What is a hot runner in injection molding?

1, Overview of Hot Runner Technology
Hot Runner technology is a key technology in the field of injection molding, whose core is to maintain the molten state of plastic in the mold runner through a heating system, so that there is no need to remove the runner and gate during each injection cycle. This technology not only significantly improves production efficiency, but also significantly reduces production costs and enhances product quality.
2, Working principle of hot runner
During the injection molding process, plastic particles are heated and melted by the screw of the injection molding machine. Molten plastic enters the hot runner system of the mold through the nozzle of the injection molding machine. The hot runner system consists of a series of heating elements (such as heating rods, heating coils) and a temperature control system to ensure that the plastic remains in a molten state throughout the runner. When the screw of the injection molding machine advances forward, molten plastic is injected into the mold cavity to form the desired product shape. After the injection molding is completed, the mold is opened and the product is ejected, while the molten plastic in the flow channel continues to remain in the channel, waiting for the next injection molding cycle to arrive.
3, Types of hot runners
Hot runner technology can be classified into various types based on its structural design and application requirements. Here are several common types of hot runner:
Open hot runner: simple structure, low manufacturing cost, suitable for occasions with low temperature control requirements. The sprue is directly exposed on the parting surface of the mold. After injection molding is completed, the sprue is removed together with the product for subsequent processing.
Needle valve hot runner: By setting a needle valve at the gate to control the opening and closing of the gate, precise control of molten plastic can be achieved. Needle valve hot runner has high precision and good stability, especially suitable for complex products with high quality requirements. At the same time, it can also achieve rapid color and material changes, which has significant advantages in the production of multiple varieties and small batches.
Nozzle type hot runner: With a compact structure and high thermal efficiency, it uses a nozzle to directly heat and transport molten plastic into the mold cavity. The nozzle type hot runner has precise temperature control, low heat loss, and is suitable for high-precision injection molding and high-speed production. In addition, it is easy to maintain and replace, facilitating adjustments and optimizations during the production process.
4, Advantages of hot runner
Hot runner technology has many advantages in injection molding, including:
Improve production efficiency: Due to the high temperature of the flow channel system, the molded parts can be directly ejected without waiting for the flow channel to cool down. This greatly shortens the injection molding cycle and improves production efficiency.
Save raw materials: Hot runner molds do not require cold runners, so there is no production waste. This has extremely high economic value for expensive plastic product projects.
Improving product quality: During the hot runner mold forming process, the temperature of the plastic melt is accurately controlled in the flow channel system, and the plastic flows into each mold cavity in a more uniform and consistent state, thereby producing parts of consistent quality. In addition, products formed by hot runner have good gate quality, low residual stress after demolding, and minimal deformation of parts.
Beneficial for automated production: After the parts are formed by hot runner molds, they become finished products without the need for trimming gates or processing cold runners, which is beneficial for production automation and improves production efficiency.
5, Precautions for hot runner in practical applications
Although hot runner technology has many advantages, the following points still need to be noted in practical applications:
Mold design: The design of hot runner molds should fully consider the fluidity and temperature control requirements of plastics, ensuring uniform melting and smooth flow of plastics in the flow channel.
Temperature control: The temperature control of the hot runner system needs to be precise and stable to avoid quality problems caused by plastic overheating or uneven cooling in the runner.
Maintenance: The hot runner system needs to be regularly inspected and maintained, including cleaning and replacing heating elements, as well as calibrating temperature sensors, to ensure its long-term stable operation.
Cost considerations: Although hot runner technology can significantly improve production efficiency and product quality, its initial investment cost is relatively high. Therefore, when choosing whether to adopt hot runner technology, it is necessary to comprehensively consider factors such as product value, production scale, and cost budget.