Nov 26,2025
Hot Runner system: design and optimization of the“Blood circulation system” of the mold
Hot Runner system: design and optimization of the“Blood circulation system” of the mold
In the high-speed and high-efficiency modern injection molding production, hot runner system is no longer a dispensable choice, but the core components to improve quality and reduce costs. It extends the nozzle of the injection molding machine directly to the door of the mold cavity, forming an“Internal flow channel” that continuously maintains the molten state. A well-designed hot runner system, like the body's efficient, smooth blood circulation system, breathes life into a mold, while a poorly designed system can become a source of blockage, degradation, and failure.
Deconstruction of the core components of the system: the cornerstone of precise temperature control
The steady operation of the hot runner system depends on the precise coordination of three core components:
Hot Runner Nozzle: as a system terminal, directly in contact with the cavity gate. Its type determines the surface quality of the product and production efficiency.
Open nozzle: simple structure, low cost, but easy to produce salivation and drawing, suitable for the gate trace is not high requirements of thick-walled products.
Needle-type nozzle: through independent hydraulic, pneumatic or mechanical mechanisms to control the opening and closing of the valve needle. It can realize large gate size, no wire drawing, timing sequence injection molding, completely eliminate the gate trace, perfect for the appearance requirements of the automobile, home appliances panel and large thin-walled products.
Manifold: responsible for distributing the melt from the main nozzle to the nozzles. The design of its flow passage is very important.
Runner balancing: through CAD/CAE simulation, a naturally balanced runner layout is designed to ensure that the melt reaches all cavities at the same pressure, temperature, and time.
Internal polishing and plating: the channel interior must be mirror polished, and consider the use of non-adhesive coating (such as nickel-PTFE) to reduce flow resistance, to prevent material retention degradation.
Temperature Controller: the“Brain” of a system. Each nozzle and splitter plate needs independent closed-loop control.
Precision requirement: temperature fluctuation should be controlled within ± 1 °C to ensure the stability of melt viscosity and consistency of filling.
Zoning Control: for large molds or sensitive materials, different areas of the mold, or even a single nozzle for zoning temperature control, to deal with local heat differences.
Design principles and selection strategies: balance between efficiency and reliability
Selecting and designing a hot runner is a systems engineering that takes into account product, material and production objectives.
Step 1: Initial selection based on product and material
Product appearance: Is there any appearance requirement? The valve needle type is preferred.
Material Characteristics: is the processing of heat-sensitive materials (such as PVC, POM) or highly corrosive materials (such as flame retardant materials) ? Choose a nozzle made of a small, corrosion-resistant steel (e.g. HP series stainless steel) and avoid dead ends.
Fiber reinforced material: for high glass fiber content (> 30%) material, need to choose high wear resistance nozzle head (such as cemented carbide insert) , to resist erosion.
The second step: system design based on mold structure
The number and layout of cavities determine the runner level and heating power of the splitter plate. The H-type layout is good for balance, but the volume is large; the radial layout is compact, but the balance design is difficult.
Mold cooling: the hot runner area is a huge heat source, must be designed around the dense, efficient cooling water, “Thermal isolation”, to prevent mold heat accumulation, affect the cooling cycle.
Heat insulation and expansion: the heat insulation air gap between the shunt plate and the mold must be accurately calculated, and the displacement space for thermal expansion must be reserved to prevent the system from being stuck or deformed after thermal expansion.
Common challenges and optimization strategies: from“Usable” to“Easy to use”
Even if the selection is correct, it will still face many challenges in practical applications, requiring forward-looking optimization strategies.
Challenge 1: Drooling and drawing
Cause: the melt pressure at the gate after the release of viscoelastic material due to incomplete retraction caused.
The Solution:
The use of valve needle nozzle, fundamentally solve the problem.
Optimization of holding curve and Suck Back parameters, after the end of the injection screw slightly Suck Back to release the pressure.
For open nozzles, a gate design with a“Drip proof” geometry can be used.
Challenge 2: material degradation and black spots
Cause of formation: dead angle in runner, long melt retention time, local overheat leading to carbonization.
The Solution:
The pursuit of the flow channel“Streamlined” design, eliminate all acute angles and steps.
Select coating or surface treatment, reduce the melt adhesion.
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Start-up/stop program: establish strict start-up heating, stop cooling and refueling cleaning procedures, using high fluidity, high thermal stability of cleaning materials.
Challenge three: heating element failure
Cause of formation: heating rod or heating coil burned due to improper power design, installation stress, voltage fluctuations and other reasons.
Prevention strategy:
Power rationalization: the higher the power is not the better, according to the system quality and heating time to calculate the reasonable power density.
Select high-quality sheathed heater, longer life, better stability.
The sealing and protection of the junction box prevents water vapor and oil pollution from invading and leading to short circuit.
Return on value: long-term benefits beyond hardware investment
Although the initial investment in a hot runner system is high, the life-cycle returns are huge:
Material Savings: completely eliminate runner waste (cold runner) , for large molds or expensive engineering plastics, saving the cost of raw materials can quickly pay back the investment.
Efficiency: no need to take out and recycle runner, shorten the opening and closing stroke and ejection times, molding cycle can be shortened by 15%-30% .
Quality Leap: more direct pressure transfer, reducing the product internal stress and warping deformation; valve needle gate provides the perfect appearance.
Automation-friendly: products and flow channel automatic separation, for fully automated, unmanned production paved the way.
Conclusion
The hot runner system is a The Crown Jewels of modern injection moulding technology. Its design and application is a deep fusion of materials science, mechanical engineering and control technology. The Secret of success is to treat the hot runner system as a complete, sophisticated subsystem that needs to be seamlessly integrated with the mold and process, rather than simply stacking standard parts. Starting from the precise selection, through rigorous design, fine debugging and scientific maintenance, this“Blood circulation system” can really inject lasting and strong vitality into the mold, finally, in the fierce market competition, win the double victory of efficiency and quality.
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