guarantee, and the integration and coordination requirements between the hot runner system and the mold are extremely strict. Otherwise, many serious problems may occur during the production process of the mold.
Complex operation and maintenance: Due to the complex structure of the hot runner system, its operation and maintenance are also relatively complicated, requiring professional personnel to operate and maintain it.
Application of Hot Runner in Mold Industry
With the continuous development of injection mold technology, hot runner technology has been widely used in industrialized countries and regions around the world. In North America, Europe and other places, hot runner technology has been used for a long time, with more experience and higher level. In Asia, Singapore, South Korea, Taiwan, China and Hong Kong are also in the lead. Although the hot runner mold in Chinese Mainland is still in its infancy, it is growing rapidly and the proportion is increasing.
Hot runner technology has been widely used in various fields such as automobiles, electronics, home appliances, and medical devices. For example, many plastic parts in MOTOROLA phones, HP printers, and DELL laptops are produced using hot runner molds. In addition, hot runner technology has also promoted the development of advanced plastic molding processes such as PET preform production, multi-color co injection, and multi material co injection.
